Fatigue Mechanisms Under Low Energy Repeated Impact of Composite Laminates

This investigation deals with the fatigue behaviour under low energy repeated impact (LERI) of quasi-isotropic graphite/epoxy composite plates. The damage growth during the test was monitored by ultrasonic C-scan imaging. The damage area plotted as function of the number of impacts displays a three stages pattern behaviour. Stage I corresponds to a matrix cracking of the region under the impactor, stage II corre sponds to a rapid delamination propagation and stage III to a slow delamination propaga tion. The relative extent and the damage growth rate in stage II increase with the impact energy E I . The number of impacts N IF corresponding to the transition between stage I and stage II is governed 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 delamination in one impact and C constant denoting the damage tolerance of the material.