Common features of fretting-fatigue cracking in steels
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Fretting can occur when repeated loading on a structure or part causes repetitive relative movement at contacting metallic surfaces. The fretting process may cause local metal loss and impact the initiation and/or propagation of fatigue cracks. There are some features of fretting-fatigue cracking that are unique. Several of these features are illustrated in three case histories described in this paper: the failure of a splined papermaking refiner shaft, the failure of two coal-pulverizer shafts, and the cracking of a crankshaft flange from a ship’s engine. Fretting fatigue usually results in recognizable damage to at least one of the contacting surfaces. The fretted areas are roughened and, in steel, are usually decorated with reddishbrown deposits. Cracks may be initiated in the damaged region but are located close to the boundary between the damaged areas. Cracking normally starts at an angle of less than 90° to the surface. The geometric stress concentrations present on the component may be overridden because of fretting, and cracks may initiate on previously smooth surfaces. Some cracks may initiate and grow to only a shallow depth before ceasing propagation.
Keywordsfatigue cracking fretting nonpropagating cracks shafts steel
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