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.

中文翻译：

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碳纤维增强聚合物 (CFRP) 层压板在冲击疲劳和环境条件下的损伤容限

本文提出了一种针对碳纤维增强聚合物（CFRP）在冲击疲劳和湿热降解作用下的无损损伤评估技术。对原始和浸泡的准各向同性板进行 2J 的低周重复冲击，导致几乎不可见的冲击损伤 (BVID)。采用立体数字图像相关（DIC）和虚拟场方法（VFM）在静态弯曲载荷下的冲击后样本上创建平衡间隙（EG）图，同时定位和测量损伤。基于从 EG 图收集的数据进行标准化，以测量损坏严重程度，结果表明，与环境样本相比，吸收约 1% 的水分后，损坏增加了 2 至 5 倍，而吸收约 2% 后，损坏增加了一个数量级。这些发现强调了冲击疲劳下水分对 CFRP 结构完整性的不利影响，并证明在这些条件下，可以使用无损全场运动学和虚拟场方法测量 BVID。