High-strength steel wires containing corrosion pits : stress analysis and critical distance based fatigue life estimation

The present paper deals with the problem of assessing the fatigue lifetime of high-strength steel wires containing corrosion pits, with this investigation being based on a large number of experimental data selected from the technical literature. To evaluate the stress concentration phenomena characterising corroded metallic wires, according to the state-of-the-art knowledge, pits were modelled either as semi-ellipsoidal cavities or as hemispherical notches. The stress concentration factors, Kt, associated with these simplified pit geometries were calculated numerically by solving numerous three-dimensional FE models. Subsequently, the Kt values being determined according to this standard numerical procedure were post-processed systematically to derive simple analytical solutions suitable for estimating, in situations of engineering interest, the stress concentration factors associated with pitting corrosion. Finally, after making some assumptions to derive the necessary fatigue properties, the Theory of Critical Distances was used in the form of the Point Method and the Line Method to re-analyse the literature data being collected. This systematic validation exercise allowed us to prove that the Theory of Critical Distances is successful also in assessing the fatigue lifetime of high-strength metallic cables containing corrosion pits, with the obtained estimates falling within an error factor of 3. Therefore, as far as wires weakened by corrosion pits are concerned, it was demonstrated that the Theory of Critical Distances can be used to post-process the local linear-elastic stress fields when they are not only determined numerically, but also estimated by using those standard analytical solutions which are strictly valid solely for conventional notches.