Tribology is generally defined as the study of lubrication, friction, and wear, and it plays a significant role in machine element life and performance. The importance of tribology should not be underestimated — the famous Jost Report [1966] attributed tribology-related failures and design

shortcomings to be in excess of 10% of gross domestic product in developed countries. For machine elements to be designed properly, not only must the design stress be less than the allowable stress and the deformation not exceed some maximum value, but also tribological considerations must be properly addressed. The interaction of surfaces in relative motion should not be regarded as a special subject; like the strength of materials, tribology is basic to most machine elements.