Nonmetallic Inclusions and Rolling Contact Fatigue

Abstract

Rolling contact fatigue tests were carried out on an angular contact ball bearing test rig at a low unit pressure (Po = 260 kp/mm2). The results show a sound “relative correlation” between the rolling contact fatigue and the content of nonmetallic inclusions. The theory and actual knowledge of the mechanism of contact fatigue infer that the effect of nonmetallic inclusions is influenced by other material properties, material stressing, and residual stress built up from rolling contact. Hence, a definite correlation between nonmetallic inclusions and the rolling contact fatigue cannot be existent. Nevertheless, it seems to be feasible to develop a simple technique for evaluating the nonmetallic inclusions based on the relative correlation.

White structure flaking (WSF) in wind turbine gearbox bearings: Effects of ‘butterflies’ and white etching cracks (WECs)

“…Butterfly formation theory has been discussed extensively in early literature, 18,25,40,41,45,79,80,107,109,112,113 where areas of disagreement with the latest work, 23,26,29 are inclusion debonding, dislocation movement during plastic damage accumulation and which one forms first with regard to the butterfly crack and wing. 26 The elastic modulus differences, differing CTE and/or the weak interfacial energy between the inclusion and matrix generate tensile and shear stresses in the locally surrounding matrix, 18,40,79,80 causing deformation and crack generation extending in the direction of the unidirectional shear stress, perhaps due to its influence.…”

“…26 The elastic modulus differences, differing CTE and/or the weak interfacial energy between the inclusion and matrix generate tensile and shear stresses in the locally surrounding matrix, 18,40,79,80 causing deformation and crack generation extending in the direction of the unidirectional shear stress, perhaps due to its influence. 18,107,113 Reversing rolling direction after a period of overrolling forms a second pair of wings in the symmetric orientation; 79 thus, microstructural change is not thermal, but stress induced. 40 A microcrack being a prerequisite for the formation of butterflies has been postulated.…”

“…40 A microcrack being a prerequisite for the formation of butterflies has been postulated. 18,25,28,113 As WEA is hard, cracks may nucleate within prior formed WEA to relax localised stress during cycling, as it cannot plastically yield like the surrounding matrix, 40 or cracks may nucleate when a critical density of dislocations is reached, 107 though the later does not relate to other observations. 23,25,29,45,80 O ¨sterlund et al 40 proposed successive grain nucleation out into the matrix, at the stress concentration zone on the interface of inclusion/ matrix, this stress concentration zone propagating ahead of newly formed grains.…”

“…Other earlier investigations supposed that crack closure results in heating to austenitising temperature, self-quenching and rehardened martensite forming. 18,113 Other investigations supposed that severe deformation of the carbides is what causes their dissolution, rather than heating to high temperatures, 80 which is not thought to occur in operation. Polygonisation has also been suggested for WEA formation 45 (Fig.…”

“…Butterfly formation theory has been discussed extensively in early literature, 18 25 40 41 45 79 80 107 109 112 18,25,40,41,45,79,80,107,109,112,113 where areas of disagreement with the latest work, 23 26 23,26,29 are inclusion debonding, dislocation movement during plastic damage accumulation and which one forms first with regard to the butterfly crack and wing 26…”