Damage tolerancing in carbon fiber-reinforced polymer (CFRP) laminates under combined impact fatigue and environmental conditioning

This paper presents a non-destructive damage evaluation technique for carbon fiber-reinforced polymers (CFRP) subjected to combined impact fatigue and hygrothermal degradation. Low-cycle repetitive impacts at 2J were performed on pristine and soaked quasi-isotropic plates, resulting in barely visible impact damage (BVID). Stereo-digital image correlation (DIC) and the virtual fields method (VFM) were employed to create equilibrium gap (EG) maps on post-impact specimens under a static bending load, locating and measuring damage simultaneously. A normalization based on data gathered from EG maps was developed to measure damage severity and showed that damage increased two to five-fold after approximately 1% moisture absorption compared to ambient specimens, and by an order of magnitude after approximately 2% absorption. These findings highlight the detrimental effect of moisture on the structural integrity of CFRP under impact fatigue, and demonstrate that under these conditions BVID can be measured using non-destructive full-field kinematics and the virtual fields method.