Prediction of endurance limit of hardened parts with account of operational factors

Fracture endurance limit is one of the main parameters used in calculating the strength of surface hardened parts.  The influence of various operational factors along with hardening should be taken into account in predicting this parameter. Prediction of the endurance limit under stress concentration was carried out according to the criterion that takes into account the influence of residual stresses on the surface of the dangerous section of a hardened part, as well as the criterion of the average integral residual stresses over the thickness of the hardened surface layer equal to the critical depth of a non-propagating fatigue crack. The effect of surface hardening on the endurance limit was analyzed taking into account such operational factors as the type of deformation, working temperature, the asymmetry of the loading cycle of specimens made of steels and aluminum alloys. Fatigue tests of cylindrical specimens with circular notches of a semicircular profile were carried out under torsion, bending and tension-and-compression. It was established that the use of the criterion of the average integral residual stresses is quite a good indicator of the effect of surface hardening on the fracture endurance limit taking into account the operational factors studied.