Unsteady underwater JPC penetration model incorporating resistance effect and attenuation mode transition

Traditional Bernoulli-based steady underwater penetration models exhibit limitations, particularly in their inability to describe velocity attenuation at low velocities accurately or to account for the observed resistance effect (the deceleration of penetrator elements under resistance) on the JPC (Jetting Projectile Charge) penetrator. To address these limitations, a novel attenuation mechanism of JPC underwater penetration is proposed and an unsteady penetration model is established in this study. According to the stress distribution, the JPC precursor penetrator is in a state of fluid and elastic-plastic coexistence. As underwater penetration progresses, the velocity attenuation mode shifts from the combined effects of resistance and hydrodynamic erosion to resistance alone. In this study, the solution for the penetration velocity U accounting for the dynamic strength and changes in the shock wave region is obtained, which characterizes the transition of the attenuation mode. The critical values for the attenuation mode transition of materials with different dynamic strengths are presented. In addition, an unsteady motion model that accounts for stress distribution is introduced to characterize penetration under resistance. The X-ray experiments on JPC formation and underwater penetration were carried out further. The penetrator morphology and penetration velocity at the typical time were obtained. The results show that, compared with the Bernoulli-based steady model in existing research, the proposed model can more accurately predict the penetration velocity U corresponding to the penetrator velocity V_p and more effectively describe the attenuation process under low-velocity conditions. An important theoretical basis can be provided by this study for the design of underwater shaped charges.