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2009 MRS Fall Meeting & Exhibit

November 30 - December 4, 2009 | Boston
Meeting Chairs: Kristi Anseth, Li-Chyong Chen, Peter Gumbsch, Ji-Cheng Zhao

Symposium FF : Mechanical Behavior of Nanomaterials--Experiments and Modeling

2009-11-30 Show All Abstracts

Symposium Organizers

Jun Lou Rice University

Brad Boyce Sandia National Laboratories

Erica Lilleodden GKSS Forschungszentrum

Lei Lu Chinese Academy of Sciences

FF1: Fracture and Fatigue of Nanomaterials

Session Chairs

David Bahr

Jun Lou

Monday PM, November 30, 2009

Room 304 (Hynes)

9:30 AM - **FF1.1

In-situ Nanomechanics of the Brittle to Ductile Transition.

William Gerberich ¹, Aaron Beaber ¹, Julia Nowak ², Lucas Hale ¹, Yuye Tang ³, Roberto Ballarini ³, Fredrik Oestlund ⁴, Johann Michler ⁴
¹Chem. Engng. Mat. Sci., U. of Minnesota, Minneapolis, Minnesota, United States, ², Hysitron, Inc., Minneapolis, Minnesota, United States, ³Civil Engng., U. of Minnesota, Minneapolis, Minnesota, United States, ⁴Mechanics of Materials and Nanostructures, EMPA, Swiss Federal Laboratory for Materials, Thun Switzerland

10:00 AM - FF1.2

Brittle and Ductile Fracture of Gold nanowires: A Quantitative In Situ Transmission Electron Microscopy Study.

Yang Lu ¹, Jianyu Huang ², Jun Lou ¹
¹Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States, ²Center for Integrated Nanotechnologies (CINT) , Sandia National Laboratories, Albuquerque, New Mexico, United States

10:15 AM - FF1.3

Saccharine Effects on Mechanical Behavior of Electrodeposited Ni Thin Films.

Sumit Soni ^{1 2}, Sean Hearne ², Brian Sheldon ¹
¹Division of Engineering, Brown University, Providence, Rhode Island, United States, ²Center for Integrated Nano-Technologies, Sandia National Laboratories, Albuquerque, New Mexico, United States

This research presents experimental results of an investigation aimed at understanding grain size driven mechanical processes in electrodeposited Ni thin films, where Saccharine additions are commonly used to improve mechanical properties. Ni films were fabricated using salfamate based electro chemical baths, where it is empirically known that mMol/L concentrations of saccharine will reduce the observed tensile stress in addition to lowering the grain size upto a few nanometer scales. Some previous observations and several theoretical models suggest that Saccharine incorporation results in sulfur segregation at grain boundaries. Since grain boundary formation is also associated with tensile stress evolution, a plausible hypothesis is that saccharine additions are directly altering grain boundary energetics. This suggests that saccharine additions should also have an observable effect on intergranular fracture in these films. To test this prediction, in-situ stress measurements during film growth and fracture testing of these same films were compared. Lithographically patterned substrates were used to produce films with ordered arrays of uniform islands, which improved our understanding of island size effects on stress evolution, and also allowed us to produce a well defined notch along one of the island boundaries (for fracture tests). In-situ uniaxial tensile testing under in a scanning electron microscope (SEM) was then used to obtain the fracture strength of these specimens. This technique also enabled us to capture the real-time microscopic images of deformation while specimens were subjected to the applied load. The observed relationships between residual stress, grain size, and fracture strength were then analyzed with detailed models of both film growth and fracture. This work was supported by the National Science Foundation (Brown University) and the DOE office of Basic Energy Science Center for Integrated Nano-Technology. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

10:30 AM - FF1.4

Water Diffusion and Fracture Behavior in Nano-porous low-k Dielectric Film Stacks.

Han Li ¹, Joost Vlassak ¹
¹SEAS, Harvard University, Cambridge, Massachusetts, United States

10:45 AM - FF1.5

An In-situ Electron Microscopy Study of Crack Growth in Nanocrystalline Copper and Copper-Chromium Composite Thin Films.

Seong-Woong Kim ¹, Sharvan Kumar ¹
¹Division of Engineering, Brown University, Providence, Rhode Island, United States

11:00 AM - *

Break

11:30 AM - **FF1.6

Interaction of Materials Defects with External Length Scales – from Simple to Complex Geometries.

Ralph Spolenak ¹
¹Department of Materials, Laboratory for Nanometallurgy, ETH Zurich, Zurich Switzerland

12:00 PM - FF1.7

In-situ Thermal and Lattice-strain Evolution of the Nano-particle-strengthened Alloys Subjected to Low-cycle-fatigue Experiments.

E-Wen Huang ¹, Peter Liaw ¹, Kyle Woods ¹, John Strange ¹
¹Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee, United States

12:15 PM - FF1.8

Fatigue Enhancement in Nanocrystalline Metals via Grain-Boundary Stabilization.

Henry Padilla ¹, Brad Boyce ¹, Elizabeth Holm ¹
¹, Sandia National Laboratories, Albuquerque, New Mexico, United States

12:30 PM - FF1.9

Wear Properties and Surface Hardness Evolution in Nano-twinned Copper Subjected to Repeated Contact Sliding.

Aparna Singh ¹, Ming Dao ¹, Lei Lu ², Subra Suresh ¹
¹Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, ², Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang China

12:45 PM - FF1.10

Detwinning and Crack Initiation in Fatigued Highly-Aligned Nano-twinned Copper.

Carla Shute ¹, Benjamin Myers ¹, Sujing Xie ¹, Andrea Hodge ², Troy Barbee ³, Julia Weertman ¹
¹Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, ²Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, California, United States, ³, Lawrence Livermore National Laboratory, Livermore, California, United States

FF2: Modeling & Simulation of Mechanical Behavior of Nanomaterials

Session Chairs

Erica Lilleodden

Amit Misra

Monday PM, November 30, 2009

Room 304 (Hynes)

2:30 PM - **FF2.1

Multi-scale Modeling of Crack Growth in Ductile Metals.

Alan Needleman ¹, Mathias Wallin ², William Curtin ³, Matti Ristinmaa ²
¹Materials Science and Engineering, University of North Texas, Denton, Texas, United States, ²Division of Solid Mechanics, Lund University, Lund Sweden, ³Division of Engineering, Brown University, Providence, Rhode Island, United States

3:00 PM - FF2.2

Hydrogen Assisted Crack Propagation in Aluminum: An Atomistic Study.

Donald Ward ¹, K. Solanki ¹
¹Center for Adavanced Vehicular Systems, Mississippi State University, Starkville, Mississippi, United States

3:15 PM - FF2.3

Multiscale Materials Modeling Using Coupled Density Functional Theory and Discrete Dislocation Mechanics.

Arun Nair ¹, Derek Warner ¹, Richard Henning ²
¹Civil and Environmental Engineering, Cornell University, Ithaca, New York, United States, ²Material Science and Engineering, Cornell University, Ithaca, New York, United States

Increasing evidence indicates that dislocation nucleation plays a key role in the deformation of nano-structured and nano-dimensioned metals. Yet our understanding of the nucleation process, whether it is from a free surface, grain boundary, or stress concentration, has remained clouded. An important tool for gaining insight into dislocation processes has been atomic-scale computer modeling. However, atomistic simulations of deformation processes have long been plagued by the challenge of accurately and efficiently describing the complexities of multispecies bonding. In the case of metals, this has lead to the majority of the atomistic modeling effort focusing on pure elemental metals in a vacuum, rather than more technologically relevant problems involving alloys with impurities and surface oxides in realistic environments. At the root of the challenge is a trade-off between accuracy and computational expense. At one end of the spectrum lies Kohn-Sham Density Functional Theory (KSDFT). Although KSDFT can produce the interatomic forces originating out of many multi-element bonding situations to reasonable accuracy, its computational expense is severely limiting. Most studies are restricted to less than 1,000 atoms. At the other end of the spectrum lie empirical interatomic potentials. While these are computationally much less expensive, scaling to millions of atoms, they often struggle to accurately capture multi-element bonding.Here we use a concurrent multi-scale approach to address this long-standing challenge. We couple an atomistic region whose forces are calculated via Kohn-Sham Density Functional theory to a continuum region described by linear elasticity. Each domain in the simulation framework is governed by its own energy functional with the constraint that the forces be zero across the domain interface. The KSDFT domain is solved using a plane-wave basis set and pseudo-potentials, while the finite element method is employed for the continuum domain. This approach enables us to examine large simulation cell sizes and thus properly account for the long-range elastic fields associated with key defects such as dislocations. In this talk, we will discuss our application of the above method to study dislocation nucleation from a stress concentration at a crack-tip in aluminum in the presence of various impurities. The competition between dislocation nucleation and its competing mechanism, crack-tip propagation, will be discussed.

3:30 PM - FF2.4

Dislocation Source Strengths and Internal Stress in Nanocrystalline Metals: Predictions from a Fitted Quantized Crystal Plasticity Model.

Peter Anderson ¹, Lin Li ¹, Steven Van Petegem ², Helena Van Swygenhoven ²
¹, The Ohio State University, Columbus, Ohio, United States, ²Materaisl Science and Simulation, Paul Scherrer Institut, Villigen Switzerland

Compared to coarse-grained counterparts, nanocrystalline (nc) metals usually display distinct stress-strain features, such as extremely high strength, an extended micro-to-macro plastic transition regime, and limited ductility [1]. Also, nc Al and Au films are able to recover an abnormally large amount of plastic deformation after unloading [2]. Finally, in situ X-ray diffraction studies of electrodeposited Ni with a 30 nm grain size reveal that at room temperature, the peak broadening observed upon loading is fully reversible upon unloading at room temperature [3]. These features are studied in the context of a quantized crystal plasticity (QCP) model, in which individual grains can spontaneously slip at a critical stress, as observed in molecular dynamics simulations [4]. A consequence is that grains do not accumulate plastic strain incrementally, but rather in discrete jumps.Two key material parameters in the QCP model are the distribution of source strengths for dislocation slip and the distribution of internal stress. Here, we discuss a strategy by which the source strength distribution in nc-Ni can be determined through a comparison of experimental measurements and QCP model predictions of monotonic and cyclic stress-strain response. The model demonstrates how pre-compressive or pre-tensile processing can dramatically affect the monotonic and cyclic properties, particularly at small strain. It also shows how quantized plasticity generates a highly inhomogeneous stress state that can drive large recoverable strain upon unloading, particularly at small strain.[1] Kumar KS, Van Swygenhoven H, Suresh S. Mechanical behavior of nanocrystalline metals and alloys. Acta Materialia 2003;51:5743.[2] Rajagopalan J, Han JH, Saif MTA. Plastic deformation recovery in freestanding nanocrystalline aluminum and gold thin films. Science 2007;315:1831.[3] Budrovic Z, Van Swygenhoven H, Derlet PM, Van Petegem S, Schmitt B. Plastic deformation with reversible peak broadening in nanocrystalline nickel. Science 2004;304:273.[4] Li L, Anderson PM, Lee MG, Bitzek E, Derlet P, Van Swygenhoven H. The stress-strain response of nanocrystalline metals: A quantized crystal plasticity approach. Acta Materialia 2009;57:812.

3:45 PM - FF2.5

A Molecular Dynamics Study of Dislocation Propagation in Nanocrystalline Al containing Oxygen.

Andreas Elsener ¹, Olivier Politano ², Peter Derlet ³, Helena Van Swygenhoven ¹
¹NUM/ASQ, PSI, Villigen Switzerland, ²Institut Carnot de Bourgogne, CNRS-Universite de Bourgogne, Dijon Cedex France, ³NUM/CMT, PSI, Villigen Switzerland

4:00 PM - *

Break

4:30 PM - FF2.6

Mechanism for Material Transfer in Nanoscale Asperity Contact.

Jun Song ¹, David Srolovitz ²
¹Division of Engineering, Brown University, Providence, Rhode Island, United States, ²Department of Physics, Yeshiva University, New York, New York, United States

4:45 PM - FF2.7

Responses of Twin and Grain Boundaries at Nanometer Scale to Mechanical Attacks – A Molecular Dynamics Simulation Study.

Lei Yue ¹, Dongyang Li ¹, Hao Zhang ¹
¹Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada

5:00 PM - FF2.8

Twin Instability of Peierls Distortion in Trans-Polyacetylene, a Spontaneous Soliton Induced Actuation Mechanism.

Minghai Li ¹, Xi Lin ¹
¹Mechanical Engineering dept, Boston University, Brookline, Massachusetts, United States

5:15 PM - FF2.9

Silk Fiber Mechanics: Multi-scale Modeling of Spider Silk.

Murat Cetinkaya ^{1 2}, Senbo Xiao ^{1 3}, Frauke Graeter ^{1 2 3}
¹Protein mechanics and evolution, Max-Planck Institute for Metals Research, Stuttgart, BW, Germany, ²Bioquant, Heidelberg University, Heidelberg, BW, Germany, ³, MPG-CAS Partner Institute of Computational Biology, Shanghai China

5:30 PM - FF2.10

Hierarchical Nanomechanics of Alzheimer's Aβ(1-40) Amyloid Fibrils.

Raffaella Paparcone ¹, Markus Buehler ¹
¹, MIT, Cambridge, Massachusetts, United States

5:45 PM - FF2.11

Continuum Modeling of Boron Nitride Nanotubes.

Jizhou Song ¹, Jian Wu ², Yonggang Huang ², Keh-Chih Huang ³
¹, University of Miami, Coral Gables, Florida, United States, ², Northwestern University, Evanston, Illinois, United States, ³, Tsinghua University, Beijing China

Boron nitride nanotubes (BNNTs) possess unique mechanical, thermal, electrical and chemical properties. Their tensile rigidity is comparable to that of carbon nanotubes. They have high thermal conductivity along the nanotube, and good resistance to oxidation at high temperature. Contrary to carbon nanotubes, BNNTs have large band gaps regardless of the chirality and diameter, and are therefore semiconductors.There are two types of continuum studies of BNNTs. One is to model a BNNT as a linear elastic shell [1], with the Young’s modulus and the shell thickness to be fitted by the atomistic simulation results of BNNT tension rigidity and bending rigidity. Such a linear elastic shell theory cannot account for the nonlinear, multi-body atomistic interactions characterized by the interatomic potential [2]. It also neglects the importance effect of BNNT chirality on their mechanical behavior. The other type of continuum studies of BNNTs is to incorporate the nonlinear, multi-body interaction potential for boron nitride into the continuum analysis [3-5]. Such an atomistic-based continuum theory has been used to study the Young’s modulus, stress-strain curve, and Stone-Wales transformation of BNNTs [3-5]. However, this atomistic-based continuum theory is a membrane theory that is not applicable to BNNTs in bending, nor to the instability analysis under compression.We developed a finite-deformation shell theory for single-wall BNNTs based on the interatomic potential in this paper [6]. The theory incorporated the effect of moment and curvature for a curved surface, and accurately accounts for the nonlinear, multi-body atomistic interactions as well as the BNNT chirality. It provides the constitutive relations between stress/moment and strain/curvature in terms of the interatomic potential. The theory is then used to study the buckling of BNTTs under tension and compression.[1]B.I. Yakobson, C.J. Brabec, J. Bernholc, Phys. Rev. Lett. 76, 2511 (1996).[2]Albe K, Möller W and Heinig K H 1997 Radiat. Eff. Defects Solids 141 85-97.[3]Song J, Huang Y, Jiang H, Hwang K C and Yu M F 2006 Int. J. Mech. Sci. 48 1197-1207.[4]Song J, Jiang H, Wu J, Huang Y and Hwang K C 2007 Scripta Mater. 57 571-574.[5]Song J, Wu J, Huang Y, Hwang K C and Jiang H 2008 J. Nanosci. Nanotechnol 8,3774-3780.[6]Song J, Wu J, Huang Y, and Hwang K C 2008 Nanotechnology 19 445705.

2009-12-01 Show All Abstracts

Symposium Organizers

Jun Lou Rice University

Brad Boyce Sandia National Laboratories

Erica Lilleodden GKSS Forschungszentrum

Lei Lu Chinese Academy of Sciences

FF3: Mechanical Behavior of Low Dimensional Nanomaterials I

Session Chairs

Jeff De Hosson

Ju Li

Tuesday AM, December 01, 2009

Room 304 (Hynes)

9:30 AM - **FF3.1

Dislocations in Nanowires and the Eshelby Twist.

William Nix ¹, David Barnett ¹
¹Materials Science and Engineering, Stanford University, Stanford, California, United States

10:00 AM - FF3.2

Investigations of Deformation Mechanisms in Ultra High Strength Nanowhiskers.

Daniel Gianola ^{1 2}, Gunther Richter ³, Andreas Sedlmayr ¹, Reiner Moenig ¹, Burkhard Roos ⁴, Cynthia Volkert ⁴, Oliver Kraft ¹
¹Institute for Materials Research II, Forschungszentrum Karlsruhe, Karlsruhe Germany, ²Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, ³, Max-Planck Institute for Metals Research, Stuttgart Germany, ⁴Institue for Materials Physics, University of Göttingen, Göttingen Germany

Metal nanostructures proposed as fundamental building blocks for nanotechnological devices will often be subject to extreme duress during operation, particularly high mechanical stresses. Investigations of size-dependent deformation have shown that “smaller is stronger” in metals, yet the underlying mechanisms that give rise to this departure from bulk behavior are still elusive. The emerging picture is that plasticity in extremely small volumes is fundamentally different than in large materials; the law of averages gives way to discrete processes that dominate the response. Systematically probing the mechanical response and uncovering the underlying deformation mechanisms of diminishingly small structures at the micro- and nanoscale requires new strategies and approaches that circumvent difficulties associated with handling, gripping, loading, and measuring small specimens. The need for in situ experiments that give a one-to-one correlation between mechanical response and deformation morphology is exacerbated by the fact that electron optics are needed to image and manipulate nanostructures.Here we describe quantitative in situ tensile experiments on quasi-1D nanostructures in a dual-beam scanning electron microscope (SEM) and focused ion beam (FIB). Examples showing results for single-crystalline metallic nanowhiskers, or defect-free wires having diameters between 30 and 300 nm, will be presented in the context of size effects on mechanical behavior. Tensile measurements of individual nanowhiskers reveal strength on the order of the theoretical strength. Plasticity occurs in a highly localized heterogeneous manner, and fracture morphology indicates a size-dependent failure mode. Experiments which introduce defects in the specimens using Ga-ion irradiation during tensile testing are performed to ascertain the influence of defects and their proximity to surfaces on the accommodation of plasticity in small volumes. Transmission electron microscopy (TEM) is also employed to characterize defects in pristine and ion-irradiated nanowhiskers and to correlate with measured tensile behavior.

10:15 AM - FF3.3

In-Situ TEM Studies of Nanomechanics in One-Dimensional Materials.

