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Research Papers: Gas Turbines: Structures and Dynamics

Fatigue Life Prediction for Large-Diameter Elastically Constrained Ball Bearings

[+] Author and Article Information
Jerzy T. Sawicki1

Center for Rotating Machinery Dynamics and Control, Cleveland State University, Cleveland, OH 44115-2425j.sawicki@csuohio.edu

Samuel A. Johansson

 Philips Medical Systems, Cleveland, OH 44143-2131andreas.johansson@philips.com

John H. Rumbarger

 Rolling Bearing Consultant, Nazareth, PA 18064jhrinc@aol.com

Ronald B. Sharpless

 Philips Medical Systems, Cleveland, OH 44143-2131ron.sharpless@philips.com

1

Corresponding author.

J. Eng. Gas Turbines Power 130(2), 022506 (Mar 05, 2008) (8 pages) doi:10.1115/1.2772632 History: Received April 26, 2007; Revised May 10, 2007; Published March 05, 2008

The application of large-diameter bearing rings and the thereof inherited low stiffness make them susceptible to local distortions caused by their surrounding structures, which are often under heavy loads. The standard accepted design criteria for these bearings are based on the estimation of the internal load distribution of the bearing, under the assumption of rigid circular and flat supporting structures, that keep the bearing inner and outer races in circular, flat, i.e., not deformed shapes. However, in the presence of structural distortions, the element load distribution can be severely altered and cannot be predicted via the standard design criteria. Therefore, the application of large-diameter ball and roller bearing rings as the critical components in rotating machines becomes more of a design task than making a catalog selection. The analytical and finite element approach for fatigue life prediction of such a bearing application is presented. The undertaken approach and the results are illustrated based on the analysis and fatigue life simulation of the computed tomography scanner’s main rotor bearing. It has been demonstrated that flexibility of the rings can significantly reduce the fatigue life of the ball bearing.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Four-point contact ball bearing load lines and initial contact angles (forces shown acting on ball)

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Figure 2

Race curvature and ball center movements; 1–3 path

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Figure 3

Force and moments, acting on inner race (shaft)

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Figure 4

CT scanner, cover removed (courtesy of Philips Medical Systems, 2005)

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Figure 5

Rotor and bearing finite element model

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Figure 6

Bearing distortions—inner and outer race

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Figure 7

Load cases with corresponding L10 and a3

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Figure 8

Bearing load distribution for load case no. 9

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Figure 9

Bearing load distribution for load case no. 12

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Figure 10

Bearing load distribution for load case nos. 9 and 12 with perfect raceways

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