A pseudo-3D computational approach for ultrasonic inspection of thin composite laminates with delamination emanating from a countersunk hole

The work presented in this article focused on the development of a pseudo-3D computational approach for visualizing computational ultrasonic inspection models for thin composite laminates with complex geometry. The approach creates a 3D dataset by merging several 2D models along different cross-sectional slices of the material under inspection. The approach was applied to a 2.6 mm thick carbon fiber epoxy laminate with an annulus-shaped artificial defect concentric with a 4 mm diameter through hole, shadowed by a 100° countersink. Investigations were performed using water immersion ultrasonic pulse-echo and single-sided pitch-catch setups operating at a 5 MHz frequency. Time-of-flight comparisons between computational and experimental A-scans validated the computational results, demonstrating a calibration error of 4%. Defect sizes measured in the C-scans of the computational model matched the actual outer diameter and width of the annulus, with a difference of 18% and 6%, respectively. Findings within the experimental dataset were similar, with the largest difference associated with the defect width being off by 0.088 mm. The pseudo-3D approach revealed that a normal incidence water immersion setup was ineffective in detecting defects from the countersunk geometry, while an oblique incidence inspection at 8.4375° was successful in capturing the defect with reasonable accuracy.