Comparative analysis of damage mechanisms in ballistic soaps: single fragment vs. fragment cluster under low-speed impact

This study investigates the penetration effects of fragment cluster using ballistic soap, which simulates human soft tissue. Through a combination of experimental tests and numerical simulations, we analyzed the differences in the damage mechanisms and damage patterns of a single large fragment compared to small fragment cluster. A numerical simulation model was constructed using the finite element method (FEM) and its validity was confirmed by comparing the experimental and numerical results. The effects of the number of fragment cluster, spacing between them, and loading time sequence on the damage mechanisms of a ballistic soap target were investigated and analyzed under the same total kinetic energy conditions. The results indicated that the damage patterns caused by single-fragment loading were primarily characterized by temporary cavity damage, localized shear, and plastic deformation of the substrate. In contrast, the damage patterns resulting from the penetration of fragment cluster were predominantly influenced by group-coupled, temporary cavity-independent perforation mixing damage, large-area tensile tearing damage, and plastic deformation of the substrate. With the increase of the number of fragments, the coupling effect between the fragment cluster was enhanced, resulting in increased mass erosion and absorbed energy of the ballistic soap. The increased the spacing between fragment cluster enhances their penetration capability and a critical spacing value (S = 5 mm) occurs at which the sum area and volume of the temporary cavity entrance reach their maximum, measuring approximately 3.21 and 2.46 times that of a single large fragment, respectively. In addition, the loading time sequence of the fragment cluster significantly influences the damage pattern and extent of damage to the ballistic soap. The first fragments arriving at the soap target create a pre-damage effect, which allows the subsequent fragments to inflict more severe damage.