Improved Method of Rolling Bearing Fatigue Life Prediction Under Edge Loading Conditions

More than half a century has passed since Lundberg and Palmgren (referred to as LP in the following) established a theory on the life of rolling bearings 1) 2), and problems with the theory such as its lack of capability of considering shear force (tangential force) on the surface caused by slip or the initial or residual stress due to fit have been pointed out, with correction to these problems having been reported in many ways. 3)-6) However, these problems occur only when the theory is used under special conditions, and in most cases, the subjects above do not pose problems. For this reason, designing and examination based on the LP theory is still in practice now from the viewpoint of respecting past track records also. On the other hand, the design of crowning is important in designing roller bearings. When an imbalance in sharing of load exists between the edge section and the middle section or when misalignment exists, that region will be damaged in a short time should a greater load is exerted on either of both. To avoid a problem of this kind, it is necessary to provide a suitable crowning. The method of Ito and Sugiura 7) is well-known as a method of determining a crowning profile. On the basis of results of various life tests conducted with the amount of crowning of full-crowning rollers being varied, they used the method of Harris 8) and Moyer et al. 9), proposing an optimum crowning design method. However, this method cannot be applied to (a) the edge load problem occurring in the necking section for grinding on a rolling surface and to (b) the one occurring in the joint between the cylinder section and the crowning section in cut crowning as shown in Fig. 1. Other methods 10) 11) of determining a crowning profile have been suggested; however, those methods are intended to determine crowning profiles to reduce contact pressure and stress, not intended to calculate the bearing life. Recently, as is seen in the theory of Ionnides and Harris (referred to as IH in the following) 12), various methods have been suggested that determine the life of the entire bearing by dividing the surface loaded by stress into finite pieces, calculating the life of each, and then combining them. These methods are considered to be applicable to any stress distribution condition and should be applicable to the life projection for cases where edge load occurs; however, this has not been ascertained adequately.