Reza Shahbazian Yassar ¹, Anjana Ashtana ¹, Hessam Ghasemi ¹, Anahita Pakzad ¹, Kasra Momeni ¹, Yoke Yap ²
¹Mechanical Engineering, Michigan Technology University, Houghton, Michigan, United States, ²Physics, Michigan Technological University , Houghton, Michigan, United States

10:30 AM - FF3.4

Ultralow Harmonic Resonance in Zinc Oxide Nanowires.

Nan Yao ¹, David Cohen-Tanugi ¹, Austin Akey ¹
¹PRISM, Princeton University, Princeton, New Jersey, United States

10:45 AM - FF3.5

Dynamic Behavior of Long-Range Ordered Carbon Nanotubes Chains.

Luigi De Nardo ¹, Chiara Daraio ²
¹Chimica, Materiali e Ingegneria Chimica "G. Natta", Politecnico di Milano, Milano, Milano, Italy, ²Graduate Aeronautical Laboratories (GALCIT) and Applied Physics, California Institute of Technology, Pasadena, California, United States

Since the Fermi-Pasta-Ulam model was first described, chains of nonlinear oscillators have received an ever-increasing amount of attention in the scientific community. They have been reported in a broad range of physical settings, offering the opportunity to discover new physical phenomena. In this communication, we report on the synthesis and characterization of discrete periodic structures composed of alternating CNT foams and stainless steel cylinders. To assemble our long-range ordered chains, Vertically Aligned CNTs (~50 nm in diameter) have been synthesized via Chemical Vapor Deposition of ferrocene and toluene precursors. Free standing VACNTs forests (800 µm tall) have been partially embedded in poly(dimethylsiloxane) (PDMS) films (50-100 µm thick). This process resulted in the double anchoring of CNT forests between two PDMS films, in which the vertically aligned tubes stand perpendicular to the polymer layers. Obtained PDMS-sandwiched VACNTS showed a super-compressible foam-like hysteretic behavior and a highly nonlinear quasi-static compressive stress-strain response. We subsequently used these structures as building blocks for assembling periodic systems, in which PDMS-embedded VACNTs foams have been alternated to metallic cylinders to form a one dimensional chain of masses (steel cylinders) and springs (CNTs layers), up to 15 elements long. The chains were oriented horizontally to avoid gravitational preload. To study the dynamics of the system, we excited single impulses by controlled impacts of a striker dropped from different heights. Wave propagation at specific locations was measured by calibrated piezosensors embedded in selected cylinders within the chain. We added variable constant static pre-compressive forces to the chain, controlled by means of pulleys supporting different weights, and tested the tunability of the response as a function of the applied static and dynamic load. We report a unique, tunable highly-nonlinear dynamic response of this system; The results showed a dramatic variation of the propagating pulse shape and speed, resulting in the generation of characteristic solitary-like waves when a small amount of static force was added. This work represents the first attempt to assembling CNTs based periodic structures, composed of alternating layers of metallic cylinders and VACNT foams partially embedded in PDMS films; The resulting characteristic dynamics provide a new and interesting platform for acoustic wave control in micro- and nano-structured systems.

11:00 AM - *

Break

11:30 AM - FF3.6

Mechanistic Understanding of the Ductility of Thin Nanocrystalline Metal Films on Polymer Substrates.

Teng Li ^{1 2}, Zhao Zhang ¹, Benoit Michaux ¹
¹Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States, ²Maryland NanoCenter, University of Maryland, College Park, Maryland, United States

Recent applications in flexible electronics require that thin metal films grown on polymer substrates be deformable. It has been reported that, when a laminate of a thin metal film (~100 nm thick) on a polymer substrate (10s~100s microns thick) is stretched, the metal film may rupture at strains ranging from 1~2 percent up to 50 percent. The mechanistic understanding of this large variation in the ductility of thin metal films on polymer substrates have been uncertain. Recent experiments have suggested that the rupture strain of a metal film is sensitive to its adhesion to the polymer substrate, and the fracture of the film is formed by a mixture of metal film necking and grain boundary cracking. To reveal the underlying origins for the large variation in ductility, we report a systematic study of the governing mechanisms by considering two completing failure processes: debonding along the interface and cracking along the grain boundaries. We model the interface and the grain boundaries as arrays of non-linear springs, and model the metal and the polymer as elastic-plastic solids. The simulations show that the ductility of the thin metal film is modulated by both the interfacial adhesion and the grain boundary toughness. If the grain boundaries are strong but the interface is weak, interfacial debonding occurs and the thin metal film fractures at a small strain by forming a single neck. If the interface is strong but the grain boundaries are weak, the thin metal film fractures at a small strain by grain boundary cracking. If the interface and the grain boundaries are intermediately strong, the thin metal film fractures at a modest strain by both grain boundary cracking and film necking. If both the interface and the grain boundaries are strong, the thin metal film can deform to a large strain without appreciable necking and grain boundary cracking. The study also explores the effect of grain size on the ductility of thin nanocrystalline metal films on polymer substrates. The simulations depict a deformation map of thin nanocrystalline metal films on polymer substrates, in which the ductility can be quantitatively determined by the interfacial adhesion, grain boundary toughness, and nanocrystalline grain size. Such a map can be used as the guidance for the material design for flexible electronics devices.

11:45 AM - FF3.7

The Effect of Film Thickness on the Strain-to-failure of Polymer-supported Metal Films.

Nanshu Lu ^{1 2}, Zhigang Suo ¹, Joost Vlassak ¹
¹SEAS, Harvard University, Cambridge, Massachusetts, United States, ²Beckman Institute, University of Illinois at Urbana-Champaign, Urbana-Champaign, Illinois, United States

12:00 PM - FF3.8

Effects of Substrate Compliance and Yielding on Thin Film Delamination-Tests and Simulations.

Neville Moody ¹, E. David Reedy ², Edmundo Corona ², Marian Kennedy ³, Megan Cordill ⁴, David Adams ², David Bahr ⁵
¹, Sandia National Laboratories, Livermore, California, United States, ², Sandia National Laboratories, Albuquerque, New Mexico, United States, ³, Clemson University, Clemson, South Carolina, United States, ⁴, Erich Schmid Institute, Leoben Austria, ⁵, Washington State University, Pullman, Washington, United States

12:15 PM - FF3.9

Directly Accessing Plasticity and Hardening Energetics in nm-thick Copper Films on Silica by Atomic-level Partitioning of Interfacial Toughness.

Ashutosh Jain ¹, Saurabh Garg ¹, Gopal Pethuraja ¹, Narayanan Ravishankar ¹, Michael Lane ², Ganapathiraman Ramanath ¹
¹Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, ²Chemistry Department, Emory and Henry College, Emory, Virginia, United States

12:30 PM - FF3.10

Time- and Temperature-Dependent Behavior of Au-based Nanocomposite Thin Films.

Kittisun Mongkolsuttirat ¹, Mark McLean ¹, Walter Brown ¹, Richard Vinci ¹
¹Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States

12:45 PM - FF3.11

Integration of Nano Scale Thin-film Samples with MEMS Actuators during Fabrication.

Mehmet Yilmaz ¹, Jeffrey Kysar ¹
¹Department of Mechanical Engineering, Columbia University, New York, New York, United States

Recent experiments have demonstrated that mechanical properties of nanoscale objects are often stochastic in nature. Hence, one can not characterize the mechanical behavior with individual samples; rather one must characterize the distribution of possible values. In this study we discuss the development of methods to integrate a nanoscale mechanical specimen with a MEMS transducer so that many nominally identical specimens to be tested under nominally identical conditions in order to probe the stochastic properties. The current state-of-the-art of the MEMS device for this purpose consists of either a comb-drive or a thermal actuator to apply the required forces, and two differential capacitive sensors to extract the resulting displacements in order to obtain the stress-strain diagram of the tested nanoscale samples. The only drawback to their device is that the nanoscale test specimens must be mounted in the MEMS device using a nanomanipulator and an electron-beam welder after the MEMS device has been microfabricated. The goal of our study is to circumvent the difficulties associated with mounting the nanoscale thin-film specimens into the MEMS device. We do this, in essence, by co-fabrication the thin-film specimens and the MEMS devices. In that way, the nanoscale thin-film mechanical structure of interest is integrated in the microscale actuator during the microfabrication process. The capability of microfabricating the devices and the nanoscale thin-film samples at the same time gives us the opportunity to have many, and nominally identical nanoscale sample-device pairs in a single microfabrication batch while still having the capability of real-time observation of the deformations and extracting the quantitative properties of the nanoscale test samples. Using conventional optical lithography techniques, we are capable of microfabricating almost perfectly aligned integrated sample-device pairs, and geometrically well defined nanometer scale small test samples made from gold. While further reduction in the dimensions is possible, we integrated nanoscale thin-film samples with 100nm thickness, 500nm width, and 7 micrometer length with our MEMS device.

FF4: Mechanical Behavior of Low Dimensional Nanomaterials II

Session Chairs

George Pharr

Rick Vinci

Tuesday PM, December 01, 2009

Room 304 (Hynes)

2:30 PM - **FF4.1

Quantitative Size Effects in Deformation of Metallic Glasses Pillars.

Jeff De Hosson ¹, C. Chen ¹, Y. Pei ¹
¹Applied Physics, Un. of Groningen, Groningen Netherlands

3:00 PM - **FF4.2

The Nature of Deformation Twinning and a Model for its Size Dependence.

Ju Li ¹, Qian Yu ², Zhi Wei Shan ^{3 2}, Lin Xiao ², Jun Sun ², Xiao Xu Huang ⁴, Evan Ma ^{5 2}
¹Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, ²State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, ShanXi, China, ³, Hysitron Incorporated, Minneapolis, Minnesota, United States, ⁴ Riso National Laboratory for Sustainable Energy, Technical University of Demark, Roskilde Denmark, ⁵Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States

3:30 PM - FF4.3

Length Scale Dependence of Elastic Strain in Metallic Glasses by Molecular Dynamics Simulations.

Uday Vempati ¹, Pavan Valavala ¹, Michael Falk ^{1 2 3}, Todd Hufnagel ¹
¹Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, ²Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, United States, ³Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States

3:45 PM - FF4.4

Size Matters: Nano-scale Plasticity in FIB-less Single Crystals and Nanocrystalline Metals.

Julia Greer ¹, Dongchan Jang ¹, Michael Burek ², Ju-Young Kim ¹
¹Materials Science, California Institute of Technology, Pasadena, California, United States, ²Nanotechnology Engineering, University of Waterloo, Waterloo, Ontario, Canada

4:00 PM - *

Break

4:30 PM - FF4.5

Modeling of Indentation and Pillar Compression in Nanolayered Al/SiC Composites.

Guanlin Tang ¹, Yu-Lin Shen ¹, Danny Singh ², Nikhilesh Chawla ²
¹Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States, ²School of Materials, Arizona State University, Tempe, Arizona, United States

4:45 PM - FF4.6

Shock Response of Cu-Nb Nanolayer Composites.

Timothy Germann ¹, Richard Hoagland ¹, Shengnian Luo ¹, Nathan Mara ¹, Amit Misra ¹, Dennis Paisley ¹
¹, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

5:00 PM - FF4.7

Effects of Chemistry and Microstructure on the Strengthening Behavior of Nanolayered Films.

Aikaterini Bellou ¹, Nicole Overman ¹, Hussein Zbib ¹, David Bahr ¹
¹Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States

Multilayer films offer unique possibilities in tailoring material properties for high strength and fatigue resistant operation conditions. The ability to control both the chemistry of the system by choosing the metals that will be used in the stacking sequence and the thickness of the individual layers results in very high strength films. Cu- based composites, a model system that has been of interest for a number of applications, were used to investigate the effects of varying chemistry on the properties of the films. Maintaining the thickness of the individual layers at 20 nm, Cu/Ni, Cu/Nb and Cu/Nb/Ni films were sputtered to a total thickness of approximately 2000 nm. The mechanical properties and especially the strength of the resulting structures were evaluated using both nanoindentation and bulge testing and conclusions were drawn on how the differences in chemistry affect the observed behavior. The hardness values of the films ranged from 1.9 to 3.4 GPa with the higher value corresponding to the Cu/Nb films. Although the Cu/Nb films have the highest hardness in nanoindentation, they have a lower initial yield strength than the other two systems when measured with bulge testing; a higher strain hardening coefficient is responsible for the differences between the initial yielding condition and the subsequent hardness measurements. The addition of a third layer of Ni does not significantly impact the initial yield behavior in bulge testing. A relatively new system of interest, Pt/Mo multilayers, was used to investigate the effects of varying microstructure, by changing layer thickness, on the mechanical behavior of the films. Pt/Mo composites with layer thicknesses varying from 20 to 100 nm were sputtered and their mechanical properties were again evaluated. The hardness values of these films ranged from 3.7 to 6.6 GPa with the higher value corresponding to the thinner layer used. While the general behavior of Pt/Mo is similar to many of the previously studied Cu systems, variations in performance are shown to be impacted by oxidation of the Mo layers. The films appear harder after aging in air, with hardness values increasing up to 18% over a period of three months after deposition. This presentation will discuss both systems in light of comparisons to established models of strengthening, and in particular the effects of alterations of the softer layer on the overall hardness of the nanolaminate.

5:15 PM - FF4.8

Deformation Processes in Nano-scale Al-TiN Metal-ceramic Multilayers.

Dhriti Bhattacharyya ¹, Nathan Mara ², Patricia Dickerson ², Richard Hoagland ³, Amit Misra ¹
¹MPA-CINT, Los Alamos National Laboraotry, Los Alamos, New Mexico, United States, ²MST-6, Los Alamos National Laboraotry, Los Alamos, New Mexico, United States, ³MST-8, Los Alamos National Laboraotry, Los Alamos, New Mexico, United States

5:30 PM - FF4.9

Uniform and Functionally Graded Oxide-Dispersion Strengthened Nanocomposite Thin Films.

Stephen Farias ¹, Patrick Breysse ^{2 1}, Chia-Ling Chien ^{1 3}, Robert Cammarata ^{1 4}
¹Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, ²Eberly College of Science, Pennsylvania State University, University Park, Pennsylvania, United States, ³Physics and Astronomy, Johns Hopkins University, Lexington, Kentucky, United States, ⁴Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States

5:45 PM - FF4.10

Analysis of the Mechanical Behavior and Dislocation Mechanisms in Trimetallic Nanolaminates.

Firas Akasheh ¹, Cory Overman ², Hussein Zbib ², David Bahr ²
¹mechanical engineering, Tuskegee University, Tuskegee, Alabama, United States, ²School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States

FF5: Poster Session: Mechanical Behavior of Nanomaterials---Experiments and Modeling

Session Chairs

Brad Boyce

Erica Lilleodden

Jun Lou

Lei Lu

Wednesday AM, December 02, 2009

Exhibit Hall D (Hynes)

9:00 PM - FF5.1

In-situ Strain/Stress Measurements during the Compression of GaAs Micropillars by High Resolution EBSD.

Xavier Maeder ¹, William Mook ¹, Christoph Niederberger ¹, Johann Michler ¹
¹Laboratory for Mechanics of Materials and Nanostructures, Empa, Thun Switzerland

9:00 PM - FF5.10

Stain Rate and Creep Response of Nanocrystalline FCC Thin Films at Room Temperature.

Nikhil Karanjgaokar ², Ioannis Chasiotis ¹
²Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, ¹Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

9:00 PM - FF5.11

Mechanical Properties of Nanostructured hard coating of ZrO2.

Renat Sabirianov ^{1 2}, Fereydoon Namavar ^{3 2}, Wai-Ning Mei ^{1 2}, Xiao Cheng Zeng ^{4 2}
¹Physics, University of Nebraska at Omaha, Omaha, Nebraska, United States, ²Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska, United States, ³Department of Orthopaedic Surgery and Rehabilitation,, University of Nebraska Medical Center, Omaha, Nebraska, United States, ⁴Department of Chemistry University of Nebraska, University of Nebraska , Lincoln, Nebraska, United States

9:00 PM - FF5.12

The Mechanical Properties and Structure of Silica Nanowires via Simulations.

Lilian Davila ¹, Valerie Leppert ¹, Eduardo Bringa ²
¹School of Engineering, University of California Merced, Merced, California, United States, ², Universidad Nacional de Cuyo, Mendoza Argentina

Inorganic nanostructures such as nanosprings, nanowires and nanorings are important morphologies of great scientific interest for future technological progress. We have focused our work on the nature and properties of silica nanowires. Nanowires have useful mechanical, electrical and optical properties that could make them useful in small-scale sensing and micro-system applications. We have performed large-scale molecular dynamics (MD) simulations to study the nature and mechanical properties of amorphous silica nanowires. The behavior of non-crystalline silica nanowires is studied using empirical interatomic potentials developed by Feuston and Garofalini. We have applied MD simulations to study the response of the silica nanowires to elevated compressive loads. We have centered our studies on the nanostructural changes occurring in the material and the correlation between the medium-range order (~10 nm), through the characteristic ring distribution of this material. Several glassy nanowires ranging in diameter from ~1.4 nm to ~14 nm are investigated. We also derived the elastic modulus of the nanowires from the stress-strain curves and found a distinctive dependence on nanowire diameter. For a nanowire length of ~14 nm and a diameter of ~4 nm, we do not observe any change in the amorphous structure up to 36% uniaxial compression because the nanowires expand laterally to accommodate uniaxial stresses. A longer nanowire, with length of ~57.3 nm and diameter of ~4 nm, shows a buckling instability and reduced strength at similar strain conditions. In both cases, the ring size distribution reveals the glassy nanostructures remain essentially unaffected at elevated compressions. The ring structure and Young’s modulus for thicker nanowires, with diameters above ~6 nm and lengths of ~14 nm, increasingly resemble those typical of the bulk material. Results are compared with recent experimental findings and theoretical predictions. This investigation contributes to an understanding of the nature of silica nanowires and their mechanical properties, influencing structure-dependent applications and design of nanoscale devices, with implications in nanotechnology, materials science, photonics and medicine.

9:00 PM - FF5.13

Stiffness of Frictional Contact of Dissimilar Solids.

Jinhaeng Lee ¹, Yanfei Gao ^{1 2}, Allan Bower ³, George Pharr ^{1 4}
¹Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, ²Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ³Division of Engineering, Brown University, Providence, Rhode Island, United States, ⁴Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

9:00 PM - FF5.14

Transition Pathway Analysis of Homogeneous Dislocation Nucleation in a Perfect Silicon Crystal.

