Ultrasonic Welding Stress Distribution Measured with Optical Rosette/Ring-Core Method

Ultrasonic spot welding is a novel solid-state joining technique for automotive body structures. The residual stresses, caused by the inhomogeneous deformation during the welding process, are considered to be a major factor affecting the strength and quality of the weld. Many conventional measurement methods cannot be applied because of the small size of the spot weld. In this study, the ISSR/ring-core cutting method is applied to measure the residual stresses on the ultrasonic spot weld. The ISSR possesses the short gage length and high sensitivity. The ring-core cutting was conducted on the back of the spot weld. The tensile residual stresses were obtained. The measured tensile residual stresses added to the operation stresses could cause the initiation of the cracks.