Study on the formation characteristics of underwater hemispherical shaped charge jet and its penetration performance into concrete

Shaped charge has been widely used for penetrating concrete. However, due to the obvious difference between the propagation of shock waves and explosion products in water and air, the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied. In this paper, we introduced a modified forming theory of an underwater hemispherical shaped charge, and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically. The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%. The underwater jets exhibit at least 3% faster and 11% longer than those in air. Concrete shows different failure modes after penetration in air and water. The depth of penetration deepens at least 18.75% after underwater penetration, accompanied by deeper crater with 65% smaller radius. Moreover, cracks throughout the entire target are formed, whereas cracks exist only near the penetration hole in air. This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water. • A reliable modified theory for underwater hemispherical shaped charge jet formation is proposed. • Differences in jet velocity and shape formation between water and air are analyzed. • Post-penetration failure modes of holes and cracks in concrete differ in water and air. • Optimal standoff for underwater jets is shorter than in air, with more obvious shock wave effects.