Study on rolling contact fatigue under micro-elastohydrodynamic lubrication from a standpoint of fracture mechanics

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In lubricated rolling-sliding contact of rough surfaces, a method of elastohydrodynamic analysis was developed. In the case of transverse roughness where the surface texture is perpendicular to rolling-sliding contact direction, transient Reynolds equation and elastic equation were simultaneously solved providing the geometry was simusoidal or trapezoidal. In the case of longitudinal roughness where the direction of surface texture is same with rolling-sliding direction, three dimensional elastohydrodynamic analysis was conducted while periodic boundary condition was assumed. When the surface roughness became large, the converged solution could not be obtained. However, the converged solution in smaller roughness approached to direct elastic contact condition as increasing in roughness, therefore the unconverged case could be approximated by elastic contact solution.Combining a contact stress analysis of rough surfaces and a stress intensity factor analysis, the influence of asperity c … More ontact conditions upon rolling contact fatigue was investigated theoretically. Traverse and longitudinal roughness models were used for the calculation. Different asperity contact conditions during several passages of crack through loading zone had a significant effect on the stress intensity factor range of shear mode, especially on the surface of lower velocity. On the surface of higher velocity, an asperity contact produced a protuberance of the upper layr of crack (i.e., a rising shear mode) at the entrance side of loading zone and then the same asperity was supposed to tear off the upper layr of crack. This effect would promote abrasive wear by asperity. On the surface of lower velocity, a large depression of the upper layr (i.e., a sinking shear mode) and a rising shear mode had to be caused by different asperity crack positioning. By these different asperity contact conditions during several passages, reversed stress intensity factors were produced.Experimental study on pitting of gear materials has been conducted using two-roller machine. The surfaces of test rollers were recorded in Video Tape at every adequate loading cycles and evident pitting cracks observed after a long running were followed from an early stage of running by reversing the time. This technique makes the observation of initiation and propagation of cracks possible. The behaviors of surface cracks were investigated using rollers with three different roughness orientations at higher hardness side : circumferentially ground roller, axially ground roller and obliguely ground roller. Pitting cracks were most easily caused at oblique roughness compared with at circumferential roughness or at axial one. Less