High-precision measurement of crack length and angle in structural materials using point-focused electromagnetic ultrasound

Crack detection and quantitative evaluation in aircraft aluminum plate structures hold significant application value in aerospace engineering. However, existing non-contact inspection techniques face limitations in achieving high-precision measurements, particularly in terms of crack length and angle estimation. To address this challenge, this study focuses on fatigue cracks propagating from the surface into the interior of metallic plates and proposes a crack characterization method based on point-focused electromagnetic acoustic transducer (PF-EMAT) technology. The method utilizes point-focused surface waves generated by electromagnetic ultrasound, and accurately calculates the crack inclination by analyzing wave propagation characteristics and applying geometric principles. Meanwhile, the crack length is quantitatively measured using a relative sensitivity approach, enabling precise evaluation of crack geometry. Experimental results demonstrate that this method can effectively detect cracks with lengths of 10  mm or more and angles ranging from 0° to 90°, while maintaining length measurement errors within 0.2  mm and angle errors within 1°. The findings confirm the reliability of PF-EMAT technology in non-contact geometric crack characterization, offering a novel solution for the structural health monitoring of plate-like components.