Influence of the Ductility Exponent on the Fatigue of Structural Steels

Fatigue models using the strain-life method do not show exact conformity with the empirical results. Therefore, the use of the mean-stress correction approach is to be evaluated, with a particular focus on mild and higher-strength steel. The influence of the ductility parameters will be studied. A potential favorable development of structural steels with regard to ductility will be checked. The paper will focus on two types of structural steel: S355 and S700. Initially, the mechanical properties of the steel test specimens were measured via a tensile testing rig. In addition, a fatigue test was carried out by applying various mean-stresses. Surface roughness was measured at the notch and introduced into the initial model. The strain amplitudes were determined using the Ramberg-Osgood and Masing material models. Subsequently, a curve fitting was applied to the strain-life data for the fatigue ductility exponent. The multiparameter model was fitted with only one parameter. The resulting model showed a good fit between the strain-life curve and the test results. During the course of the optimization, the error and the scatter were calculated separately for steel types S355 and S700. Based on the ductility exponent, a favorable behavior of the materials was determined.