**3.1. RCF statistical data**

Cycles versus contact-stress for two RCF test loads using configuration 3 is presented in Figure 5. The shape factor shown in the legend of Figure 5 is within the expected range for bearing and gear type RCF testing and therefore the results reflect true film/coating performance. An eta-line has been added as well for extrapolation to testing at stress levels between the data presented in Figure 5. The shaded areas represent the fitted probability density function (PDF) based on the RCF data at that stress level.

**Figure 5.** Cycles versus stress for 12.7 mm M50 steel balls with M50 races against a Si3N4 rod. Test rotation of 130 Hz in high vacuum with approximately 200 nm of silver on the balls.

Figures 6 and 7 contain reliability prediction information for two thin film systems: evaporated silver and, ion plated nickel copper silver. The Weibull shape factor for each set of data in Figures 6 and 7 is shown in the upper right corner as 2.54 and 2.76, respectively. These beta-factors are within the expected range for bearing RCF testing and therefore the data is an accurate representation of coating and rod performance. The stress-use parameter used in the reliability calculation is also presented in the figures. The stress-use parameter is a modeling tool used to extrapolate reliability data to a loading other than those actually tested. When choosing the stress-use parameter, make sure the data is collected over a sufficient range of contact stresses that includes the stress-use value. The data presented in Figures 6 and 7 was taken over a stress-use range of 1.4 to 3.5 GPa. The results in Figures 5 through 7 strongly suggest rolling contact fatigue failure since the contact stresses for each of these tests are 1/3 less than the calculated tensile yield strength of each component as calculated from the hardness measurements presented in Table 2.

**Figure 6.** Reliability data for RCF elements in configuration 1 of Table 1.

102 Performance Evaluation of Bearings

**3.1. RCF statistical data** 

process or inadequate test preparation.

indicate a flawed test method or infant failure. It is good practice to fit the RCF data to a Weibull distribution model starting after the fifth test so that one may confirm right away that the test results reflect coating and material performance and not a flawed assembly

Cycles versus contact-stress for two RCF test loads using configuration 3 is presented in Figure 5. The shape factor shown in the legend of Figure 5 is within the expected range for bearing and gear type RCF testing and therefore the results reflect true film/coating performance. An eta-line has been added as well for extrapolation to testing at stress levels between the data presented in Figure 5. The shaded areas represent the fitted probability

**Figure 5.** Cycles versus stress for 12.7 mm M50 steel balls with M50 races against a Si3N4 rod. Test

Figures 6 and 7 contain reliability prediction information for two thin film systems: evaporated silver and, ion plated nickel copper silver. The Weibull shape factor for each set of data in Figures 6 and 7 is shown in the upper right corner as 2.54 and 2.76, respectively. These beta-factors are within the expected range for bearing RCF testing and therefore the data is an accurate representation of coating and rod performance. The stress-use parameter used in the reliability calculation is also presented in the figures. The stress-use parameter is a modeling tool used to extrapolate reliability data to a loading other than those actually

rotation of 130 Hz in high vacuum with approximately 200 nm of silver on the balls.

density function (PDF) based on the RCF data at that stress level.

**Figure 7.** Reliability data for RCF elements in configuration 2 of Table 1.
