To further improve the strike accuracy and penetration power of explosively-formed projectile (EFP) after long-distance flight, a polygonal charge capable of forming EFP with tail fins was designed during the study. A model for calculating the EFP velocity was derived from the effective charge and detonation projection theories with the integration of calculus. The circumferential velocity distributions of EFP formed using polygonal charges were obtained using this model, and the mechanisms underlying the formation of tail fins were elucidated. The feasibility of using this polygonal charge to form tail fin EFP was verified by conducting multi-media soft recovery tests and numerical simulations. Furthermore, the feasibility of forming tail fin EFP using polygonal charges with different numbers of sides and the effects of the structural parameters of a hexagonal charge on the formation of tail fin EFP were investigated by simulation. The ranges of optimal values for the structural parameters of a hexagonal charge capable of forming high-performance tail fin EFPs were determined.

Given the significantly large deformation and high strain exhibited by explosively formed projectiles (EFP) in penetration, their penetration performance into multi-layer targets differs from that of ordinary bullets or rigid projectiles. Therefore, it is necessary to investigate the ballistic performance and the damage mechanism of target deformation when an EFP penetrates a multi-layer target. This study conducted high-velocity impact tests of EFPs on four types of multi-layer steel targets, analyzing the damage morphology and deformation characteristics of multi-layer steel targets subjected to EFP penetration from both macro and micro levels. To investigate the anti-penetration performance of more target combinations at different EFP velocities, an accurate symmetrical finite element model of EFP penetration into multi-layer targets was established using Autodyn 16.0 finite element software and the SPH-FEM algorithm based on the symmetrical characteristics of the EFP and target structure. The experimental and simulation results showed that for a three-layer composite target, when the thickness of the middle layer remained constant, using the target layers with a front–rear target thickness ratio of less than one was beneficial for enhancing the anti-penetration performance of the targets against EFPs; when the EFP velocity was low and the residual velocity for penetrating a single-layer target was no more than 200 m/s, the anti-penetration performance of the two-layer target was optimal. When the EFP velocity exceeded 1500 m/s, the single-layer target exhibited the best anti-penetration performance to the EFP, and the more layers, the smaller the ballistic resistance. When the number of layers was more than six, the ballistic resistance of the multi-layer targets gradually tended to remain constant.

To investigate the influence of spaced targets with large angle of obliquity on the penetration performance of tungsten alloy long rod projectiles with large length-diameter ratio, this study conducted experiments and numerical simulations on the penetration of 93W long rod projectiles into oblique spaced targets. By experiments, the fracture morphology of the long rod projectile after penetrating the target was successfully captured. The recovered cores and were systematically analyzed by scanning electron microscopy (SEM). The results indicate that the fracture mode of the long rod projectile was mainly manifested as transgranular fracture of tungsten grains. In addition, the J-C constitutive parameters of 93W were determined. The mechanism of action for long rod projectiles penetrating spaced targets with large angle of obliquity was ballistic deflection and the fracture of long rod projectiles. By altering structure of the long rod projectiles, the penetration effectiveness against oblique spaced targets could be significantly enhanced.

Equivalent-thickness conversion among metallic targets is important for vulnerability assessment and protection modelling, but conventional coefficients are often treated as material constants and seldom include fragment morphology. Penetration tests were conducted on 616 armor steel, Q235 steel, and LY12 aluminum alloy using steel spheres, tungsten spheres, and tungsten block fragments. A V50-based database was established, and failure mechanisms were examined from perforation morphology, exit-side SEM, and metallography. A semi-empirical ballistic-limit model was developed from key variables, with a residual correction term to describe the coupled deviation between fragment geometry and target response. The corrected model achieved a mean absolute percentage error of 7.91% and a coefficient of determination of 0.852. The conversion matrices show strong dependence on fragment type. For 616 steel converted to LY12 aluminum alloy, the coefficient increases from 2.50 for spherical fragments to 3.48 for tungsten blocks, giving a morphology-induced deviation of 39.03%. Thus, conversion should be defined by fragment type and target material rather than by a single material constant.

The radius of jetting projectile charge (JPC) varies significantly from the head to the tail, resulting in the crater formed with a large and uniform radius when penetrating steel target. Current methods for calculating crater radius typically use the average radius without considering JPC radius distribution, leading to large errors in the calculation. Therefore, it is necessary to introduce JPC radius distribution when predicting JPC penetration and cratering. By incorporating the radius distribution in the calculation of JPC break-up time, the modified break-up time model was used to obtain the prediction model for penetration depth. Based on the current jet (JET) cratering theory, JPC radius distribution was introduced to derive the prediction model for crater radius of JPC penetration. The X-ray tests and numerical simulations were used to obtain the radius and velocity distribution of JPC. Finally, the prediction model was verified using data from static penetration tests and literature. The results show that the penetration depth calculated using the modified model had a small error compared to the test results, therefore, the modified model could predict the variation of the crater radius with the penetration depth. And the variation of crater radius was in good agreement with the tests, and accorded with the characteristics of uniform crater radius of JPC penetration. The findings have important guiding significance for JPC design and evaluation.