Deformation and fracture simulation of explosive charges under low velocity impact by numerical manifold method

Numerical Manifold Method (NMM) integrates continuous and discontinuous features with mathematical and physical cover systems (MC and PC), enabling it to solve problems related to crack initiation and propagation. This study aims to analyze the fracture characteristics of explosive charges subjected to low-velocity impact, elucidating the underlying patterns in their mechanical behavior. The existing NMM framework has been innovatively extended to enable the solution of large deformations, multi-crack fields, and crack interactions. Based on the Mohr-Coulomb criterion, the novel integration of PC subdivision, element deletion, and data transmission algorithms within the NMM framework has been developed and implemented. The division technique ensures multiple tension and shear cracks can be captured, while the deletion algorithm addresses program errors caused by the distortion of the fine elements during the impact process. A simulation of the standard Steven test was conducted to evaluate stress distribution in explosive charges under low-velocity impact; consequently, the results of our NMM framework are in agreement with the LS-DYNA model. Furthermore, systematic simulations of the Steven test with varying specimen sizes and impact velocities are analyzed. The simulation results indicate that as specimen thickness increases, fragmentation intensity significantly decreases; whereas, as specimen diameter increases, the confining pressure in the impact area decreases, resulting in more severe fragmentation. The enhanced NMM developed in this study effectively simulates the dynamic deformation and fracture behavior of explosive charges.