Fatigue life assessment of imperfective cast steel components in the medium-cycle regime by stress- and energy-based concepts

Abstract

Manufacturing process-based imperfections, such as shrinkage porosities, severely limit the fatigue strength of cast steel components. Due to the complexly shaped spatial geometry of such defect structures, the application of local fatigue assessment concepts is recommendable. This work applies the Theory of Critical Distances (TCD) to assess the fatigue life of imperfective cast steel components made of G12MnMo7-4+QT in the medium-cycle regime. Based on a calibration procedure utilizing generalized S-N curves of plain and notched specimens at various load ratios, the relationship between the critical distance LM and the number of cycles to failure Nf is parametrized first. At second, the implemented planar framework is validated with specimens featuring a different notch geometry. The presented linear-elastic methodology is furthermore extended to arbitrarily shaped spatial imperfections, resulting in reasonable predictions of experimentally derived fatigue life results. Moreover, a strain energy density-based fatigue assessment methodology is formulated, introducing a relationship between the control radius Rc and Nf. The yielded fatigue strength assessment values correspond to the results of the initially implemented TCD-framework. Concluding, the presented stress- and energy-based concepts depict engineering-feasible methodologies to assess the fatigue life of cast steel components affected by complexly shaped shrinkage imperfections.