Fatigue crack propagation in locally heat-treated ductile iron

Abstract

The article presents the results of an experimental–analytical study of the cyclic fracture process in a locally austempered ductile iron (LADI). A heat treatment is realized in such a way as to form three layers with different microstructure, mechanical properties and resistance to cyclic loading. The fracture criterion, the stress intensity factor K, dependent on stresses of cyclic loading and induced residual stresses, was chosen as a criterion for analyzing the process of cyclic fracturing. The limiting values of threshold stress intensity factor range ΔKth were determined for the compact tension (CT) specimens after application of loading and they were found to be different. It was determined that residual stresses increase the ΔKth factor when the crack propagation rate is less than 10-11 m/cycle.