Energy absorption properties and failure modes of flexible UHMWPE foam protective sandwich structure subjected to low-velocity impact

Flexible materials play a crucial role in protecting against behind armour blunt trauma (BABT). However, their compliance complicates the understanding of failure mechanisms and energy absorption. This study used a combined experimental and numerical approach to investigate the response and failure modes of a flexible ultra-high-molecular-weight polyethylene (UHMWPE) foam protective sandwich structure (UFPSS) under low-velocity impact (LVI). A finite element (FE) model, accounting for nonlinear large deformation and strain-rate-dependent material behavior, was developed for a woven-UFPSS (featuring a plain-woven fabric structure) subjected to a 50 J impact. Experimental and numerical results showed strong agreement in peak force (error < 5%), maximum displacement (error < 6%), and buffer time (error < 8%). The impact's kinetic energy was mainly converted into internal energy of the fabric and foam materials (∼50%), viscous dissipation in the foam core (12%–15%), frictional work at the contact interfaces (5%–6%), and work by the pneumatic fixture clamping force (∼38%). This study provides the first investigation of the LVI performance of sandwich structures with all soft material layers, offering significant insights for the application of compliant materials in protective fields.