A study into effects of surface defects on rolling contact fatigue of 60/40 brass under a maximum contact pressure of 600 MPa and a slide–roll ratio of ?1% was undertaken on a twin-disc rolling–sliding test machine. Furrows (transverse and longitudinal) and dents (conical and diamond) were artificially introduced into a disc surface, and surface microcracks and pits were monitored by means of surface replication. The detailed analyses revealed that high surface contact pressure and subsurface stresses from the indentation shoulders are the main cause of surface spall failure. There is a clear defect size effect on the disc cycling life. The transverse and longitudinal furrows have a less damaging effect than the conic and diamond dents. The presence of a surface indentation can modify the elastohydrodynamic lubrication condition and the film thickness, which increase pressure and stress concentration on the trailing edge of the defect. The shape of the dent changes during the first few contact cycles. The spall initiating site is coincident with the edge of the original dent instead of the edge of the deformed dent. The spall starts with a crack initiating near the surface at the trailing edge and propagating downward to the depth of the maximum stress in a smooth Hertzian contact. The residual compressive stress around the dents, following indentation, is beneficial to prolonging the contact fatigue life
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