Open hole fatigue testing of laser machined MD-CFRPs

The effect of fiber laser machining (FLM) on multi-directional carbon fiber reinforced plastics (MD-CFRP) with [0/90/45/−45]s lay-up was studied under tension-tension fatigue with stress ratio R = 0.1 for an open hole fatigue (OHF) test configuration. The FLM parameters were chosen to yield a heat affected zone (HAZ) corresponding to a damage factor of approximately 1.4. The growth of this initial damage under tension-tension fatigue was investigated using digital image correlation (DIC), and damage growth characterization was carried out using scanning acoustic microscopy (SAM) and micro computed tomography (micro-CT). The endurance limit of the MD-CFRPs was evaluated by examining the fatigue life at 70, 50 and 30% of its ultimate tensile strength. Results show a strong correlation of damage mode on the applied load levels like conventionally machined samples.