Tuning Local and Global Disorder in Architected Materials via Frequency-Based Noise

The beauty of architected materials lies in the opportunity to tune their properties <i>via</i> their geometrical and topological features [1-3]. We are not limited by the material constituents and can surpass classical engineering materials. Inspired by nature, where structural and mechanical heterogeneity enhances energy dissipation [4] and ductility [5], recent efforts in the metamaterials’ community are targeted to harness the effect of irregularities to achieve superior functionalities [6]. These include stress de-localization and imperfection insensitivity, and recent advancements in additive manufacturing allow us to fabricate architectures that incorporate this randomness. However, current efforts to introduce disorder in metamaterials are often restricted to periodicity-disturbances on a global scale. Here, we propose a new design approach that allows us to study the influence of both local and global disorder on the material performance of periodic and random metamaterials. Shell-based topologies are used throughout as model architectures, due to their mechanical advantages (e.g., higher specific strength and energy absorption) over more common truss-based lattices [7]. The mathematically described shell topology is superimposed with frequency-based signals to disturb the “short-range” order, with different frequencies and amplitudes used to tune this local disorder parameter. Characteristic power spectral densities [8] of three frequency-based noise signals – white, pink, brown – are then used to tune the local disorder across the structure, thus introducing a global disorder gradient. To test the influence on both periodic and random metamaterials, triply periodic minimal surfaces (TPMS) and spinodal shell architectures are printed using two-photon lithography, which provides the necessary resolution to incorporate local features in the printing process. The impact of the various levels of disorder on the elasto-plastic behavior of the metamaterial is characterized by means of <i>in situ</i> micro-compression tests performed at different strain rates. Our approach allows us to study the effect of local disorder on globally periodic and random structures by overlaying local features with frequency-based signals. In addition, the charactersitic rates of power loss from three different colors of noise introduce a global and tunable disorder gradient opening up new opportunities to design highly multifunctional (meta-)materials.<br/><br/>References:<br/>[1] Wang et al., <i>Phys Rev Lett</i>, 2016. [2] Torquato et al., <i>J Appl Phys</i>, 2003. [3] Bertoldi et al., <i>Nat Rev Mater</i>, 2017. [4] Tai et al., <i>Nat Mater</i>, 2007. [5] Groetsch et al., <i>Sci Rep</i>, 2021. [6] Soyarslan et al., <i>Acta Mater</i>, 2018. [7] Hsieh et al., <i>J Mech Phys Solids</i>, 2019. [8] Davenport & Root, IEEE Press, 1987.