Nondestructive Testing Of Residual Stress In Metal Components Based On Laser Ultrasound

The internal stress information of steel member under the current state is the key to study the failure mechanism and safety evaluation of steel structure.How to realize the nondestructive testing of absolute stress of steel member is an urgent problem to be solved.As a new testing method,laser ultrasound can excite a variety of ultrasonic modes such as surface wave,shear wave and longitudinal wave at the same time.Because of its incomparable advantages of ordinary ultrasonic detection,it has attracted widespread attention in the nondestructive measurement field at home and abroad.Due to the great influence of the actual environmental factors in the actual stress detection,some errors will be caused to the measured results,so it is necessary to adopt the numerical simulation method to carry out research.In this paper,the surface stress of 45 steel plate and the internal stress of 45 steel pipe were studied by using laser ultrasonic technology based on acoustoelasticity method.The surface stress of 45 steel plate was detected by a self-built laser ultrasonic stress detection system combined with finite element analysis.Among them,finite element method has many problems,such as large amount of calculation,limited calculation area and complex artificial boundary.To solve these problems,the three-dimensional finite element model is simplified and the artificial boundary of stress is set up.The main contents are as follows:(1)Various factors affecting stress detection were investigated by numerical simulation,including ultrasonic propagation Angle,ultrasonic propagation sound range,45 steel pipe thickness,45 steel plate surface roughness and curvature radius.The results show that the ultrasonic surface wave propagating along the direction of the principal stress field is the most reasonable method to evaluate the principal stress.With the increase of ultrasonic propagation path,the stress error caused by acoustic measurement error decreases significantly,and the stress error decreases significantly when ultrasonic propagation path is greater than 20 mm.As the thickness of 45 steel tube decreases,a large number of echo signals are generated,which makes the arrival time of ultrasonic echo difficult to distinguish,and increases the difficulty of detecting internal stress by ultrasonic longitudinal wave.The increase of surface roughness and curvature radius will make the stress detection result smaller.(2)The ultrasonic waveform suitable for stress detection is determined according to the numerical simulation results.Ultrasonic surface waves were used to detect the surface stress of 45 steel plate.By extracting the amplitude ratio characteristic quantity of Hilbert envelope signal and the amplitude ratio characteristic quantity of envelope spectrum frequency,it was found that the amplitude ratio of Rayleigh wave basically showed a negative correlation trend with the increase of stress.The amplitude ratio of characteristic frequency fe3 decreases significantly with the increase of stress.Ultrasonic reflected longitudinal wave was used to detect the stress in 45 steel tubes.By extracting the amplitude ratio characteristic of ultrasonic signals in time domain and frequency domain,it was found that the amplitude ratio of odd-order reflected longitudinal wave showed a positive correlation trend with the increase of stress.In the amplitude-frequency graph,the amplitude ratio of peak 1,peak 2 and peak 3basically showed a negative correlation trend with the increase of stress,and peak 2 had the largest linear fitting slope and the best fitting effect.(3)A set of non-contact laser ultrasonic stress detection system for 45 steel plate was established for uniaxial tensile stress detection.By extracting the acoustic time difference characteristic and ultrasonic surface wave frequency characteristic,it is found that the ultrasonic surface wave velocity changes little in the range of low stress,and the ultrasonic surface wave velocity changes greatly in the range of high stress.In the amplitude-frequency diagram,the frequency of main peak 1 shifts to the left with the increase of stress in the range of 9MPa～76MPa and to the right with the increase of stress in the range of 76MPa～144MPa.The amplitude of main peak 1 shows a negative correlation trend with the increase of stress.Compared with the simulation results,the uniaxial tensile stress increases the ultrasonic surface wave velocity and decreases the frequency amplitude,which indicates that the test results are correct.The research results of this paper are helpful to the further development and application of laser ultrasonic stress nondestructive testing technology.