IHS ESDU The effect of mean stress on fatigue strength (test piece with stress concentration). FAT A.00.02

ESDU Fat A.00.02 shows how the R-M diagram for a notched specimen is obtained from one for a plain test piece of the same material. If elastic conditions existed the R-M diagram would be constructed simply; the radial distance from the origin to the curve for the plain test piece divided by the stress concentration factor yields a corresponding point on the curve for the notched specimen. The behaviour of the stress cycle when yielding occurs is illustrated, the peak stress being limited to the material proof stress. The R-M diagram is then a line parallel to the mean stress axis from the point at which yield initially occurs. Two worked examples show how the method is applied in practice.