Hasan Saeed ¹, Satoshi Izumi ¹, Shotaro Hara ¹, Shinsuke Sakai ¹
¹Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan

Nucleation of dislocations in solid materials is directly related to their key mechanical properties of ductility and ideal strength. This nucleation, which occurs either from homogeneous or from heterogeneous sources, is a classical example of stress mediated, thermally activated transitions, and is well-defined within the framework of the Transition State Theory (TST). Therefore, even at stresses lower than the athermal threshold, where the activation barrier for the transition disappears, there is a wide range of stresses for which dislocation nucleation is feasible provided thermal energy sufficient to overcome the activation barrier is available.Owing to the high strain rates resulting directly from the limited simulation times accessible with current computational resources, dynamic atomistic simulation techniques such as Molecular Dynamics (MD) are ill-equipped to access thermally activated transitions. It is so because at such high strain rates, the stresses driving the transition typically exceed the athermal threshold, resulting in a complex mix of multiple simultaneous phenomena (phase transformations, interaction of dislocations, etc); making it impossible to focus on nucleation under low stress conditions. We use the Nudged Elastic Band (NEB) method, which is an efficient transition pathway search algorithm, to examine homogeneous dislocation nucleation in a perfect Silicon crystal. We focus on homogeneous nucleation for two reasons: Firstly, the athermal stress for homogeneous nucleation is effectively the ideal strength of the material, and hence holds considerable academic interest. Secondly, it serves as a useful reference for comparison between results for different materials (comparison with homogeneous nucleation in a perfect Copper crystal); and between different configurations of the same material (comparison with heterogeneous nucleation from a sharp corner in Silicon). Input configurations are provided to the NEB algorithm by artificially introducing a shuffle set dislocation loop into the otherwise perfect crystal. We determine the minimum energy path and the saddle point configuration corresponding to a range of stress values. This gives the relationship between the activation energy and the resolved shear stress for homogeneous dislocation nucleation in Silicon. The process of converging onto the correct solution is an iterative one, and the quality of input configurations is critical. The results obtained are compared with results for other nucleation cases as reported in literature.We show that for a range of resolved shear stress values (typically for stresses near the athermal threshold), the dislocation embryo is far from perfect, and the critical nucleate transitions to an in-plane shear perturbation where the shear displacement of most particles is considerably less than the Burger’s vector. With decreasing resolved shear stress values, the embryo approaches that of a perfect dislocation.

9:00 PM - FF5.15

Delamination Mechanics of a Rectangular Film in the Presence of Long-range Intersurface Forces.

Guangxu Li ¹, Kai-tak Wan ¹
¹Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States

9:00 PM - FF5.18

In-situ X-ray Diffraction during Synthesis of Nanoporous Gold.

Steven Van Petegem ¹, Stefan Brandstetter ¹, Robert Maass ¹, Andrea Hodge ^{2 3}, Juergen Biener ³, Helena Van Swygenhoven ¹
¹NUM/ASQ, PSI, Villigen Switzerland, ²Aerospace and Mechanical Engineering Department, University of Southern California, Los Angeles, California, United States, ³Nanoscale Synthesis and Characterization Laboratory, Lawrence Livermore National Laboratory, Livermore, California, United States

9:00 PM - FF5.19

Nano-indentation Study of Three-dimensional Periodic Nanoframes.

Jae-Hwang Lee ^{1 2}, Steven Kooi ², Edwin Thomas ^{1 2}
¹Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, ², Institute for Soldier Nanotechnologies, MIT, Cambridge, Massachusetts, United States

9:00 PM - FF5.2

Length Scale of Thermodynamic, Kinetic, and Mechanical Stabilities of Metallic Glass.

Hiroki Ushida ¹, Shigenobu Ogata ¹, Hajime Kimizuka ¹
¹Department of Mechanical Science and Bioengineering, Osaka University, Osaka Japan

Metallic glasses (MG) are one of the promising structural materials because of their high elastic limit, high toughness, and high corrosion resistance. In these days, MGs are begun to apply to the nanostructures such as nanowires and nanopillers. An understanding of thermodynamic and kinetic stabilities of MG is essential for explaining and predicting the glass forming ability and the mechanical properties, e.g., yield strength and toughness. We should note that yield strength of nanometer-sized MG is controlled by the nucleation of local shear deformation, while the yield strength of millimeter-sized MG is dominated by the shear band propagation property. A number of analyses have been done on macroscopic thermodynamic and kinetic stabilities of MG, e.g., glass forming ability analysis, critical cooling rate analysis, by means of experimental observations and atomistic modeling. In addition, the local atomic structural orderings (LASO), e.g., short range order (SRO) and middle range order (MRO) are also actively analyzed by using atomistic modeling. However, unfortunately relations between the local thermodynamic and kinetic stabilities and the LASO in view of its length scale and energetics of the local atomic structures have not been fully discussed, even though the fact of the nonexistence of the long range order in MG strongly suggests that the local stabilities are governing the stabilities of whole MG. In the present study, we firstly analyze thermodynamic and kinetic stabilities of local regions in the CuZr bulk MG at finite temperature (300K-600K) and its region size dependency using an atomistic modeling based on the metadynamics. This method reproduces the free energy profile of configuration space for the atomic structures in the local region surrounded by bulk MG and thus, allows to find all the free energy minima corresponding to metastable atomic structures of the local region and to estimate activation energies between the metastable atomic structures. From these analyses, we find the stabilities of whole MG are determined by the stabilities of the atomic structure in ~10nm sized local region. This result suggests that the length scale of LASO is also ~10nm. We secondly analyze local strength of MG which can be defined a maximum stress against a local uniform deformation using newly developed local strain constrained molecular dynamics. The local strength varies with the size of the region applied uniform deformation. We find the weakest size is of ~10nm. This size is conceptually corresponding to the size of the shear transformation zone (STZ). We proposed a concept of length scale of thermodynamic, kinetic and mechanical stability of MG. This brings the fundamental understanding of mechanical properties of MG nanostructures.

9:00 PM - FF5.22

Reduction of Residual Stress in Density Modulated Thin Films.

Arif Alagoz ¹, Toh-Ming Lu ², Tansel Karabacak ¹
¹Department of Applied Science, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, ²Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States

Control of residual stress in thin films is critical in obtaining high mechanical quality coatings without cracking, buckling, or delamination. In this work, we present a simple and effective method of residual stress reduction in sputter deposited thin films by stacking low and high material density layers of the same material. This multilayer density modulated film is formed by successively changing working gas pressure between high and low values, which results in columnar nanostructured and dense continuous layers, respectively. In order to investigate the evolution of residual stress in density modulated thin films, we deposited ruthenium films using a DC magnetron sputtering system at alternating argon pressures of 20 and 2 mTorr. Wafer’s radius of curvature was measured to calculate the intrinsic thin film stress of multilayer ruthenium coatings as a function of total film thickness by changing the number of high density and low density layers. Morphology and crystal structure of the thin films are also investigated by scanning electron microscopy (SEM) and x-ray diffraction (XRD), respectively. It is shown that low material density nanostructured layers act as compliant layers and significantly reduce the total film stress mainly originating from high density layers under high compressive stress. By engineering the film density, we were able to reduce film stress more than one order of magnitude compared to the conventional dense films produced at low working gas pressures. Due to their low stress and enhanced mechanical stability, we were able to grow these density modulated films to much higher thicknesses without suffering from buckling. Compressive stress in high density regions of our multilayer films is believed to be relaxed by deformation of low density layers through the formation of nanocracks. It is proposed that nanocrack propagation in thin film is localized in nanostructured layers avoiding the buckling or delamination of the whole film.

9:00 PM - FF5.23

Size Dependence of the Mechanical Properties of Au Nanoparticles.

Leila Costelle ¹, Vladimir Tuboltsev ¹, Jyrki Raisanen ¹
¹Department of Physics, Division of Materials Physics, University of Helsinki, Helsinki Finland

9:00 PM - FF5.24

Nanoindentation-induced Phase Transformations in Silicon at Elevated Temperatures.

Simon Ruffell ¹, David Munoz-Paniagua ², Jim Williams ¹, Jodie Bradby ¹, Peter Norton ³
¹, Australian National University, Canberra, Australian Capital Territory, Australia, ², National Institute for Nanotechnology, Edmonton, Alberta, Canada, ³Department of Chemistry, University of Western Ontario, London, Ontario, Canada

9:00 PM - FF5.25

Nonlinear Large Deformation of Diamond Crystals during Indentation by DFT-Based FEM.

Naohiro Toda ², Hajime Kimizuka ¹, Shigenobu Ogata ¹, Yuan Zhong ³, Ting Zhu ³
²Super Hard Materials Development Department, Sumitomo Electric Hardmetal Corp., Itami, Hyogo, Japan, ¹Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan, ³Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States

We have developed a new framework of a finite-element method (FEM) analysis, with a constitutive relation based on density functional theory (DFT), as an efficient method to characterize the nonlinear elastic deformation of diamond crystal. In the present method, the stress-strain relations are obtained during FEM analysis on the fly based on the plane-wave-based DFT total-energy calculations and their numerical database is simultaneously constructed, which enables us to obtain high-precision stress without any empirical parameters even under finite strained conditions. The database significantly improves the total computational efficiency without loss of accuracy. Once the stress-strain database is constructed, total computational cost of DFT-based FEM analysis is reduced by 99 % and above. Using our DFT-based FEM, we conducted the (111)<11-2> shear-deformation tests of diamond crystal under various stress conditions, to examine the external-stress dependence of its deformation characteristics. The each obtained stress-strain relation exhibits nonlinear elastic behavior, and the stress reaches the maximum value and then rapidly decreases at large deformation. This fact indicates that the body begins to undergo permanent deformation, and the stress at this point is defined as the ideal maximum shear stress. It is also noted that the present results and the direct DFT results agree very well each other. Thus our method has potential to estimate nonlinear elastic behavior and ideal strength of crystal under various external stress conditions. The effectiveness of the present method is demonstrated through numerical simulations for the load-displacement response during indentation of diamond single crystal (DSC). Calculations are performed for indentation on the (111), (110) and (100) surfaces of DSC. During the indentation, the shear stress in small volumes beneath the indenter can achieve the theoretical limit of a perfect crystal. The ensuing nonlinear elastic instability can trigger homogeneous slip and/or cracking inside the crystal, which is at the onset of permanent deformation. We quantify the critical conditions of the permanent deformation occurring, including critical indentation load, instability occurring location, critical stress and instability mode at the instability point.

9:00 PM - FF5.26

Atomistic Mechanisms in Fracture of Graphene Sheets under Peeling Loading.

Dipanjan Sen ¹, Markus Buehler ²
¹Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, ²Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

9:00 PM - FF5.27

Formation of Nanostructures in Face Centered Cubic Metal Powder Particles Impacted at High Velocities.

Yu Zou ¹, Eric Irissou ², Jean-Gabriel Legoux ², Stephen Yue ¹, Jerzy Szpunar ¹
¹Mining and Materials Engineering, McGill University, Montreal, Quebec, Canada, ²Industrial Materials Institute (IMI), National Research Council Canada (NRC), Boucherville, Quebec, Canada

9:00 PM - FF5.28

Mechanical Characterization of the Cement Line in Bovine Bone through Nanoindentation.

Timothy Montalbano ¹, Gang Feng ¹
¹Mechanical Engineering, Villanova University, Villanova, Pennsylvania, United States

9:00 PM - FF5.3

Twining and Slip Activity in Magnesium <11-20> Single Crystal.

Gyu Seok Kim ^{1 2}, Sangbong Yi ¹, Yuanding Huang ¹, Norbert Huber ¹, Marc Fivel ², Erica Lilleodden ¹
¹Institute of Materials Research, GKSS Research Center, Geesthacht Germany, ²Science et Ingénierie des Materiaux et Procédés, (SIMaP-GPM2), Grenoble Institute of Technology, Grenoble France

9:00 PM - FF5.30

Rougness of Fracture Surfaces in a Model Nanosilicate Gel Determined from Magnetic Resonance Imaging.

Henrik Hemmen ¹, Eduardo de Azevedo ², Christian Nielsen ¹, Knut Magnus ¹, Ricardo de Souza ³, Mario Engelsberg ³, Jon Otto Fossum ¹
¹Physics, Norwegian University of Science and Technology, Trondheim Norway, ²Programa de Pós-Graduação em Ciência de Materiais , Universidade Federal de Pernambuco, Recife Brazil, ³Departamento de Física, Universidade Federal de Pernambuco, Recife Brazil

9:00 PM - FF5.31

Effect of Alloying Elements on the Elastic Properties of γ-Ni and γ'-Ni3Al from First-principles Calculations.

Yunjiang Wang ¹, Chongyu Wang ^{1 2}
¹Physics Department, Tsinghua University, Beijing China, ², The International Center for Materials Physics, Chinese Academy of Sciences, Shengyang China

9:00 PM - FF5.32

Application of Strip Bending Test to Mechanical Characterization of Transfer-printed Metallic Film with Nano-scale Thickness.

Jae-Hyun Kim ¹, Hyun-Joo Choi ¹, Sun-Ah Song ¹, Hak-Joo Lee ¹, Byung-Ik Choi ¹
¹Nano-Mechanics, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of)

9:00 PM - FF5.34

Strength of Nanotubes, Filaments and Nanowires from Sonication Induced Scission.

Yan Yan Huang ¹, Tuomas Knowles ¹, Eugene Terentjev ¹
¹Department of Physics, University of Cambridge, Cambridge United Kingdom

9:00 PM - FF5.35

Simulation of Plastic Deformation in Nanoparticles.

Yoshiaki Kogure ¹, Masao Doyama ¹, Tadatoshi Nozaki ¹
¹, Teikyo University of Science and Technology, Uenohara, Yamanashi, Japan

9:00 PM - FF5.36

On Effective Indenters Used in Nanoindentation Data Analysis.

Guanghui Fu ¹, Tiesheng Cao ², Ling Cao ¹
¹, LC Dental, Fremont, California, United States, ²Ultrasonographic Diagnostics, Fourth Military Medical University, Xi'an China

9:00 PM - FF5.37

Modeling Adhesion Contact between a Compliant Cylinder and a Rigid Substrate.

Jiayi Shi ¹, Sinan Mueftue ¹, Kai-tak Wan ¹
¹Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States

9:00 PM - FF5.38

The Effects of Alloying Components on the Adhesion Strength of the Oxides on Carbon Steels.

Chaewon Song ¹, Seungmok Cho ², Yoonhee Kang ³, Jongsub Lee ³, Jinwoo Park ¹
¹Dep. of Materials Science and Engineering, Yonsei university, Seoul Korea (the Republic of), ²Materials Science and Technology Research Division, Korea Institute of Science and Technology, Seoul Korea (the Republic of), ³Joining Research Group, Technical Research Laboratory, POSCO, Pohang Korea (the Republic of)

9:00 PM - FF5.39

Mechanical Properties of Colloidal Silica Particles after MeV Ion-Induced Shape Tailoring.

Juan-Carlos Cheang-Wong ¹, Ulises Morales ¹
¹Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Mexico, D.F., Mexico

Colloidal silica particles are being intensively studied due to their potential applications in catalysis, intelligent materials, optoelectronic devices and coating technology. The properties of these SiO₂ particles depend on their size, size distribution and shape, which in turn determine the different roles they can play as electronic substrates, electrical and thermal insulators, photonic bandgap crystals, masks for lithographic nanopatterning, etc, in technologically expected nanodevices. Ion irradiation induces damage and structural changes in solids due to energy losses of multi-MeV heavy ions via ionization events and atomic collisions occurring in the near-surface region of the irradiated sample. Indeed, it has been observed that amorphous glassy materials like silicon dioxide can undergo extreme deformations under exposure to high-energy beams. This ion-beam induced anisotropic deformation of amorphous materials such as silica has been observed in the case of SiO₂ films on Si substrates as well as in colloidal silica particles.For this work, spherical submicrometer-sized silica particles were prepared by the Stöber process, from a reaction mixture containing tetraethoxysilane, ammonia and ethanol, and deposited into silicon wafers. Monodisperse spherical particles were obtained with a narrow size distribution. In order to tailor the particle shape, the samples were irradiated at room temperature with 8 MeV Si ions and fluences up to 5×10¹⁵ Si/cm², following an angle of 45° with respect to the sample surface. After the Si irradiation the as-prepared spherical silica particles turned into ellipsoidal particles, as a result of the increase of the particle dimension perpendicular to the ion beam and a decrease in the direction parallel to the ion beam. This effect increases with the ion energy and fluence, and depends on the electronic energy loss of the impinging ion. The size and shape of the silica particles were determined by SEM. The effect of the particle deformation on the mechanical properties was studied mainly by hardness measurements and will be discussed in this paper.

9:00 PM - FF5.4

An In Situ Scanning Electron Microscopy Study of Size Dependent Mechanical Behaviors of Metallic Nanowires.

Cheng Peng ¹, Yang Lu ¹, Yogeeswaran Ganesan ¹, Yongjie Zhan ¹, Jun Lou ¹
¹Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States

9:00 PM - FF5.40

Micromechanical Testing of Nanostructured NbTiNi Hydrogen Permeation Membranes.

Tetsuya Kusuno ¹, Yusuke Shimada ¹, Mitsuhiro Matuda ¹, Masaaki Otsu ¹, Kazuki Takashima ¹, Minoru Nishida ², Kazuhiro Ishikawa ³, Kiyoshi Aoki ³
¹, Kumamoto University, Kumamoto Japan, ², Kyushu University, FUKUOKA Japan, ³, Kitami Institute of Technology, HOKKAIDO Japan

9:00 PM - FF5.41

Size Effects and Deformation Mechanisms in Multi-layer Metallic Composites with Coherent and Incoherent Interfaces.

Ioannis Mastorakos ¹, Hussein Zbib ¹
¹School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States

9:00 PM - FF5.45

Mechanical Properties of the Nanocrystalline High Pressure Phases of Silicon Si-III and Si-XII.

Bianca Haberl ¹, Jodie Bradby ¹, Simon Ruffell ¹, Naoki Fujisawa ¹, Jim Williams ¹
¹Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory, Australia

It is well known that the diamond-cubic form of silicon, Si-I, undergoes a phase transformation to a metallic phase, Si-II, when pressurized to ∼11 GPa in a diamond-anvil cell. On pressure release this Si-II undergoes further phase transformation to the crystalline phases Si-XII and Si-III, which in turn re-transform completely to Si-II upon re-pressurization. The formation of a metallic Si phase has also been observed at similar pressures under indentation loading. Depending on the unloading conditions, nanocrystalline high pressure phases can be nucleated under the indentation tip. However, cyclic loading experiments to moderate load levels have reported elastic behavior after the initial formation of the high pressure phases. Thus, it was concluded that the high pressure phases might either have a higher indentation hardness than Si-I or that the high pressure phases created by indentation do not re-transform to Si-II when pressurized. The reasons for this different behavior are unclear and this study addresses this issue. A relatively large volume (9 μm diameter extending approximately 500 nm below the surface) of the high pressure phases (a mixture of Si-III and Si-XII phases) is created by indentation using a microscale spherical tip. This volume is then probed for its mechanical properties with a small Berkovich tip. The indentation behavior of these high pressure phases is compared to the indentation behavior of Si-I, bulk as well as nanocrystalline material, whereby the nanocrystalline material itself was created from the high pressure phases by thermal annealing. Indentation data as well as Raman microspectroscopy and cross-sectional transmission electron microscopy reveal that the nanocrystalline silicon (Si-I) phase transforms in a similar manner to single crystal silicon. Interestingly, the high pressure phases (Si-III/Si-XII) seem to deform plastically at moderate loads via slip along the grain boundaries rather than through phase transformation. Additionally, the indentation hardness of these different materials was determined by two different methods, by instrumented indentation according to the method of Oliver and Pharr and by directly scanning the projected area of the residual indent impression with an atomic force microscope. A lower indentation hardness of the nanocrystalline silicon compared to bulk material is found, whereas the high pressure phases exhibit a higher indentation hardness than either.

