Design of Cellular Lattices by Atom-Mimetics—How to reproduce Elastic Anisotropy of Metals

Owing to the development of layered manufacturing processes, it has become common to fabricate cellular lattices as functional materials with peculiar mechanical properties, i.e., metamaterials. On the other hand, the relationships among the crystal lattice structures and materials properties of crystalline structures have been extensively investigated by preceding studies in materials science. It should be quite natural to design cellular lattices with desired properties based on the property–structure relationships of the crystalline materials. In this study, we intend to develop a method to design cellular lattices by mimicking the atomic arrangement of face-centered cubic (FCC) structure consisting of spheres representing atoms and sticks with various thicknesses representing atomic bonds for the first and the second nearest neighbors. The lattices were additively manufactured by a powder bed fusion process of thermoplastic urethane. The elastic properties of the lattices were evaluated by measuring Young’s modulus, shear modulus, and Poisson’s ratio utilizing a mechanical testing machine and image analysis. The elastic anisotropies of the lattices were compared to those of FCC metals and body-centered cubic (BCC) metals. Interestingly, we found that the anisotropies are close to those of BCC metals rather than those of FCC metals. This implies that the elastic anisotropies of crystalline metals can be reproduced by cellular lattices with pillars mimicking the interatomic free-volume space rather than the spheres of the hard-sphere model. Also, this result might be a clue to the problem of why copper with isotropic electronic structure exhibits higher elastic anisotropy than aluminum with anisotropic electronic structure.