PNNL

Abstract

The presence of exit holes in friction stir welded T-Peel joints is known to reduce joint strength. However, the aspect of the joint's structure at the exit location that is the most detrimental to the strength remains to be discovered. This study used finite element simulations to explore the effect of modifications to the joint's structure at the exit location on increasing joint strength. The simulations relied on characterizing the weld's structure and local hardness distribution and considered fracture property variation. Through modeling work, it was predicted that effective bonding around the exit hole would significantly increase joint strength even with the presence of the exit hole. In the subsequent experimental task, the rotating tool "dwelled" at the exit hole before it exited the workpiece. In other words, the weld scheme was modified to include different dwell times at the exit location. Effective bonding around the hole was observed because of the dwell time. Using dwell times of 1, 2, and 5 secs increased the T-peel joint's strength by 29%, 31%, and 41%, respectively.