Tribological and Wear Testing

Abstract

Tribology is the science of friction, wear, and lubrication. More fundamentally, tribology is concerned with the interaction of contacting surfaces in relative motion. Friction is the resisting tangential force that occurs between two surfaces in contact when they move or tend to move relative to one another. For solid surfaces the magnitude of this force is characterized by the coefficient of friction, defined as the dimensionless ratio of the magnitude of the friction force to the magnitude of the normal force. In the absence of an externally applied normal force, this tangential force is sometimes referred to as sticktion. Wear is damage to a solid surface due to the relative motion between that surface and a contacting substance or substances. It involves the progressive loss of material. Lubrication is the ability of an interposing material to reduce either the friction between or the wear of surfaces. The tribological behavior that a material exhibits is dependent on both the properties of the material and the contact conditions. As a result, parameters used to characterize the friction, wear, and lubrication of a material are system properties of the material, not intrinsic properties such as an elastic modulus or coefficient of thermal expansion. The collection of all those elements that can influence tribological behavior is referred to as the tribosystem. The primary elements of a tribosystem are (1) materials, (2) shapes and contours, (3) surface roughness, (4) motions, (5) loading, (6) lubrication, and (7) environment.