.DISCUSSION.

A mathematical model for the pitting fatigue life of pinion and gear or entire meshing train is needed for more accurately repre-senting the reliability of mechanical transmissions. This load-life model for gears can then be combined with rolling element bearing life models for overall reliability studies or trade-off studies of high reliability systems such as helicopter transmissions. It is doubtful that such a model will replace the accepted design tools of the AGMA [31, 32]3 for commercial quality gears. Using the Lundberg-Palmgren model [17, 18] for rolling element bearings is a good choice because of the similarity of concentrated contacts in gears and bearings. One should proceed with caution since this model is basically formulated for subsurface oriented fa-tigue caused by reversing sub-surface shear stresses. Liu [33] es-tablished that the maximum shear stress occurs on the surface whenever the coefficient of traction equals or exceeds 0.1. Thus th