Systematic Generation, Analysis, and Characterization of 3D Micro-architected Metamaterials.

Controlling the unit-cell topology of microlattice structures can enable the customization of effective anisotropic material properties. A wide range of properties can be obtained by varying connectivity within the unit cell, which then can be further used to optimize structures specific to applications. A methodology for a systematic generation of microlattice structures is presented that focuses on controlling discrete topology instead of average porosity (as is done in conventional porous media). An algorithm is developed to create valid lattice structures without redundancies from a given set of template nodes. A set of possible permutations of structures from an eight-node cubic octant of a unit cell are generated for evaluation of the degree of anisotropy. Generic models are developed to calculate the effective thermal and mechanical properties as an effect of topology and porosity of the micro-architected structure. The thermal and mechanical anisotropies are investigated for the effective properties of micro-architected materials. A few of the structured materials are fabricated using 3D printing technology and their effective properties characterized. Structures are represented as graphs in the form of adjacency matrices. Effective thermal conductivity is analyzed using a resistance network model, and effective stiffness is evaluated using a self-consistent elastic model, respectively. A total of 160 000 structures are generated and compared to porous-metal foams in which porosity is one of the design variables. The results show that it is possible to obtain a wide range of properties spanning more than an order of magnitude in comparison to porous-metal structures. Structures with a maximum anisotropy ratios of 7.1 and 8.2 are observed for thermal and mechanical properties, respectively. Preliminary experimental results validated the anisotropy ratio for the thermal conductivity and stiffness.