Tailoring 3D printed graded architected polymer foams for enhanced energy absorption

Graded material design strategy has been exploited to achieve enhanced mechanical performance compared to their uniform counterpart. Using a combined numerical and experimental approach, we investigated the effects of three graded designs on the compressive mechanical performance of 3D printed architected polymer foams. The architected foam is composed of beam binders and spherical shells, which have pronounced effects on the mechanical performance under large deformations. It was found that three failure mechanisms dominate the mechanical behavior of foams for different binder sizes, including binder-failure-only, shell-failure-only, and binder-shell-failure. The investigation of shell thickness variation showed that the relation between relative stiffness and relative density is E/Es~(ρ/ρs)1.56, indicating a bending-dominant deformation behavior. Guided by these findings, we studied the mechanical behavior of three types of graded designs, including graded binder, graded shell thickness, and a hybrid strategy. It was found that the specific energy absorption of hybrid foam is enhanced by 125 %, 185 %, and 34 % compared to uniform foam, graded binder foam, and graded thickness foam, respectively. Furthermore, compared with existing lattice-based and shell-based graded foams, the stiffness of hybrid graded foam increases by 346 % and 33 %, respectively; the specific energy absorption of hybrid graded foam increases by 141 % and 32 %, respectively. The findings presented open a new avenue to engineer architected materials with enhanced mechanical properties, finding applications ranging from structural components of defense systems to protection systems in vehicles.