Effect of Nanoclay Addition on Fatigue Behavior of Glass/Epoxy Tapered Laminates

Abstract

Tapered laminates have been used in many engineering applications such as composite yokes to hold the blades in helicopters, wing structures etc. The tapering configuration requires cut fibers along the length of the laminate. This provides flexibility. However this also creates stress concentration which can accelerate fatigue crack propagation. One possibility to improve the performance of this type of structure is to modify the epoxy matrix with nanoclay. In our previous work, it was shown that addition of clay can improve the fatigue performance of regular laminates of glass/epoxy. In this work, epoxy modified with nanoclay was incorporated into glass fibers and tapered laminates were made using these materials. Three different types of laminate stacking sequence were investigated. Tension-tension fatigue tests were performed. The results show that significant improvement in fatigue lives was indeed obtained. The incorporation of nanoclay seems to speed up the delamination at the initial stage of the fatigue. However the rate of crack propagation is slower subsequently. The net result is longer fatigue live to reach a certain crack length. It is believed that the improvement is due to the enhancement in mode II fracture toughness. Stacking sequence also has an effect on rate of fatigue crack propagation.