Micro-support effect consideration in fatigue analysis of corroded steel based on real surface geometry

Abstract

The service life of steel structures is significantly reduced by corrosion. In particular, pitting corrosion leads to high local stress concentrations and can reduce the expected fatigue strength. Previous studies on corroded specimens have shown that crack development in fatigue tests is correlated with stress concentrations. To consider stress concentrations in local fatigue concepts, the so-called micro-support effects must be quantified. This can be usually considered with the theory of critical distances, including the stress averaging approach by Neuber. For stress concentrations from pitting corrosion, the applicability of this method is limited because of the large number of notches in corroded surfaces. In this study, as an alternative approach, the implicit gradient model is presented, in which the influence of the micro-support effect is considered numerically on 3D FEM models by averaging the stresses over a defined volume around the notch. The consideration of the micro-support effect revealed for most of the specimens a coincidence of the crack location with the location of the maximum notch stress. For some of the specimens, where no coincidence could be observed before micro-support consideration, the maximum stress concentration shifted to the crack location after consideration of micro-support effect. Based on this, a notch stress SN-curve for pitted steel was derived.