A methodology for modelling the effects of nitriding on fatigue life

A methodology is presented for modelling the effects of nitriding for fatigue life prediction. The method is illustrated by application to tooth bending fatigue failure in notch conditions representative of the fillet regions in spline teeth. The methodology first involves the prediction of nitrided layer stress distributions which take account of the graduation in material stress-strain curve through the nitrided layer and the effects of residual stresses. Second, the life prediction aspect requires that the effects of the graded material properties and residual stresses on mean stress levels and thus on fatigue constants be accounted for. Comparisons between predicted and experimentally-determined lives show that the methodology significantly improves the predictions for nitrided specimens.