9:00 PM - FF5.6

Effect of Oxygen and Hydrogen Concentration on Nanoindentation-induced Phase Transformations in Amorphous Silicon.

Simon Ruffell ¹, Jyotsna Vedi ¹, Jodie Bradby ¹, Jim Williams ¹
¹, Australian National University, Canberra, Australian Capital Territory, Australia

During nanoindentation, silicon undergoes a series of pressure-induced phase transformations. On loading, diamond cubic Si-I transforms to a metallic phase (Si-II) at a pressure of ~11 GPa. During unloading Si-II further phase transforms to either amorphous silicon (a-Si) or a mixture of high pressure polycrystalline phases (Si-III and Si-XII) depending on unloading rate. “Pure” a-Si formed by ion-implantation undergoes these pressure-induced phase transformations. However, chemical vapour deposited a-Si does not. One possibility for this is the high impurity content in such films.The effect of the local oxygen and hydrogen concentration in ion-implanted amorphous Si (a-Si) on nanoindentation-induced phase transformations has been investigated. Implantation of O and H into the a-Si films has been used to controllably introduce an approximately constant concentration of each species, ranging from ~1018 to ~1021 cm-3, over the depth range of the phase transformed zones. Nanoindentation was performed under conditions that ensure a phase transformed zone composed completely of Si-III/XII in the nominally O and H-free a-Si. The effect of the local concentration has been investigated by analysis of the unloading curves, Raman micro-spectroscopy, and cross-sectional transmission electron microscopy (XTEM). The formation of Si-III/XII from Si-II on unloading is suppressed with increasing oxygen and hydrogen concentration, favouring a greater volume of a-Si within the zones. Raman and XTEM verify that the volume of Si-III/XII decreases with increasing O and H concentration. With the smaller volumes of Si-III/XII, the pop-out normally observed on load versus penetration depth curves during unloading decreases in magnitude, becoming more kink-like and is barely discernable at high concentrations of oxygen and hydrogen. The probability of forming any high pressure phases is reduced from 1 to ~0.1 for concentrations of ~1021 cm-3. We suggest that the bonding of O and H with Si reduces the formation of Si-III/XII during unloading through a similar mechanism to that of oxygen-retarded solid phase crystallization of a-Si. In the case of H, the formation of gas bubbles may also play a role. These findings open up the possibility to engineer subsurface nanostructures composed of the high pressure crystalline phases by a combination of selective area implantation and tailoring of impurity concentration-depth profiles.

9:00 PM - FF5.7

Mechanomutable Carbon Nanotube Arrays.

Steven Cranford ¹, Markus Buehler ¹
¹Department of Civil and Environmental Engineeirng, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

9:00 PM - FF5.9

Dislocation Dynamics Simulations of Metal Nano- and Micro-Imprinting.

Yunhe Zhang ¹, Erik Van der Giessen ², Lucia Nicola ¹
¹Materials Science and Engineering, Delft University of Technology, Delft Netherlands, ²Department of Applied Physics, University of Groningen, Groningen Netherlands

9:00 PM - FF5: PosterI

FF5.20 Transferred to FF2.11

2009-12-02 Show All Abstracts

Symposium Organizers

Jun Lou Rice University

Brad Boyce Sandia National Laboratories

Erica Lilleodden GKSS Forschungszentrum

Lei Lu Chinese Academy of Sciences

FF6/DD6: Joint Session: Nanomechanics for MEMS/NEMS Applications

Session Chairs

Brad Boyce

Henry Padilla

Kevin Turner

Wednesday AM, December 02, 2009

Room 304 (Hynes)

9:30 AM - **FF6.1/DD6.1

Measuring and Mapping Mechanical Properties with Nano-Scale Resolution.

Robert Cook ¹
¹Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States

10:00 AM - FF6.2/DD6.2

Imperfection and Size Dependent Ductility of Thin Freestanding Metallic Films.

Thomas Pardoen ¹, Charles Brugger ¹, Michael Coulombier ¹, Alexandre Boe ¹, Marie-Stephane Colla ¹, Joris Proost ¹, Thierry Massart ², Jean-Pierre Raskin ¹
¹, Université catholique de Louvain, Louvain-la-Neuve Belgium, ², Université libre de Bruxelles, Brussels Belgium

10:15 AM - FF6.3/DD6.3

Improved In-situ On-chip Microelectromechanical Uniaxial Tensile Tester.

Siddharth Hazra ¹, Jack Beuth ¹, Maarten de Boer ²
¹Mechanical engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, ², Sandia National Laboratories, Albuquerque, New Mexico, United States

10:45 AM - FF6.5/DD6.5

Size-dependent Mechanical Properties of Polymer-nanowires Fabricated by Two-photon Lithography.

Satoru Shoji ¹, Sana Nakanishi ¹, Tomoki Hamano ¹, Satoshi Kawata ^{1 2}
¹Department of Applied Physics, Osaka University, Osaka Japan, ²Nanophotonics Laboratory, RIKEN, Saitama Japan

Two-photon lithography allows us to fabricate arbitrary three-dimensional structures with micro/nano-spatial resolution. The intrinsic three-dimensional spatial resolution of two-photon lithography is a promising tool for developing a variety of novel photonic and mechanical nano-devices. In addition, two-photon lithography makes it possible to study the properties of polymers of micro/nano-meter dimension [1-4]. In this presentation, we show the evidence that the elasticity and the transition temperature of polymers start to show size-dependent characteristics when the size of the polymer decreases down to a few hundreds of nanometers. We fabricated free-standing polymer nano-wires in the shape of coil spring by two-photon lithography, and measured the elasticity of the nano-wires by applying a mechanical tension onto the springs through laser trapping technique under temperature control. From the stretching length of the spring generated by a certain optical force, the spring constant of the spring and the shear modulus of polymer were calculated from simple Hook’s law. The material we used is a compound of methyl-methacrylate, dipentaerythritol hexaacrylate, benzil, and 2-benzyl-2-(dimethylamino)-4’-morpholino-butyrophenone. We scanned a light spot of a Ti:Sapphire laser at 780 nm with a pulse width of 80 fs focused by a 1.4 NA microscope objective to shape the polymer nano-wires suspended by a thick pillar. We observed that the elasticity of the polymer, which is usually an invariable coefficient, changes according to the thickness of the polymer wire. Furthermore, we changed the temperature of the entire polymer structures from -20 to 40 °C with measuring the elasticity of the springs. We observed phase transition of polymer wires with a rapid change of the share modulus, which also shows a size-dependent behavior. Recently, the similar experimental results, i.e. the drop of the glass transition temperature, were also reported in thin polymer nano-films. Our result is a clear evidence of such a nano size-effect of mechanical properties in polymers confirmed from free-standing polymer nanostructures. [1]S. Nakanishi, H. Yoshikawa, S. Shoji, Z. Sekkat, and S. Kawata, J. Phys. Chem. B 112, 3586-3589 (2008). [2] S. Nakanishi, S. Shoji, S. Kawata, and H.-B. Sun, Appl. Phys. Lett. 91, 063112 (2007). [3]H. Ishitobi, S. Shoji, T. Hiramatsu, H.-B. Sun, Z. Sekkat, and S. Kawata, Opt. Express 16, 14106-14114 (2008). [4]S. Kawata, H.-B. Sun, T. Tanaka, and K. Takada, Nature, 412, 697 (2001).

11:00 AM - FF6/DD6:MEMS

BREAK

11:30 AM - **FF6.6/DD6.6

Nano- and Micron-Scale Fracture and Fatigue: From MEMS to OLED Structures.

Winston Soboyejo ^{1 2}
¹Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, ²Princeton Institute of Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States

12:00 PM - FF6.7/DD6.7

Performance and Reliability of Ru-coated Microrelays.

Maarten de Boer ¹, David Czaplewski ^{1 3}, Michael Baker ¹, Steven Wolfley ¹, Gary Patrizi ¹, David Tallant ², James Ohlhausen ²
¹Microsystems Science, Technology and Components, Sandia National Labs, Albuquerque, New Mexico, United States, ³Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, ²Materials Science and Engineering, Sandia National Labs, Albuquerque, New Mexico, United States

12:15 PM - FF6.8/DD6.8

Investigating the Dynamics of Adhesion and Separation of Microscale Silicon Contacts.

David Grierson ¹, John Nguyen ², Kevin Turner ¹
¹, UW-Madison, Madison, Wisconsin, United States, ², Sandia National Laboratories, Albuquerque, New Mexico, United States

Controlling adhesion is a primary challenge for improving the performance and reliability of micro-electromechanical systems (MEMS). Microscale components are highly susceptible to the influence of surface forces, and systematic micromechanical investigations into the nature of adhesion between MEMS materials need to be undertaken in order to fully characterize and ultimately surmount the constraints that adhesive forces impose upon successful device creation. Interfacial behavior is typically described by a single quantity such as the work of adhesion, but the adhesion and separation behavior of an interface is more complex, and a more complete description of the mechanical interaction between contacting surfaces is needed. To investigate this and other adhesion-related issues, we have constructed a novel micromachined test structure to characterize room-temperature adhesion of MEMS-material surfaces with nanoscale roughness. The measurement approach shares some similarities with on-chip micromachined beam arrays that have been employed previously, but is unique in that the microscale beams are not fabricated directly on the test substrate. Instead, a chip with micromachined silicon cantilever beams is controllably contacted with a separate test surface to form the interface to be studied. The separation gap between the beams and the substrate is controlled with a piezoelectric nanopositioner, and the deformed profiles of the adhered beams are measured with an interferometer. The use of a separate beam and test surface allows for the investigation of a broader range of materials and facilitates the inspection and analysis of the contacting surfaces before and after testing. The test method allows for dynamic, time-dependent characterization of both the adhesion and separation of microscale contacts. Here, we describe the technique, report theoretical and finite element analysis of the test structure, and present measurements of adhesion between hydrophilic, single-crystal silicon surfaces with nanoscale roughness (r.m.s. ~0.3 nm) as a function of relative humidity (RH). We find that the work of separation is three to seven times higher than the work of adhesion, which is considerably different than the conventional assumption that the work of adhesion and fracture are the same for room temperature contacts, and we find that the adhesion energy and hysteretic behavior are influenced by the RH. The underlying mechanisms that lead to adhesion and hysteresis in these contacts will be discussed. This work was partially supported by AFOSR MURI Contract #FA9550-08-1-0337.

12:30 PM - FF6.9/DD6.9

Mapping Nanoscale Wear Field by Combined Atomic Force Microscopy and Digital Image Correlation Techniques.

Zhi-Hui Xu ¹, Michael Sutton ¹, Xiaodong Li ¹
¹Department of Mechanical Engineering, University of South Carolina, Columbia, South Carolina, United States

FF7: Novel Nanomechanical Characterization Methods

Session Chairs

Chris Xiaodong Li

Cynthia Volkert

Wednesday PM, December 02, 2009

Room 304 (Hynes)

2:30 PM - **FF7.1

Deformation Mechanisms of Nanostructured Metals Studied by In-situ Electron Microscopy.

Gerhard Dehm ^{1 2}
¹Materials Physics, Montanuniv. Leoben, Leoben Austria, ²Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben Austria

3:00 PM - FF7.2

In situ Characterization of the Electrical and Mechanical Properties of Oxide Nanowires using STM-STEM.

Hye Jung Chang ¹, A. Borisevich ¹, S. Kalinin ², E. Strelcov ³, A. Kolmakov ³, B. Mirman ⁴, S. Pennycook ¹
¹Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ²Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ³Department of Physics, Southern Illinois University Carbondale, Carbondale, Illinois, United States, ⁴Department of Mathematics and Computer Science, Suffolk University, Boston, Massachusetts, United States

Oxide nanowires are promising materials for chemical and biological sensors, photonics and photovoltaics. The macroscopic properties have been widely studied and efforts to characterize the individual wires’ properties and their surface also have been made recently using scanning electron microscopy (SEM) and scanning probe microscopy (SPM) [1]. However, the mechanisms of lattice-transport coupling and interplay between chemical changes, mechanical deformation, and transport still remain largely unexplored. In this study, combined STM-STEM technique was used to enable in situ structural/mechanical/electrical analysis. Single-crystal nanowires (SnO₂, ZnO, VO₂) were vapor grown in a tube furnace by thermal evaporation under Ar atmosphere. In-situ measurement of electrical properties and observation at the nanometer level was carried out by using a Nanofactory Instruments Scanning Tunneling Microscope (STM) holder in the Scanning Transmission Electron Microscope (STEM) (FEI Titan S 80-300) operating at 300 kV. A W tip for STM probe was fixed on the 3 dimensionally moveable end of a piezotube in the holder and was used as both a current probe and a mechanical manipulator. The nanowires were attached to other W rod acting as a counter electrode. Individual nanowire’s I-V characteristics were used to characterize transport properties. The nanowires were (elastically) bent to a varying degree, and then changes in transport properties were concomitantly recorded. While the changes in transport properties caused by mechanical deformation were interpreted as a signature of a strain-induced insulator-metal transition in a previous study [2], we find that in the experimental setup of STM-STEM there are many factors contributing to the observed changes. Even in the case of SnO₂, where no phase transitions or piezogalvanic effects are expected, the apparent conductivity increases as the nanowire is bent. We attribute this change to the increase in tip-wire contact area driven by increasing contact strain. Detailed data analysis and estimates of the magnitudes of different contributions for VO₂ and ZnO nanowires will also be presented. Research supported by ORNL’s SHaRE Use Facility (AYB) and Center for Nanophase Materials Sciences (SVK), sponsored by the Scientific User Facilities Division; by the Division of Materials Science and Engineering (SJP), Office of Basic Energy Sciences, U.S. Department of Energy, and by the ORNL LDRD program via a postdoctoral appointment administered jointly by ORNL and ORISE (HJC). The research at SIUC was supported through ACS PRF-G grant.[1] A. Kolmakov, U. Lanke, R. Karam, et al., Nanotechnology 17, 4014 (2006).[2] X. Bai, D. Golberg, Y. Bando, C. Zhi, C. Tang, M. Mitome, K. Kurashima, Nano Lett. 7 (2007) 632.

3:15 PM - FF7.3

In situ Nanoindentation Studies of Deformation Mechanisms in Nanoscale Al/Nb Multilayers.

Nan Li ¹, Jian Wang ², Jianyu Huang ³, Amit Misra ², Haiyan Wang ¹, Xinghang Zhang ¹
¹, Texas A&M University, College Station, Texas, United States, ², Los Alamos National Laboratory, Los Alamos, New Mexico, United States, ³, Sandia National Laboratory, Albuquerque, New Mexico, United States

3:30 PM - FF7.4

Strain Gradients and Interface Strengths in NiAl-Mo Composites from 3D Spatially Resolved X-ray Microdiffraction.

R. Barabash ^{1 2}, H. Bei ¹, Y. Gao ^{2 3}, G. Ice ¹, E. George ^{1 2}
¹Materials Science and Technology Div., Oak Ridge National Laboratory, Oak Ridge TN, Tennessee, United States, ²2.Materials Science and Engineering Department, The University of Tennessee, Knoxville, Tennessee, United States, ³3.Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

3:45 PM - FF7.5

Atomic Force Microscopy Measurements of High Resonance Frequency of Isolated Nanostructures.

Tom Parker ¹, Gwo-Ching Wang ¹, Toh-Ming Lu ¹
¹Physics Department and Center for Integrated Electronics, RPI, Troy, New York, United States

One of the most important physical properties in the performance of MEMS (microelectromechanical systems) and NEMS (nanoelectromechanical systems) is the mechanical frequency response. More specifically the resonance frequency of functionalized micro-cantilevers has been used to detect individual viruses and absorbed chemical species in the biological/chemical research. As devices/structures shrink to the nanometer size scale there is a corresponding increase in the resonance frequency that can range from the MHz into the GHz frequencies. Not only that, when the device components are in the nanoscale, the conventional techniques, including the traditional optical techniques such as doppler interferometry, become impractical. In this presentation, we demonstrated the use of a non-contact atomic force microscope (NCAFM) to measure the high frequency resonance of a PZT (piezoelectric transducer) and AFM cantilevers up to the tens of MHz range [1]. We also demonstrated that the effect of the coupling between the AFM probe and the sample such as a sample cantilever is insignificant, i.e., a shift of <0.3%. In addition one can also measure the mode shape of the characteristic first vibrational mode of the sample cantilever along its length. This shape agrees well with the theoretical shape of a single end-clamped vibrating cantilever. Both the measured small shift in resonance frequency and mode shape support a negligible coupling of the probe cantilever and the sample. Applying this NCAFM technique we measured high resonance frequency of individual nanostructures including nanorods and nanosprings. These nanostructures were fabricated using the oblique angle deposition technique [2]. We showed that individual nanostructures such as slanted amorphous Si (a-Si) nanorods and a-Si 4-turn nanosprings with resonance frequency ranging from kHz to hundreds of MHz can be measured directly using this NCAFM technique. Acknowledgement: Work partially supported by the NSF 0506738 and NSF 0333314. [1] T.C. Parker, F. Tang, G.-C. Wang, T.-M. Lu, Non-contact atomic force microscopy characterization of micro-cantilevers and piezo electric transducers with frequencies up to the tens of MHz, Sensors and Actuators A: Physical A 148, 306 (2008). [2] D.-L. Liu, D.-X. Ye, F. Khan, F. Tang, B.K. Lim, R.C. Picu, G.-C. Wang, T.-M. Lu, Mechanics of patterned helical Si springs on Si substrate, Journal of Nanoscience and Nanotechnology 3(6), 492 (2003).

4:00 PM - *

Break

4:30 PM - **FF7.6

Critical Issues in Making Small-Depth Mechanical Property Measurements by Nanoindentation with Dynamic Stiffness Measurement.

George Pharr ^{1 2}, Jeremy Strader ¹, Warren Oliver ³
¹Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, ²Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ³, Agilent Technologies, Oak Ridge, Tennessee, United States

5:00 PM - FF7.7

An Analytical Solution for the Stress Field around an Elastoplastic Spherical Indentation/Contact.

Gang Feng ¹, Timothy Montalbano ¹
¹Mechnical Engineering, Villanova University, Villanova, Pennsylvania, United States

5:15 PM - FF7.8

Lattice Misorientation Patterns and Strain Gradient Effects in Single Crystals under Spherical Indentation.

Yanfei Gao ^{1 2}, Bennett Larson ³, George Pharr ^{1 3}
¹Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, ²Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ³Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

5:30 PM - FF7.9

Microcompression as a Quantitative Technique: A Case Study on Fused Silica.

