Fragments dispersion characteristics of the uncoupled asymmetric grid composite shell structure under internal explosive loading

Understanding the dynamic response and fragment dispersion of uncoupled asymmetric charge structures is important for both directional warhead design and fragment hazard assessment. However, the matrix-mediated regulation mechanism of fragment dispersion in additively manufactured (AM) grid composite shells under uncoupled internal explosive loading remains insufficiently understood. In this study, a coupled cylindrical charge and an uncoupled cyclo-square charge incorporating AM grid matrices and preformed steel spheres were designed. Blast experiments, coupled Eulerian-Lagrangian (CEL) simulations, and simplified theoretical analysis were combined to investigate the loading response and fragment dispersion behavior of these composite structures. The numerical model was validated by the experimental results and reproduced the fragment distribution characteristics with good accuracy. The results show that, for the coupled cylindrical configuration, the low-strength grid mainly affects fragment velocity magnitude while exerting little influence on the dispersion direction. In contrast, for the uncoupled cyclo-square configuration, the grid matrix significantly modifies fragment trajectories in the uncoupled region, causing them to deviate toward the local outward normal direction of the shell and producing a more concentrated distribution on the directional side. Increasing the matrix density and strength further enhances this convergence effect, with metallic grids showing much stronger regulation than the ABS grid. Theoretical analysis indicates that this behavior originates from the coupled effects of inertial confinement and structural resistance of the grid matrix. Higher density enlarges the quasi-vertical dispersion zone by reducing the effective initial velocity, whereas higher strength suppresses end rotation and decreases the divergence angle of peripheral fragments. These findings clarify the governing mechanism of fragment dispersion in uncoupled grid composite shells and provide a mechanics-based reference for the design and optimization of directional fragmentation structures.