SUMMARY

The fatigue performance of bearing steels is controlled by localized cyclic plasticity at inhomogeneities/inclusions in the microstructure. The objective of this study is to examine the effects of orientation, shape, and spacing of small inclusions on the fatigue life of bearings under rolling contact loading. Inclusions are a common occurrence in bearings, with orientations affected by material flow during primary processing. A 3D finite element model, consisting of a cubic volume of bearing steel surrounding an aluminum oxide inclusion, is the primary simulation tool. A strategy involving application of conventional elasto-plasticity remote from inclusions and crystal plasticity in the near field is utilized to parametrically study the driving force for crack nucleation from alumina primary inclusions. To calibrate the parameters of this model, uniaxial cyclic loading experiments are conducted on specimens with different volume fractions. The experimentally calibrated model is a useful tool in computing candidate driving forces phenomena such as spall and fatigue crack formation/growth, which depend on microstructural features such as crystallographic orientation, grain size, etc. Loading consists of prescribed tractions derived from a Hertzian contact formulation, at intervals as a roller bearing passes over a section of the race. Multiple rolling passes are conducted, and the accumulation of plastic strain and residual stresses are examined. Fatigue indicator parameters motivated by critical plane multiaxial fatigue approaches are used to study the relative influence of different microstructure attributes on fatigue life.