Erica Lilleodden ¹, Alfred Cornec ¹
¹Institute of Materials Research, GKSS Research Center, Geesthacht Germany

5:45 PM - FF7.10

Measuring the Elastic Modulus of Anisotropic Materials using Micro-compression Testings.

Gan Yixiang ¹, Daniel Kaufmann ^{1 2}, Ruth Schwaiger ², In-suk Choi ¹
¹IMF II, Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany, ²IZBS, University of Karlsruhe, Karlsruhe Germany

2009-12-03 Show All Abstracts

Symposium Organizers

Jun Lou Rice University

Brad Boyce Sandia National Laboratories

Erica Lilleodden GKSS Forschungszentrum

Lei Lu Chinese Academy of Sciences

FF8: Mechanical Behavior of Nanocrystalline, Nanoporous & Nanotwinned Materials I

Session Chairs

John Balk

Ke Lu

Thursday AM, December 03, 2009

Room 304 (Hynes)

9:30 AM - FF8.1

Microstructure, Mechanical Behavior and Deformation Mechanisms of Nanocrystalline Ni-50wt%Fe.

Steven Van Petegem ¹, Julien Zimmermann ¹, Stefan Brandstetter ^{2 1}, Xavier Sauvage ³, Marc Legros ², Bernd Schmitt ⁴, Helena Van Swygenhoven ¹
¹NUM/ASQ, Paul Scherrer Institut, Villigen Switzerland, ², CEMES-CNRS, Toulouse France, ³Faculte des Sciences, University of Rouen, Saint-Etienne du Rouvray France, ⁴Swiss Light Source, Paul Scherrer Institut, Villigen Switzerland

It is well known that the strength of metals increases with decreasing grain size, a behaviour that is well described by the phenomenological Hall-Petch relation down to grain sizes of 100 nm and even lower. Deformation mechanisms in coarse grained metals are based on a dislocation mechanism where dislocations are created during deformation with their propagation and multiplication being an essential mechanism for the resulting ductility and strength. However with decreasing grain size a transition towards grain boundary dominated plasticity mechanisms is expected.Molecular dynamics simulations suggest that in nanocrystalline materials slip is generated at the grain boundaries (GB); dislocations nucleated at GBs propagate through the grains and are absorbed at the opposing GB, leaving no dislocation debris in the grain interiors. In order to understand the elastic and plastic deformation properties of nanocrystalline metals we have developed an in-situ synchrotron x-ray-diffraction technique which allows the simultaneous measurement of many diffraction peaks continuously during mechanical testing, providing a direct link between the evolving microstructure and macroscopic mechanical data (Rev. Sci. Instr. 77 (2006) 013902). Here we present recent results obtained for electrodeposited Ni-Fe with a nominal iron content of 50%. The microstructure of this alloy is characterized by a narrow grain size distribution with a mean grain size of 10nm. Atom probe tomography and electron energy loss spectroscopy indicate that the NiFe matrix is nearly randomly ordered without significant segregration at the grain boundaries. Geometrical phase analyses show that local strain gradients are present in most of the grains, especially near the grain boundaries. X-ray diffraction reveals the presence of high internal strain variations and a significant <100> texture.Uni-axial mechanical tensile tests indicate that Ni-Fe exhibits a transient regime after reloading or strain rate jump tests. This regime is characterized by an upper or lower yield point, which is not observed during continuous loading. Furthermore the strain rate sensitivity is relatively low. In-situ x-ray diffraction experiments reveal strong relaxation effects during initial loading in the microplastic regime. In contrast to nanocrystalline Ni (Adv. Mater. 18 (2006) 1545) no increase of the elastic inhomogeneous strain variations after loading in the macroplastic regime was observed.

9:45 AM - FF8.2

Grain Boundary Shear-migration Coupling: From Experiments to Modelling.

Frederic Mompiou ¹, Marc Legros ¹, Daniel Caillard ¹
¹, cemes/cnrs, toulouse France

10:00 AM - **FF8.3

Interface Effects on the Mechanical Properties of Nanocrystalline Nanolaminates.

Alan Jankowski ¹, H.S. Tanvir Ahmed ¹
¹Mechanical Engineering, Texas Tech University, Lubbock, Texas, United States

10:30 AM - FF8.4

Deformation Crossover: From Nano to Meso Scales.

Xun-Li Wang ¹, Sheng Cheng ², Alexandru Stoica ¹, Joe Horton ³, Chain Liu ^{3 4}, Yang Ren ⁵, Jon Almer ⁵, Donald Brown ⁶, Bjorn Clausen ⁶, Peter Liaw ², Liang Zuo ⁷
¹Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ²Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, ³Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ⁴Mechanical Engineering Department, Hong Kong Polytechnic University, Hong Kong China, ⁵X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States, ⁶Los Alamos Neutron Science Center, Los Alamos National Laboratory, Oak Ridge, New Mexico, United States, ⁷Key Laboratory for Anisotropy and Texture of Materials, Northeast University, Shenyang China

10:45 AM - FF8.5

De-twinning Mechanisms of Growth Twins in Face Centered Cubic Metals.

Jian Wang ¹, Nan Li ², Osman Anderoglu ², Xinghang Zhang ², Amit Misra ¹, John Hirth ¹
¹, LANL, Los Alamos, New Mexico, United States, ², Texas A&M, College Station, Texas, United States

11:00 AM - *

Break

11:30 AM - FF8.6

New Mechanisms for Ultrahigh Strength and Ductility in Nano-Twinned Metals.

Zhaoxuan Wu ¹, Yong-Wei Zhang ^{2 3}, David Srolovitz ^{3 4}
¹NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore Singapore, ²Materials Science and Engineering, National University of Singapore, Singapore Singapore, ³, Institute of High Performance Computing, Singapore Singapore, ⁴Department of Physics, Yeshiva University, New York, New York, United States

11:45 AM - FF8.7

Nanotwins and Partial Dislocations in Ultrafine-grained Gold Wires.

Effie. Y. H. Chew ^{1 5}, Hui Kim Hui ², C. Ferraris ³, Yong Hao Zhao ⁴, E. Lavernia ⁴, Johnny Yeung ⁵, Chee Cheong Wong ¹
¹5School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, ⁵, Heraeus Materials Singapore Pte Ltd, Singapore Singapore, ², Institute of Materials Research and Engineering, Singapore Singapore, ³, Laboratoire de Minéralogie, Paris France, ⁴, University of California Davis, California, California, United States

Simultaneous high ductility and strength is a much sought-after goal by researchers studying mechanical properties of nanocrystalline (NC) and ultrafine-grained (UFG) materials. As predicted from both computational and experimental studies, dislocation activity and twinning are known to behave differently in NC and UFG materials vis-à-vis conventional coarse-grained (CG) materials.Firstly, in materials having grain size < ~ 50 nm, partial dislocations are believed to become activated in face-centered cubic (FCC) metals, that grains may be sheared by partial dislocations, which are absorbed in the opposite grain boundaries (GB), leaving an intrinsic stacking fault (SF) behind. This is so-called the partial dislocation mediated process (PDMP). In the next regime (grain size between ~50 nm and ~1000 nm), deformation is believed to take place via conventional unit dislocations, i.e. the trailing partial can be nucleated before the entire grain is sheared by the leading partial. The major difference of this regime with traditional CG metals is that the lattice dislocations are nucleated from the GB, while both boundary and intragranular sources are important in traditional metals. Besides deformation mechanisms, twinning effect also change as a function of grain size. Twinning is harder to occur in metals with finer grain size, as the twinning stress gets higher with reduced grain size. However, molecular dynamics simulation has suggested a transition of twin nucleation mechanism, from pole mechanism to partial dislocation initiated, as grain size gets into the very fine size regime. Also, twinning was reported to give rise to simultaneous high ductility and strength, and is therefore receiving much attention.In this work, large amount of localized partial dislocations and twins, generating from the GB, are observed on UFG Gold (Au) wire. This shows that PDMP has taken place. Our grain size range of 100-500 nm is much higher than the suggested boundary for PDMP, which is between 10 to 50 nm. Here, the smallest possible nanotwins are observed, consisting of only two atomic layers (~ 0.12 nm) at each side of the twin plane. Detailed characterization of the types of partial dislocations revealed that the partial are of both Shockley and Frank type. It is seen that twinning density in the UFG Au wires gets higher with more addition of calcium inside the Au wires. It is known that in CG metals, dopants that segregate to GB can create ledges which are conducive to dislocation generation. Similar scenarios can happen in UFG or NC materials, but probably partial dislocations instead of full dislocations shall be emitted, as dictated by the grain size, eventually giving rise to twinning. It is postulated that dopant that can preferentially segregate to the GB shall lead to the proliferation of SF and twin.

12:00 PM - FF8.8

Yielding and Plasticity of Periodically-Twinned Nanowires in FCC Metals from Molecular Dynamics Simulations.

Chuang Deng ¹, Frederic Sansoz ¹
¹School of Engineering and Materials Science Program, The University of Vermont, Burlington, Vermont, United States

12:15 PM - FF8.9

Maximum Strength of Copper with Nano-scale Twins.

Lei Lu ¹
¹SYNL, Institute of Metal Research, Shenyang China

12:30 PM - FF8.10

Temperature-Induced Amorphization in Periodically-Twinned III-V Zinc Blende Nanowires During Tensile Loading.

Rassin Grantab ¹, Vivek Shenoy ¹
¹Mechanics of Solids, Brown University, Providence, Rhode Island, United States

12:45 PM - FF8.11

On the Role of Nanoscale Twins in the Deformation of fcc Metals: A Competition of Hardening or Softening Mechanisms.

Karsten Albe ¹, Alexander Stukowski ¹, Diana Farkas ²
¹Materials Modeling Division, Institute of Materials Science, Darmstadt Germany, ²Materials Science and Engineering, VirigniaTech, Blacksburg, Virginia, United States

FF9: Mechanical Behavior of Nanocrystalline, Nanoporous & Nanotwinned Materials II

Session Chairs

Alan Jankowski

Lei Lu

Thursday PM, December 03, 2009

Room 304 (Hynes)

2:30 PM - **FF9.1

Mechanical Behaviors of Bulk Nanostructured Metals Synthesized by Means of Dynamic Plastic Peformation (DPD).

Ke Lu ¹, Nairong Tao ¹
¹SYNL, Institute of Metal Research, Shenyang, Liaoning, China

3:00 PM - FF9.2

High-strain Rate Behavior of Nanocrystalline Tantalum Processed by High Pressure Torsion.

Zhiliang Pan ¹, Xiaolei Wu ², Brian Schuster ³, Laszlo Kecskes ³, Qiuming Wei ¹
¹Mechanical Engineering, University of North Carolinat at Charlotte, Charlotte, North Carolina, United States, ², Institute of Mechanics, CAS, Beijing China, ³, US Army Research Lab, Aberdeen Proving Ground, Maryland, United States

Nanocrystalline (NC grain size < 100 nm) metals exhibit some fascinating properties, particularly very high strengths under quasi-static loading (strain rates below 10^-1 s^-1 ) due to the presence of large population of grain boundaries which greatly impede dislocation activities, as well as the very small grain size which disallows the multiplication of dislocations through the conventionally well known Frank-Read source. In the past two decades, a great amount of work has been undertaken to understand the mechanical properties and their relation to the microstructure of NC metals, with tremendous progress. However, not much has been known about the dynamic high-strain rate mechanical behavior of such materials. Recent experimental results have shown that many nanocrystalline and ultrafine grained body centered cubic metals exhibit adiabatic shear localization under impact loading. This is explained by the vanishing strain hardening and reduced strain rate hardening, combined with the much elevated strength. However, the smallest grain size achieved thus far has been at best in the upper bound of the nanocrystalline regime. No work has been available on the dynamic mechanical behavior of fully-dense, truely nanocrystalline metals. In this work, we have examined the dynamic response (i.e., strain rate >10³ s^-1) of nanocrystalline tantalum (Ta) (grain size ~40 nm), processed by high-pressure torsion. To test the very small dynamic samples (~1.0 mm thick) at high strain rates, we used a miniaturized Kolsky bar (or Split-Hopkinson Pressure Bar) system, for which the input and output bars are made of high-strength maraging steel of 5 mm in diameter. Combined with the quasi-static testing results, we have found that the NC Ta has increased strain rate sensitivity compared to its coarse-grain counterpart. Unlike other typical body-centered cubic NC metals such as Fe, V, or W which exhibit strong tendency to adiabatic shear localization under dynamic compression, NC Ta dynamic specimens deform in a uniform manner. This is explained by the persistent strain hardening and the increased strain rate sensitivity of the NC Ta.

3:15 PM - FF9.3

Effect of Annealing on the Residual Stress in Electrodeposited Nanocrystalline Ni-W Alloys.

Tiffany Ziebell ¹, Christopher Schuh ¹
¹Dept. of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States

3:30 PM - FF9.4

Atomic Scale Studies of Micro-Mechanisms related to Dynamic Failure in Ultra-Fine Grain Sized Nanocrystalline Cu.

Avinash Dongare ^{1 2}, Arunachalam Rajendran ³, Bruce LaMattina ⁴, Mohammed Zikry ², Donald Brenner ¹
¹Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, ²Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, United States, ³Mechanical Engineering, University of Mississippi, Uinversity, Mississippi, United States, ⁴, U. S. Army Research Office, Research Triangle Park, North Carolina, United States

4:00 PM - *

Break

4:30 PM - **FF9.6

The Mechanical Behavior on Nanoporous Au: Tailoring Properties by Changing Length Scale.

Eike Epler ¹, Burkhard Roos ¹, Cynthia Volkert ¹
¹Institite of Material Physics, University of Göttingen, Göttingen Germany

5:00 PM - FF9.7

The Micromechanisms of Deformation in Nanoporous Gold.

Rui Dou ¹, Brian Derby ¹
¹School of Materials, University of Manchester, MANCHESTER United Kingdom

5:15 PM - FF9.8

Mechanical Behavior of Gold Nanofoams using Atomistic Simulations.

Kedarnath Kolluri ¹, Michael Demkowicz ¹
¹Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

5:30 PM - FF9.9

Anelastic Behavior of Nanocrystalline Nickel and Nanoporous Metals.

Nicolas Briot ¹, Jochen Lohmiller ^{1 2}, Christoph Eberl ², Oliver Kraft ^{2 3}, T. John Balk ¹
¹Chemical & Materials Engineering, University of Kentucky, Lexington, Kentucky, United States, ²Institut für Zuverlässigkeit von Bauteilen und Systemen, Universität Karlsruhe, Karlsruhe Germany, ³Institut für Materialforschung II, Forschungszentrum Karlsruhe, Karlsruhe Germany

5:45 PM - FF9.10

Porosity Dependence of Elastic Constants of Nanoporous Silicon.

Gazi Aliev ¹, Bernhard Goller ¹, Paul Snow ¹
¹Department of Physics, University of Bath, Bath United Kingdom

FF10: Poster Session: Mechanical Behavior of Nanomaterials---Experiments and Modeling

Session Chairs

Brad Boyce

Erica Lilleodden

Jun Lou

Lei Lu

Friday AM, December 04, 2009

Exhibit Hall D (Hynes)

9:00 PM - FF10.10

Mechanical Behaviors of Nanoporous Carbon.

Mi Xi ¹, Yunfeng Shi ¹
¹Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States

9:00 PM - FF10.11

Localized Characterization of Carbon Nanotubes and Carbon Nanotube Reinforced Nanocomposites using Novel Micromechanical Devices.

Yogeeswaran Ganesan ¹, Yang Lu ¹, Cheng Peng ¹, Hao Lu ¹, Roberto Ballarini ², Boris Yakobson ¹, Jun Lou ¹
¹Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States, ²Civil Engineering, University of Minnesota, Minneapolis, Minnesota, United States

9:00 PM - FF10.12

Size Effects in Nanomechanical Behavior of Protein Materials.

Sinan Keten ¹, Markus Buehler ¹
¹Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

9:00 PM - FF10.15

Computational Simulations of Blast Response of Biological Cell.

Guoxin Cao ¹, Namas Chandra ¹
¹, university of Nebraska-Lincoln, Lincoln, Nebraska, United States

Traumatic brain injury (TBI) caused by the blast wave resulting from primary explosions to head is one of the main casualties of military personnel. TBI can cause the short or long term effect on daily life and work of victims, such as debilitating cognitive deficits, severe headaches, depression, memory deficits and personality changes. The mechanism of TBI induced by blast wave is still not clear. One of the most possible reasons is the severe stretch of brain cells (neuron or glial cell) caused by blast wave. Therefore, it is very important to study the blast response at cellular level.In the present work, the blast response of cell is studied using numerical simulations. Cell is modeled as a two-phase composite system: Phase I comprising microfilaments and intermediate filaments (main components of cytoskeleton); Phase II is the cytoplasm. Since these filaments behave more like strings, Phase I can only resist tensile deformation. Phase I is modeled as a group of linear viscoelastic fibers with the same properties using standard linear solid (SLS) model. Phase II behaves like liquid and can resist only compressive deformation, and is simulated using a Maxwell model. The effects of the volume fraction and the diameter of viscoelastic fibers on blast response are also examined. The blast loading applied on cell surface is modeled by a pressure history: a compressive pressure pulse with less than 1ms duration and sharply reduce to zero. For the sake of reference, the blast response of homogeneous and shell-core cell models are also computed. The blast response of cells can be described by the following parameters: cell pressure, volumetric tension, Von Mises stress. The qusistatic behavior of cell is also shown based on AFM indentation with a flat tip and a similar load as the applied blast pressure. The results in this work show the blast response at cellular level and the effects of geometric cytoskeleton components on the dynamic behavior of biological cells, which can provide a useful guideline to understand the mechanism of blast induced TBI.

9:00 PM - FF10.16

Correlating Nanoparticle Dispersion to Surface Mechanical Properties of TiO2/Polymer Composites.

Yongyan Pang ¹, Stephanie Watson ¹, Aaron Foster ¹, Chang Kwon Moon ¹, Li-Piin Sung ¹
¹, National Institute of Standards and Technology, Gaithersburg, Maryland, United States

9:00 PM - FF10.17

Temperature Variation in Energy Absorption System Functionalized by Nanomaterials.

Aijie Han ¹, Yu Qiao ², Weiyi Lu ², Venkata K. Punyamurtula ², Zhongyuan Sun ¹
¹Chemistry, University of Texas-Pan American, Edinburg, Texas, United States, ²Structural Engineering, University of California-San Diego, San Diego, California, United States

9:00 PM - FF10.18

Mechanics of Silica-PDMS Nanocomposites.

Adrian Camenzind ¹, Thomas Schweizer ², Michael Sztucki ³, Sotiris E. Pratsinis ¹
¹Particle Technology Laboratory, Mechanical & Process Engineering, ETH Zurich, Zurich Switzerland, ²Institute of Polymers, ETH Zurich, Zurich Switzerland, ³, European Synchrotron Radiation Facility (ESRF), Grenoble France

9:00 PM - FF10.19

Multiscale Computer Simulation of Tensile and Compressive Strain in Polymer-Coated Silica Aerogels.

