### Hydrodynamic Lubrication (HL): Theory and Definition

Definition of Hydrodynamic Lubrication (HL) Hydrodynamic lubrication is a term that defines a situation in which two rubbing surfaces are separated by a thin film of a lubricant. This situation is often beneficial and lubrication […]

### Coefficient of Friction

Friction is a force resisting relative motion and may occur at the interface between the bodies, but may also occur within the bodies. The concept of friction coefficient was first formulated by Leonardo da Vinci […]

### Elastohydrodynamic Lubrication (EHL): Theory and Definition

Definition of Elastohydrodynamic Lubrication (EHL) Elastohydrodynamic Lubrication – or EHL – is a lubrication regime (a type of hydrodynamic lubrication (HL)) in which significant elastic deformation of the surfaces takes place and it considerably alters […]

### Rolling Contact Fatigue

Rolling-contact fatigue (RCF) is defined as a failure or material removal driven by crack propagation caused by the near-surface alternating stress field.  It is typically considered that if a bearing is properly mounted, aligned, lubricated, […]

### Generalized Reynolds Equation: Derivation

Reynolds equation is one of the fundamental equations of lubrication theory and tribology. In the simplest case, it considers incompressible and Newtonian lubricant. This model is sufficient to describe lubricant friction in some cases (relatively […]

### Fatigue Wear

Fatigue wear is a type of wear where a number of cycles is needed to generate debris. The fatigue process in metals may induce the generation of surface and subsurface cracks, which after a critical […]

### Greenwood and Williamson Contact Model

Surface roughness was recognized to play a major role in forming friction and transition from one lubrication regime to another [1]. Greenwood pioneered with first rough contact model in 1966 [2]. Inspired by this milestone […]

### Corrosive Wear

Corrosive wear occurs when the component operates in a corrosive media, liquid or gas [1, 2]. In this type of wear, the tribochemical reaction between corrosive agent and the bulk material generates a reaction (protective) […]

### Abrasive Wear

Abrasive wear occurs when a hard surface or hard particles pass over a soft surface, causing loss of material [1]. However, the abrasive grooves can be found on the wear tracks of the sliding friction […]