Investigation on shock wave mitigation performance and crashworthiness of density gradient foam structures

In recent years, hazardous chemical explosions have occurred frequently, and explosion shock wave and crash injuries are the main causes of death. Existing studies mostly focus on single injury factors and lack systematic protection studies for shock wave and crash. In this study, a density gradient foam structure (DGFS) was designed and evaluated to provide comprehensive protection against shock wave and crash injuries. The mechanical properties of different density foams were investigated through quasi-static tests and Hopkinson experiments. Shock wave mitigation and crash experiments were conducted using the Multi-purpose Shock Cannon (MSC) and Digital Image Correlation (DIC) techniques, and the baseline shock wave pressure was modeled for three different shockwave pressures. The results show that under quasi-static conditions, both yield stress and failure stress increase with increasing sample density. Under high strain rate conditions, both the peak linear elastic stress and maximum strain of the specimen tended to increase with increasing sample density. The single gradient- drop DGFS was the most effective in shock wave protection, and the specific pressure mitigation ratio was increased by more than 50% compared to the no-gradient DGFS. the double gradient-first-up-then-drop DGFS has a significant advantage in impact energy dissipation at low and medium impact velocities, with a maximum increase of 47.71% in peak crash force attenuation rate and 40.95% in specific energy absorption compared to other DGFS. The single gradient-drop DGFS have the better crash force efficiency, and the performance enhancement can be up to 49.00% compared with other DGFS.