A criterion of fatigue strength of a round bar subjected to combined static and repeated out-of-phase bending and torsion was derived.
Tests were performed for heat treated (tempering at 650℃ after water quenching at 850℃) SM45C steels.
Uniaxial fatigue tests were performed with Schenck fatigue testing machine and those data show clearly the mean stress effect. And new criterion can be applied in this simple case.
Multiaxial fatigue tests were performed 90 degree out-of-phase bending and torsion with and without bending mean stress. From those data, we could see the fact that the new criterion represents the mean stress effect well.
By applying the new criterion to fatigue design of machine components, such as crankshaft or axleshaft, whose state of stress is combined repeated out-of-phase bending and torsion plus coexistent static bending, we can forecast the fatigue life and prevent the fatigue failure.
