Residual Stress Analysis in Arc Welded Lap Joints of High Strength Steel Sheets and Welding Wire Using Material Properties at Heating and Cooling

A technical approach is presented for the precise analysis of residual stress in arc welded lap joints of high strength steel sheets. This approach involves the development of a method to measure material properties during both the heating and cooling processes. The measured material properties are then utilized in a thermal elastic-plastic finite element method (FEM) to analyze the welding residual stresses in the lap joints. The analysis accuracy is investigated by comparing the results using material properties measured during heating, cooling, or both. The maximum temperature distribution on the surface of the heat affected zone (HAZ) is measured and accurately predicted through welding thermal conduction analysis. When the material properties measured on heating only or cooling only or both were, respectively, used in thermal elastic-plastic FEM, the analyzed results showed that the stress history in arc welded joints of 780MPa high strength steel sheets are different. The analyzed residual stress using material properties measured during cooling is closer to that obtained using properties measured during both heating and cooling. This result suggests that considering the cooling phase is crucial for accurately predicting the residual stress distribution in the lap joints. When a narrow specimen for tensile-shear strength test is cut from specimen from original welded joint, the analysis and measurement confirm that the maximum longitudinal tensile residual stress in the original arc welded lap joint is significantly reduced. Additionally, the transverse residual stress exhibits notable changes in its distribution characteristics. These findings emphasize the importance of incorporating both heating and cooling material properties when analyzing welding residual stresses in arc welded lap joints.