Simplification of Dynamic Capacity and Fatigue Life Estimations for Oscillating Rolling Bearings

Abstract

A Dynamic capacity for oscillating rolling bearings was published in 1968 and correlated with available laboratory fatigue life data. That development of the Dynamic Capacity extended the classic fatigue life theory of Lundberg and Palmgren (1947 and 1952) to oscillating rolling bearings. The calculation of the Dynamic Capacity is simplified as a modification of present ABMA and ISO load rating and life standards for continuously rotating rolling bearings. The simplified formulas agree with the Harris, 1991, text book formulation for oscillation amplitudes (greater than the critical amplitude) which cause an overlapping of stressed contact areas by adjacent rolling elements. Oscillation amplitudes less than the critical amplitude result in separate, discrete contact areas on each raceway. Use of the Harris equations will lead to overestimation of the fatigue for oscillation amplitudes which are less than the critical amplitude.

Rating of a Pitch Bearing for a 1.5-Megawatt Wind Turbine

“…The calculation of the equivalent load and number of loading cycles for oscillatory applications was later presented (Houpert 1999). These formulations were then simplified and applied to wind turbine pitch bearings (Rumbarger 2003). A dither angle was defined for pitch motions even smaller than the critical amplitude, for which the stressed area is only partially uncovered and retraced.…”

WEC prototype advancement with consideration of a real-time damage accumulation algorithm

“…Since this particular WEC operates in a very bi-directional, noncontinuous manner, the following equation will be used with (4), as described in [19]:…”

Review of rolling contact fatigue life calculation for oscillating bearings and recommendations for use, with examples for wind turbine bearings

“…Appendices A and B. 7 Called Cosc in Rumbarger and Jones (1968), Cao and Cro for axial and radial bearings in Rumbarger (2003), and Ca,osc in Harris et al (2009). 8 Called aprt in App.…”

“…For θ < θ crit , only part of the raceway volume is loaded during operation. For this case, Rumbarger (2003) and Harris et al (2009) give a load rating that is derived in Appendix A. This derivation makes some simplifications, and Appendix B shows the errors that occur when using Rumbarger's derivation.…”

“…For values of θ ≥ θ crit , the simplified approach published in Rumbarger (2003) and Harris et al (2009) is identical to using the Harris factor. This, too, is merely an approximation: Strictly speaking, the life of an unevenly stressed volume (as illustrated in Fig.…”