Research On The Performance Of Welding Residual Stress Under The Effect Of Alternate Loadings

The dynamic stress and strain distribution during welding process is the main reason to the appearance of welding cracks and the reduction of welding joint's strength. It has a great effect on the structural performance such as static strength, fatigue strength, stability, stress corrosion cracking and etc. Therefore, it is necessary to take residual stress in consideration when analysis of structural strength and evaluation of structure's life are carried out.Welding is a complicated process in which arc physics, heat transfer, metallurgy and mechanics are involved. When it comes true to simulate the welding process with computer technic, residual stress information can be evaluated during design process. Thus necessary measures will be taken to decide the optimum projects and welding parameters to reduce the residual stress as much as possible. Based on heat transfer theory, thermal elasto-plastic theory and numerical simulation with FEM, finite element model of the real experimental specimen with welding information is formed. Calculation of the transient temperature field, the induced instantaneous thermal stress field and the final residual stress are performed in the thesis. The results are proved to be credible compared with academic results and the experimental results. The methods and programs provided in this thesis are valuable to the practical application.As for material's performance under the effect of dynamic loading, it plays an important role for welding residual stress in the analysis of material fatigue strength. It is recorded that residual stress distribution will change as the alternate loading changes. Based on the blind-hole method, series of experiments are carried out to analyze the effect of alternate loading to the redistribution of residual stress. It concludes that the alternate loading does make contribution to the redistribution of the residual stress field. The longitudinal residual stress is inclined to decline in numerical value compared with the transverse residual stress. Furthermore, a critical alternate loading exists. When the alternate loading is less than the critical value, it makes a great effect on the residual stress. Otherwise the overtopping part does not make an effect any more.