Effect of lay-up orientation on ballistic impact behaviors of GLARE 5 FML beams

This paper examines experimental and numerical investigations on ballistic impact behaviors of GLARE 5 (3/2) fiber-metal laminated (FML) beams of various stacking sequences. The ballistic impact tests were conducted using a high-speed gas gun equipped with a high-speed camera. Optical imaging and mechanical sectioning techniques as well as high-speed-camera footage were used to characterize the impact damage in the specimens. The incident projectile impact velocity versus the residual velocity (VI ∼ VR) was plotted and numerically fitted according to the classical Lambert–Jonas equation for the determination of ballistic limit velocity, V50. The results showed that the unidirectional [90°4] specimen offered the least resistance to the projectile perforation. In addition, except for the unidirectional [90°4] specimen, the ballistic limit was almost insensitive with respect to change in stacking sequence. The interfacial delamination/debonding as well as bending and stretching in aluminum layers played significant roles in dissipating the impact energy in the GLARE 5 (3/2) FML beams. The ballistic impact tests were modeled using a 3D finite element (FE) code, LS-DYNA. The FE prediction was validated using the experimentally obtained VI ∼ VR trends, damage patterns and bullet residual length. Good agreement between experimental and numerical results was achieved. Moreover, the FE predicted V50 as a function of specimen stacking sequence was in good agreement with its experimental counterpart. The validated FE model was then utilized to obtain some insights to the ballistic impacts of which experimental results were not available. It was found that the cross-ply specimen offered the highest contact resistance force while the unidirectional [90°4] lay-up orientation offered the lowest. The maximum contact force for the unidirectional [0°4] and quasi-isotropic panels were almost the same. The results showed that when subjected to ballistic impact, the specimen with [0°/90°]s lay-up orientation dissipated more energy compared to the other lay-up orientations.

► Various types of damage were seen in the specimens.
► Different damage contours were found for different lay-up orientations.
► The ballistic limit was almost insensitive with respect to change in stacking sequence.
► Cross-ply specimen offered the highest contact resistance.
► Cross-ply specimen could dissipate more energy.