Multi-hit ballistic impact on S-2 glass/SC15 thick-section composites: experiments

Abstract

Multi-hit ballistic impact and damage behavior of thick-section composites are of interest to many military and aerospace applications. The effect of support spans on single-hit penetration resistance and the effect of relative distance between multiple impacts on the penetration resistance are the subject matter of the present investigation. In order to study the effect of support spans on penetration resistance, single-hit ballistic experiments are conducted on two plain-weave (PW) S-2 glass/SC15 composite laminates of thickness, 13.5 mm (22 layers, 22L) and 20.4 mm (33 layers, 33L), respectively at two different support span diameters, i.e. 102 mm and 203 mm. On the other hand, the effect of multiple impacts on penetration resistance has been investigated by impacting both the laminates (22L and 33L) at four additional radial shot locations (90 degrees apart) with a support span diameter of 203 mm. In both the impact scenarios, 0.50cal fragment simulating projectiles (0.50cal FSP) were used while the composite laminates were clamped between a cover and a support plate. In addition, the maximum dynamic deflection of the composite laminates were recorded using a thin aluminum witness plate at the rear end of the laminate, and the through-thickness ballistic damage of the composite laminates was investigated by sectioning through the impact centers, dying with an ink-alcohol solution, and taking optical photographs of the cross-sections. Results show that the single-hit ballistic limit velocity increases marginally with support span diameter investigated. The curvatures of the dynamic deflection profiles at the support edge suggest that the dynamic deflection was constrained by the smaller support span while the dynamic deflection was not constrained by the larger support span. There was no noticeable difference in the single-hit maximum dynamic deflection between the two laminate thicknesses as a function of impact velocity to ballistic limit velocity ratios. Single-hit through-thickness damage extended toward the edges of the larger support spans such that the subsequent multiple impacts were on partially damaged laminates; however, the pre-existing ballistic damage showed about 4.5% and 9.0% decrease in site specific multi-hit ballistic limit and energy, respectively.