Effect of residual stress on fatigue behaviour of notches

The effects of surface-rolling-induced residual stresses on the endurance limit and the growth behaviour of short cracks were investigated for notched steel parts. Unlike the case of smooth specimens tested in laboratory conditions, the endurance limit of notches under axial loading was enhanced by surface rolling, but the improvement was limited owing to the detrimental effect of tensile residual stresses at a distance from the surface. The second fatigue origin, which was just ahead of the crack tip and destroyed the condition of slowed propagation rate of the short crack in the compressive residual stress field, would be produced at the position where the maximum tensile residual stress was acting. This effect could be effectively eliminated by tensile preloading in such a way that the tensile residual stresses were greatly released by plastic deformation and the short fatigue crack in the compressive residual stress field became non-propagating at the loading of endurance limit. The effect of compressive residual stress on growth behaviour of short fatigue cracks lies in two aspects: (a) increasing the crack closure effect; and (b) decreasing the maximum stress intensity factor. A predicted d a/dN versus ΔK eff curve based on this assumption agreed with the experimental results.