Enhancing the bending performance of SLA-printed TPMS sandwich structures through the core topology optimization

Triply Periodic Minimal Surface (TPMS) structures, e.g., Diamond (D), Gyroid (G), and I-WP, possess excellent specific strength and geometric designability, thereby achieving high load-bearing capacity and lightweight design. However, when serving as the core in sandwich structures, the uniform relative density (uni-den) design and conventionally functionally graded (con-fun-gra) design do not fully utilize the mechanical properties of materials. To overcome this limitation, a variable-density topology optimization (var-top-opt) design is adopted in the D, G, and I-WP cores to enhance the bending performance of sandwich structures, and the enhancement effects are explored. The fitting functions between the isosurface threshold and relative density are constructed for the D, G, and I-WP cells. The var-top-opt design, taking the relative density of the topology element as the design variable and the structural compliance minimization as the design objective, is performed to obtain the optimal relative density field (ORDF). The ORDF is divided into multiple segments, and the relative densities in every segment are fitted to construct the relative density function matrix of topology elements. The isosurface threshold function matrices of the optimized D, G, and I-WP cores are constructed through the relative density mapping relationship between the topology elements and TPMS cells. The D, G, and I-WP sandwich structures from the uni-den, con-fun-gra, and var-top-opt designs are fabricated using the SLA technology, followed by the three-point bending test and numerical simulation. The results show that the var-top-opt design significantly enhances the bending stiffness and energy absorption of the TPMS sandwich structures at different core volume fractions, and the improvement is larger than that of the con-fun-gra design.