Detection of surface defects for longitudinal acoustic waves by a laser ultrasonic imaging technique

The main objective of this paper was to use the p-waves to quantitatively evaluate the surface cracks by a laser ultrasonic imaging technique. The p-waves were generated by a pulsed laser illuminated on the specimen with a surface damage and received by a piezo transducer. According the relationship between the propagation distances with the p-waves velocity, we analyzed the time (1.5 μs) of the maximum forward amplitude of the once P-waves arrived at the receiver when the pulse laser illuminated at different excitation points, and analyzed the vibration of the p-waves at different distance from the surface damage at 1.5 μs. At last, C-scan image and estimated size and location as determined by p-waves amplitude at 1.5 μs were used to detect the sizes of the damage. The experimental results showed that using longitudinal acoustic waves by a laser ultrasonic imaging technique is an effective way for the investigation of surface damage.