Plain bearing failure - Fatigue - Fatigue of White Metal Journal Bearing Caused by Vibration

PLAIN BEARING FAILURE

Plain bearing failure index

Fatigue

3.3 Premature fatigue of a White Metal Journal Bearing

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	Premature fatigue caused by poor bonding of white metal to bearing shell.
	Exposed dovetails in machined oil groove showing lack of bonding between the edges of the dovetail and the white metal (the black lines at the edges of the dovetails). Note the dirt escape grooves at the corners of the main oil supply groove (these are considered to be a beneficial feature for bearings).
Main Characteristics	This has the appearance of typical fatigue cracking. The tell-tale 'bubbles' in the central oil groove that have been caused by vaporisation of oil trapped in the cast iron bearing shell point to poor bonding. This suggests that the fatigue damage has also been the result of poor bonding. For further details see Fatigue failure summary.
Cause	Premature fatigue from inadequate bonding of the white metal to the bearing shell resulting in decreased fatigue strength of the white metal lining.
Note	Note the presence of the dovetails in the bearing shell. This has been used in the mistaken impression that the strength of the white metal is increased by giving it a mechanical bond. The harmful effect of dovetails in preventing the formation of a metallic bond because of the different thermal conductivities and rates of expansion in steel and white metal is shown in photograph 'b' where the machined oil groove has exposed the dovetails revealing lack of bonding between the white metal and the sides of the dovetails.
Possible Confusion with Other Types of Damage	The appearance of premature fatigue is very similar to that of normal fatigue. It can be confirmed by removing loose pieces and examining the bearing shell. In the case of normal fatigue the tin lining on the shell will still be present.
Comment	Cast iron should not be used for bearing shells. Cast iron is porous and absorbs lubricating oil in service. This oil is almost impossible to remove and prevents satisfactory re-metalling of the shell. The bonding should be checked by ultrasonic testing before re-metalled bearings are put into service.