Research On The Interaction Of Laser Ultrasound And Metal Defects Based On COMSOL

Laser ultrasound is a new type of detection technology,which has many advantages over traditional ultrasonic detection technology.The modulation of the excitation light source can adjust the excitation ultrasonic parameters,and finally achieve non-destructive detection of materials.In this paper,the finite element simulation software COMSOL is used to model the physical process of pulsed laser excited ultrasound under thermoelastic effect.The numerical method was used to study the excitation characteristics and propagation characteristics of the excited ultrasonic waves,the interaction between the shear wave excited by the line source and the defect was explored,and a set of metal internal defect detection system based on the line source shear wave was established.The main research contents of this article are as follows:1.Established two excitation source models of point source and line source.In the excitation model,the corresponding ultrasonic waves of the transverse wave,longitudinal wave and surface wave modes were found.The effects of parameters such as the peak power of the excitation light source,the spot radius,and the laser rise time on the characteristics of the excitation ultrasound were studied respectively.The directionality of shear wave propagation was studied by finite element method simulation,and the conclusion that its energy is strongest near the normal angle of 30 ° is verified.It is concluded that the energy attenuation of the line-source excited shear wave is smaller than that of the point source.2.The reflection and transmission characteristics of laser-induced ultrasonic transverse wave are studied.According to the reflection simulation experiment,according to different incident angles,different reflection effects will appear,and the reflection waveform will have waveform conversion.In transmission simulation experiments,when the defect size reaches the ultrasonic wavelength level or less,there will be obvious diffraction phenomena,which will negatively affect the detection accuracy.It is concluded that reducing the excitation ultrasonic wavelength can improve the defect detection capability.3.Established an experimental model of dual detectors to detect internal defects of metals through transverse wave transmission.In the form of simulation experiments,the model with circular defects inside was scanned and detected,and the peak amplitudes of the two detection points on the scanning path were recorded,and then the defect coordinate information obtained by data processing was calculated.The position of the defect obtained by calculation coincides with the actual position of the defect.This method provides a theoretical basis for the detection of internal defects in metals.