An Approach for Fatigue Cracking Failure Prediction of Ceramic Rolling Elements under Hertzian Loading

Abstract

In highly stressed rolling element contacts of ceramics, cracking along the edge of the rolling track is a well-recognized mode of failure. Using the maximum value of principal tensile stress which a material element experiences under the passage of the contact load as critical stress for failure, the failure probability of the ceramic rolling element is formulated according to Weibull probability theory using a volumetric flaw assumption. The formulation contains material parameters, such as fatigue exponent, crack growth constant and Weibull modulus, which are obtained previously from (static and cyclic fatigue) bending testing of two advanced silicon nitrides. For the two ceramic materials, the Hertz contact stress field is analyzed to determine the failure probability in terms of maximum tensile principal stress, aspect ratio and sliding friction coefficient. Numerical examples have been calculated for ceramic rods and balls with and without sliding friction. The strong effect of friction on failure probability indicates the need for good lubrication in reducing friction and increasing the reliability of the hybrid ceramic bearings.

Presented as a Society of Tribologlsts and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

KEY WORDS:

• Ceramic Bearings
• Stress Analysis
• Life Prediction Methods

Notes

Presented as a Society of Tribologlsts and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998