Near-field underwater explosion and its interaction with a sandwich composite plate

Polymeric composite sandwich materials are critical for marine structures, but their behavior under near-field underwater explosions is not well understood. This study investigates the dynamic response of carbon-fiber-reinforced sandwich composites with varying core densities subjected to near-field underwater explosions. Lab-scale experiments were conducted at two explosive stand-off distances using high-speed imaging and Digital Image Correlation (DIC) to capture the evolution of gas bubble dynamics, surface cavitation, and structural deformation. Results showed that reducing the stand-off distance led to a 0.7 ms increase in gas bubble period, along with an 80 mm increase in horizontal migration of the bubble, while vertical migration remained unaffected. The interaction between the gas bubble and surface cavitation, driven by fluid-structure interaction (FSI), significantly influenced the structural response. In particular, the simultaneous collapse of the gas bubble and surface cavitation resulted in higher localized impulsive loading, causing catastrophic failure in low-density core panels. Meanwhile, panels with higher core densities exhibited a 40 % reduction in out-of-plane deflection, demonstrating enhanced resistance to blast loading. This study provides new insights into the fluid-structure interaction mechanisms that occur during near-field underwater explosions and offers a basis for improving the design of marine structures by optimizing material selection and geometric configurations. These findings contribute to a deeper understanding of shock mitigation strategies in composite materials and inform future research in marine structural design under extreme loading conditions.