FATIGUE MECHANISMS UNDER LOW-ENERGY REPEATED IMPACT OF COMPOSITE LAMINATES

This investigation deals with the fatigue behaviour under low energy r epeated impact (LERI) of quasi-isotropic graphite/epoxy composite plat es. The damage growth during the test was monitored by ultrasonic C-sc an imaging. The damage area plotted as function of the number of impac ts displays a three stages pattern behaviour. Stage I corresponds to a matrix cracking of the region under the impactor, stage II correspond s to a rapid delamination propagation and stage III to a slow delamina tion propagation. The relative extent and the damage growth rate in st age II increase with the impact energy E(I). The number of impacts N-I F corresponding to the transition between stage I and stage II is gove rned by an impact-fatigue curve in the form of E(I) = C log (N-IF) + E (0) where E(0) is the threshold impact energy that induces a delaminat ion in one impact and C constant denoting the damage tolerance of the material.