Theoretical analysis for the enhanced mechanism and optimal design of the backing layer on improving the ballistic resistance of the ceramic composite armor

Ceramic composite armor, mainly composed of ceramic and backing layers, has been widely used in impact protection. However, the quantitative understanding and analysis for the role of the backing layer in improving the ballistic resistance of the ceramic composite armor system is still lacking. In this paper, by taking the B₄C/UHMWPE bi-layer armor system as an example, the enhanced mechanism of the UHMWPE layer in improving the ballistic resistance of the ceramic composite armor and the appropriate UHMWPE thickness are systematically studied theoretically. A theoretical model predicting the residual velocity of a bi-layer armor system is developed and verified. Specifically, the dissipated energy associated with plasticity, fracture and friction and the stored energy composed of the elastic strain energy and kinetic energy, is theoretically obtained, respectively. The theoretical results show that as the increase of the UHMWPE thickness, the dissipated energy monotonically increases, while the stored energy first increases and then decreases with the appearance of a turning point due to the dominant mechanism of the stored energy changing from the maximum stored energy of the system inherently to residual kinetic energy. Furthermore, for a given ballistic resistance, a reference value for the optimal UHMWPE thickness to lower the areal density is proposed according to the transition of the stored energy, which is related to the ceramic thickness, impact velocity and the mass of the projectile. The study in this paper helps guide the lightweight design of ceramic composite armor.