Laser Ultrasonic Detection Of Metal Surface Defects Theoretical And Experimental Studies

In this paper, we mainly used experiments and finite element method (FEM) to research the laser ultrasonic flaw detection and provided some methods to investigate the location, size and some other information of the flaw. The main content of this work are listed as follows:FEM was used to simulate the physical process of surface ultrasonic which excited by laser line source on aluminum plate. Further, some analysis was made on interactions between the surface ultrasonic and surface rectangular flaw, and the various ultrasonic model when the flaw existed; Finally, we extract the surface displacement signal to analyze the affect of laser ultrasonic produced by flaws, at the same time, inverse the flaw location, size and other relevant information.We established the flaw detecting experimental platform which used the PVDF piezoelectric sensor to receive ultrasonic signal and the laser line source to excitated the laser ultrasonic. Application of the platform, we studied the various ultrasound modes and the relationship between ultrasonic and flaw under the receiver and the excitation source place the same or different side.In this paper, both experiments and numerical simulations analyzed the influence of flaws to the surface ultrasonic signal. The relation between the ultrasonic signal and flaws was discussed from two respects:one is reflected wave, the other is transmission wave. We put forward some characters of reflection signal such as peak to peak value and time indifference of the Rayleigh wave of the double peak region. Some characters of transmissive wave were also given such as time broadening, peak to peak value of the double peak region. And we put forward same characters for the surface skimming longitudinal waves. Finally, we analysis spectrums of the reflective and transmissive wave with different flaw depth, we summarize the conclusion as follows the defects have frequency effect to the reflection and transmission of ultrasonic signal.This research result will provide an experimental basis for laser ultrasonic detection of metal surface flaw, and theoretical basis for the technology of ultrasonic nondestructive testing.