ABSTRACT
Bearings are expected to provide relative motion between the components, for example, balls and race, with little or no service for the life of the machine. ˜e components must be strong enough to carry the load without permanent deformation and smooth enough to allow a lubricant to cover the asperities in the contact zone. Ideally, the lubricant would always separate the two surfaces, to prevent any contact between the mating surfaces. But that is not possible when the relative speed is zero, that is, at start-up and slow down, so bearings are o§en designed to run in the mixed asperity contact/lubrication condition. Ideally, the surfaces would be durable enough to withstand contact. But even when the utmost care is taken, from initial processing of raw materials to Ÿnal Ÿnish, there is no guarantee that the component is free of damage-inducing surface or subsurface defects. A§er the bearing is assembled, tested, and put into service, what type of damage might occur? Damage can range from mild scoring to gross spallation, and the causes can range from di²cult to avoid contamination like dust (e.g., silica particles) to mechanical instability of the assembly that houses the bearing. Why? Because real bearing materials can deform, transform, form oxides on their surfaces, and accumulate superŸcial Ÿlms-for good or for bad-as illustrated by the schematic (a) and real1 (b) cross sections of worn-bearing surfaces in Figure 2.1. Bearing engineers need to be aware that even the best prepared components can be damaged by the various mechanisms detailed in the following chapters. Here we focus on how one uses surface characterization methods to discover and identify surface and subsurface damage.
