Haruo Nagatani

Improved Method of Roller Bearing Fatigue Life Prediction under Edge Loading Conditions

It has been deemed to be proper to use subsurface stress distributions in life predictions of roller bearings under edge loading conditions. But by using this method the decreased life caused by edge stresses is normalized in the process of relating them to the lives of other parts, and therefore life prediction accuracy is lessened. The life calculation method by relating elements is irrelevant in this case. For this measure, an improved method is proposed. It is mainly based on Lundberg and Palmgrens (L-P) theory but differs in calculating the lives where the peak stresses arise; both edges and the center in a full crown roller case, for example. In this method, the center raceway life is corrected by multiplying by the stress uniformity factor. The stress uniformity factor considers the scatter of the material strength, like size effect. It varies according to the uniformity of stress distribution. The results of this method correspond very well to the results of roller endurance testing. In addition, not using the stress uniformity factor results in a good correlation.

Ball Bearing Fatigue Life Estimation Under the Condition of Contact Ellipse Being Over Shoulder

There are no prediction methods of bearing fatigue life when ball bearing is used under the condition of contact ellipse being over shoulder. To enable this prediction there are two difficulties. The first is contact problem shifts from non-conforming contact problem to conforming contact problem because of large load. The second is there is no practical method for bearing life estimation under the condition like as edge load occurring, though there exist many decision methods about optimal crowning when edge load occurs. For each problem, authors have proposed each solution. Combining those methods, we propose the bearing life ratio estimation method under the condition of contact ellipse being over shoulder. To verify this method, we compare the calculation result with bearing life test result for 50 samples that have different 3 inner ring outer diameters. The both result agree well, therefore the validation of this method was achieved. Ahead of that, we propose improved solution to the first difficulty, and verify the contact pressure and shear stress by comparing FEA result with improved solution when contact ellipse being over shoulder. This solution has been used to estimate above-mentioned bearing life.