Initiation and early growth of short fatigue cracks at inclusions

In this study, the initiation and early growth behaviour of short fatigue cracks in En7A steel with a high content of elongated MnS inclusions was investigated by generating and evaluating data on the growth of short fatigue cracks under various stress levels and stress ratios for the six principal specimen orientations. Short cracks usually initiated at the debonded interfaces between the matrix and the inclusions. If there was no debonding, cracking sometimes occurred in the inclusions. In the early stages, short cracks propagated by a mechanism of inclusion influenced growth. Under low stress levels, usually one short crack was initiated which dominated most of the fatigue life, while under high stress levels there was multicrack interaction. (C) 1996 The institute of Materials