Structural response and failure modes of armor steel plates under dynamic underwater explosions

In this research, we examine the dynamic deformation and blast-tolerance of all-metal plates and sandwich panels under underwater explosive (UNDEX) loading. The blast performance of four alloys, Mild Steel (MS), SS304, AL6XN, and AISI 4340, was based on the Johnson–Cook (JC) plasticity model as the shock factors increased from 0.42 to 0.73. The Fluid-Structure Interaction (FSI) model and nonlinear finite-element simulations were employed in the present computational analysis to yield measurable results for the deformation and equivalent plastic strain (PEEQ) of the target plates and the plastic dissipation energy of the sandwich panels. AISI 4340 consistently showed the most stability after each blast series, indicating that the material undergoes the least deformation and exhibits the lowest PEEQ due to its extremely high yield strength and resistance to plastic deformation. AL6XN exhibited appreciable performance under moderate shock and stress levels due to its pronounced strain-hardening behaviour; however, higher load levels reduced performance due to thermal softening. The SS304 exhibited reasonable deformation in addition to exhibiting a generous energy absorption capacity. Mild Steel deformed the most and had the highest PEEQ, while also having the most plastic energy dissipation. The sandwich panels subjected to underwater shock conditions demonstrate that at lower blast intensities, most of the blast energy is absorbed by the front face sheet. However, at higher blast intensities, the core’s contribution to energy absorption increases, thereby aiding energy distribution and enhancing overall stability. The blast-mitigation properties of AISI 4340 were outstanding, whereas SS304 and AL6XN improved the suitability of moderate designs for blast-tolerant applications. These analyses will help select the steels that optimize performance in marine, defense, and subsea applications for blast-resistant protective structures.