Investigation of Residual Stress in the Ultrasonic Assisted Constraint Groove Pressing Process of Copper Sheets

In this research, Constraint Groove Pressing (CGP) process, which is one of the most important and effective methods of severe plastic deformation processes has been studied. Ultrasonic assisted CGP (UCGP) process has been conducted to investigate and compare the effects of applying ultrasonic vibrations on the residual stress with the conventional method. Contour method was applied to measure the residual stresses distributions in the CGPed and UCGPed samples. Pure copper sheet samples were tested both with and without ultrasonic vibrations up to 2 passes. The measured values of the residual stresses indicated a relative reduction of stress in the presence of ultrasonic vibrations. By investigation of residual stress normal to the surface in thickness direction, it was observed that residual stresses are compressive on the edge and tensile in the middle of the thickness of the sheet. This reflects the self-balancing feature of residual stresses. In all conditions for both passes, residual stress reduced about 20MPa while using ultrasonic vibrations compared to traditional CGP method.