Evaluation of UHMWPE prepreg laminates under near simultaneous multiple projectile impacts: Effects of structural shapes and projectile dispersions

Multiple projectile impacts are significant threats in real-world military and anti-terrorism operations. Previous researches have mainly focused on the protection mechanism and structure design against a single projectile impact. However, these conclusions cannot be well applied to the scenario of multiple projectile impacts. Furthermore, flexible low-stiffness materials can adapt to protected targets with diverse geometric profiles more quickly than hard high-stiffness materials. Therefore, this study aims to investigate the flexible UHMWPE prepreg laminates with different shapes under different projectile dispersions from response characteristics, ballistic limit velocity, energy absorption mechanism, and residual velocity. The competition of multiple projectiles against limited protective materials would reduce the ballistic limit velocity. The ballistic tests show that the residual velocities of the three-projectile impacting the conventional planar UHMWPE are higher than those of the single-projectile when the impact velocities are slightly above the ballistic limit velocity. Still, the difference will disappear with the increase of the impact velocity. To reduce the negative influence of the synergistic effect of multiple projectile impacts on protective efficiency, a bio-inspired corrugated structure formed by pre-folding is proposed. The finite element numerical model validated by ballistic experiment results is used for full-scale simulations. Compared with the conventional planar UHMWPE with identical apparent surface density, the ballistic limit velocity of a corrugated structure corresponding to the projectile dispersion of 1, 2, and 3 can be increased by 21%–36%. Corrugated prepreg laminates exhibit superior followability and load-bearing capacity. They reserve materials in advance for rapid extensions and alleviate the high in-plane stress of the synergistic effect, which has great potential to protect against multiple projectiles.