Ballistic performance of bioinspired nacre-like aluminium composite plates

Abstract

Inspired by the hierarchical structure of nacre, an aluminium alloy (AA) 7075-T651 based composite plate is developed for ballistic applications. The proposed nacre-like composite plates are made of 5, 7 or 9 layers consisting of many ~1 mm thick AA7075-T651 tablets bonded together with toughened epoxy adhesive. Experimental ballistic tests on these composite plates, using a hemispherical nosed steel projectile at impact velocities in the range of 340–450 m/s, were performed. Both the 5-layer and 7-layer plates exhibited a better ballistic performance than their bulk counterparts based on the observation that the measured residual velocity of the projectile through the composite plate was lower than that through the corresponding bulk plate with similar areal density. However, the performance improvement is reduced as the composite plate thickness increases (from 5 to 9 layers) due to the increased likelihood of ductile failure occurring prior to perforation in the thicker bulk plates. The failure pattern analysis of the impacted specimens confirmed that the impact performance enhancement of the nacre-like composite plates can be attributed to the hierarchical structure facilitating both localized energy absorption (by tablet deformation and interlocking) and more globalized energy absorption (by inter-layer delamination and friction).