Bending performance and failure mechanisms of composite sandwich structures with 3D printed hybrid triply periodic minimal surface cores

In this paper, a novel hybrid triply periodic minimal surface (TPMS) core with a nonlinear transition region was designed by combining two types of TPMS (Diamond and Schwarz P) structures using the sigmoid function. The width of the transition region was precisely regulated by adjusting the gradient control parameter r in the sigmoid function. Composite sandwich structures (CSS) were fabricated by bonding two carbon fiber reinforced polymer (CFRP) face sheets to a 3D printed polylactic acid (PLA) core. The bending performance and failure mechanisms of the CSSs with the hybrid TPMS cores were analyzed through three-point bending tests and finite element analysis (FEA). The results indicate that as r increases, the transition region of the hybrid TPMS cores becomes narrower, leading to a gradual decrease in bending strength, bending stiffness, and core shear stress. The failure process of the CSSs in the experiment aligns well with the FEA results. Through comparative analysis of the stiffness-to-weight and strength-to-weight ratios of the CSSs with the native TPMS cores, the hybrid TPMS cores with a wider transition region enhance the structural efficiency of the CSSs, while those with a narrower transition region negatively impact the performance of the CSSs.