Rolling contact fatigue tests were conducted on M-50 VIMNAR and on Crucible Particle Metallurgy (CPM) M-50, T-15 and REX-45 using two different test methods for Hertzian contact stresses between 5.16 GPa (746 KSI) and 5.90 GPa (865 KSI). Data for the CPM T-15 and REX45 show a significant life improvement for the conditions tested. The T-15 exhibited a rolling contact fatigue life almost one order of magnitude greater than that of either the CPM or M-50 VIMNAR, with a similar Weibull m value (1.82).; The results of the rolling contact fatigue tests are also used to determine material parameters in a power law relationship that is commonly used for conventional strain controlled fatigue. These parameters and the endurance limit of the M-50, as determined from the rolling contact fatigue tests, are given for comparison with similar results from conventional fatigue tests.; From the fractogtaphic observation of failed test specimens, a failure mechanism was developed. It is believed that cracks are nucleated below the surface at the depth of the maximum shear stress. These cracks then propagate parallel to the surface at this depth. Eventually, a crack will turn and propagate to the surface, causing a piece of the material to break loose.; A finite element model of the proposed failure mechanism indicates that for a Hertzian oontact stress of 5.90 GPa (856 KSI) cracks with length equal to 1/5 the width of the contact area propagate in mode II with a {dollar}rmDelta Ksb{lcub}II{rcub}{dollar} = 60.5 MPa {dollar}rmsqrt{lcub}m{rcub}{dollar} (55,038 psi {dollar}rmsqrt{lcub}in{rcub}).{dollar} As the crack length increases, crack propagation becomes mixed mode in nature and a {dollar}rmDelta Ksb{lcub}I{rcub}{dollar} = 22.28 MPa {dollar}rmsqrt{lcub}m{rcub}{dollar} (20,264 psi {dollar}rmsqrt{lcub}in{rcub}){dollar} was found for a crack with a length of 2 1/4 times the width of the contact area.
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