Section 6.6 Overlay Fatigue

Section 6.6
Overlay Fatigue

Section 6.6.1
Appearance

The bearing appears to have part of the overlay, or top layer, missing in sections. See Figure "Example of Overlay Fatigue" ‪

Figure 1. Example of Overlay Fatigue

Section 6.6.2
Damage

The overlay is a soft material used for embedding foreign material. The material begins to form small cracks which break off. Small pieces of the layer flake away exposing the harder layers. See Figure "Progression of Overlay Fatigue" .‪

Figure 2. Progression of Overlay Fatigue

Section 6.6.3
Possible Causes

There are several possible causes for the damage: ‪

1. High internal oil pressure during normal engine operation.
2. An unintentional load concentration.
3. Exceeding normal bearing life.

Section 6.6.4
Recommendation

When overlay fatigue occurs, replace bearings.‪