Numerical investigation of anisotropic crack growth resistance of elastoplastic lattice structures

Lattice structures have considerable potential in various engineering applications due to their remarkable mechanical properties, such as light weight, high specific stiffness, strength, and energy absorption. However, their complex microstructure often leads to anisotropic fracture behavior under extreme loading conditions. Despite the growing interest in lattice materials, the anisotropic crack growth resistance remains poorly understood. This study investigates the anisotropic crack growth resistance of elastoplastic lattice structures through numerical simulations, focusing on the effects of material ductility (high-ductility vs. low-ductility) and loading rates (quasi-static vs. dynamic). The effect of lattice cell type is also examined. The results show that the ductility of the lattice structure has a significantly effect on the anisotropy of its fracture properties. Low-ductility triangular lattices and hexagonal lattices exhibit pronounced anisotropy in crack growth resistance. In contrast, high-ductility triangular lattices show nearly isotropic crack growth resistance, as the large plastic zone at the crack tip can mitigate the microstructural anisotropy of the lattice. The study also shows that the low-ductility of lattice structures enhances the rate dependence of fracture resistance. Under high-speed loading conditions, when crack propagation speeds exceed 350 m/s, significant inertia-induced toughening occurs. These findings offer valuable insights for designing lattice structures with improved fracture toughness and performance under various loading scenarios.