Rolling Contact Fatigue Life of Hybrid Bearings

More than two decades of research have gone into the theory and application of ceramic materials as metal-alternatives in rolling contact bearing arrangements. However, much of that research has focused on the fatigue characteristics of ceramic materials, generating limited knowledge on their effects on their metallic counterparts. Since bearing life is determined by the first component to satisfy failure criterion, it is necessary to examine the factors that influence fatigue failure in the most susceptible components. Some factors that may affect bearing rolling contact fatigue (RCF) life include material mechanical properties, lubrication mechanism, lubricant performance, material porosity, surface crack defects, operating conditions, etc. Other factors that significantly influence bearing rolling element performance include components configuration as well as surface roughness of contacting surfaces. For this research, a vendor-modified Four-ball Tester was used to experimentally investigate the impact of components configuration and surface roughness on the RCF life of steel-silicon nitride hybrid bearings.;The Four-ball Tester simulates the rolling conditions inside a single-row, deep groove ball bearing, where the upper ball and the ball cup simulate the bearing inner and outer rings, respectively. The planetary balls represent the rolling elements between them. The metallic components were made from two widely used bearing steels, AISI 52100 steel and M50 steel, while the ceramic rolling elements were made from hot isostatically pressed (HIPed) silicon nitride. The ceramic rolling elements were ground and lapped to various surface finishes using diamond and alumina particles in solutions of oil and water.;All RCF tests were conducted in accordance with the IP-300 standard, "Determination of rolling contact fatigue failure-Modified four ball machine method" at a rotational speed of 10,000 rpm. The fatigue life and friction data were collected via a PC-interfaced data acquisition system supplied by the equipment manufacturer. All tested samples were examined for fatigue-induced damage using Optical and Scanning Electron Microscopes.;Experimental results have shown that although silicon nitride exhibits far superior fatigue performance than both AISI 52100 and M50 bearing steels, in the hybrid rolling combinations, the overall bearing performance is undermined. Experimental results showed a 57% reduction in the L10 life of the AISI 52100 steel upper balls, and an 83% reduction in the L10 life of the M50 upper balls in the hybrid arrangements, compared to that of the corresponding all-metallic arrangements.;The results for RCF tests involving rough-lapped silicon nitride show that the fatigue performance of both the bearing steels and the silicon nitride is reduced with increasing peak-to-valley (PV) roughness of the silicon nitride. L10 life of the silicon nitride upper ball was reduced between 16-48 %, while the L10 life was reduced between 50-76% when the PV roughness was increased from 0.388mum to 1.259mum.