Numerical Simulation Method and Analysis for the Formation of EFP with Variable-density Charge

For the formation issue of explosively formed projectile (EFP) caused by the change in the density distribution of charge due to high temperatures, the JWL equation of state parameters for the charges with different densities are obtained based on a genetic algorithm. The formation of EFP with variable-density charge is simulated and calculated using a high-precision Euler explicit solver, and the propagation mechanism of charge detonation wave and the formation morphology of EFP under different density layering levels are obtained. Additionally, the influences of the charge density gradient and the radius ratio of charge layers on the length-to-diameter ratio and compactness of EFPs with variable-density charges are investigated. The results indicate that the expansion behavior of detonation products in variable-density charges and their driving process on a metal liner can be described using the JWL equation of state. The length-to-diameter ratio of EFP increases first and then stabilizes with the increase in the number of density stratification levels in the variable-density charge. A three-layer density gradient charge structure can be adopted to effectively characterize EFP with variable-density charge. Under high-temperature conditions, the density difference inside the explosive charge can lead to an increase in the velocity difference between the head and tail of EFP, thereby exacerbating the risks of tensile deformation and fracture. In order to adapt to a wide range of environmental temperatures and ensure the armor-piercing capability, a 15%-20% design margin is reserved for the length-to-diameter ratio in the design of long-rod EFP to maintain the structural integrity of EFP in harsh environments.