Brian Good ¹
¹Materials Division, Glenn Research Center, Cleveland, Ohio, United States

9:00 PM - FF10.20

Investigation of the Mechanical Properties of High Nanoparticle Loading Fraction Polymer Nano-Composites.

Theodore Kramer ¹, Jeffrey Kysar ², Irving Herman ¹
¹Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States, ²Department of Mechanical Engineering, Columbia University, New York, New York, United States

9:00 PM - FF10.21

Novel Nanostructured Metals by High Rate Severe Plastic Deformation.

Shashank Shekhar ¹, Jiazhao Cai ¹, Ravi Shankar ¹
¹Department of Industrial Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Highly refined nanostructured materials created by imposing Severe Plastic Deformation (SPD) at low strain-rates in Equal Channel Angular Pressing, High Pressure Torsion etc. offer substantial improvements in weight specific strengths in an array of metal alloys. However, the resulting materials are usually bedeviled by limited ductility and thermal stability. Recently, we explored consequences of SPD, but over a much larger range of strain rates than conventional SPD, spanning several orders of magnitude ranging from 10^0 – 10^3/s using a machining-based approach. The ability to control strain-rate by modifying the deformation rate, in addition to the usual control of SPD strains, can engender intriguing nanostructural characteristics in two prototypical systems - low stacking fault energy (SFE) brass and medium SFE Cu. In a particular subset of these studies that involved High Rate Severe Plastic Deformation (HRSPD) characterized by strains >2 at rates > 10^3/s, we will demonstrate control not only over distributions of the size of the nanostructures, but also the distribution of the character of their interfaces. Manipulating these two attributes help design nano-scale microstructures that may help overcome the usual problems of ductility and stability. Our characterizations will also reveal how the interplay of strain and strain-rates in HRSPD intrinsically offers control over the in situ temperature rise in the deformation zone. This obviates the need for an explicit modification of deformation temperature by say, external thermal agitation that characterizes conventional deformation processing paradigms. These observations will also be shown to be interwoven with an overarching influence of HRSPD on the stored energy in the fine-grained system.In brass, the utility of HRSPD at modifying the density of nanotwins that strengthen and possibly stabilize the microstructure will be presented. In Cu, HRSPD can manipulate the grain boundary misorientation distribution as well as nanostructure size distribution. The control over the distribution of the size of the fine grains also involved the generation of unimodal and multimodal grain sizes, as and when needed, to control the resulting levels of ductility and toughness. Manipulation of the stored energies and the interface structure in nanostructured metals from HRSPD will be shown to offer clues for enhancing their stability.

9:00 PM - FF10.22

High-Throughput Optimization of Adhesion in Multilayers by Superlayer Gradient.

Sergey Grachev ¹, Coraly Cuminatto ¹, Alexander Mehlich ¹, Jan-Dirk Kamminga ¹, Elin Sondergard ¹, Etienne Barthel ¹
¹, Saint-Gobain Recherche, Aubervilliers France

9:00 PM - FF10.23

Electrospun Polymer/MWCNTs Nanofiber Reinforced Composites.

Elif Ozden ¹, Yusuf Menceloglu ¹, Melih Papila ¹
¹Material Science and Engineering, Sabanci University, Istanbul Turkey

9:00 PM - FF10.24

Improving the Crack Resistance of Indium-Tin-Oxide (ITO) Films on Polymeric Substrates using Ductile Metal Interlayers.

Eunhye Kim ¹, Chan-woo Yang ¹, Kyeong-hwi Min ¹, Jin-woo Park ¹
¹, Yonsei University , Seoul Korea (the Republic of)

9:00 PM - FF10.25

Thermo-Mechanical Analysis of the Polymer Materials with High Spatial Resolution.

Maxim Nikiforov ¹, S. Gah ², L. Germinario ³, Stephen Jesse ¹, R. Composto ², Sergei Kalinin ¹
¹CNMS, ORNL, Oak Ridge, Tennessee, United States, ², University of Pennsylvania, Philadelphia, Pennsylvania, United States, ³, Appalachian State University, Boone, North Carolina, United States

Behavior of the materials at the nanoscale determines the macroscopic properties of the materials. The origin of many failures lies at the nanoscale, for example, crack nucleates at the mechanical defects in the material, electrical failure happens at the electrical defects etc. In polymeric materials mechanical behavior of the components determines the mechanical behavior of the mixture as well. Phase separation commonly causes failure in polymeric materials, explaining the amount of attention attracted to study local thermomechanical properties of mixed-phase polymeric materials and composites in recent decade.We developed a quantitative method for local thermomechanical analysis of polymers. Commercial atomic force microscope was used as a platform for our method. Our measurements of the mechanical properties are based on the determination of tip – surface contact resonance frequency as a function of the temperature. Measurements of the dynamic property, such as resonance frequency, provide us with the increased sensitivity to the changes in materials properties. To date, local thermal analysis techniques utilize either the displacement of the tip due to penetration into the sample or the change in thermal impedance as detection mechanisms for the onset of melting transition. Due to the large noise inherent in static cantilever deflection detection systems, a measurable signal cannot be determined before a large-scale (>100nm) cavity is formed, thus limiting the spatial resolution. Our approach allows to measure mechanical properties with 50 nm spatial resolution. The experimental protocols that provide reproducible measurement of a polymer's thermomechanical properties were validated on several polymer materials (PET, acrylic polymers and PETG). The theory for the mechanical response of the material to the localized heating was built in order to convert measured parameters (contact resonance frequency and quality factor of the oscillations) to Young’s and loss moduli of the material.Glass transition temperatures of PMMA-rich and SAN-rich domains obtained during the phase separation in PMMA:SAN system was measured with 50 nm spatial resolution. The effect of the annealing time on spatial distribution of the glass transition temperatures is discussed.This research at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

9:00 PM - FF10.27

Characterization of Mechanical Properties of Polymer Nanocomposites by Nanoindentation and Influence of Nanoparticulate Filler on the Viscolastic Response.

Jiri Nohava ², Nicholas Randall ¹
², CSM Instruments, Peseux Switzerland, ¹, CSM Instruments, Needham, Massachusetts, United States

Nanostructured polymers have recently gained high importance due to the possibility of tailoring their mechanical properties by the amount and type of nanofillers. This is mainly due to the fact that the nanofillers have large surface to volume ratio and therefore can significantly affect the overall mechanical properties, even in small amounts, including the creep characteristics of the polymer. At early stages of development these materials are not always available in sufficient volume for standard tensile testing and therefore the nanoindentation procedure has become one of the only methods available to test the mechanical properties. Although the nanoindentation method is now established for measurement of hardness and elastic modulus, determination of creep and viscoelastic properties in general is still quite a challenge mainly due to the existence of thermal drift. This paper presents the results of ongoing research on several types of polymeric materials with various ratios of nanoparticulate fillers. The characterization was done by instrumented indentation with a Berkovich indenter at loads of several tens and hundreds of micronewtons. The creep properties were determined during a pause at maximum force in duration of 60 s to 300 s. The thermal drift of the instrument was verified by indentation on fused silica at the same load and pause duration and it was found that the nanoindentation system has thermal drift of less than 0.5 nm/min while the creep of the tested polymers was in the range of hundreds and tens of nanometers. The level of creep of all samples was measured and its amount was related to the nanofiller content and loading rate. It was found that irrespective of the content of the nanofiller, the amount of creep was higher when the loading rate was higher. At the same time, oscillation indentation measurements were performed to determine the storage and loss moduli of the tested materials. Results show that even very small amounts of nanofiller have a significant influence on the viscoelastic properties of the polymer.

9:00 PM - FF10.28

Training Effect in Artificial Muscle using Polyaniline.

Hikaru Hashimoto ¹, Kazuo Tominaga ¹, Wataru Takashima ², Keiichi Kaneto ¹
¹Biological Functions and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu, Wakamatsu-ku Hibikino 2-4, Japan, ², Research Center for Advanced Eco-fitting Technology, Kyushu Institute of technology, Kitakyushu Japan

9:00 PM - FF10.30

A Comprehensive Study of Cuticle Organisation at Different Hierarchical Levels in Functionally Differentiated Parts of the Exoskeleton of the Edible Crab Cancer pagurus .

Keerthika Balasundaram ¹, Helge Fabritius ¹, Dierk Raabe ¹
¹, MPIE, Düsseldorf Germany

9:00 PM - FF10.31

A Mechanically Actuated Plasmonic Nanoparticle Fluid.

Rama Bhattacharjee ², Ruipeng Li ^{1 2}, Emmanuel Giannelis ², Aram Amassian ¹
²Materials Science and Engineering, Cornell University, Ithaca, New York, United States, ¹Materials Science and Engineering, King Abdullah University of Science and Technology, Jeddah Saudi Arabia

9:00 PM - FF10.32

Deformation Behavior of Nanocrystalline Co-Cu Alloys.

Motohiro Yuasa ¹, Hiromi Nakano ², Kota Kajikawa ¹, Takumi Nakazawa ¹, Mamoru Mabuchi ¹
¹Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Kyoto Japan, ²Cooperative Reserach Facility Center, Toyohashi University of Technology, Toyohashi Japan

9:00 PM - FF10.33

Adhesion Influence of Diamond Coatings on WC-Co Turning Inserts for High Performance Machining Applications.

Humberto Gomez ^{1 4}, Feng Qin ², Ashok Kumar ¹, Kevin Chou ², Bob Johnson ³
¹Mechanical Engineering, University of South Florida, Tampa, Florida, United States, ⁴Ingenieria Mecanica, Universidad del Norte, Barranquilla Colombia, ²Mechanical Engineering, The University of Alabama, Tuscaloosa, Alabama, United States, ³, Seki Technotron USA, Santa Clara, California, United States

9:00 PM - FF10.34

Effect of Nitrogen Doping on the Mechanical Properties of Sol-gel Prepared TiO2 Thin Films: A Nanoindentation Study.

Murat Kurtoglu ^{1 2}, Travis Longenbach ^{1 2}, Yury Gogotsi ^{1 2}
¹Drexel Nanotechnology Institute, Drexel University, Philadelphia, Pennsylvania, United States, ²Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States

9:00 PM - FF10.35

Microstructural and Mechanical Properties of Boron Carbide Ceramics by Methanol Washed Powder.

Kyoung Hun Kim ¹, Jong Pil Ahn ^{1 2}, Joo Seok Park ¹, Jae Hong Chae ¹, Hyung Sun Kim ², Sung Min So ^{1 2}
¹, KICET, Seoul Korea (the Republic of), ², Inha university, Incheon Korea (the Republic of)

9:00 PM - FF10.36

Dispersion Rheology of Carbon Nanotubes in a Polymer Matrix.

Yan Yan Huang ¹, Samit Ahir ¹, Eugene Terentjev ¹
¹Physics, University of Cambridge, Cambridge United Kingdom

9:00 PM - FF10.37

Variable Elastic-Plastic Properties of the Grain Boundaries and Their Effect on the Macroscopic Flow Stress of Nano-Crystalline Metals.

Malgorzata Lewandowska ¹, Romuald Dobosz ¹, Krzysztof Kurzydlowski ¹
¹Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw Poland

The effect of the grain boundaries on flow stress of metals, which is especially prominent in the case of nano-sized ones, has been a subject of numerous experimental and theoretical studies in the past. Recently, remarkable progress has been made in the understanding of this effect due to the new experimental results obtained on metals subjected to nano-grain refinement via Severe Plastic Deformation and as a result of advances in modelling of plastic behaviours of nano-polycrystalline aggregates. In particular, so called composite approach to the properties of the nano-metals proved to be successful in explaining such unique properties of nano-metals as reverse Hall-Petch relationship. However, some key questions with regard to the role of grain boundaries remain unanswered and quantification of their effect on the macroscopic properties is still a challenge.The present paper describes new experimental results obtained on nano-metals produced via hydrostatic extrusion, HE. Nano- and sub-micron structures have been produced by HE in a series of aluminium alloys. Size of grains and mis-orientation of the grain boundaries in the sample subjected to HE have been quantified using high resolution microscopic techniques. It has been found that the obtained nano-structures differed in the average size of grains, normalized width of grain size distribution and grain boundary mis-orientation distribution functions, in the way which seem to be typical of nano-metals obtained by SPD. As HE processed billets are relatively large in dimensions, it was possible to characterize the mechanical properties of the processed materials in tensile tests with relatively good statistics. The results of the tensile tests showed that the flow stress significantly depends on the average grain, grain size distribution and the distribution function of mis-orientation angles. In order to explain the observed difference in the properties of nano- and micro-sized structures, a Finite Element Method models have been developed, which assumes that both grain boundaries and grain interiors may accommodated elastic and non-linear plastic deformation. These models assumed true geometry of grains (which differed in size and shape). Also, variable mechanical properties of grain boundaries have been taken into account (elastic modulus, yield strength and work hardening rate). The results of modelling explain in a semi-quantitative way macroscopic deformation of nano-crystalline aggregates. In particular, they illustrate the importance of the interplay between properties of grain boundaries and grain interiors in elastic and plastic regime. These results provide also insight in such phenomena as nano-scale strain localization. Finally they can be used to optimize the structure of nano-metals in terms of their mechanical properties.

9:00 PM - FF10.39

The Measurement of Mechanical Properties on Chars with Nanoclays Using Nanoindentation.

Seongchan Park ¹, Miriam Rafailovich ¹
¹Materials Science and Engineering, Stony Brook University, Stony Brook, New York, United States

During combustion char formation becomes a crucial factor to reduce flammability of polymeric materials. The char acts as a barrier against combustible gases, conducts heat away from the interior of the sample and reflects the heat from the approaching heat front. We have previously observed that large aspect ratio nanoparticles can act synergistically with flame retardant formulation, rendering a large group of polymers flame retardant. Cone calorimety data has shown that this phenomenon is also related to the formation of chars, even in systems which normally burn without char formation. In order to understand the mechanism through which the nanoparticles increase the flame resistance, we must also study the properties of the chars that are formed. Here we describe a study on Polystyrene (PS) and polymethacrylate (PMMA) polymer blends where neither of the polymers forms a char upon burning and where they can only be rendered flame retardant with the addition of clay and tube nanoparticles. SEM images of the chars indicate that they consist of carbonateous remains mixed with clay platelets or carbon nanotubes. High magnification images reveal that the clay particles are folded, forming long tube-like structures. These structures are only observed in blends and result from differential combustion of the two components where the pressure collapses the clays adsorbed at the polymer interface regions. The mechanical properties of the chars were measured with a micro-indentor since the chars are too brittle to be measured using standard mechanical testing apparatus. We found that the mechanical response of chars from compounds with different compositions varied greatly in their mechanical properties. In particular, the PMMA/C30B char was the hardness, with a modulus of G= 0.2GPa, Similarly PS/C15A and PS/PMMA/C20A had modulii of 0.06GPa and 0.035GPa, respectively. Examination of the, the morphology of the PMMA/C30B residue showed many more small cracks when compared to that of the PS/PMMA/C20A compound. Video images obtained during the cone calorimetry combustion studies revealed that the chars swelled by more than a factor of 4 and then collapsed abruptly. The elasticity of the chars can then be directly related to their degree of swelling and the lack of cracks when the char is deflated, after heat treatments. The compound which had the most elastic chars, also had the best flame retardant performance, passing the UL-94 V0 criterion.

9:00 PM - FF10.4

Micromechanical Modeling of Layer-by-Layer Coated Electrospun Nanofiber Mats for Proton Exchange Membrane Fuel Cells.

Meredith Silberstein ¹, Mary Boyce ¹, J. Ashcraft ², Chia-Ling Pai ²
¹Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, ²Chemical Engineering, MIT, Cambridge, Massachusetts, United States

Proton exchange membrane fuel cells are a promising alternative energy conversion method for low to moderate temperature applications. The polymer electrolyte membrane (PEM) is responsible for rapid conduction of protons from anode to cathode. The PEM is subject to hygro-thermal cycling within tight physical constraints during cell operation. This can lead to plastic deformation and thinning of the membrane contributing to gas crossover and accelerating fuel cell failure. The multifunctional requirements of a PEM (high conductivity, low gas crossover, resistance to chemical corrosion, and mechanical durability) indicate exploring a nanocomposite solution for an alternative membrane design. Novel processing techniques are used to produce a nanocomposite PEM. Layer by layer (LbL) processing has recently been found to successfully produce a highly proton conductive PEM (Argun et. al. Adv. Mat. 2008). Mechanical integrity is provided to the membrane by using an electrospun nanofiber mat as the substrate. Preliminary results show that the nanocomposite design provides damage tolerance and increased failure strain while maintaining conductivity comparable to the LbL film alone.Here the mechanics of the nanofibrous mats and the LbL/mat nanocomposite are studied through experiments and micromechanically-based constitutive modeling. The behavior of the mats is studied from the fiber level to the mat level. Single fibers are extracted from the mats and evaluated to obtain the elastic-plastic stress-strain behavior of the constituent fibers. The electrospun mats are characterized and modeled in both randomly oriented and aligned configurations. The mats exhibit linear elastic-plastic behavior similar to the single fibers but with a much lower elastic modulus and yield stress due to the high porosity and fiber orientation. The elastic-plastic stress-strain behaviors and failure of the LbL films and the nanocomposite are found to be strongly dependent on hydration, rate, and temperature. A constitutive model has been developed treating the random mat as a superposition of triangulated networks of the single fiber material. This model is able to predict the elastic-plastic behavior of the network as well as the increased stiffness and yield that arise from initial orientation of the mats. This model is then combined with a constitutive model of the LbL to obtain a model of the nanocomposite. By building the continuum model from the microstructure up, the rate, temperature and hydration dependence of the composite structure is naturally incorporated via these dependencies of the constituent materials. The model is shown to successfully capture the mechanical behavior of this particular PEM. Further, it establishes a method for predicting the mechanical behavior of composites synthesized in the same manner with different fiber dimensions or from different base polymers. This can then be used to parametrically screen prospective PEMs for mechanical suitability.

9:00 PM - FF10.40

A Comparison of Dry Sliding Wear of Conventional and Nanocrystalline Eutectic Al-Si.

Ian Baker ¹, Michael Gwaze ¹, Ye Sun ¹, Adam Dohner ¹, Annika Grosse ¹, Francis Kennedy ¹, Paul Munroe ²
¹Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States, ²Electron Microscope Unit, University of New South Wales, Sydney, New South Wales, Australia

9:00 PM - FF10.41

Independent Characterization of Second Phase Particle in a Dual Phase Material using Nanoindentation.

Akbar Aftabi Gilvan ¹, Vis Madhavan ¹, Mahdi Saket Kashani ¹
¹Industrial and Manufacturing, Wichita State University, Wichita, Kansas, United States

9:00 PM - FF10.42

Structural Carbon Aerogels for High Temperature Thermal Insulation.

Wendell Rhine ¹, Shannon White ¹, Nicholas Zafiropoulos ¹, Redouane Begag ¹, Wenting Dong ¹, Irene Melnikova ¹
¹, Aspen Aerogels, Northborough, Massachusetts, United States

9:00 PM - FF10.43

Theoretical Modeling of Isostructural Decomposition in Cubic M(1-x)AlxN (M=Ti, Cr, Sc, Hf).

