Study on impact damage in laminated composites

Abstract

An investigation was performed to study impact damage of laminated composites caused by a line-nose impactor. The major objective of the study was to fundamentally understand the failure mechanisms in composites caused by impact, and to identify the essential parameters causing the damage in composites. The primary concern of the failure modes were matrix crackings and delaminations. An unique and special impact test facility was designed and built for the investigation. The major characteristic of the facility was the use of a rectangular barrel so that a line-nose impactor could be adopted to produce uniformly distributed, transient dynamic loadings across the specimen's width and substantially simplify impact damage patterns. T300/976 graphite/epoxy prepregs were selected to fabricate specimens. All specimens were X-rayed and C-scanned before and after impact to examine damage caused by impact. An analytical model was also developed for simulating the impact response of the specimens and to determine the important parameters dominating the impact damage in composites. An excellent agreement was found between the data and the predictions. Based on the experiments and the numerical calculations, it can be concluded that (1) matrix cracks were the initial impact damage mode, (2) delamination was initiated by the matrix cracks during impact (3) laminates with inherent cracks, resulting from manufacturing, are much more susceptible to impact than laminates without, and (4) the interlaminar shear stresses and in-plane tensile stresses are the dominating stresses causing the initial matrix cracking.