Determining Fatigue Crack Propagation Rates in Lubricating Environments through the Application of a Fracture Mechanics Technique

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Abstract
A fracture mechanics technique has been used to determine the rate of fatigue crack propagation in rotating-beam SAE 52100 steel specimens in several lubricating environments. Experiments were conducted in a mineral and antiwear hydraulic oil under wet and dry conditions, a water-in-oil emulsion, distilled water, and air. Differences as high as 8:1 in crack propagation rates were observed among these environments; the differences were found to depend on the magnitude of the stress-intensity factor at the crack tip. A method is outlined for separating the crack initiation stage from the propagation stage in rotating-beam specimens. This method is expected to provide new insights regarding the chemical influence of lubricants on the mechanisms responsible for fatigue crack development in bearings.