Mean stress sensitivity of ductile iron with respect to technological and statistical size effect considering defects

Chair of Mechanical Engineering, Montanuniversität Leoben, 8700 Leoben, Austria

^a Corresponding author: paul.kainzinger@unileoben.ac.at

Abstract

Specimens of two sizes have been taken from two sampling locations within a wind turbine hub made of nodular cast iron (EN-GJS-400-18-LT) for constant amplitude fatigue testing. The sampling positions exhibit varying cooling conditions, resulting in different microstructures. Fatigue tests have been carried out at R-ratios of R = −1 and R = 0. The coarse microstructure as well as the larger specimens yielded in lower fatigue strengths. No effect of the microstructure or the specimen size on the mean stress sensitivity has been found. Fractographic analysis of the fractured specimen's surface revealed micro-shrinkages to be the source of crack initiation for all specimens. Micro-shrinkage size increases from fine to coarse microstructure and with increasing specimen size. The El-Haddad equation using the √area parameter was used to describe the fatigue limit. The results were in good agreement with the experiments.