Tailoring combined impact loading using gradient foam composite projectiles with variable fragment shapes

The combined effects of explosive shock waves and high-velocity fragments pose critical challenges to the structural integrity of protective systems. Traditional experimental approaches often oversimplify the problem, lacking systematic investigation into how fragment geometry and foam density gradients influence the synergistic damage mechanisms. To address this gap, this study proposes a novel composite projectile consisting of gradient aluminum foam embedded with rigid fragments of various contact-end shapes (cylindrical, hemispherical, and truncated conical). Finite element models were developed and validated against experimental data to analyze the effects of fragment shape, embedding depth, loading sequence, and foam density gradient on loading characteristics and target plate responses. Results reveal that fragment geometry significantly affects the stress distribution and failure modes of the target plate. Hemispherical fragments, due to their smaller initial contact areas, induce concentrated stress and early penetration, thereby weakening the combined loading effect. Additionally, gradient foam composition regulates the contact force profile, with higher front-end densities producing stronger initial forces but shorter interaction durations. These findings offer new insights into the design and optimization of gradient composite projectiles for simulating realistic explosive loading conditions and improving structural impact resistance.