Introduction

Tribology, the study of friction, wear, and lubrication has become a multidisciplinary endeavor. Historically, mechanical engineering was the home of tribology. Much of the early studies were focused on contact stresses, lubricant film thickness, flash temperatures, and wear modeling, mostly in powertrain and manufacturing components. In lubricated contacts, one can minimize wear by operating under conditions where two sliding surfaces are separated by a lubricant film, with thickness at least three times that of the composite surface roughness to ensure full separation. This is known as the full-film or hydrodynamic lubrication regime. However, whether driven by economics or the nature of technology never satisfied to be left alone, the performance of mechanical systems continues to be pushed to higher levels—higher loads, higher temperatures, smaller form factors, and lighter structures. As a result, sliding interfaces no longer have the luxury of being separated by a full lubricant film, and direct contact between surfaces often occurs.