Ballistic resistance of gradient ceramic ball composite armor

Ceramic/metal composite armor has attracted extensive attention in lightweight protective structures because of its high hardness, excellent energy dissipation capability, and strong resistance to repeated impacts. However, most existing studies focus on uniformly distributed ceramic balls and single-impact scenarios, leaving the damage evolution and protective mechanisms of gradient ceramic-ball composites under multiple impacts insufficiently understood. To address these limitations, a gradient ceramic-ball metal composite structure was proposed to improve the multi-hit resistance of composite armor. Penetration experiments using 12.7 mm armor-piercing incendiary projectiles were conducted to investigate the ballistic response of the composite target. Based on the experimental conditions, numerical simulations were carried out using the LS-DYNA software to analyze the penetration behavior of successive projectiles impacting the composite target plate. A three-dimensional finite element model was established to reproduce the penetration process, in which the Johnson-Cook constitutive model was employed to describe the mechanical behavior of metallic components and the Johnson-Holmquist ceramic constitutive model was adopted to characterize the dynamic response and failure behavior of ceramic materials. Appropriate contact algorithms and erosion criteria were implemented to simulate the interaction, damage, and fragmentation processes between the projectile and the target materials. Parametric numerical simulations were further performed to analyze the penetration characteristics of successive projectiles during the multi-impact process. The effects of ceramic ball diameter, impact spacing between successive projectiles, and gradient arrangement direction of ceramic balls on the ballistic performance of the composite structure were systematically investigated. In addition, the penetration depth, energy absorption characteristics, damage morphology of the target, and projectile deflection behavior were analyzed to reveal the influence of structural heterogeneity and pre-existing damage on the penetration response. The results show that increasing the diameter of ceramic balls significantly enlarges the damage region and enhances the structural non-uniformity, thereby increasing the sensitivity of the structure to impact location. Under multiple projectile impact conditions, the pre-existing damage caused by the first projectile significantly reduces the energy absorption capacity of the target plate and alters the penetration behavior of the subsequent projectile, especially when the impact point of the latter is located within the damaged region. Within a certain range of impact spacing, projectile deflection induced by damage heterogeneity effectively reduces the penetration depth of the backing plate even when the absorbed kinetic energy remains nearly unchanged. Compared with the negative-gradient configuration, the positive-gradient ceramic-ball composite armor reduces the damage area of the first ceramic layer by 14.8%–57.8% under the same areal density and effectively restricts the expansion of the initial damage region, thereby maintaining higher structural integrity under repeated impacts. These results indicate that a properly designed gradient distribution of ceramic balls can significantly improve the multi-hit resistance of ceramic/metal composite armor and provide useful guidance for the lightweight design and structural optimization of gradient ceramic-ball composite armor.