EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Metallic programmable mechanical metamaterials implement the bioinspired functionalities, for example, adaptability enabled by logical calculations and memory, in hierarchical structured metallic materials, and create huge design space for mechanically robust and functionally smart materials for biomedical, environmental, energy-related applications. The programmability of these materials systems arises primarily from their mesoscopic design (e.g. auxetic structures of hundreds of microns) among the design hierarchies from the atomic to the macroscopic shape levels. The unit cells of these metamaterial systems require the capability of producing large macroscopic or accumulative elastic deformation, compared to typical metallic metamaterials, to achieve the desired functions. The elements in the unit cells can also be loaded under rather complex conditions. In addition, these material systems are constructed hierarchically, which is made possible by minimizing the dimension of the elements in the unit cell, i.e., 100-200 microns in cross-section diameter. The intricate hierarchical structures are usually manufactured by selective laser melting. Structural defects are inevitable and critical for a better understanding and prediction of the micromechanical properties of unit cells. However, the systematic structure-property correlations with the focus on the surface roughness are still missing for metallic cylindrical beam elements, e.g., Ti64, 316L stainless steel, and MS1 steel. Presented here is firstly the quantification of the roughness of the printed beams from the computed x-ray microtomography scans. The comprehensive micromechanical characterization (e.g. tension, compression, bending, and torsion) of the elements are then performed with a micromechanical tester, and the strain distributions are calculated with digital image correlation. Finite element simulation approaches with beam elements are then optimized by the correlation obtained to represent the manufactured elements more accurately. Thus an improved prediction of the mechanical behavior of the unit cell and the cell arrays constructed upon these elements are possible.