Design of shear thickening fluid/polyurethane foam skeleton sandwich composite based on non-Newtonian fluid solid interaction under low-velocity impact

The shear thickening fluid (STF) with unique rheology is generally combined with polyurethane (PU) skeleton to manufacture flexible sandwich composites which is widely applied in impact resistence field. In this work, experiments and numerical simulations were comparatively analyzed to investigate the non-Newtonian fluid–solid interaction (NFSI) between STF and PU skeleton during low-velocity impact. Optimization of materials selection is proposed to achieve a higher impact resistance performance. It has been found that the synchronous gradient thickening and flow of STF facilitate the load-bearing and stress diffusion performance. In contrast to Newtonian fluids, the internal STF displays both shear resistence of high-viscosity fluid and easy flow characteristic of low-viscosity fluid, creating areas of low stress in composites and improve the impact resistance performance. The fluid-optimized STF-2 sandwich composite exhibits an up to 154.7% lower peak load and 118.82% higher energy absorption. In terms of the skeleton, a lower modulus of PU foam is conductive to a stronger NFSI, which facilitates the energy exchange between STF and skeleton and further improve the impact resistance performance. As a result, the skeleton-optimized composite containing PU-1 exhibits a 20.10% lower peak load and 17.41% higher energy absorption. The NFSI mechanism and material selection optimization between non-Newtonian fluid and large deformation materials proposed in this work provide an analysis idea and design method for flexible buffering composites.