Relation between Residual and Hoop Stresses and Rolling Bearing Fatigue Life

Abstract

Rolling-element bearings operated at high speed or high vibration may require a tight interference fit between the bore of the bearing and shaft to prevent rotation of the bearing bore around the shaft and fretting damage at the interfaces. Previous work showed that the hoop stresses resulting from tight interference fits can reduce bearing lives by as much as 65%. Where tight interference fits are required, case-carburized steel such as AISI 9310 or M50 NiL is often used because the compressive residual stresses inhibit subsurface crack formation and the ductile core inhibits inner-ring fracture. The presence of compressive residual stress and its combination with hoop stress also modifies the Hertz stress life relation. This article analyzes the beneficial effect of residual stresses on rolling-element bearing fatigue life in the presence of high hoop stresses for three bearing steels. These additional stresses were superimposed on Hertzian principal stresses to calculate the inner race maximum shearing stress and the resulting fatigue life of the bearing. The load life exponent p and Hertz stress life exponent n increase in the presence of compressive residual stress, which yields increased life, particularly at lower stress levels. The Zaretsky life equation is described and is shown to predict longer bearing lives and greater load and stress life exponents, which better predicts observed life of bearings made from vacuum-processed steel.