Comparison of Laser Ultrasonic Testing and traditional Ultrasonic Testing

Abstract

Ultrasonic inspection is a widely accepted method in the aerospace industry for detecting defects and characterizing materials. However, the traditional ultrasonic technique requires precise alignment and couplant between the ultrasonic scanner and the material, or even complete water immersion. This can be impractical and limits its application. Laser ultrasonics overcomes these inconveniences by generating and detecting ultrasonic waves by lasers. This enables fast contactless ultrasonic inspection without couplant or immersion. While laser ultrasonic inspection has advantages over traditional ultrasonic inspection, the generated ultrasound is relatively broadband and its intensity is limited by the ablation threshold, i.e. the maximum laser energy without damaging the material. Therefore a comparative study between ultrasonics and laser ultrasonics was conducted on representative aerospace components, focusing on defect detectability, signal-to-noise ratios, and inspection speed. Laser ultrasonics is up to 10 times faster than traditional single element ultrasonics. Both techniques can easily discriminate defects of 0.25 inch, however laser ultrasonics is less suited for defect detection in thick (> 5 mm) components. Furthermore, the relaxed alignment conditions of laser ultrasonics allow for the fast inspection of complex-shaped components.