Fatigue Mechanisms Under Low Energy Repeated Impact of Composite Laminates

Abstract

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 corresponds to a rapid delamination propagation and stage III to a slow delamination propagation. 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.

Low Energy Impact Performance of Interleaved Carbon Fibre Reinforced Epoxy Laminates

“…When N > N ef the impact load kept almost a constant. Similar results were obtained by Boukhili et al [13] through measurement of the delamination area with the multiple impact tests.…”

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“…The damage area remains constant at low impact numbers and increases rapidly at high (n > 10) impact numbers. Similar multistage delamination pattern behaviour has also been reported by Boukhili et al [33], where stage 1 corresponds to matrix cracking in the region of the impactor and stage 2 to rapid delamination propagation. It is also shown in Figure 10 that, for systems based on the ductile vinyl ester resin, deviations between the laminates based on woven fabric and multiaxials only occur at high impact numbers, whereas at low impact numbers the delaminated areas in both laminates are the same.…”

“…Relatively few studies have been directed towards the problem of repeated impact or impact fatigue of laminated composites and the corresponding damage mechanism. Again also here most studies reported in literature are related to CFRP [29][30][31][32][33]. Rotem [30] showed that when a low energy impact was exerted on a laminate, invisible damage might occur as a result of contact stresses between impactor and the laminate.…”

“…The PPS composites possessed a better resistance to impact damage than the epoxy composites. A more recent investigation by Boukhili et al [33] deals with the fatigue impact behaviour of quasi-isotropic carbon/epoxy laminates. Damage growth during the test was monitored by ultrasonic C-scan imaging.…”

Effects of external patch configuration on repaired composite laminates subjected to multi-impacts

“…On the other hand, in terms of impact loads, matrix cracking is chronologically the first damaging mode [34,35], which is followed by a rapid interlaminar fracture propagation. According to Green et al [21], the matrix cracks occur in the lower lamina, and they will extend from the region directly below the impact to the edge of the holes.…”