Law of Fatigue Limit : Part III. Fatigue under Non-uniform Stresses

Abstract

Fatigued region in mild steel can be detected by etching. The data of the depth of etched layers of round bars fatigued under cyclic torsion and rotating bending were examined. The conclusions are that the degree of fatigue of a point cannot be determined by the stress at that point only, but it is determined by a mean value of the stress in a certain region around that point, the area of the region being a constant for the material. When the fatigue is a function of radius only as in cases of torsion and rotating bending, a certain length along the radius may be taken instead of the area.