Ballistic impact of GLARE™ fiber–metal laminates

Analytical solutions to predict the ballistic limit and energy absorption of fully clamped GLARE panels subjected to ballistic impact by a blunt cylinder were derived. The analytical solutions were based on test results from NASA Glenn. The ballistic limit was found through an iterative process such that the initial kinetic energy of the projectile would equal the total energy dissipated by panel deformation, delamination/debonding and fracture. The transient deformation of the panel as shear waves propagate from the point of impact was obtained from an equivalent mass–spring system, whereby the inertia and stiffness depend on the shear wave speed and time. Predictions of the ballistic limit from the resulting non-linear differential equation were within 13% of the test data. The deformation energy due to bending and membrane accounted for most of the total energy absorbed (84–92%), with the thinner panels absorbing a higher percentage of deformation energy than the thicker panels. Energy dissipated in delamination represented 2–9% of the total absorbed energy, with the thinner panels absorbing a lower percentage of delamination energy than the thicker panels. About 7% of the total energy was attributed to tensile fracture energy of the glass/epoxy and aluminum.