Simulations for Internal Defect Inspection Using Laser Generated Ultrasonic Wave in Ablation Regime

Abstract

In the present study, the characteristics of laser ultrasound in the ablation regime are investigated using simulations and experiments. The laser ultrasonic technique has been recognized as a noncontact method in the field of nondestructive tests (NDTs). In hostile environments (such as hot temperatures), this method has various advantages over the conventional contact ultrasonic method. In particular, in the ablation regime, the laser ultrasonic technique is suitable for inspecting internal defects because of the high amplitude and directivity of the longitudinal wave. In this paper, a simulation model for laser ultrasound in the ablation regime was developed. This model was subsequently applied to a defective specimen using the B-scan method to locate defects. Finally, we performed an experimental test to verify the simulation results. Consequently, the simulation demonstrated good agreement with the experimental test.

Defect Visualization of a Steel Structure Using a Piezoelectric Line Sensor Based on Laser Ultrasonic Guided Wave

“…If the intensity of the incident light is high, melting, plastic deformation, and cracks occur inside the test specimen, and ablation causes the formation of plasma on the surface. Figure 3 shows the generation mechanism of laser ultrasonics [15,16,17,18].…”

“…This occurs when the incident power of the laser falls below the threshold for the permanent deformation of the material, and no defects or traces are left on the surface. This state is called the thermoelastic regime [15,16,17,18].…”

“…Such a regime is called the ablation regime. In contrast to the incidence of low laser power that does not cause damage, the incidence of high laser power involves damage to the specimen surface [15,16,17,18,19].…”

“…The laser ultrasonic guided wave method is a non-destructive testing method which has almost no restrictions on the medium to be inspected and can be adjusted to a very wide frequency band. It has the advantage that the non-contact distance is much longer than conventional methods [17,18].…”