Effect of the cold-drawing process on fatigue behaviour of V-shaped notched round bars.

The state of stress in a structural component is generally influenced by both service loadings and mechanical effects due to production processes, such as residual stresses generated by inhomogeneous plastic deformations. Sometimes the effect of residual stresses on the mechanical and fatigue properties is beneficial, sometimes it is detrimental. Since the component failure can be caused by both applied and residual stresses, it is important to understand the role of residual stresses. In the present paper the effect of residual stresses, due to the cold-drawing process, on the fatigue behaviour of a metallic cracked round bar with a V-shaped circumferential notch is examined. The stress-intensity factors related to tension loading and to a residual stress field are numerically evaluated. Then, the crack propagation under cyclic tension is analysed through a theoretical model, by also including the effect of residual stresses. Such an effect is taken into account considering, for some values of residual stress severity, the actual stress ratio which is different from the nominal one due to cyclic tension only.