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Research Papers

Stability Analysis of On-Board Friction Modifier Systems at the Wheel–Rail Interface

[+] Author and Article Information
C. P. Sharma

Department of Mechanical Engineering,
The University of British Columbia,
2069-6250 Applied Science Lane,
Vancouver, BC V6T 1Z4, Canada

A. Srikantha Phani

Department of Mechanical Engineering,
The University of British Columbia,
2069-6250 Applied Science Lane,
Vancouver, BC V6T 1Z4, Canada
e-mail: srikanth@mech.ubc.ca

1Corresponding author.

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received January 31, 2013; final manuscript received March 27, 2015; published online May 20, 2015. Assoc. Editor: Corina Sandu.

J. Vib. Acoust 137(5), 051007 (Oct 01, 2015) (13 pages) Paper No: VIB-13-1035; doi: 10.1115/1.4030345 History: Received January 31, 2013; Revised March 27, 2015; Online May 20, 2015

Friction control at the wheel–rail interface, using on-board solid stick friction modifier systems can lead to enhanced track life, reduced wear, and increased fuel economy in railroads. Frictional contact between the solid stick and the railway wheel itself can potentially cause vibrations within the modifier systems, influencing their stability and performance. A frequency domain linearized stability analysis of the state of steady sliding at the frictional contact between the solid stick and the wheel is performed. The proposed approach relies on individual frequency response functions (FRFs) of the wheel and the applicator–bracket subsystems of the on-board friction modifier. Stability characteristics of three representative bracket designs are qualitatively compared, using the FRFs generated by their respective finite element (FE) models. The FE models are validated by comparing the predicted natural frequencies with corresponding experimentally measured values on a full wheel test rig (FWTR) facility. The validated FE models are then used to compute stability maps which delineate stable and unstable regions of operation in the design parameter space, defined by train speed, angle of applicator, friction coefficient, and bracket design. Strong dependence of stability upon the bracket designs is observed. The methodology developed here can be used by design engineers to assess the effectiveness of design changes on the stability of the applicator–bracket assembly in a virtual environment—thus avoiding costly retrofitting and prototyping. Directions for further model refinement and testing are provided.

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Figures

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Fig. 1

Schematics of a typical on-board friction modifier system at the wheel-rail interface: (a) applicator–bracket system, (b) top view showing angle of application, (c) simplified contact model, and (d) simplified coupled-system model for stability analysis

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Fig. 2

Three representative bracket designs for on-board friction modifier system: (a) bracket design-A, (b) bracket design-B, and (c) bracket design-C

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Fig. 3

(a) FWTR facility and (b) measurement axes orientation

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Fig. 4

Experimental setup for: (a) bracket design-A, (b) bracket design-B, (c) bracket design-C, and (d) wheel. Note that bracket design-C has a supporting bracket different from that of A and B which have the same supporting bracket.

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Fig. 5

Measured FRFs: (a)–(c) for different bracket designs and (d) wheel response spectrum

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Fig. 6

FE modes: (a) for the wheel and (b)–(d) models of applicator with bracket with supporting rail in Fig. 3

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Fig. 7

Summary of FRF matrix, 1H, for bracket designs A–C in the frequency range 0–600 Hz

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Fig. 8

Wheel FRFs: (a) stationary wheel and (b) split mode-shapes owing to wheel rotation at a train speed of 16 km/hr

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Fig. 9

A typical unstable system: the zeros indicated as dark circles are also present in the lower half of the complex plane

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Fig. 10

Stability diagram for bracket design-A for: (a) a fixed coefficient of friction and (b) fixed angle of applicator

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Fig. 11

Stability diagram for bracket design-A: angle of applicator versus coefficient of friction at several train speeds

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Fig. 12

Stability diagram for bracket design-B: angle of applicator versus coefficient of friction for different train speeds

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Fig. 13

Stability diagram for bracket design-C: angle of applicator versus coefficient of friction for different train speeds

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