High fracture toughness micro-architectured materials

We investigate the possibility of achieving high fracture toughness and high strength by the design of lightweight (density below water) metallic micro-architectured materials. The micro-architectured materials were manufactured by drilling a hexagonal array of holes in plates of an aluminum alloy, and the fracture toughness was evaluated via three-point bend tests of single-edge notch specimens. The results show that the fracture toughness of micro-architectured materials increases with increasing relative density and remarkably, a micro-architectured material can be 50% lighter than the parent material but maintain the same fracture toughness. Additional tests on geometrically similar specimens revealed that the fracture toughness increases linearly with the square-root of the cell size. The experiments are complemented by finite element calculations of ductile fracture. In the calculations, the fracture toughness of single-edge notch specimens subjected to three-point bending are evaluated using both, a procedure similar to the experiments and direct computation of the J-contour integral. The fracture toughness as calculated by both methods are consistent with the experimental results. In addition, the calculations are also carried out for single-edge notch specimens subjected to tensile loading, confirming the validity of the measured fracture toughness as a useful material property independent of specimen geometry.