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

提出了一种粗糙表面润滑滚动滑动接触的弹流分析方法。在表面粗糙度垂直于滚动滑动接触方向的横向粗糙度情况下，假设几何形状为似四边形或梯形，则可同时求解瞬时雷诺方程和弹性方程。在纵向粗糙度为表面纹理方向与滚动滑动方向相同的情况下，采用周期边界条件，进行了三维弹流分析。当表面粗糙度变大时，不能得到收敛解。然而，随着粗糙度的增加，在较小粗糙度下的收敛解更接近于直接弹性接触条件，因此不收敛的情况可以用弹性接触解来近似。结合粗糙表面的接触应力分析和应力强度因子分析，粗糙度c…的影响从理论上研究了影响滚动接触疲劳的更多接触条件。计算中采用了横向和纵向粗糙度模型。裂纹通过加载区时，不同的粗糙面接触条件对剪切模式的应力强度因子范围有显著影响，尤其是在低速表面。在速度较高的表面，粗糙接触在加载区的入口侧产生了上层裂纹的突起(即上升剪切模式)，并被认为是撕裂了上层裂纹。这种效应会促进粗糙表面的磨粒磨损。在速度较低的表面，由于不同的粗糙度裂隙位置，导致了上层的较大下沉(即下沉剪切模式)和上升剪切模式。在多道不同的粗糙度接触条件下，产生逆应力强度因子。在双辊机上进行了齿轮材料点蚀的实验研究。每隔适当的加载周期将试辊的表面记录在录像带中，并通过倒转时间从运行的早期阶段跟踪长期运行后观察到的明显的点蚀裂纹。这项技术使观察裂纹的萌生和扩展成为可能。研究了三种不同粗糙度取向的轧辊在高硬度侧的表面裂纹行为：周向磨辊、轴向磨辊和斜磨辊。与周向粗糙度和轴向粗糙度相比，斜向粗糙度更容易产生点蚀裂纹。较少

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