Delamination Damage in Central Impacts at Subperforation Speeds on Laminated Kevlar/Epoxy Plates

Abstract

An experimental research program has shown that in central impacts at normal incidence by small hard impactors at subperforation speeds on continuous-filament fiberreinforced, laminated composite plates with brittle matrices, the major damage is delamination at the interfaces between unidirectionally reinforced layers of different orientation. This is accompanied by some matrix cracking between the fibers of the layers. Composites with three kinds of fibers (glass, Kevlar, and graphite), each in a brittle epoxy matrix, have been investigated. This paper reports new results on Kevlar and compares them with some previously published results on glass and graphite. Postimpact visual examination of the semitransparent glass and Kevlar laminates revealed the extent of the delamination. Relationships between projected delamination area and the kinetic energy imparted to the plate are reported. For those plates where the overlapping delaminations could be resolved and the total delamination area could be determined, the evidence supports the assumption of a single linear relation between total delamination area and imparted kinetic energy for each system observed at these subperforation speeds, but there is a limited amount of this kind of data available. Bending strength and stiffness reductions of the damaged panels are also reported.