**4.4 Fretting wear**

Cyclic motion between contacting surfaces is the essential ingredient in all types of fretting wear. It is a combination process that requires interaction of two surfaces, and exposed to minor amplitude of oscillations.

According to the material properties of surfaces, adhesive, two-body abrasion and/or solid particles may produce wear debris. Wear particles detach and become comminuted (crushed) and the wear mechanism (**Figure 15**) changes to three-body abrasion when the work-hardened debris starts removing metal from the surfaces.

**Figure 15.** *Fretting wear mechanism.*

Fretting wear arises as a result of the following order of events:

