Triboelectricity

What is triboelectricity? Triboelectricity refers to the electrification of dissimilar objects or materials occurred due to the collision resulting in the phenomenal flow of electrons from one material to other balancing the potential difference. The […]

Power Spectral Density of Rough Surfaces

Roughness is known to be an important factor in friction, wear and related performance of the machine parts. It was shown recently that Power Spectrum Density (PSD) can be used as a metric to describe […]

Hertzian contact theory

Hertzian contact stress Hertzian contact theory is a classical theory of contact mechanics and is a very useful tool for engineers and researchers. Even though the derivation of the theory is relatively difficult, the final […]

Hertzian contact equations for elliptical, spherical and cylindrical contacts

A theoretical background to the Hertz contact theory can be found here. Line Contact (Cylindrical contact) In case of two cylinders in contact (with radii ), as shown in Fig. 1, the Hertzian radius of […]

Grease

The ASTM definition of lubricating grease is: “A solid or semi-solid lubricant consisting of a thickener agent in a liquid lubricant. Other ingredients imparting special properties may be included” A commercial lubricating grease usually consists […]

Coefficients of Kinetic and Static Friction

What is friction? Friction is a force resisting relative motion and it occurs at the interface between the bodies, but also within the bodies, like in case of fluids. The concept of friction coefficient was […]

Archard Wear Equation

The importance of wear losses leads to considerable effort in establishing theories and predictive models of wear. Meng and Ludema  [1] have identified 182 equations for different types of wear. Among them were empirical relations, […]

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 […]

Elastic Deformation

Definition Elastic deformation is a change of the shape of the body as a reaction to applied stress. This deformation is only temporary and once the stress is released, the undeformed shape of the body […]

Tribometers

Tribometers are the devices used to analyze and characterize tribological systems. The most common direct measurement is the measurement of friction coefficient (and shear strength). During the post processing stage other quantities can be measured, […]