A study on the surface overpressure distribution and formation of a double curvature liner under a two-point initiation

The formation mechanism of an EFP(explosively formed projectile) using a double curvature liner under the overpressure effect generated by a regular oblique reflection was investigated in this paper. Based on the detonation wave propagation theory, the change of the incident angle of the detonation wave collision at different positions and the distribution area of the overpressure on the surface of the liner were calculated. Three-dimensional numerical simulations of the formation process of the EFP with tail as well as the ability to penetrate 45# steel were performed using LS-DYNA software, and the EFP velocity, the penetration ability, and the forming were assessed via experiments and x-ray photographs. The experimental results coincides with those of the simulations. Results indicate that the collision of the detonation wave was controlled to be a regular oblique reflection acting on the liner by setting the dimensions of the unit charge and maintaining the pressure at the collision point region at more than 2.4 times the CJ detonation when the incident angle approached the critical angle. The distance from the liner midline to the boundary of the area within which the pressure ratio of the regular oblique reflection pressure to the CJ detonation pressure was greater than 2.5, 2, and 1.5was approximately 0.66 mm, 1.32 mm, and 3.3 mm, respectively. It is noted that pressure gradient caused the liner to turn inside out in the middle to form the head of the EFP and close the two tails of the EFP at approximately 120μs. The penetration depth of the EFP into a 45# steel target exceeded 30 mm, and there was radial expansion between the head and tail of the EFP, increasing the penetration resistance of the EFP. Therefore, the structural size of the unit charge and the liner can be further optimized to reduce resistance to increase the penetration ability of the EFP.