El?l?IICTOF?X3RICANT BASE STOCK ON ROIZJXG-CONTACT FMTGUE LlJ?13

Five lubricants of different base stock were tested using groups of l/2-inch air-melt AISI M-1 tool-steel balls under rolling-contact fatigue conditions in the fatigue spin rig. A methyl silicone, a mineral oil, a glycol, a sebacate, and an adipate were used. The particular fluids chosen all had alout the same atmospheric pressure viscosity (10 centi-stokes) at the test temperature of 100 ° F. Other test conditions such as ball loading were held constant. Ball.loading was held at that level necessary to produce a maximum theoretical Hertz stress of 725,000 pounds per square inch in compression at the contacting surfaces and 225,000 pounds per square inch in shear at a depth of 0.009 inch below the surfaces. This investigation studies the effect of lubricant base stock upon rold.ing-A contact fatigue life and correlates any observed differences in 15fe re-sults with unique properties of the Mfferent base-stock fluids.. The tests showed differences in rolling-contact fatigue life for the five d5fferent base-stock fluids tested. The observed lives appeared to correlate with the pressure-viscosity coefficients of ltiricants of the same base stock. Lubricants whose viscosities were increased the greatest by pressure produced the longest fatigue lives. However, other h-ibricant properties, such as bulk modulus and chemical activity, may well influence fatigue life, and more data are reqtied to determine their relative importance. Chemical activity did not appear to be significant in these tests, and the spans obtained in all tests compsred closely with those obtained in full-scale beariugs. Metallurgical transformation in the material was consistent for all test runs