Fatigue Strength Estimation for Metallic Components With Compressive Residual Stress and Hardness Distributions

The present work is focused on the analysis of configurations in metallic components subjected to cyclic loading, in which fatigue crack nucleation is generated in zones where hardness gradients and/or residual stress gradients are present. In the first case, a gradient of resistance to the nucleation and propagation of small cracks is produced, whereas in the second case, gradients in load ratios are generated as the crack propagates. A fatigue crack propagation prediction approach based on fracture mechanics is proposed, through which the influence of the hardness gradient on the definition of the fatigue crack growth resistance curve and the effect of the compressive residual stress gradient on the quantification of the resulting driving force are accounted for. The approach is applied to a carburized steel with surface shot peening, for which fatigue failure results, including those in the presence of artificial semicircular planar defects with depths of 0.15, 0.2, and 0.3 mm, have been reported in the literature. The results of the estimations are analyzed and found to be highly satisfactory, and several important aspects are discussed.