Wear and the science used to study it, tribology, is a complex world at an intersection between science and engineering. The approach here will be one where we try to understand how the damage is proceeding. When I first started doing failure analysis and someone handed me a worn-out component, I felt lost. Over half of the load-bearing cross section was gone. Worst of all, what wore out was gone, so there was nothing to analyze!
If you are lucky, you will have multiple components displaying a range of severity of damage or multiple areas of a worn component that display a range of severity. If you are lucky, you may have some access to the debris particles created by the wear process. This may include bits of the damaged component(s), and it may also include abrasive particles that facilitated the damage. And, of course, you will gather as much information as possible about the background.
In common, everyday failure analysis, you probably won’t have access to a tribology specialist. You must have some understanding of the basic ways in which wear takes place, including abrasion, adhesion, deformation and removal, contact fatigue and fretting (which is sometimes classified as a type of corrosion damage). If your clients or customers expect you to propose a fix to the problem as part of your analysis, you will be able to find some ideas to suggest in various failure-analysis and tribology references.
We must note the special needs of evidence preservation for wear failure analysis. If the wear debris is available, such as when it is trapped in the grease in a ball-bearing assembly, it should be retained. If the component is to be cleaned for microscopic examination, care must be taken to save the grease. It is often a good idea to do this prior to sectioning. It may be confusing if bits of the material resulting from the sectioning operation contaminate the “natural” debris specimen.
Next time, we will specifically discuss an all-metallic ball bearing and follow that up with some additional examples. Stay tuned.