Analysis of Residual Stresses Resulting from Cold Rolling of Notches and Their Effect on Fatigue Behavior

摘要

The effects of cold forming on the fatigue behavior of threads were analyzed using slip-line field and finite-element analyses. Bolt threads were simulated using notched rotating cantilever-beam fatigue specimens of Inconel 718. The slip-line fields for wedge indentations, with some modifications, were used to analyze the deformation process of notch rolling. Stresses on the deepest slip lines were used in an elastic finite-element analysis of the internal stresses existing outside the slip-line field during deformation. Negatives of the loads on the notch surface from the indentor were used in a second elastic finite-element analysis to determine the internal stresses resulting from unloading. These two stress analyses, with a correction for yielding, were employed to map the residual stress distribution around the rolled notch. The predicted residual stress distribution showed an intense compressive region below the notch root. However, a short distance away from and to the side of the notch, there began a region of residual tensile stresses. This stress distribution was then used to rationalize the fatigue crack propagation behavior of Inconel 718 rotating cantilever-beam fatigue specimens with rolled and machined notches.