0
Research Papers: Gas Turbines: Structures and Dynamics

Measurement of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing

[+] Author and Article Information
Luis San Andrés

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123lsanandres@tamu.edu

Thomas Abraham Chirathadam

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

Tae-Ho Kim1

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

The shaft can be characterized as rigid for the range of loads applied. The procedure calls for the operator to first apply loads on the shaft and record its deflection. Typically shaft deflections are two orders of magnitude smaller than those from the MMFB.

1

Presently at Korea Institute of Science and Technology, Energy Mechanics Research Center, 39-1 Hawolgok-dong, Songbuk-gu, Seoul, Korea 136-791, Senior Research Scientist, e-mail: thk@kist.re.kr.

J. Eng. Gas Turbines Power 132(3), 032503 (Dec 03, 2009) (7 pages) doi:10.1115/1.3159379 History: Received March 23, 2009; Revised March 27, 2009; Published December 03, 2009; Online December 03, 2009

Engineered metal mesh foil bearings (MMFBs) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. This paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients that agree well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and re-assembly processes, showed significant creep or sag that resulted in a gradual decrease in its structural force coefficients.

FIGURES IN THIS ARTICLE
<>
Copyright © 2010 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Metal mesh foil bearing

Grahic Jump Location
Figure 2

Photograph of a metal mesh foil bearing

Grahic Jump Location
Figure 3

Dimensions in a MMFB and views of (a) tabs at one end of top foil before assembly and (b) two apertures in metal mesh ring

Grahic Jump Location
Figure 4

Schematic view of setup for static load versus deflection tests in MMFB

Grahic Jump Location
Figure 5

Typical applied static load versus measured MMFB displacement

Grahic Jump Location
Figure 6

Estimated structural stiffness versus MMFB displacement

Grahic Jump Location
Figure 7

Schematic view of setup for dynamic load tests with MMFB supported on rigid shaft

Grahic Jump Location
Figure 8

Waterfall plot of dynamic load for bearing with motion amplitude of 38.1 μm and excitation frequencies from 25 Hz to 400 Hz

Grahic Jump Location
Figure 9

Waterfall plot of bearing displacements for motion amplitude of 38.1 μm and excitation frequencies from 25 Hz to 400 Hz

Grahic Jump Location
Figure 10

Estimated MMFB dynamic stiffness (K−ω2M) versus excitation frequency for three motion amplitudes (12.7 μm, 25.4 μm, and 38.1 μm)

Grahic Jump Location
Figure 11

Experimental and predicted MMFB structural stiffness (K) versus frequency. Results for three motion amplitudes (12.7 μm, 25.4 μm, and 38.1 μm).

Grahic Jump Location
Figure 12

Experimental and predicted MMFB viscous damping (C) versus excitation frequency for three motion amplitudes (12.7 μm, 25.4 μm, and 38.1 μm)

Grahic Jump Location
Figure 13

MMFB structural loss factor (γ) versus excitation frequency for three motion amplitudes (12.7 μm, 25.4 μm, and 38.1 μm)

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In