An Electron Fractographic Study of Spalls Formed in Rolling Contact

A technique is described for making fractographs of spalls formed in bearings during rolling contact. Results are given which illustrate the usefulness of the method in identifying the fracture modes encountered in spalls. Regions of fatigue striations, cleavage, dimpled rupture, and quasi-cleavage were identified in each spall examined. All of the fractures observed were transgranular with no evidence of any intergranular fractures. In a spall which initiated at an identifiable defect (grinding furrow), the region at the initiation point failed by a fatigue mechanism. The final stages of fracture were by cleavage and quasi-cleavage.