Micropitting is a form of surface fatigue damage that happens at the surface roughness scale in lubricated contacts in commonly used machine elements, such as gears and bearings. It occurs where the specific film thickness (ratio of smooth surface film thickness to composite surface roughness) is sufficiently low for the contacts to operate in the mixed lubrication regime, where the load is in part carried by direct asperity contacts. Micropitting is currently seen as a greater issue for gear designers than is regular pitting fatigue failure as the latter can be avoided by control of steel cleanliness. This paper describes the results of both theoretical and experimental studies of the onset of micropitting in test disks operated in the mixed lubrication regime. A series of twin disk mixed-lubrication experiments were performed in order to examine the evolution of micropitting damage during repeated cyclic loading of surface roughness asperities as they pass through the contact. Representative measurements of the surfaces used in the experimental work were then evaluated using a numerical model which combines a transient line contact micro-elastohydrodynamic lubrication (micro-EHL) simulation with a calculation of elastic sub-surface stresses. This model generated time-history of stresses within a block of material as it passes through the contact, based on the instantaneous surface contact pressure and traction at each point in the computing mesh at each timestep. This stress time-history was then used within a shear-strain-based fatigue model to calculate the cumulative damage experienced by the surface due to the loading sequence experienced during the experiments. The proposed micro-EHL model results and the experimental study were shown to agree well in terms of predicting the number of loading cycles that are required for the initial micropitting to occur.

中文翻译：

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微弹性流体动力润滑系统中实际粗糙表面微点蚀引发的实验和数值研究。

微点蚀是表面疲劳损伤的一种形式，这种损伤会在齿轮和轴承等常用机械元件的润滑触点的表面粗糙度等级上发生。当特定的膜厚（光滑的表面膜厚与复合材料表面粗糙度之比）足够低时，就会发生这种情况，以使触点在混合润滑方式下工作，其中载荷部分由直接的粗糙接触引起。与常规的点蚀疲劳失效相比，微点蚀目前对齿轮设计者来说是一个更大的问题，因为可以通过控制钢的清洁度来避免后者。本文介绍了在混合润滑方式下运行的测试盘中微点蚀的发生的理论和实验研究结果。进行了一系列的双盘混合润滑实验，以检查表面粗糙度粗糙物在通过接触时重复循环加载过程中微点蚀损伤的演变。然后使用数值模型评估在实验工作中使用的表面的代表性测量值，该模型将瞬态线接触微弹性流体动力润滑（micro-EHL）模拟与弹性次表面应力的计算相结合。该模型基于在每个时间步的计算网格中每个点处的瞬时表面接触压力和牵引力，在材料通过接触时在块内产生的应力时程。然后，在基于剪切应变的疲劳模型中使用该应力时程，以计算由于实验过程中经历的加载顺序而导致的表面累积损伤。拟议的微型EHL模型结果和实验研究在预测初始微点蚀发生所需的加载循环数方面显示出良好的一致性。