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    PLAIN BEARING FAILURE

    Fatigue

      Fatigue Index

      3.2 Fatigue of White Metal Journal Bearing Caused by Vibration

    Click on photograph to enlarge 
    White metal journal bearing showing fatigue in both bearing halves.
    Main CharacteristicsFatigue of journal bearing removed from a high-speed centrifugal compressor (16,000 rev/min) following a 12-hour vibration incident. For further details see Fatigue failure summary.
    CauseSynchronous vibration causing excessive loading on the white metal. Note that the fatigue patches are diametrically opposed, showing that the vibration mode was elliptical.
    NoteThe circumferential bands of fatigue correspond to the dovetail grooves that were machined in the bearing shell which probably contributed to the occurrence of fatigue damage (although not the primary cause).
    Possible Confusion with
    Other Types of Damage    		 Damage due to fatigue can result in contact between the shaft and the bearing resulting in melting of the white metal (wiping) which can in some cases cover up the primary cause of failure.
    CommentThis bearing remained in service for six weeks after the vibration had been suppressed, showing the remarkable load-carrying capacity of the oil film formed by hydrodynamic action. The loss of bearing material would of course have prevented the bearing from starting up satisfactorily.

    This particular machine was prone to a peculiar type of intermittent synchronous vibration instability. In one machine, with a rotational speed of 26,000 rev/min, the manufacturer supplied lead-bronze bearings with a lead overlay in an attempt to prevent fatigue failure, though this was treating the symptoms rather than addressing the real problem. Bearing fatigue still occurred, leading to lubricant film breakdown and cracking of the expensive rotor by thermal shock (see Lubrication Breakdown with Lead-Bronze Bearing) that incorporated an integral gear. The problem was successfully solved by changing to a modified design of bearing (elliptical bore) that inhibited the instability.