Bidirectional impact protective performance of bioinspired polyvinyl chloride/thermoplastic polyurethane foam composite with anti-sandwich structures

Polymer foams are widely used in human body protection but require combination with impact-resistant materials for adequate performance. Inspired by walnut shells, this study developed a novel bidirectional protective anti-sandwich structure (BPAS) for bidirectional protection. The nonlinear hyperelastic and viscoelastic behaviors of TPU foam were simulated using the compressible Hyperfoam model with Rayleigh damping, and the accuracy of the finite element model was verified by falling ball impact tests. By comparing with pure foam structure (PFS) and traditional sandwich structure (TSS), the BPAS showed more uniform and moderate stress distribution, transfer, and deformation under impact demonstrating a special bidirectional protection property, which is attributed to the energy dispersion of its upper foam, lateral stress redistribution, and energy dissipation effects of its rigid core. The developed model is effective in assisting structural design and performance prediction of BPAS, and the BPAS also exhibited excellent bidirectional protection capability in boxing.