Imaging and reconstruction of asymmetric wrinkles in carbon fibre composites using high-frequency eddy current and full matrix capture-based ultrasound

Ply wrinkles are a common defect found in Carbon Fiber Reinforced Polymer (CFRP) laminates that can lead to failure in composite structures if not correctly evaluated during manufacture stages. The mechanical performance of a structure depends on multiple parameters of a wrinkle, such as amplitude, wavelength, and asymmetry, which ideally need to all be measured to characterise the wrinkle properly. To address this issue, the authors designed and manufactured a set of complex wrinkles with various asymmetry offsets and amplitude and obtained raw data by testing them with a high-frequency eddy-current system. A unique trajectory in the complex Nyquist plot was found on asymmetric wrinkles, demonstrating the dominant influence of wrinkle asymmetry on electrical resistance. The authors also used full matrix capture ultrasound to characterise the wrinkles and measured the profiles by extracting texture phase randomness. The study revealed the superior capability of FMC UT for characterising and retrieving the profile in wrinkle coupons, while HF ECT was more adaptable for identifying the region of interest effectively. This work also implements a state-of-the-art deep fusion strategy to demonstrate a lightweight architecture can be easily used to combine multiple sources of wrinkle profiles and generate a more accurate prediction than traditional methods. Overall, the demonstrated work can be further applied to CFRPs with increasing geometric complexity and defects to facilitate the design efficiency and testing of CFRP components.