Simulation And Experimental Research On Welding Residual Stress Relieving By High Frequency Vibratory Stress Relief Technology

This dissertation is composed based on the project of National Natural Science Foundation of China—"Research on mechanism and related technology of multi-dimensional, high frequency, microscopic viewed Vibration Stress Relief (VSR)" (No.50305036).In the way of both theoretical simulation and experimental study, the effect of reducing the welding residual stress by high frequency VSR has been deeply researched. This dissertation consists of five chapters as followingIn chapter 1,the background and significance of the research were introduced. Then the current research situations of residual stress and VSR technology both at home and abroad were summarized. Meanwhile, the technology of how to test residual stress were specifically introduced. Finally, the framework of contents and researching methods were proposed.In chapter 2, the theories of welding residual stress and its process of numerical simulation were researched. Firstly, the mechanism and distribution of welding residual stress was introduced. Then, the finite element models for the thermal field and the relation of elastic plastic stress-strain in the process of welding were theoretically analyzed, and the calculation method of thermal field and residual stress field was deduced. At last, the numeric simulation of welding residual stress by using FEM software ANSYS was achieved, and the distribution of welding residual stress was got. The results of analysis indicate that the maximum tensile residual stress is in the fusion zone; moreover, following the increase of the distance away from the weld, the stress turns into the compressive stress and with the distance increasing from the weld, the compressive stress is becoming smaller.In chapter 3, the mechanism of high frequency VSR and its numerical simulation were studied. Firstly, regular VSR and high frequency VSR were analyzed from the view of metal stress-strain mechanism and mesomechanics, and from which the mechanics expressions of the stress in VSR were obtained, then the regular VSR and high frequency VSR were contrasted to show their difference. Finally, the simulation model of VSR was established and its numerical simulation was implemented by FEM software ANSYS, following, the outcome of these two kinds of VSR was analyzed comparatively. The results of the simulation indicate that high frequency VSR has a better effect, especially in the peak value area of weld joints, on relieving residual stress than regular VSR. Furthermore, the homogenization condition of residual stress is better by using high frequency VSR than regular VSR.In chapter 4, a series of experiments about high frequency VSR were carried out. At first, the measurement technique of blind hole method was introduced. Then the experiment of releasing residual stress of welded specimens by VSR device was tested. We analyzed the test process and results systematically and compare the effects of VSR between different drive frequencies. The experimental outcome indicated the feasibility of releasing stress by high frequency VSR, and the higher the drive frequency is, the higher the depletion rate of residual stress is.In chapter 5, all achievements of the dissertation were summarized and the further research work, which will be done from now on, was put forward.