A simplified 3-D finite element simulation of cold expansion of a circular hole to capture through thickness variation of residual stresses

Cold expansion technique is a mechanical method of inducing beneficial compressive stresses around circular holes to offset the applied tensile stress resulting in improved fatigue life. The beneficial effect derived from the cold expansion process is entirely dependent on the magnitude and distribution of the induced residual stresses around the hole. In the present work a 3-D finite element simulation of cold expansion of a circular hole has been developed employing a new approach. In this approach, expansion is simulated by enlarging the hole layer by layer successively from one side of the plate to the other side resulting in simulation of gradual and complete expansion of the hole in the first stage. This process is followed by removal of applied boundary conditions again layer by layer resulting in gradual spring back of the hole completing the simulation of cold expansion process in the second stage. The present approach is capable of capturing the variation of residual stresses at various sections along the thickness as it happens in the actual split sleeve cold expansion process. The results in terms of the residual stress distribution and its variation along the thickness are presented, compared and found to be in close agreement with the published data.