Thickness effect on ballistic impact behavior of hybrid carbon/Kevlar composites

Carbon fiber composites have poor impact resistance that constrains their wider application in advanced engineering structures, and hybridizing carbon fibers with Kevlar fibers is an effective method to enhance their impact resistance. The ballistic impact resistance can be optimized through regulating the hybridization layout and hybrid ratio, which requires systematically exploration on the inherent failure mechanism. In this work, the ballistic impact behavior of hybrid carbon/Kevlar fiber reinforced epoxy laminates against flat-head projectile are systematically investigated. Hybrid specimens with different thicknesses and hybridization ratios are designed, tested and compared. The results reveal the strong correlation between thickness and ballistic impact performance. When laminates are relatively thin, Kevlar fiber layers at the back surface impart superior impact resistance. In contrast, the opposite result is observed when the thickness is beyond a threshold value. With an increase in the Kevlar fiber hybridization ratio, this threshold value will occur in thinner laminates. Further analysis indicates that this phenomenon is related to a shear plugging effect that dominates the different modes of impact failure.