Effect of specimen shape on micro-crack growth behavior under fatigue in reduced activation ferritic/martensitic steel

The effect of specimen shape on the micro-crack growth behavior of F82H was investigated by the low cycle fatigue test at room temperature in air at the total strain range of 0.4–1.5% using three types of the miniature hourglass-type specimens with different stress concentration factors. In case of the high strain range conditions above 0.8%, almost no effect of the specimen shape on the fatigue life, micro-crack initiation life and the crack growth rate was observed. In case of the low strain range conditions below 0.6%, the effect of specimen shape on the fatigue life was observed. The fatigue life was considered to be dependent on the stress concentration factor. Based on the micro-crack growth analysis, the difference of the fatigue life under the low strain range conditions was attributed not to the crack growth rate but to the micro-crack initiation life dependent on the specimen shape.