Effect of design on the performance of steel-alumina bilayers and trilayers subject to ballistic impact

Composite armors systems containing ceramic components are capable of offering greater ballistic protection than those of monolithic metals alone. The level of protection afforded by a composite armor depends sensitively on the materials utilized and their spatial configuration. Using numerical simulation, we investigate the effects of relevant design parameters on the ballistic performance of thin, unbonded ceramic-metal bilayers and trilayers subject to normal impact by steel spheres. The deformation behavior of the constituent phases is described by established constitutive laws. The predictive capability of the numerical model is validated through comparisons of simulation results with experimental measurements of displacement profiles of the back facesheet of a reference trilayer. The simulation results indicate that the ceramic-metal bilayer with the ceramic at the impact side offers the highest ballistic resistance; removing metal from the rear of the structure and placing it on the impact side (forming a trilayer) results in reduced ballistic resistance. Additionally, the onset of target penetration is found to correlate with high levels of energy dissipated within the target. The implication is that composite armors should be designed to maximize the energy dissipated in the projectile, not in the armor. Accordingly, effective designs at resisting failure are found to have high ceramic-to-metal mass ratios, with a finite (though small) amount of metal on the back face.