The effect of a single peak overload on fatigue crack propagation rate and crystallographic path in Fe-3%Si single crystals

Abstract

The effect of a single peak overload on fatigue crack path and propagation rate in a Fe-3%Si single crystal was studied. Two specimen orientations were considered. For the same propagation rate (3 × 10 −6 mm/ cycle), the A specimen was in the threshold regime of the d a/d n- ΔK relationship and the B specimen was in the mid-growth rate regime. Related growth occurred in both types of specimen, when the ratio of the overload stress intensity factor, K ov , to K max due to baseline cycles was set to 2. The direction of crack growth in specimenA was not changed after the overload, but in specimen B, the crack path was changed from noncrystallographic to crystallographic, and produced a crystallographic step. The step was changed from noncrystallographic to crystallographic, and produced a crystallographic step. The step was approximately on the (001) plane. The fatigue crack growth increment associated with the retardation was found to be proportional to the square of K ov . These results suggest that the cause of retardation is not only the overload plastic zone size and decrease of ΔK efl but also the dislocation rearrangement at the crack front associated with plastic deformation caused by the overload.