Laser Ultrasonic Wave Mode Conversion for Depth Quantification of Surface Cracks in Additive Manufacturing

To address the challenge of accurately quantifying surface crack depth in additively manufactured components, a novel method based on the mode conversion of laser ultrasonic surface waves is proposed. By analyzing the propagation paths and time-domain signal characteristics of mode-converted surface waves (RSR waves) at the crack location, a quantitative model relating crack depth to time is established. Finite element simulations are employed to investigate the mode conversion and propagation mechanisms of surface waves, and a non-contact laser ultrasonic testing system is developed accordingly. An optimized C-VMD algorithm is further proposed to extract the characteristic signals effectively. Experimental results demonstrate that the proposed method achieves a quantitative detection error of less than 4% for cracks with depths ranging from 0.6 mm to 1.4 mm, indicating its suitability for detecting small-sized cracks in metal additive manufacturing components.