Effect of Mean Stresses on the Endurable Amplitude of Sintered Iron and Steel

摘要

In the past, the mean stress sensitivity in fatigue testing of metallic materials has been considered a function of the general material strength, mostly characterised by the tensile strength. For sintered iron and steel this reasoning has also been applied, but was never too convincing. A rather straight forward consideration of the slopes of S-N curves in double logarithmic coordinates proves that there must be a parabolic relationship between the endurable pulsating and alternating stress amplitudes. Experimental results from a large variety of materials fit into that general picture. The evaluation can successfully be applied to notched geometries, and for sintered iron and steels the amplitude slopes seem to obey linear extrapolations to compressive mean stresses. Since the brittle-ness - and not the strength - determines the mean stress sensitivity, a ductility criterion is needed for quantitative predictions.