Fatigue analysis of cast iron components considering the influence of casting skin

The assessment of the fatigue strength of castings with remaining casting skin still constitutes a challenge. Until now, only the roughness of the casting skin has been considered through a reduction factor during the design process. This reduction factor, however, neglects the influence of discontinuities such as inhomogeneous microstructures, imperfections, pores etc. In this work, the casting skin represents the rim zone of the casting, consisting of surface roughness and a deviating microstructure. To assess the influence of the casting skin on the fatigue strength, stress- and strain-controlled fatigue tests were conducted on EN-GJS-400-15 specimens with deviating casting skins. The cyclic behavior of the rim zone microstructure was determined via cyclic axial strain-controlled tests under alternating loading Re = -1 on small flat specimens removed from the rim zone. For the integration of the results from the axial fatigue tests with the influence of the surface roughness, as well as stress gradients present in cast components, on fatigue strength, cyclic bending tests under alternating Rs = -1 and pulsating loading Rs = 0 were performed. The test results are used to develop a fatigue approach to consider the influence of the rim zone on the fatigue life of cast iron components.