MIXED LUBRICATION, WEAR AND CONTACT FATIGUE OF ROUGH SURFACES

全膜流体动力润滑是一种理想的润滑方式，但在实际应用中很少能实现。在大多数实际的滚动/滑动接触中，如齿轮，轴承和替代人体关节中的接触，表面的粗糙度在其润滑，磨损和表面疲劳中起着重要作用。例如，在齿轮中，即使是质量最好的地面表面的综合粗糙度通常也与流体动力产生的油膜的粗糙度相当。由于润滑剂的有效粘度低，在低速或高温下的滚子轴承和更换人体关节中也会发生类似的情况。这导致了一种被粗略地描述为混合（即流体动力和边界润滑的混合）的润滑状态，或者更具体地说是微弹性流体动力润滑（micro-EHL），在这种润滑状态下，高纹波压力会发生，两个表面上的碰撞凹凸面充当了单独的、瞬态的弹性流体动力/固体接触。该项目解决了混合润滑的两个重要工程后果：(1)轻度磨损/磨损颗粒的产生，以及(2)近表面滚动接触疲劳/微点蚀。在微观ehl的数值模拟方面已经取得了很大的进展，但是这种分析，如果要实际使用，现在必须发展到包括固体接触事件在磨损模型方面的详细行为。因此，该项目将分析接触时间、牵引力、附着力、闪蒸温度和颗粒去除情况。为了推进疲劳引起的近表面损伤的研究，需要的第二个主要发展是在关键的磨合阶段，当机器表面第一次接触时，凸起的初始塑性变形的影响。这将包括一个详细的处理塑性变形，永久设置和残余应力场的粗糙特征。我们的具体目标是：1。为真实表面开发一致的混合水动力/固体接触处理，包括瞬态干燥粗糙接触的详细建模。基于瞬态接触时发生的详细摩擦、粘附、变形和温度，建立轻度磨损颗粒生成模型。3 .建立一个与微点蚀和滚动接触疲劳现象相关的近表面疲劳模型，其中包括从弹/塑性接触分析中获得的永久集和残余应力场。在实际的工程负荷和速度条件下进行控制实验，以验证这些建模的每一个发展。

Full-film hydrodynamic lubrication is an ideal which is rarely achieved in practice. In most practical rolling/sliding contacts such as those in gears, bearings and replacement human joints the roughness of the surfaces plays an important part in their lubrication, wear and surface fatigue. In gears, for example, the combined roughness of even the best quality ground surfaces is usually of the order of the oil film which can be generated hydrodynamically. A similar situation occurs in roller bearings at low speed or high temperature and in replacement human joints because of the low effective viscosity of the lubricant. This leads to a lubrication regime which has been loosely described as mixed (meaning a mixture of hydrodynamic and boundary lubrication), or more specifically as micro-elastohydrodynamic lubrication (micro-EHL) in which high ripple pressures occur and colliding asperities on the two surfaces act as individual, transient elastohydrodynamic/solid contact encounters. This project addresses two important engineering consequences of mixed lubrication: (1) mild wear/wear particle generation, and (2) near-surface rolling contact fatigue/micropitting. Much progress has been made in numerical modelling of micro-EHL, but such analyses, if they are to be of practical use, must now be developed to include the detailed behaviour of solid contact events in terms of a wear model. The project will therefore produce an analysis of contact duration, traction, adhesion, flash temperatures and particle removal. The second major development required, in order to advance the study of near-surface distress due to fatigue, is the effect of initial plastic deformation of asperities during the crucial running-in phase when machine surfaces are brought into heavy contact for the first time. This will include a detailed treatment of plastic deformation, permanent set and residual stress field of asperity features.Our specific objectives are to:1. Develop a consistent mixed hydrodynamic/solid contact treatment for real surfaces which includes the detailed modelling of transient dry asperity contacts.2. Develop a model of mild wear particle generation based on the detailed friction, adhesion, deformation and temperatures occurring at transient contacts.3. Produce a model of near-surface fatigue, relevant to the phenomenon of micropitting and rolling contact fatigue, which includes the permanent set and residual stress field obtained from elastic/plastic contact analysis.4. Carry out controlled experiments under realistic engineering load and speed conditions to validate each of these modelling developments.