Low-Velocity Impact Damage Detection in CFRP Laminates Based on Ultrasonic Phased-Array NDT Technique

To investigate the delamination characteristics of CFRP laminates in barely visible impact damage (BVID) state, low-velocity impact tests (LVIT) and nondestructive testing (NDT) were employed. The energy thresholds of six diverse ply-stacking sequences of laminates in the BVID state were established utilizing visual inspection and contact measurement methods. Ultrasonic phased-array NDT techniques were employed to evaluate quantitatively the magnitude of delamination damage from different viewpoints, including delamination area, shape, and trend variation. Furthermore, the impact resistance of laminates was qualitatively evaluated by analyzing the distinctive delamination damage forms of various specimens to identify the effects of the ply-stacking sequence. The findings of this study demonstrate that reducing the angle disparity between adjacent plies and minimizing the repetition of identical plies can mitigate delamination damage. Additionally, enhancing the ratio of +/- 45 degrees and 0 degrees plies can improve the flexural stiffness of the structure. Specifically, the ultrasonic phased-array NDT technique was shown to effectively detect delamination damage within the laminate in the BVID state.