Study on penetration characteristics of three typical shaped charge to double-layer spaced target in water

In order to select the shaped charge structure suitable for large-distance non-contact penetration damage in water, three typical shaped charge structures, explosively formed projectile ( EFP ), jetting projectile charge ( JPC ) and shaped charge jet ( JET ), were selected. The velocity tests of different penetrators before entering water, before hitting the target and after penetrating the target were carried out, and the penetration tests of double-layer spaced targets in water were carried out.Firstly, a comparative test of penetration of three kinds of shaped charge in air was carried out to verify the rationality of the structure of shaped charge. The air explosion height of 35 cm was selected to meet the requirements of penetration of the three kinds of shaped charge. At the same time, the velocity of the three kinds of shaped charge before penetrating into water was measured, which provides the basis for underwater penetration test. Secondly, the penetration test of three kinds of shaped charge on underwater double-layer spacer target was carried out when the air height was 35 cm and the length of water medium in front of the target was 20 cm, 45 cm and 100 cm. The reflected pressure curves of shaped charge penetration in water were measured by wall pressure sensor and PVDF sensor respectively. The velocity of the penetrator at the time of water entry, before the target and after the target is measured by the double-layer on-off net target. Through the damage effect of the double-layer interval target plate, the damage performance of the three shaped charge structures to the water medium in front of the near, middle and far targets is obtained.Based on the projectile-target structure used in the experiment, a two-dimensional finite element model of shaped charge penetrating into a double-layer spaced target in water was established by using ANSYS / LS-DYNA finite element software. The measured velocity values of the shaped charge penetrator before entering the water, before hitting the target and after passing through the target were compared with the numerical simulation values to verify the accuracy of the model. The error rate is about 3 %. Based on the verified finite element model, the time series characteristics of the underwater damage element of the shaped charge, the peak characteristics of the forward shock wave in the water, the variation law of the penetration velocity in the water, and the penetration performance of the shaped charge against the double-layer spacer target in the water were studied.The results show that the forward shock wave reaches the target plate before the penetrator when the three shaped charge penetrates the water spaced target plate. As the length of the water medium increases, the peak pressure of the forward shock wave at the front target plate decreases linearly, and the peak pressure of the forward shock wave at the rear target plate decreases nonlinearly. The velocities of EFP, JPC and JET decrease nonlinearly with the increase of water medium, and the velocity in front of JET target is about twice that of JPC. When the length of the water medium in front of the target is not more than 25 cm, the maximum perforation diameter formed by EFP on the front target plate reaches 5 cm, which is 1.3 times that of JPC perforation diameter and 3 times that of JET perforation diameter. When the length of water medium in front of the target is 0~100 cm, both JPC and JET have good penetration effect on the double-layer spacer target, and the penetration performance of JPC is better than that of JET. Therefore, it can be concluded that both JPC and JET can meet the design requirements of shaped charge structure for non-contact penetration damage at large distance in water.