Quantitative characterization of laser ultrasonic based on energy loss and resonance phenomenon

A novel method is proposed for quantitative characterization of cracks by laser ultrasound. It is found that cracks with different depth will have different feedbacks to sound waves based on crack closure effect, energy loss theory and resonance phenomenon. Therefore, damage sensitive characteristic parameters can be extracted from the acoustic waves and used to quantitatively characterize the crack size, including the waveform duration, the reflection energy coefficient and frequency spectral area. In this paper, cracks with gradient depth are used as experimental objects, and the relevant data is obtained through simulation and experiments. The defects are positioned, and the positioning error is less than 3%. The study found that as the crack depth increases, the waveform duration and the reflection energy coefficient gradually decrease, and the frequency spectral area first increases and then decreases. When the crack depth is larger than 0.9mm, characteristic parameters tend to be fixed values. When the crack depth is 0.5mm-0.7mm, abrupt phenomena occurred in both the reflection energy coefficient and the frequency spectrum area due to resonance phenomenon. By analyzing the corresponding relationship between damage sensitivity characteristic parameters and depth, the ability of laser ultrasonic quantitative measurement can be improved.