Study On Non-destructive Testing Of Residual Stress On Metal Surface Based On Laser Ultrasonic Technology

Metal materials especially aviation aluminum alloy are widely used in aerospace,military industry,etc.Nevertheless,these materials are prone to produce residual stress in the manufacturing process due to processing technology and heat treatment.Thus,it is critically essential to inspect the production quality so as to ensure the required functionalities.In recent years,more and more efforts have been devoted to achieving rapid and accurate non-destructive testing of residual stress in metal materials.Among the non-destructive testing methods,laser ultrasonic has the advantages of non-contact detection,high resolution of time and space,and easy to achieve high-precision measurement.Therefore,in this thesis,laser ultrasonic technology is adopted to realize non-destructive testing of residual stress in metal materials.The first chapter starts from the introduction for the use of aviation aluminum alloy and other metal materials,followed by the analysis of the stress generation,classification and its influence,as well as the statement of the research significance of this thesis.Then,the research progress of laser ultrasound in the residual stress measurement is summarized by means of concluding the advantages and disadvantages of the residual stress detection technology.Finally,the main research contents are proposed in the thesis.In the second chapter,the excitation mechanism and detection technology of laser ultrasonic technology are analyzed.Then,the propagation characteristics of surface wave are elaborated.Finally,the wave equation of surface acoustic wave in medium,and the acoustic elasticity formula of residual stress measurement by surface acoustic wave are deduced.In the third chapter,the hardware platform of the laser ultrasonic measurement system is set up.The key components were properly selected and the corresponding brackets were designed for fixing.Secondly,the multistage amplification circuit and the filter circuit were designed and produced to improve the signal-to-noise ratio of the ultrasonic signals in the experiments.Finally,the scanning distance of the galvanometer was adjusted by using the digital microscope.In the fourth chapter,the synchronous acquisition program of ultrasonic signal is designed to realize the rapid acquisition of ultrasonic signals.The type and characteristics of ultrasonic signal noise are introduced.Finally,the ultrasonic signal preprocessing method is presented and the velocity of surface wave is calculated by using the method of waveform correlation analysis.In the fifth chapter,the tensile test of 6061 aluminum alloy for the acoustic elastic coefficient is firstly performed,and then the residual stress of 6061 aluminum alloy welded parts is tested using the built-in laser ultrasonic system.Based on the results,the surface wave velocity distribution of the sample is obtained,and the residual stress distribution of the sample is calculated according to the acoustic elasticity formula.Finally,the X-ray stress analyzer test was conducted for comparison.In the sixth chapter,the research summary of the dissertation are drawn,meanwhile the existing problems and the prospects of improvement are presented.