Igor Abrikosov ¹, Bjoern Alling ¹
¹Department of Physics and Measurement Technology (IFM), Linkoping University, Linkoping Sweden

To increase the hardness and prolong the lifetime of cutting tools, coating with nanocomposite thin films of multicomponent transition metal nitrides has become standard procedure within the industry. Today, complex multicomponent nitrides have, to a large extent, replaced the binary nitrides such as TiN. For example, it has been found that the alloying of TiN with AlN increases the cutting performance of the coating. This has been attributed to increased oxidation resistance, but more recently also to an age-hardening mechanism. A related coating material, Cr(1−x)AlxN, has also been very successful in cutting tools applications. We have used first-principles calculations to investigate the mixing enthalpies, lattice parameters and electronic density of states of the ternary nitride systems Ti(1−x)AlxN, Cr(1−x)AlxN, Sc(1−x)AlxN and Hf(1−x)AlxN in the cubic B1 structure, where the transition metals and aluminium form a solid solution on the metal sublattice. The inclusion of Sc(1−x)AlxN and Hf(1−x)AlxN systems in a common comparison adds an extra dimension to the study of the mixing thermodynamics since ScN and HfN, in opposite to TiN and particularly CrN, show a large lattice mismatch with c-AlN. Thus we are able to analyze the contribution of both the band structure effect and volume mismatch to the atomic level driving force for isostructural decomposition in M(1−x)AlxN-systems [1,2]. It was found that in all four systems, the non-bonding transition metal d-state developed into a narrow almost atomic like state as the AlN content increased. However this development effects the mixing enthalpy only in the cases of Ti(1−x)AlxN and Hf(1−x)AlxN leading to a high and asymmetric mixing enthalpy and an accelerating driving force for isostructural decomposition at higher AlN concentrations. A large lattice mismatch adds a symmetric contribution to the mixing enthalpy in the Sc(1−x)AlxN and Hf(1−x)AlxN systems. A large size mismatch however, although adding to the driving force for decomposition, might hinder coherent decomposition and instead promote an incoherent decomposition through nucleation and growth of hexagonal AlN, a process believed to be unfavorable for coating performance. It is also shown that the magnetism is the key to understand the difference between the Cr-containing system and other systems considered in this study [3]. Our results indicate that the use of the disordered local moments approximation rather than nonmagnetic simulations is important to model the Cr(1−x)AlxN system at elevated temperatures.[1] B. Alling, A. V. Ruban, A. Karimi, O. E. Peil, L. Hultman, and I. A. Abrikosov, Phys. Rev. B 75, 045123 (2007).[2] B. Alling, A. Karimi, and I. A. Abrikosov, Surface & Coatings Technology 203, 883 (2008).[3] B. Alling, T. Marten, A. Karimi, and I. A. Abrikosov, J. Appl. Phys. 102, 044314 (2007).

9:00 PM - FF10.45

Thermomechanical Behavior of Aligned Carbon Nanotube Composites with Ideal Morphology.

Hulya Cebeci ¹, Roberto Guzman de Villoria ¹, Brian Wardle ¹
¹, MIT, Cambridge, Massachusetts, United States

Similar to advanced composites, nanocomposites with controlled morphology can be tailored at the nanoscale to achieve property enhancement, particularly anisotropy. Many fundamental questions related to carbon nanotube (CNT) inclusion in polymer nanocomposites (PNCs) are studied using novel processing to achieve a unique aligned-CNT composites up to high volume fractions (exceeding 20%) of CNTs. This allows assessment of properties without the typical issues and uncertaintly associated with the inhomogeneous distribution, agglomeration and dispersion challenges, and lack of orientation that arise due to uncontrolled morphology in the literature. In this study, aligned, as opposed to randomly-oriented, aligned-CNT polymer nanocomposites (A-PNCs) are fabricated, characterized, and tested to assess thermo-mechanical property effects of the CNTs on the resulting composite. Particularly important is the continuous nature of the CNTs across the sample, reaching lengths of ~2 mm. Such ideal morphology CNTs are important to characterize as they form a constituent in larger-scale nano-engineered composites containing advanced fibers such as carbon.A-PNCs are fabricated using capillarity-driven wetting [1], avoiding dispersion issues and then mechanically densified [2] to obtain desired volume fractions so that the CNTs can dominate composite properties. Cured samples are machined to mm scale and several techniques used to characterize their morphology such as alignment, dispersion, voids, and the effect of the closely-packed CNTs on polymer curing. Thermal properties are assessed with differential scanning calorimetry and thermogravimetric analysis with good agreement in weight/volume fraction of CNTs with curing kinetics studies. Thermo-mechanical behavior was studied by dynamic mechanical analysis. Overall, the A-PNC properties show a volumetric effect from the CNTs, and CNT waviness is noted as a dominant morphological effect controlling modulus by comparing the experimental results to standard composites theories modified to account for fiber (CNT) waviness.1.Garcia, E.J., Hart, A. J., Wardle, B. L., Slocum, A. H., Fabrication of composite microstructures by capillarity-driven wetting of aligned carbon nanotubes with polymers. Nanotechnology, 2007, Vol. 18 (16), 165602 (11pp).2.Wardle, B.L., Saito, D.S., Garcia, E.J., Hart, A.J., deVilloria, R.G.,, Fabrication and Characterization of Ultra-High Volume Fraction Aligned Carbon-Nanotube-Polymer Composites, Advanced Materials, Vol. 20, 2008, pp. 2707-14.

9:00 PM - FF10.46

Finite Element Modeling of Nanoindentation of Nanowires on a Deformable Flat Substrate

Davood Askari ¹, Gang Feng ¹
¹Mechanical Engineering, Villanova University, Wayne, Pennsylvania, United States

The fascinating properties of nanostructured materials and their promising applications have been the main driving force for the development of more advanced material characterization tools and techniques. It should be mentioned that the accuracy of calculated results directly depends on the capability of employed techniques and the assumptions that have been made for the analysis of measured data. In general, due to the complexity of material’s behavior in small scales and difficulties in data reductions and analysis, many simplifying assumptions have been made for the calculation of material properties. Among the many mechanical properties measurement techniques, indentation/nanoindentation has been a very effective technique for the properties measurements of thin films and nanostructured materials. However, in majority of the published reports regarding the nanoindentation of nanowires/nanotubes, deformations and the compliance of substrate material (i.e., upon which nanowires/nanotubes are laid) are completely ignored for the material properties calculations and data analysis. Here in this work, we present a more sophisticated approach that accommodates the substrate deformations for the calculations of hardness and stiffness of nanowires/nanotubes using a depth-sensing nanoindentation technique. Furthermore, receding of the nanowires during the nanoindentation is allowed in our simulation and thoroughly investigated. A 3-dimensional nanoindentation finite element model of a GaN nanowire on a flat surface Si substrate is created as a double contact receding problem. An indentation load is applied over the nanowire by means of a rigid spherical nanoindenter tip, incrementally, and solved. The stiffness and the hardness results are calculated for both the contact interfaces as a function of indentation load and then discussed in details. It is concluded that the substrate deformations has a significant influence on material properties calculations. Finally, the results are compared to those obtained from experiments and analytical solutions reported in authors’ earlier works.

9:00 PM - FF10.5

Nanomechanical Characterization of Raspberry-like Core-shell Nanocomposite.

Xinnan Wang ¹, Li Tao ², Xiaodong Li ², Qian Wang ²
¹, North Dakota State University, Fargo, North Dakota, United States, ², University of South Carolina, Columbia, South Carolina, United States

9:00 PM - FF10.6

Influences of Crystallization Behavior of Poly(L-Lactide) and Morphologies of Hydroxyapatite Particles on the Mechanical Properties of Co-Electrospun Scaffolds.

Fei Peng ¹, Montgomery Shaw ^{1 2}, James Olson ³, Mei Wei ¹
¹Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, ²Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, ³, Teleflex Medical, Coventry, Connecticut, United States

9:00 PM - FF10.8

Deformation of Nanocrystalline Mg by Large-Scale Molecular Dynamics Simulation.

Dong-Hyun Kim ¹, M. Manuel ¹, F. Ebrahimi ¹, J. Tulenko ², S. Phillpot ¹
¹Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, ²Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, Florida, United States

9:00 PM - FF10.9

Atomistic Simulations of the Mechanical Response of Copper/Polybutadiene Joints under Stress.

Fidel Valega Mackenzie ¹, Barend Thijsse ¹
¹Materials Science and Engineering, Delft University of Technology, Delft Netherlands

9:00 PM - FF10: PosterII

FF10.1 Transferred to FF12.11

9:00 PM - FF10: PosterII

FF10.29 Transferred to FF9.4

2009-12-04 Show All Abstracts

Symposium Organizers

Jun Lou Rice University

Brad Boyce Sandia National Laboratories

Erica Lilleodden GKSS Forschungszentrum

Lei Lu Chinese Academy of Sciences

FF11: Electromechanical, Thermomechanical & Chemomechanical Behaviors of Nanomaterials

Session Chairs

Ioannis Chasiotis

Lei Lu

Friday AM, December 04, 2009

Room 304 (Hynes)

9:30 AM - **FF11.1

Electrical, Mechanical, and Thermal Damage Modes during High Current Stressing of Damascene Copper Interconnects.

Robert Keller ¹, David Read ¹, Roy Geiss ¹
¹Materials Reliability Division, NIST, Boulder, Colorado, United States

We present observations of several different forms of damage to damascene copper interconnects subjected to various types of thermal and electrical stressing expected in processing and use. Two factors were varied in these studies: (i) AC versus DC stressing at high current densities (typically in the range ~ 10 MA/cm² and higher), and (ii) full encapsulation versus partial encapsulation (top surface uncovered, specimens tested in vacuum). We measured lifetimes to open circuit as well as changes and damage to microstructure. Plots of lifetime as a function of applied temperature range due to joule heating during electrical testing revealed that AC-stressed specimens exhibited somewhat longer lifetimes (by a factor of approximately two to five) than DC-stressed specimens for a given temperature range and level of constraint. Both forms of stressing resulted in the formation of voids early in the testing of fully encapsulated specimens. However, their morphologies differed, with AC voids being rounder and DC voids being more faceted. AC stressing produced a density of voids higher than that induced by DC stressing, and those AC voids remained largely stationary during continued testing. Conversely, DC stressing produced voids that moved toward the anode, suggesting behavior typical of electromigration damage. DC stressing of samples containing voids initially produced by AC stressing resulted in the motion of only some of those voids. AC stressing also resulted in considerable grain growth, whereas this was negligible for DC-stressed specimens. One prominent effect of mechanical constraint due to full encapsulation by rigid dielectric was to increase AC lifetimes by a factor of up to approximately fifty over partially encapsulated specimens, for a given applied temperature range. Further, whereas a transition from low temperature range voiding to higher temperature range dislocation-induced damage was observed at around 250 °C during AC stressing of partially encapsulated lines, this did not take place in fully encapsulated specimens, which exhibited only void damage. We will discuss these observations in terms of the relative contributions and interactions of diffusive, thermal, and mechanical damage mechanisms for the different test conditions.

10:00 AM - FF11.2

Computational Studies of Effect of Electron Doping on the Hardness of Aluminum Magnesium Boride.

Scott Beckman ¹
¹Material Science and Engineering, Iowa State University, Ames, Iowa, United States

10:15 AM - FF11.3

Modeling the Sliding Wear of Single Asperity Copper/Aluminum Contacts Under Electromagnetic Stress with Atomistic+Continuum Multi-Scale Simulations.

John Crill ¹, Douglas Irving ¹, Don Brenner ¹
¹, North Carolina State University, Raleigh, North Carolina, United States

10:30 AM - FF11.4

Thermo-mechanical Behavior of Nano Scale Al Thin Films using a Resonance System.

Seungmin Hyun ¹, Jungmin Park ¹, Hak-Joo Lee ¹, Byung-Ik Choi ¹, Walter Brown ²
¹, Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of), ², Lehigh Unviersity, Bethlehem, Pennsylvania, United States

10:45 AM - FF11.5

Thermal Stability and Stress Relaxation of Nanostructured Cu–Nb-based Wires.

Jean-Baptiste Dubois ¹, Ludovic Thilly ¹, Pierre-Olivier Renault ¹, Florence Lecouturier ², Marco Di Michiel ³
¹PHYMAT, University of Poitiers, Futuroscope France, ², LNCMI, Toulouse France, ³, ESRF, Grenoble France

The development of novel nanostructured materials with a combination of functional properties such as high electrical conductivity and high mechanical strength is needed to develop magnets providing non-destructive high pulsed magnetic fields over 80 T. Currently, the best candidates are the Cu-based high-strength nanocomposite wires reinforced with Nb nanostructures (nanofilaments or nanotubes) that are produced by accumulative drawing and bundling (ADB: series of hot extrusion, cold drawing and bundling stages). This severe plastic deformation (SPD) process leads to a multiscale copper matrix containing up to 85⁴ (52.2 10⁶) continuous parallel Nb nanofilaments or nanotubes. These nanocomposite wires combine low electrical resistivity (0.6 μΩ cm at 77 K) and ultra-high strength (2 GPa at 77 K) very much higher than the rule of mixtures predictions.After SPD, high internal stresses appear in the nanocomposites. The niobium exhibits a residual axial tensile stress while the copper exhibits a residual axial compressive stress. In-situ heat treatments under synchrotron high energy x-rays have been performed to study the evolution of the nanostructure and the internal stresses with temperature. Experiments have been carried at the high energy beamline ID15B at the European Synchrotron Radiation Facility (ESRF). The diffracted patterns are continuously collected on a large 2D detector giving access to (i) many reflections and (ii) information about crystalline orientation in each phase. Furthermore, peak positions allow measuring elastic strain of the different crystallographic planes and peak width can be related to microstructure evolution (grain size, inhomogeneous strains).It was evidenced that internal stresses relaxation in niobium occurs at temperatures which are far below from its normal recrystallization temperature. Experiments reveal also a very strong microstructure size dependence of the stress relaxation temperature that decreases when the dimensions become finer. This phenomenon seems to be explained by a proximity effect where the recrystallization of copper in the vicinity of niobium may cause significant early changes in internal stresses. Dimensional dependence of this phenomenon may be related to the high surface-to-volume ratio of grains in nanocrystalline materials, allowing for increased relaxation of intragranular stresses thanks to discrete changes in the atomic structure of grain boundaries and interfaces.

11:00 AM - *

Break

11:30 AM - FF11.6

Tuning the Mechanical Properties of a Nanoporous Gold.

Hai-Jun Jin ¹, Lilia Kurmanaeva ¹, Joerg Weissmueller ^{1 2}
¹Institute of nanotechnology, Forschungszentrum Karlsruhe, Karlsruhe Germany, ²Technische Physik, Universität des Saarlandes, Saarbrücken Germany

The conventional approach towards tailoring the mechanical properties of materials is to manipulate their atomic structure or microstructure, for example by changing the grain size of a polycrystalline material or by controlling the diameter of a (nano-) wire or pillar. However, instead of these “permanent” changes one might also envisage to manipulate control parameters that allow a reversible tuning of the materials mechanical response on demand and during service. Here we introduce a new concept to develop a “smart” material which allows prompt and reversible variation of its mechanical properties. The idea is essentially to combine two well-documented facts: first, the crystal deformation is greatly influenced by the surface as marked by the well known size-effect, and second, the surface parameters (e.g., surface stress, surface energy) can be controlled by chemical or electrochemical means. Thus it is expected that the mechanical properties of a high specific area crystalline material will respond to changes in the chemical or electrochemical environment.Our experiments use bulk samples of nanoporous gold prepared by dealloying, which have a very small structure size and large surface area. More importantly, the material, if prepared carefully, can undergo compression with appreciable plastic strain which even allows strain rate sensitivity measurements [1]. We demonstrate in this material that both the yield stress and the brittleness can be “tuned” in an electrochemical environment. Compression tests were preformed in situ with samples immersed in the electrolyte (HClO4) and with potentiostatic control. Potential changes allow a reversible variation of the flow stress by as much as the factor two. Furthermore, the samples are obviously more brittle at positive potential. Flow stress changes were observed during cyclic OH adsorption/desorption as well as during capacitive charging in the double layer region. Effects of structure size and solid fraction were also documented. The underlying mechanisms will be discussed in terms of surface dislocation nucleation and dislocation motion concerning the roles of the surface stress, surface energy and even the surface diffusivity. [1] H.J. Jin, L. Kurmanaeva, J. Schmauch, H. Rösner, Y. Ivanisenko, J. Weissmüller, Acta Mater. 57 (2009) 2665-2672.

11:45 AM - FF11.7

Hydridation and De-hydridation Behavior of Nanoporous Palladium-Nickel Ultra-thin Films.

Wen-Chung Li ¹, T. John Balk ¹
¹Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States

12:00 PM - FF11.8

Multi-scale Simulation on H embrittlement and H-Pd interactions.

Hieu Pham ¹, Tahir Cagin ^{1 2}
¹Chemical Engineering, Texas A&M University, College Station, Texas, United States, ²Materials Science and Engineering, Texas A & M University, College Station, Texas, United States

The hydrogen-charged palladium system has been the subject of tremendous experimental studies for the last two decades, as the reports on its anomalous behaviors draw such a big interest. However, due to the complication of their microscopic origins, the controversy over many phenomena still continues that needs novel approaches to elucidate the problem. In our work, various levels of theory, namely Density Functional Theory (DFT) and classical molecular dynamics (MD) simulations, will be used to study the problem of H-Pd interaction, H-loading and H-embrittlement in Palladium under different thermal and mechanical conditions. This study focuses on the behaviors of Pd defects, such as vacancy, interstitials and grain boundary (GB), under the influence of H segregations. The dynamic loading of H into Pd should be in a strong coupling with chemistry, microstructure and mechanics. In the first part, ab initio calculations will be carried out (using VASP simulation program) for moderate-size cells of Pd containing point and planar defects. The interaction of H with different kinds of crystal defects will be reported. The presence of grain boundary in material is of special interest as it is essentially related to the issue of impurity diffusion, segregation and embrittlement. We use the concept of binding energy to demonstrate the tendency that H atoms are bound to the Pd GB. Big binding energy values indicate the chemical nature of these bonds, instead of physisorption. Also, the investigation on behaviors of Pd atoms around GB under the concentration of H may reveal the mechanism of H-embrittlement in Pd and the efficiency of H-charging. To overcome the size limitation and short-time scale of first-principles quantum mechanical method, we employed the condensed phase molecular dynamics simulations, in which an embedded atom method (EAM) is used to express the total energy of metal atoms. Larger-scale simulations, therefore, are conducted (by LAMMPS simulation package) for supercell models containing up to 10,000 Pd atoms. In contrast to DFT, these simulations will be able to include the mechanical and thermal effects to the H-Pd interactions, ranging from ambient to extreme conditions (high temperature, pressure and H-loads). Again, the energetics, thermodynamics and microstructure of Pd GB under H-loading are investigated in order to understand the nanoscale nature of H-Pd interactions and H embrittlement.

