FATIGUE LIFE PREDICTIONS FOR NITRIDED MECHANICAL PARTS

摘要

Fatigue life predictions of nitrided mechanical parts need two steps. First the nitrided material must be characterised in fatigue, considering on the one hand the residual stress state and on the other hand the modifications of the mechanical properties in the nitrided layer, in relation with the metallurgical transformations. Then, one must define at each point of the critical region of the mechanical part the stabilised stress state, which depends equally on the elastoplastic properties of the nitrided material. Then, this stress state must be compared to the fatigue characteristics of the material at the considered point, using some multiaxial fatigue such as Crossland's criteria extended to median cycle fatigue. This method of fatigue life calculation for nitrided mechanical parts is illustrated with the case of root tooth fatigue of a nitrided steel pinion.