Multi-axial Fatigue Behavior of Notched Composite Structures

This work proposes an investigation on the failure behavior of Glass Fiber Reinforced Polymer (GFRP) laminates with an open hole or a center crack under both multi-axial quasi-static and fatigue loading. To this end, several multi-axial stress states were applied by means of a modified Arcan rig, specifically designed for fatigue tests. It was shown that the stress-strain behavior of notched [+45/90/ - 45/0]s and [0/90]2s layups under multi-axial quasi-static loading was characterized by a significant nonlinearity. This phenomenon becomes more and more significant under shear-dominated loading conditons. It was also shown that, according to Digital Image Correlation (DIC) analysis, the damage of all the investigated laminate layups under fatigue loading is generally much more diffused compared to the one under quasi-static loading. More importantly, the damage mechanisms of investigated specimen configurations under multi-axial quasi-static loading were different compared to multi-axial fatigue loading. This is a challenge for the development of physics-based computational models, since the damage initiation and progression can be substantially different depending not only on the multi-axiality ratio but also the loading condition (quasi-static versus fatigue).