12:15 PM - FF11.9

Nanocomposites with Stimuli–Responsive Mechanical Behavior.

Kadhiravan Shanmuganathan ¹, Jeffrey Capadona ^{2 3}, Dustin Tyler ^{2 3}, Stuart Rowan ^{1 2 4}, Christoph Weder ^{1 5}
¹Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, ²Dept of Biomedical Engineering, Case Western Reserve University, Cleveland , Ohio, United States, ³Rehabilitation Research and Development, Louis Stokes Cleveland DVA Medical Center, Cleveland , Ohio, United States, ⁴Department of Chemistry, Case Western Reserve University, Cleveland , Ohio, United States, ⁵Adolphe Merkle Institute, University of Fribourg, Route de l'Ancienne Papeterie , Marly, Switzerland

12:30 PM - FF11.10

Anisotropic Strain and Training of Conducting Polymer Artificial Muscles under High Tensile Stresses.

Keiichi Kaneto ¹, Hikaru Hashimoto ¹, Kazuo Tominaga ¹, Tomokazu Sendai ¹, Wataru Takashima ¹
¹Life Science and Systems Engineering, Kyushu Institute of Technology,, Kitakyushu Japan

Electrochemomechanical deformation (ECMD) in polypyrrole (PPy) and Polyaniline (PANi) films under tensile stresses up to 5 MPa was studied. PPy film was electro deposited in pyrrole/dodecylbenzene sulfonic (DBS) acid/methylbenzoate solution with the thickness of 20-30 μm. PANi was polymerized by the common chemical method, and the film was obtained by casting the NMP solution of emeraldine base. The PPy/DBS film was electrochemically cycled in LiCl, showing cation movement. The cyclic stroke of ECMD in PPy/DBS film was approximately 2% by insertion and extraction of cations. The stroke of ECMD depended linearly on the amount of oxidative charge. By the application of tensile stresses higher than 2 MPa, a creeping associated with conformation change, slipping and/or breaking of polymer chains was observed. The creeping was 25% at the tensile stress of 5MPa. A nonlinear ECMD against the injected charges was observed under tensile stresses above 2MPa. Upon removal of high tensile stresses, the creeping was recovered to some extent, and interestingly the cyclic stroke was slightly larger than that before the application of large tensile stresses. The increased cyclic ECMD is a training of the artificial muscle.The cyclic stroke of ECMD in PANi film was approximately 6%, which was obtained by the operation of rectangular voltage wave form in aqueous 1M HCl, showing anion movement. By the application of tensile stresses more than 1 MPa, a creeping of the PANi film was observed by 20% at 3MPa. After the removal of tensile stress, the creeping was recovered completely to the original length after15-20 electrochemical cycles. Furthermore, the magnitude of cyclic stroke of ECMD was increased by 15 % compared with that before the application of tensile stress. The larger training effect was observed in PANi film.We propose the mechanisms of creeping and training in ECMD of conducting polymers under high tensile stresses. In the electrochemical oxidation of conducting polymers the oxidation occurs by the insertion of anions into the polymer matrix near the polycations (polaron or soliton). The anion may interact with polycations nearby and bridges adjacent polymer chains (cross linkage). The cross linkage may be loosen by the reduction, and the cross linkage should be rearranged by oxidation under larger tensile stresses, resulting in the creeping or hysteresis. The training results from the relaxation of uniaxial anisotropic strain formed during the creeping by the thermal fluctuation and the elasticity of polymer chains.

12:45 PM - FF11.11

Electrochemically-Controlled Mechanical Properties of a Polymer Nanocomposite.

Daniel Schmidt ¹, Fevzi Cebeci ^{1 2}, Ilke Kalcioglu ², Samantha Wyman ¹, Christine Ortiz ², Krystyn Van Vliet ^{2 3}, Paula Hammond ¹
¹Chemical Engineering, MIT, Cambridge, Massachusetts, United States, ²Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, ³Biological Engineering, MIT, Cambridge, Massachusetts, United States

FF12: Mechanics of Nanocomposite Materials

Session Chairs

Bob Keller

Erica Lilleodden

Friday PM, December 04, 2009

Constitution B (Sheraton)

2:30 PM - **FF12.1

Multiscale Modeling of Nanoceramic Composites.

William Curtin ¹, E. Byrne ², M. McCarthy ², F. Pavia ¹, Z. Xia ³
¹, Brown University, Providence, Rhode Island, United States, ², University of Limerick, Limerick Ireland, ³, University of Akron, Akron, Ohio, United States

3:00 PM - FF12.2

Mechanical and Interfacial Properties of Individual Carbon Nanofibers in Epoxy Matrices.

Tanil Ozkan ¹, Qi Chen ², Ioannis Chasiotis ²
¹Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, ²Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

3:15 PM - FF12.3

Carbon Nanotube Pullout from a Diamond Matrix.

Fabio Pavia ¹, William Curtin ¹
¹, Brown University, Providence, Rhode Island, United States

3:30 PM - FF12.4

Direct Measurement of the Matrix-Filler Interactions in A Graphene-Polymer Nanocomposite and Their Relationship to the Composite's Macroscopic Mechanical Performance.

Minzhen Cai ¹, Sarah Cotts ², David Kranbuehl ², Hannes Schniepp ¹
¹Department of Applied Science, The College of William and Mary, Williamsburg, Virginia, United States, ²Department of Chemistry, The College of William and Mary, Williamsburg, Virginia, United States

3:45 PM - FF12.5

Design of Co-Continuous Composite Materials for Stiffness, Strength and Energy Dissipation.

Lifeng Wang ¹, Mary Boyce ¹
¹Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Mechanical behavior is a critical function across of natural and engineered solids. The combination of hard and soft materials can enable an outstanding combination of mechanical performance properties including stiffness, strength, impact resistance, toughness, and energy dissipation as has been demonstrated in biological materials such as bone, nacre and exoskeleton. The mechanical properties of the constituent materials and the relative geometric arrangement of the constituents provide avenues for truly engineering and tailoring the resulting composite properties. In this work, we demonstrate that the mutual constraints each constituent phase imposes on the other constituent phase in co-continuous microstructures can lead to unique and superior mechanical behaviors. Triply periodic minimal surfaces have been of great interest to physical scientists, material scientists and biologists; these co-continuous structures have been observed in block copolymers, micellar materials, nanocomposites, cell membranes, and biological exoskeletons. Here we consider co-continuous structures with simple cubic (SC), body-centered-cubic (BCC), and face-centered cubic (FCC) Bravais lattices, which correspond to the triply periodic minimal surfaces known as the tubular P, I-WP, and F-RD respectively. Prior works have found: (1) these level set structures to exhibit better elastic properties than their rod-connected model counterparts; 2) these structures to provide multifunctional optimization, such as simultaneous optimization of transport of heat and electricity; (3) these structures can be scaled down and fabricated at submicron length scales that enables the coupling of mechanical deformation with photonic or phononic properties. Herein, we explore the linear and nonlinear mechanical behavior of these structures including their elastic stiffness, yield, post-yield, and dissipative behaviors. Finite element based micromechanical modeling of the co-continuous composites are constructed. The large deformation mechanical responses of these 3D periodic cocontinuous composites are investigated using a periodic representative volume element (RVE) of the microstructure together with the nonlinear constituent material stress-strain behaviors where the combinations of polymer/elastomer, polymer/metal, and polymer/polymer are considered for these two-phase composites. The properties obtained for these co-continuous structures are compared with conventional particle-reinforced composites, fiber-reinforced composites, and lamellar composites. We show that 3D periodic cocontinuous composites with interfaces that are the minimal surfaces can have great mechanical performance achieving a unique combination of stiffness, strength and energy absorption. These results provide guidelines for engineering and tailoring the nonlinear mechanical behavior and energy absorption of the composites for a wide range of applications.

4:00 PM - *

Break

4:30 PM - FF12.6

The Mechanical Response of Ag-Based Metallic Nanoinks.

Andrew Birnbaum ¹, Ray Auyeung ¹, Ji Wen Wang ¹, Kathy Wahl ², Maxim Zalalutdinov ³, Alberto Pique ¹
¹Materials Science and Technology Division, Naval Research Lab, Washington, District of Columbia, United States, ²Chemistry Division, Naval Research Lab, Washington, District of Columbia, United States, ³Acoustics Division, Naval Research Lab, Washington, District of Columbia, United States

4:45 PM - FF12.7

Heterogeneity in Epoxy Nanocomposites Initiates Crazing: Significant Improvements in Fatigue Resistance and Toughening.

Iti Srivastava ¹, Yue-Feng Zhu ², Catalin Picu ¹, Nikhil Koratkar ¹
¹Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, ²Department of Mechanical Engineering, Tsinghua University, Beijing China

A major limitation of thermosetting epoxy polymers is their brittle failure, low toughness and poor resistance to fatigue. While toughness in such systems can be enhanced by adding rubber particles and plasticizers, these fillers decrease the stiffness of the composite and lower its glass transition temperature which severely limits their utility. In this paper we report that amido-amine (–NHCH2CH2NH2) functionalized multiwalled carbon nanotubes (A-MWNT) can be used to fundamentally alter the fracture behavior of thermosetting epoxies by causing them to Craze. This increases the ductility of the epoxy as manifested by a 10-fold lowering in fatigue crack growth rate coupled with significant enhancements in the strain-to-break, and fracture toughness. Importantly these enhancements were obtained without sacrificing the stiffness/strength of the composite. In fact the Young’s modulus was ~30% larger and the average hardness was ~45% larger for the nanocomposite epoxy compared to the pristine epoxy.Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. The bridging of cracks by such fibrils is an important mechanism for energy dissipation and toughening in polymers. While craze phenomena are routinely seen in the fracture of thermoplastic polymers, crazing is typically not observed in thermosetting polymers such as epoxies due to the high cross linking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. We show that the reason for crazing in our system is heterogeneous epoxy crosslinking near the A-MWNT fillers which induces large localized fluctuations in material properties. Differential scanning calorimetry analysis indicated that a significant amount of unreacted epoxy is kinetically trapped in the crosslinked matrix structure that is formed at the A-MWNT/epoxy interface. Such local heterogeneity in the curing may be caused by a variety of factors such as, for example, the fact that the chemistry may be modified locally due to the presence of amido-amine groups. Epoxy chain alignment, which is known to influence the crosslinking density, may also be modified locally due to presence of these functional groups. Heterogeneous crosslinking results in localized pockets of enhanced molecular mobility; the correlated evolution of such mobile regions under mechanical load can initiate crazing as observed in our experiments. It should be noted that the heterogeneities that we report here are localized to the nanotube–matrix interfaces since we do not observe any reduction in the global (macroscale) stiffness, hardness, or strength of the epoxy.

5:00 PM - FF12.8

Electrochemically-Induced Percolative Mechanical Properties of Polyaniline Nanofiber-Polymer Composites.

Fevzi Cebeci ¹, Daniel Schmidt ¹, Christine Ortiz ², Paula Hammond ¹
¹Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, ²Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Stimulus-responsive percolative materials are of great interest due to expected dramatic changes in properties, in particular mechanical behavior, below and above the percolation threshold whereby the responsive units contact each other and form a continuous path through the entire system. Responsive constituents with high aspect ratios are expected to produce extremely low (as low as 1% volume fraction) percolation thresholds. In this work, we expect to create an easily disruptable percolative network that will yield impactful changes in composite modulus. Here, we describe the design of an electrochemically-responsive, percolative composite composed of stiff, high aspect ratio, conducting polymer nanofibers interdispersed with more compliant macromolecular spacer layers. Specifically, the responsive nanofibers are polyaniline interdispersed with hydrogen-bonded layer-by-layer (LbL) assemblies of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA). Synthesis of polyaniline nanofibers was carried out similarly to previously published methods in the literature using an ammonium persulfate (oxidant)-hydrochloric acid (dopant) solution added to an acidic aniline and p-phenylenediamine solution. The average length and diameter of the nanofibers were calculated as approximately 2μm and 40nm by TEM, respectively, with an aspect ratio of 50. The mechanical properties of the nanocomposite films (10 layers of polyaniline embedded within 20 bilayers of PEO/PAA) were investigated upon application of an electric potential of -0.2V for reduction and 0.4V for oxidation vs. Ag/AgCl by aqueous atomic force microscopy-based nanoindentation. Incorporation of nanofibers into the PEO/PAA LbL films increased the indentation modulus of the nanocomposite film, and upon application of electrochemical potentials (at -0.2V and 0.4V vs. Ag/AgCl), the films were found to undergo several-fold changes in indentation modulus. The effects of multilayer assembly architecture (i.e., volume fraction of the nanofibers and composition of the spacer layers in the film) on the mechanical switching of the nanocomposite films were also explored. Such "mechanomutable" material systems hold great potential for a variety of applications such as responsive armor textiles and substrates for tunable cell interactions for tissue engineering.

5:15 PM - FF12.9

The Mechanical Properties of Brush-Coated Nanoparticles in Homopolymer Matrix.

Sascha Pihan ¹, Sebastian Emmerling ^{1 2}, Ruediger Berger ¹, Jochen Gutmann ^{1 2}
¹, Max-Planck-Institute for Polymer Research, Mainz Germany, ²Institute of Physical Chemistry, Johannes Gutenberg University, Mainz Germany

The central problem in preparation of nanocomposite materials is the intrinsic incompatibility between the high energy inorganic filler surfaces (e.g. SiO₂) and the lower energy polymer matrix (e.g. polystyrene). The approach to graft polymer chains to inorganic nanoparticles can drastically enhance the dispersion of particles in a homopolymer matrix. Furthermore the mixture of the brush-coated nanoparticles with different molecular weight homopolymer allows tailoring mechanical properties of the composite material [1].In our studies we prepared polysilsesquioxane nanoparticles having diameters of 15 to 30 nm [2]. Polysilsesquioxane-synthesis was chosen because it offers the possibility to create very small particles with a polydispersity down to 0.13. In a “grafting from” step we used atom transfer radical polymerization (ATRP) to grow poly-ethyl-methyl-acrylate (PEMA) brushes on these particles yielding well defined PEMA-grafted-microgels (PEMA-g-µgels). We expect that the PEMA brush interface determines the structure of homopolymer surrounding phase significantly. The above mentioned preparation route enabled us to separately control the diameter of the particles and the length of the polymer brushes (35 nm to 50 nm).The radii of individual nanoparticles were investigated by means of non-contact scanning probe microscopy (SPM) and dynamic light scattering (DLS). By analyzing the phase contrast images we were able to distinguish between the core particle and the brush. From the SPM analysis we could determine the size of the core and the surrounding, independently. We found that the calculated brush-length and the core diameter from DLS measurements are significantly smaller compared to our SPM investigations attributed to swelling effects of the core particle and the PEMA brush. Mechanical properties of the above mentioned PEMA-g-µgel system are expected to depend on the core material, grafting density, molecular weight of the grafted polymer and molecular weight of the homopolymer matrix. In order to avoid exhaustive synthesis of PEMA-g-µgels we developed a nanomechanical cantilever sensor method to analyze the mechanical properties of nanogram materials. We deposited materials by inkjet printing of toluene dissolved PEMA-g-µgels dispersed in PEMA homopolymer matrix. Dried structures were then analyzed by investigating the vibration spectra of the nanomechanical cantilever [3].The analysis of a thin, homogeneous polymer film made by plasma polymerization of norbornene has revealed that the applied nanomechanical method is suitable to determine viscoelastic properties. The Young’s modulus derived from cantilever resonance-shift is consistent with complementary measurements. The investigation of thin heterogeneous films made from PEMA-g-µgels and PEMA homopolymer is currently performed.1. McEwan, M. et al., Soft Matt., 2009, 1705-1716.2. Jakuczek, L. et al., Polymer, 2008, 843-856.3. Whiting, W. et al., Mat. Sci. Eng., 1994, 35-38

5:30 PM - FF12.10

Disclosing Mechanical Properties of Composite Magnetic Nanoparticles,

Antonio Rinaldi ^{1 2}, Veronica Salgueirino ³, Miguel Correa-Duarte ³, Silvia Licoccia ¹, Enrico Traversa ^{1 4}, Ana Davila-Ibanez ³, Pedro Peralta ², Karl Sieradzki ²
¹NAST center and Department of Chemical Science and Technology, Univ Rome Tor Vergata, Rome Italy, ²MAE, Arizona State University, Tempe, Arizona, United States, ³Departamentos de Física Aplicada e Química-Física, Universidade de Vigo, Vigo Spain, ⁴4International Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba Japan

Mechanical response is actively pursued for NEMS applications. Central to these efforts is addressing the relationship between confined volumes (nanosized structures) and applied stress. The mechanical properties of single-phase nanocrystalline materials have been typically measured and interpreted but none of the many and more complex multi-phase nanostructures that can be produced nowadays seem to have been explored yet. Part of the reasons lays in the inherent and fastly-growing complexity of the mechanical behavior of materials other then simpler single-phase or isotropic cases. The present study aims to indicate a conceptual approach to tailor or adapt the basic tools (e.g. the standard Oliver-Pharr's method) for complex composite nanostructures. By taking into account core-shell structured silica-coated cobalt boride nanocomposites (with average outer diameter of 100nm and 10nm coating skin), we discuss several fundamental processes that can govern nanomechanics. The complex nature of these nanoparticles (simultaneously composite, non-crystalline, clustery, defective, and magnetic) sets these objects apart from nanoparticles examined previoulsy. Different mechanisms (of mechanical, chemical and magnetic types) contributes to a characteristic mechanical response made of three regimes associated with elastic and plastic (with low and high hardening rates) deformation. A combination of quantitative in-situ compression tests and contact theory, aided by finite-element analysis (FE) for estimating Young’s modulus and hardness, led us to show the direct correlation between mechanical data with nanostructural evolution. A hardening effect driven by the applied pressure was observed in analogy to what reported in literature for other nanoparticles or highly confined structures under compression. Beyond elasticity, the onset of plasticity can be traced back to the presence of dislocation-like radial defects (observed via HRTEM) and resolved shear stresses supposedly greater than 1 GPa (estimated via FE). The pre-existent distribution of such radial dislocations found in the cobalt boride core represents itself a signature feature of such nanocomposites and reflect the internal ordering resulting from the inner electrostatic and magnetic interactions. Also, reverse plasticity and strain hardening are highlighted experimentally and discussed in light of this distinctive nanostructure.

5:45 PM - FF12.11

Modeling of Interfacial Friction in Amorphous Carbon/Nanotube Nanocomposites.

Lili Li ^{1 3}, Zhenhai Xia ¹, W. Curtin ², Yanqing Yang ³
¹, The University of Akron, Akron, Ohio, United States, ³School of Materials, Northwestern Polytechnic University, Xi'an China, ²Division of Engineering, Brown University, Providence, Rhode Island, United States