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Impact fatigue damage in CFRP
Mendoza, Isabella
Mendoza, Isabella
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2023
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Carbon fiber-reinforced polymer (CFRP) composites are widely used in military, marine, and aerospace applications due to their high specific strength and improved oxidation resistance compared to metals. However, given their layered structure, CFRP laminates are especially vulnerable to transverse loading. In particular, low-energy impacts that result in barely visible impact damage (BVID) can threaten the laminate structural integrity and are hard to detect. The polymer matrix is also especially susceptible to environmental conditions such as humidity and moisture uptake. To date, no study is currently available on the combined effects of environmental conditioning and repetitive impact loading on CFRPs. Commonly used techniques for evaluating impact damage typically rely on non-kinematic measurement techniques or destructive mechanical tests, contributing to high material and equipment costs. The current work addresses these concerns by investigating the combined effect of impact fatigue and environmental conditioning on CFRPs through non-destructive full-field kinematic measurements. Low-cycle repetitive impacts at 2 J were performed on unidirectional, quasi-isotropic CFRPs. Combined with the virtual fields method (VFM), full-field optical techniques of infrared deflectometry and digital image correlation (DIC) were employed to map gaps in local mechanical equilibrium on post-impacted specimens under a static bending load. A new damage parameter accounting for the severity and shape measured via the equilibrium gap (EG) maps was developed. Results indicate that damage increased two to five-fold after approximately 1% moisture absorption compared to ambient specimens and by a full order of magnitude after approximately 2% absorption. These findings demonstrate that by leveraging a VFM inverse method based on full-field kinematic measurements and constitutive parameter identification, the detrimental BVID of environmental conditioning on CFRPs subjected to impact fatigue loads can be quantitatively assessed.
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