EHD friction curves have been measured up to very high pressure (p_mean = 5 GPa, p_max = 7.5 GPa) using a newly developed, rolling-sliding, ball on disc machine, the ETM. Six base fluids have been studied, spanning the API base oil categories Group I to Group V. At high pressures, thermal effects become substantial even at quite modest slide-roll ratios, and these must be considered when analysing friction measurements in terms of the underlying rheological properties of the oils. By comparing measurements from steel/steel and WC/WC ball and disc combinations with very different thermal conductivities, the use of thermal correction to derive isothermal friction curves has been validated. At relatively low pressures (mean pressure = 1 GPa), there are substantial differences between the EHD friction properties of the various API Group base oils, but as pressure is raised these diminish and the EHD friction coefficients of all the Groups approach a similar maximum value at a given temperature. EHD friction continues to be quite strongly temperature dependent even at very high pressure. As pressure is increased, EHD friction curves become progressively steeper, so that friction coefficients at very low slide-roll ratios (1 to 2% SRR) become several times greater at high than at low pressure. This has important practical implications for the efficiency of rolling element bearings at high pressures since these components normally operate in this SRR range. There is no evidence of any of the base oils reaching a limiting shear stress over the whole pressure and temperature range studied. Instead, shear stress continues to increase with log(strain rate) in accord with the Eyring-activated flow model up to very high pressures.

中文翻译：

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在非常高的接触压力下测量EHD摩擦

EHD摩擦曲线已经在非常高的压力下进行了测量（p_均值 = 5 GPa，p _max = 7.5 GPa）使用新开发的，滚动滑动的圆盘滚珠机ETM。已经研究了六种基础油，涵盖API基础油类别I至类别V。在高压下，即使在相当适度的滑移比下，热效应也变得很显着，因此在分析摩擦测量时必须考虑这些因素，油的流变特性。通过比较具有非常不同的热导率的钢/钢和WC / WC球和圆盘组合的测量结果，已验证了使用热校正来得出等温摩擦曲线的方法。在相对较低的压力（平均压力= 1 GPa）下，各种API组基础油的EHD摩擦性能之间存在很大差异，但是随着压力的升高，这些组的EHD摩擦系数逐渐减小，并且在给定温度下EHD摩擦系数接近最大值。即使在非常高的压力下，EHD摩擦仍然与温度密切相关。随着压力的增加，EHD摩擦曲线逐渐变陡，因此在极低的滑动比（SRR为1％至2％）下，摩擦系数在高压下比在低压下大几倍。这对高压下滚动轴承的效率具有重要的实际意义，因为这些部件通常在此SRR范围内运行。没有证据表明任何基础油在整个研究的压力和温度范围内达到极限剪切应力。代替，