Underwater explosion resistance of air-backed plate with steel and polyurea: Effect of polyurea spraying position

Improving hull-structure resistance against underwater explosion (UNDEX) is an important problem for designers. It has been proved that polyurea coating on steel can reduce the deformation of a plate subjected to UNDEX. In this study, the effect of the polyurea position was explored by performing a series of UNDEX tests on air-backed plates. They had polyurea sprayed on the front side (PS type), back side (SP type), and both sides (PSP type). The deformation result was obtained using three-dimensional (3D) scanning technology, and the bubble movement was observed by a high-speed camera. The experimental results proved that the polyurea spraying position had no significant effect on the formation and movement of bubble or water jet. More importantly, the PS-type plate exhibited the best explosion resistance when standoff distance was less than 3R_explosive (radius of charge), whereas the SP-type plate did so when standoff distance exceeded R_bubble (maximum bubble radius). Numerical models for these UNDEX tests were established and verified by experimental results. The numerical results demonstrated that the PS-type plate could reflect part of the energy back into the water by compression, thus reducing the energy absorbed by steel. The SP-type plate could disperse impact stress in the steel, but the protective effect was poor within close standoff distance. This was attributed to spallation under reflected tensile wave.