Changes in static yield properties of a ferritic steel during fatigue cycling

Abstract

Changes in the macro-yield strength of a low-carbon ferritic steel induced by cyclic loading have been investigated. For zero-to-peak axial loading (R = 0) tests there is a progressive increase and for completely reversed axial loading (R = −1) a progressive decrease in the yield strength as compared with the static tensile value. The yield strength finally attained for both loadings was equal to the cyclic stress applied, which was significantly below the static yield strength in the R = −1 tests. For both loadings the change in the yield strength with cycling was preceded by a stage involving the gradual elimination of the yield drop and Lüders strain. An attempt to explain the elimination of discontinuous yielding in terms of the Johnston-Gilman theory is made by considering the premature yielding of the surface layers of the steel in the microstrain region.