Numerical research for surface-inclined cracks of unidirectional carbon fiber composites based on laser ultrasonics

Laser ultrasonic technology, operating based on the thermoelastic mechanism, is extensively utilized in non-destructive testing (NDT). However, accurately establishing a mathematical correlation between defects and signal responses remains challenging for inherently anisotropic materials. In this study, we employ numerical simulation to systematically examine the influence of temporal function and radius on the generation of ultrasonic signals. Furthermore, a quantitative inversion method is proposed to quantify the relationship between the geometric features of surface defects and the corresponding Rayleigh wave-based detection responses. Results reveal an exponential decay in surface displacement information as the defect inclination angle increases. Additionally, a third-order nonlinear correlation is observed between defect depth and displacement, while the rate of displacement growth accelerates with increasing defect width. The maximum relative errors of the crack’s angle, depth and width obtained by the method are 6.42%, 1.96% and 4.70%, respectively. This work provides optimized laser parameter guidelines and establishes a quantitative defect-signal mathematical inversion method for unidirectional carbon fiber composites, advancing quantitative defect inversion in laser ultrasonic NDT.