Influence of the cold-drawing process on fatigue crack growth of a V-notched round bar

The state of stress in a structural component is generally influenced by both service loadings and production processes. As a matter of fact, the so-called residual stresses can be generated during manufacturing and processing, and are due to inhomogeneous plastic deformations produced by mechanical, thermic or chemical phenomena. Sometimes the effect of residual stresses on mechanical and fatigue properties is beneficial, sometimes it is detrimental. In the present paper, the effect of residual stresses due to the cold-drawing process on the fatigue crack propagation in a metallic cracked round bar with a V-shaped circumferential notch is examined. The residual stress distribution in the reduced cross-section of such a bar is numerically evaluated through a FE analysis which simulates the material removing operation in the notched region. The stress-intensity factors (SIFs) related to tension loading and residual stresses are numerically evaluated. Then, the crack propagation under cyclic tension combined with the residual stresses is analysed by taking into account the above SIF values and the actual stress ratio, which is different from that due to cyclic tension only.