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Integrating full-field optical methods, inverse techniques and traditional mechanical testing for damage tolerancing in CFRPs under impact fatigue

Mendoza, Isabella
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Lamberson, Leslie
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2023-04
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2023 Graduate Research And Discovery Symposium (GRADS) posters and presentations
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GRADS2023_Isabella_Mendoza.pdf
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https://hdl.handle.net/11124/176895
 https://doi.org/10.25676/11124/176895
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Abstract
Composite structures are susceptible to transverse loading due to their inherent layered structure, particularly when under impact. Under low energy repetitive impacts (LERI), little is understood regarding damage mechanisms, damage accumulation, and the post-mortem global response of the composite material under different loading configurations. In this study, we examine carbon fiber-reinforced composite (CFRC) plates subjected to low energy repetitive impacts of 2 J to investigate their behavior under impact fatigue. Post-mortem specimens are then investigated using three main methods: digital image correlation (DIC), the virtual fields method (VFM) and compression-after-impact (CAI) tests. DIC is used to extract surface kinematics under an applied static load to observe the evolution of strain fields under bending as the number of impacts accumulate. This data is then used as input for VFM analysis which is used to reveal local gaps in mechanical equilibrium, allowing it to be used as an indicator of damage. Next, ASTM standard CAI tests are performed on the impacted specimens to compare ultimate compression strength values. X-ray computed tomography (XCT) is also used to corroborate damage detection provided by the equilibrium gap method and identify catastrophic microstructural damage pre-cursors. Using quasi-isotropic 8-ply CFRC plates, XCT results showed that interlaminar cracking appeared in as little as 10 impacts. At 100 impacts, extensive matrix cracking and delaminations were observed. After 300 impacts, severe delaminations were imaged using XCT, while barely visible surface cracks were imaged on the rear face of the specimen.
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