Consideration of the transient material behavior under variable amplitude loading in the fatigue assessment of nodular cast iron using the strain-life approach

摘要

The consideration of realistic load assumptions is important for the fatigue design of highly stressed nodular cast iron components for wind energy application. Especially in case of overloads causing elastic-plastic deformation, residual stresses may have a strong impact on fatigue life. In strain-controlled fatigue tests with constant and variable amplitudes, the influence of overloads on lifetime was investigated. During fatigue testing, the transient material behavior, cyclic hardening, cyclic relaxation of the residual stresses, and quasi-static creep effects of the EN-GJS-400-18-LT was recorded and evaluated. To quantify the influence of the transient material behavior on the calculated lifetime, fatigue analyses are carried out with the strain-life approach, both with and without consideration of the transient material behavior. The results show that conservative damage sums are derived if the transient material behavior, especially the relaxation of tensile residual stresses, is neglected.