Influences of thickness and stacking sequence on ballistic impact behaviors of GLARE 5 FML plates: Part I-experimental studies

Abstract

This two-part article examines the effects of thickness and stacking sequence on the ballistic impact behaviors of GLARE 5 (2024-T3 aluminum alloy-unidirectional S2-glass/epoxy) fiber-metal laminated plates. Part I deals with observations from tests of specimens with various thicknesses and stacking sequences. A high-speed camera was used to measure impact and residual/rebound velocities. Ballistic limit velocity (V₅₀) was determined based on the incident projectile impact velocity versus the residual velocity (V_i∼V_r) data and the classical Lambert-Jonas’ equation for each individual panel type. As expected, thicker specimens revealed more resistance to perforation. The results showed that the V₅₀ varied in a parabolic trend with respect to the specimen thickness. Furthermore, the quasi-isotropic specimen offered relatively more resistance to impact as compared to other types of stacking sequences. The interfacial debonding/delamination as well as bending/stretching in aluminum layers were considered to be important factors in dissipating impact energy in the specimens. The damage characteristics were evaluated using both nondestructive ultrasonic and mechanical sectioning techniques. Only the contour of the entire damage area could be obtained using ultrasonic C-scan, whereas more details of the damage were provided through the mechanical cross-sectioning technique. It was observed that the damage contour increased as the impact velocity reached its V₅₀ value for a given specimen thickness and then it slightly decreased for impact velocity above the V₅₀ value. In addition, the shape and orientation of damage contours were affected by lay-up orientations.