In a reinforced concrete (RC) box structure, the dissipation of blast waves is restricted, and damage to the structure can be intensified due to multiple reflections. To thoroughly investigate the load characteristics and dynamic behavior of internal explosions in an RC box structure, the applicability of the finite element method was verified by replicating internal explosion tests on fully enclosed and semi-enclosed (with venting openings) RC box structures. Based on this, numerical simulations of internal explosions were conducted for the prototypical RC box structure and the type of terrorist bombing attacks specified by the Federal Emergency Management Agency under three explosion scenarios and four venting areas. The influence of venting area on the load characteristics at the inner surfaces and corners, the load distribution on the inner surfaces, and the time histories of displacement and velocity at the centers of the inner surfaces under internal explosion loads were explored. Additionally, a formula for calculating the total impulse of the structure’s inner surface was proposed, considering both the venting area and the spatial distribution of the impulse. The results show that the venting area has a negligible effect on the overpressure, while the impulse decreases exponentially with increasing venting area. The load distribution characteristics on the structure’s inner surface are significantly influenced by the structural dimensions, exhibiting an indented or W pattern. The maximum displacement at the centers of walls and slabs is reduced by about 50% as the venting coefficient changes from 0.457 to 1.220. Finally, based on the total impulse and maximum displacement response of each component under free-field explosion loads, a calculation method for the impulse and damage enhancement coefficient was proposed based on the venting area, effectively predicting the internal explosion load and the structure’s dynamic behavior at various venting coefficients.

The effects of Ti/Mg thickness ratio (abbreviated as Ti/Mg ratio), structural thickness/projectile diameter (t/D) ratio and impact angle θ on the hypervelocity impact characteristics of Ti/Al/Mg impedance gradient structures were studied with AUTODYN finite element software. Results show that the influence of Ti/Mg ratio on the expansion characteristics of the outer bubble fragment cloud is within 5%, but increasing the Ti/Mg ratio can improve the degree of fragmentation of the projectile. The structural energy absorption characteristics are best within the range of 0.625 to 1. The expansion speed of the outer bubble fragment cloud and the mass of the large fragment at the center of the projectile decrease with the increase of t/D ratio, while the unit face density energy absorption decreases. Oblique impact is beneficial to the dissipation of projectile kinetic energy by the impedance gradient structure, but it will reduce the degree of fragmentation of the projectile. After θ exceeds 40° or 50°, the "slip effect" has a significant impact on the impact characteristics of the impedance gradient structure. The perforation area of the impedance gradient structure decreases with the increase of Ti/Mg ratio and t/D ratio, and increases with the increase of θ, and an empirical formula for the dimensionless perforation area of the impedance gradient structure is obtained based on dimensional analysis.

To thoroughly investigate the underwater motion characteristics of rod jets, the effects of liner thickness, material, and charge length-to-diameter ratio on the underwater motion characteristics of rod jets were systematically explored by combining experimental methods with numerical simulations. The results show that after entering the water, the rod jet undergoes head upsetting and experiences mass erosion effects. The effective length of the jet initially increases and then decreases during its motion, while its average velocity decays exponentially. Further analysis indicates that increasing the liner thickness and charge length-to-diameter ratio can significantly enhance the jet′s resistance to erosion and its ability to maintain velocity. The optimal range for liner thickness is 0.036D_k to 0.055D_k. When the charge length-to-diameter ratio exceeds 1.25, the influence of charge structure on the underwater motion characteristics of the rod-shaped jet gradually diminishes. Additionally, material density has a significant impact on the velocity decay law of the rod jets during underwater penetration: the higher the density, the stronger the jet′s ability to maintain velocity; when material densities are similar, the velocity decay laws of the jets tend to be consistent. The study also demonstrates that liners made of copper, tantalum, and tungsten are all suitable for underwater shaped-charge warheads. This research provides important theoretical support and reference for the design optimization of underwater shaped-charge warheads.