Study On Technology Of Ultrasonic Nondestructive Testing And Regulation Of Residual Stress

The residual stress has a great influence on the service performance of mechanical components, especially for its strength, fatigue life and dimensional stability. How to detect and regulate the residual stress in the surface or a certain depth efficiently is always a difficult and hot issue in the research.In order to solve this problem, this thesis firstly develops a theoretical study and simulation of the acoustic elasticity detection principle of residual stress, as well as the residual stress of high energy ultrasonic regulation theory. Then, the technical indexes and structure of the residual stress measurement and regulation system are formulated, and the software and hardware system of ultrasonic testing and high energy ultrasonic regulation is established. In the system, the acoustic time difference optimization algorithm is proposed, the detection and regulation system is combined creatively, and the on-line real-time monitoring system of the residual stress in the high energy ultrasonic regulation is developed firstly, realizing the closed loop control of the residual stress detection and regulation. Further, taking into account the influence of environmental factors on the detection accuracy, the calibration and calibration method of residual stress measurement system, the compensation theory and method of residual stress measurement, by the comparison test of residual stress analyzer with X-ray residual stress analyzer, and the uncertainty analysis are verified; In the regulation, to obtain the optimal regulation parameters, the effect of the factors on the stress regulation of different materials is studied by the orthogonal test of three factors and three levels in this thesis. At the end of this thesis, the application of ultrasonic testing and in situ local regulation of residual stress in the service state is carried out, which is based on the research of the residual stress detection and regulation system.The first chapter describes the purpose and significance of the research, analyses the latest status of the non destructive testing technology and residual stress regulation technology at home and abroad, and summarizes the research contents of this thesis..In the second chapter, based on the theory of acoustoelasticity, the relationship between ultrasonic velocity and stress is studied, and the sensitivity of longitudinal wave, surface wave and shear wave to the stress is studied. According to Snell’s law, the critical refraction longitudinal waves along the surface of the sample are generated, the expression of the stress coefficient K is derived by using the acoustic time method on the fixed propagation distance, and the theoretical relationship between the stress coefficient and the propagation distance of sound is obtained. The propagation law of critical refraction longitudinal waves is studied, and the finite element simulation analysis is carried out. Based on the relationship between ultrasonic frequency and penetration depth, the theoretical model of stress depth gradient detection is established, and the C shaped sample is designed for stress gradient. The accuracy of the model is verified by comparing the stress detection values of the X-ray stress analyzer with the simulation values of C-shaped specimen.In the third chapter, the theory of the residual stress and high energy ultrasonic regulation is studied. The mechanism of residual stress in high energy ultrasonic regulation is explained from two aspects. Firstly, the microscopic effect of high energy ultrasonic on the dislocation, the mathematical expressions for the high-energy ultrasonic relaxation of lattice dislocations is established. Secondly, the high-energy ultrasonic of the material macroscopic plasticity induced effect is analyzed. By simulation and experiment of plastic induced, we confirm that the high-energy ultrasonic can reduce the material yield strength, activated the wrong row atoms, and accelerate the eliminating process of the residual stress.In the fourth chapter, the software and hardware system of ultrasonic detection and regulation of residual stress is developed and established. Matlab simulation is carried out on the different algorithms of the acoustic time difference measurement. The error caused by the uneven thickness of the coupling layers and the different thickness of the measured parts is considered and the optimal algorithm of acoustic time difference is put forward. As the detection system and regulation system are combined creatively, the closed-loop control of the residual stress detection and regulation is realized through the designed closed-loop regulation experiment of the ZTC4 titanium alloy.In the fifth chapter, based on the principle of residual stress acoustoelasticity detection, a method of calibration and calibration is proposed. The research on the theory and method of the compensation for the residual stress measurement is carried out. The theoretical model of the temperature impact on the detection accuracy is established, and the experimental verification is presented. As the effects of crystal size and shape distribution on the detection accuracy are studied, the theoretical calculation method and the tensile testing method are presented. The influence of surface curvature and roughness of the surface is analyzed, and an effective solution is put forward. By the analysis of the results uncertainty of the field test, the detection accuracy of the system is confirmed. Based on the principle of residual stress ultrasonic regulation, three kinds of typical materials are used to study the influence of various factors on the regulation of different materials, so as to obtain the optimal regulation parameters. At the same time, the influence of high energy ultrasonic on the hardness, strength and micro-structure of the material is studied, and the ultrasonic regulation theory of residual stress was verified.In the sixth chapter, engineering application studies of residual stress ultrasonic testing and regulation method for aluminum alloy welding and riveting parts, structural steel weldments and non metallic components is developed by using the ultrasonic detection and regulation system. According to the experience and regulation effect of field application, the specification of detection process and regulation process are formulated respectively.