Reference-free Crack Detection and Localization by Nonlinear Laser Ultrasonic

This paper presents a study on non-destructive crack detection and localization by nonlinear laser ultrasonic and state-space-based method, without using any reference data from the undamaged structure. After irradiated by laser pulse, ultrasonic waves will be generated and propagate in a structure. The corresponding waves are recorded by a transducer placed at a fixed point on the structure. State space based attractors are reconstructed based on the recorded data, and a nonlinear crack-sensitive metric called average local attractor variance ratio (ALAVR) is extracted to detect the differences between adj acent attractors, hence the crack. Furthermore, laser scanning technique is proposed to locate the crack on the structure. The proposed technique has been successfully used for detecting and locating artificial crack in an aluminum plate and an actual sand inclusion crack in a compressor body.