A two-point fatigue strength assessment for surface-hardened notched components under consideration of residual stresses based on the local strain approach

Abstract

The “Guideline non-linear” of the German Research Association for Mechanical Engineering provides a fatigue strength assessment for machine components based on the local strain approach. Currently, this assessment is limited to homogeneous components and without the possibility to consider residual stresses. The methods are thus inadequate for surface-hardened components, where the presence of material inhomogeneity and the introduced residual stresses significantly impacts fatigue life and the potential failure origin. In the following paper, an adaptation of the proof of structural durability of the guideline is shown, that firstly includes a two-point assessment and the estimation of load cycles to crack initiation at two failure-relevant points simultaneously. This enables the consideration of inhomogeneous material states, since the failure of surface-hardened components may initiate from the notch root as well as from the transition area between the low-strength core material and the high-strength surface layer. Secondly, the consideration of the residual stress state for both failure-relevant points is also introduced as part of the adapted fatigue strength assessment.