Mechanical properties and energy absorption of CoCrNi functionally graded TPMS cellular structures

Functionally gradient triply periodic minimal surface (TPMS) structures are found widespread applications in fields such as aerospace and defense engineering, owing to flexible modulation of lightweight and energy-absorbing properties. CoCrNi medium-entropy alloy (MEA), combining both high strength and ductility, which can significantly enhance the energy absorption efficiency and resistance to failure deformation of complex energy-absorbing structures. In this study, CoCrNi uniform and functionally gradient structures based on Gyroid and Diamond topologies were designed and manufactured via selective laser melting (SLM) technique. The quasi-static and dynamic mechanical performance, deformation behavior, and energy absorption properties of each structure were investigated by universal testing machine and Split Hopkinson Pressure Bar (SHPB) system. Additionally, based on experimental validation, the Johnson-Cook constitutive model for SLM-ed CoCrNi was successfully developed and applied to finite element analysis (FEA) predictions. Notably, it is found that the multi-level absorbing feature of hybrid gradient (HG) provides new insights for the design of energy-absorbing structures, as its lower initial platform triggering threshold and multi-level hardening behavior align with the layer-by-layer collapse deformation of the structure. By integrating appropriate parameter mapping, the mechanical properties can be predicted and regulated more flexibly, thereby paving the way for novel high-performance energy-absorbing structures.