Fatigue testing and buckling characteristics of impacted composite specimens

Fatigue testing has been performed in constant amplitude tension–compression loading on impact damaged carbon fibre/epoxy composite laminates. Two layups were tested. The shape and the amplitude of the buckles were measured using an optical whole field measurement technique. The experimental conditions were chosen to be representative of damages in aircraft structures. The R-value was found to have a small influence on the fatigue life indicating that the compressive part of the load cycle has more importance than the tensile part, this because the compressive load caused local buckling around the damage zone. The buckling was inward on the impact side and outward on the backside with larger buckles on the backside. Also the backside buckles showed a larger growth. Fatigue lives were compared with an analytical model that was found to give conservative predictions.