The tribological performance of grease lubricated point-contact bearing systems

润滑是在运动部件的接触面之间引入一种物质(液体或固体)，以减少摩擦和磨损，并散热。在流体动力状态下，可以通过设计开发一种收敛的楔形润滑剂来创造理想的条件，该楔形润滑剂能够完全支撑轴承负荷，同时完全分离匹配表面。另一方面，当载荷以很小的接触面积承载时，会产生弹流动力(EHL)区域，导致表面显著的弹性变形。虽然可以准确地预测沿连接处的压力分布和膜厚，但预测牵引力是有问题的，因为膜的流变性很难预测，要记住压力可能会引起粘度的很大变化。润滑脂起到了密封剂的作用，防止泄漏并阻止腐蚀性污染物进入，是一种良好的减震和噪音抑制介质；因此，它是一种非常常见的润滑剂。尽管润滑脂用于润滑安装在大量机械系统上的至少200亿个轴承中的80%以上，但对其行为的有限了解(以前被认为类似于油)正在导致与尖端技术相关的应用中过早失效的问题。使用润滑脂的润滑被认为会产生饥饿的混合弹流润滑，这意味着薄膜更薄，因此至少会发生一些粗糙面之间的接触。因此，这些系统中摩擦力的预测变得更具挑战性，因为需要将不连续薄膜中的牵引力和由于载荷和压力以及磨损而变形的粗糙度相互作用而产生的成分结合在一起。这项研究的目的是开发和实验验证适用于润滑脂润滑的贫化滑动接触的摩擦和润滑失效预测的数学模型。成功的结果必将成为尖端技术发展和生产性能更高的轴承机构的巨大成就，将产生巨大的节能和环境效益。

Lubrication is the introduction of a substance (fluid or solid) between the contact surfaces of moving parts to reduce friction and wear, and to dissipate heat. In a Hydrodynamic regime, ideal conditions can be created through design to develop a convergent wedge of lubricant able to fully support the bearing load while separating completely the mating surfaces. On the other hand, elasto-hydrodynamic (EHL) regime is generated when the load is carried by very small contact area, causing significant surface elastic deformation. Although the pressure distribution along the conjunction and film thickness can be predicted with accuracy, anticipating the traction is problematic, as the rheological properties of the film are difficult to predict, keeping in mind that the pressure may induce a large variation of the viscosity. Grease acts as a sealant to prevent leakage and impede the entrance of corrosive contaminants, and it is a good damping and noise-suppressor medium; it is therefore a very common lubricant. Although grease is used to lubricate more than 80% of at least 20 billion bearings mounted on a large number of mechanical systems, limited knowledge of its behavior, previously thought to be similar to oil, is causing problems of premature failures in applications related to cutting-edge technology. Lubrication using grease is believed to generate starved mixed-EHL, meaning that the film is thinner and thus contact between at least some asperities takes place. Therefore the prediction of the friction in these systems becomes an even more challenging task due to the requirement to combine the traction in a discontinuous film and the component arising from the interaction of the asperities, which are deformed due to the loading and pressure as well as subjected to wear. The aim of this research is to develop and experimentally validate mathematical models for the prediction of friction and lubrication-failure applicable to grease-lubricated starved sliding contact. A successful outcome will definitely constitute a great achievement toward the development of cutting-edge technology and for the production of higher performance bearing-mechanisms, which will generate substantial energy savings and environmental benefits.