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.= semi-major axis = crack length = semi-contact width, semi-minor axis = crack growth constant = Young's modulus = friction coefticient = Mode -I stress intensity factor = fracture toughness, Mode I

Rolling contact fatigue of silicon nitride bearing balls under pure rolling condition

“…shallow surface degradation, occurred around the periphery of the ceramic spall, whereas no peeling was found surrounding the steel spall, whose bottom was relatively flat. It was verified that steel balls failed by subsurface maximum shear stress [7] whereas ceramic balls failed by the maximum principal tensile stress [12] . Materials properties given in Table 1 show that the compressive strength and shear modulus of ceramic materials were strong, whereas their tensile strength was weak.…”

Effect of Specimen Ball Diameter on Contact Stress

“…In order to evaluate the RCF properties of ceramic balls the contact stress is studied by many scholars. The contact stress of ceraminc cylinder was studied by Chiu [1], and the failure probability of ceramic rolling elements was obtained. The RCF life of ceramic balls was predicted through contact stress analysis by Zhou [2].…”