Effect of thickness matching on ballistic performance of layered composite armor: experiments and numerical simulations

Ceramic composite armor offers a promising approach to achieving lightweight and high ballistic performance. In this study, 75 vol% B₄C/6061Al composites were fabricated via vacuum gas pressure infiltration and combined with B₄C ceramic layers to produce layered composite armor. Three targets with identical areal density but different ceramic-to-composite thickness ratios, namely CM-0.12, CM-0.27, and CM-0.74, were experimentally investigated under 7.62 mm steel-core projectile impact at approximately 850 m/s. A finite element model was developed and validated against the experimental results, followed by an extended parametric study of CM-0.37, CM-0.49, and CM-0.64 to investigate structural optimization. The ballistic response exhibited a pronounced non-monotonic dependence on the ceramic-to-composite thickness ratio. Among the experimental configurations, CM-0.27 showed the best overall ballistic performance, while CM-0.49 exhibited the lowest projectile penetration and rear deformation within the investigated numerical range. Mechanistically, an insufficient ceramic thickness leads to premature ceramic failure and concentrated loading of the composite layer. Conversely, an excessive ceramic thickness promotes ceramic self-fragmentation and reduces the capacity of the composite layer for stress-wave attenuation and residual energy absorption. These results demonstrate that ballistic performance is governed by the thickness matching between functional layers rather than by maximizing the thickness or energy absorption of an individual layer.