FATIGUE CRACKING
This is caused by the imposition of dynamic loads in excess of the fatigue strength of the bearing material at operating temperature. Fatigue strength, especially of low melting point materials such as whitemetals and lead-base overlays, is greatly reduced at high temperatures, hence overheating alone may cause fatigue failure. Other causes are over-loading, cyclic out-of-balance loadings, high cyclic centrifugal loading due to over-speeding, shafts not truly cylindrical due to manufacturing defects such as honing, filing, etc. 

JOURNAL BEARINGS 
Fig. 26 - Fatigue damage of a new whitemetal-lined bearing caused by uneven journal wear (ridging) in the vicinity of the central oil groove. 

Fig. 27 - Fatigue cracking of 20% tin aluminium lining due to misalignment and consequent edge loading.

Fig. 28 - Fatigue cracking of whitemetal-lined bearing due to shaft deflection and edge loading.

Fig. 29 - Whitemetal-lined chambered top half turbine bearing, fatigue cracked on lands due to out of balance loading, and excessively wide cut-away.

RECOMMENDED ACTION 
• Scrap bearings. Investigate and, if possible, rectify causes of misalignment, shaft deflection and overloading. Increase width of lands in top half Fig. 29. Fit new bearings, possibly of stronger materials if under-design is indicated.