Numerical Study of Factors for Generating Inherent Strain in Friction Stir Welding

Although the friction stir welding (FSW) has been widely employed for fabricating the aluminum alloy structures, there have been a few papers regarding the deformation and residual stress of the joint made by FSW. In order to reveal the inherent strain produced in the process of friction stir welding, the strain induced by only the thermal process was calculated by using the thermal elastic-plastic finite element method and it was compared with the total inherent strain measured through the experiments. The computed inherent strain produced by the thermal process was found to coincide with the measured strain in about 12 mm larger range from the center of weld line while the radius of shoulder was 7.75 mm. Also, in order to examine the effect of compressive process of tool on the inherent strain, a simple thermal elastic-plastic analysis assuming a quasi-plain strain problem was conducted and it was considered that the compressive load might not be a dominant factor for the inherent strain near the weld line.