Dynamic yielding and post-yield behavior of lattice materials with different cell orientations

Yield behavior of lattice materials under general stress states is complicated by factors such as loading orientation, hydrostatic stress, and strain rate, and a unified description has yet to be developed. Also, initial yield stress was commonly used to describe the yield surface of materials; however, it may be inaccurate for lattice materials and other cellular-based materials because of the presence of geometric nonlinearities (e.g., local strut buckling) and stochastic imperfections in manufacturing (like cell-wall thickness variations and nodal connectivity defects). In contrast, plateau stress is a statistically averaged property and characterizes the macroscopic collapse strength of lattice materials during progressive cell collapse. It is more stable and representative than the initial yield stress across different samples. Therefore, this work evaluated the feasibility of using plateau stress to describe the macroscopic yielding behavior of lattice materials. Also, the Hill 48 yield formulation was generalized by incorporating anisotropy, hydrostatic sensitivity, and strain-rate dependence. The post-yield collapse deformation and energy absorption of lattice materials with different cell orientations were analyzed as well. The proposed model is able to capture the orientation-dependent collapse behavior and rate-induced strengthening while preserving a consistent yield surface shape. The results elucidate the connection between pressure-sensitive, rate-dependent yielding and energy absorption, providing guidance for the design of lattice materials with tailored performance.