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Research Papers: Contact Mechanics

Feasibility Study for Real Time Measurement of Wheel-Rail Contact Using an Ultrasonic Array

[+] Author and Article Information
R. S. Dwyer-Joyce, C. Yao, R. Lewis

Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK

J. Zhang, B. W. Drinkwater

Department of Mechanical Engineering, University of Bristol, University Walk, Bristol BS8 1TR, UK

J. Tribol 131(4), 041401 (Sep 21, 2009) (9 pages) doi:10.1115/1.3176992 History: Received December 22, 2008; Revised June 16, 2009; Published September 21, 2009

Failure of a wheel-rail contact is usually by wear or fatigue of either component. Both mechanisms depend on the state of stress, which in turn depends on size and location of the contact patch. In this work, the feasibility of an ultrasonic approach for measuring the contact, real time on a rail, has been evaluated. The approach is based on the physical phenomenon of ultrasonic reflection at an interface. If the wheel and rail surfaces make contact, and are under high stress, they will transmit an ultrasonic pulse. However, if there is no contact, or the contact is under low stress, then the wave is completely or partially reflected. By measuring the proportion of the wave reflected, it is possible to deduce the extent of the contact area and also estimate the pressure distribution. In a previous work (Marshall, Lewis, Dwyer-Joyce, Olofsson, and Bjorklund, 2006, “Experimental Characterisation of Wheel-Rail Contact Patch Evolution  ,” ASME J. Tribol., 128(3), pp. 493–504), static wheel-rail contacts were scanned using a transducer to build up a two-dimensional (2D) map of the contact. The procedure was time consuming and could in no way be used for measurements online. In this work, a method is presented that could be used at line speeds, and so provide wheel-rail contact measurements in field trials. The scan is achieved by using an array transducer that performs a one dimensional electronic line scan. This, coupled with the speed of travel of the contact patch past the sensor location, enables a 2D map of the contact to be produced. Specimens were cut from wheel and rail sections and loaded together hydraulically in a biaxial frame. An array transducer was mounted beneath the rail specimen. The array transducer consisted of 64 ultrasonic elements that could be pulsed independently, simultaneously, or with controlled phase difference. The signals were reflected back from the contact to effectively produce a line scan. The transducer was physically moved to simulate the translation of the contact patch and so generate a series of 2D reflection profiles. Contacts under a range of normal and lateral loads have been measured and compared with some simple results using a pressure sensitive film. While the map produced by ultrasonic reflection is relatively coarse, the results agree well with measurements from the pressure sensitive film. The work concludes with a discussion of how this array measurement procedure might be implemented at full line speed, and what resolution could potentially be achieved.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Contact pressure maps measured by scanning an ultrasonic transducer across the contact for a range of normal loads (data from Ref. 6)

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Figure 2

Schematic diagram of an array transducer and beam forming operations; (a) a planar wave front, (b) angled wave front, (c) a focusing wave, and (d) pulsing and receiving on each element in turn

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Figure 3

Schematic of the pulse and receive matrix (tij represents the time-domain signal received on transducer j from the emitted pulse from transducer i)

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Figure 4

An array transducer configured to measure a wheel-rail contact. Since the contact is almost planar, the non-normal reflections are small and neglected.

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Figure 5

Schematic diagram of the experimental apparatus

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Figure 6

Photographs of (a) the wheel and rail specimens and (b) the loading frame showing the location of the ultrasonic transducer

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Figure 7

Schematic diagram showing the transducer lateral (i–v) and longitudinal (a–e) locations with respect to the wheel-rail contact regions

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Figure 8

Images from pressure sensitive film experiments for normal load P=80 kN under different applied lateral forces Q; (a) Q=0 kN, (b) Q=2 kN, (c) Q=4 kN, (d) Q=6 kN, (e) Q=9 kN

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Figure 9

Reflection coefficient profiles in the transverse direction across the contact (recorded at position (iii) in Fig. 8) at the total load is increased from 5 kN to 80 kN

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Figure 10

Reflection coefficient profiles in the longitudinal direction across the contact (recorded at position (b) in Fig. 8) at the total load is increased from 20 kN to 80 kN

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Figure 11

A map of reflection coefficient obtained by assembling together five reflection coefficient profiles in the lateral direction under normal loads of (top to bottom) P=20 kN, P=40 kN, P=60 kN, and P=80 kN

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Figure 12

A map of reflection coefficient obtained by assembling together five reflection coefficient profiles in the longitudinal direction under normal loads of (top) P=20 kN and P=40 kN, and (bottom) P=60 kN and P=80 kN

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Figure 13

Experimental and theoretical approaches for contact area measurement for three normal loads 20 kN, 40 kN, and 80 kN plotted at the same scale; (a) pressure sensitive film, (b) scans of the contact using a single transducer, (c) scans of the contact using an array transducer

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Figure 14

Comparison of the total contact area determined by the three experimental methods

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Figure 15

The relationship between train speed, pulse repetition rate, and the number of lateral measurements that could be recorded

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Figure 16

A comparison of three ways of postprocessing the array data (i) pulse-echo method, (ii) the total focusing method, (iii) common source method. Two load cases are shown: (a) P=40 kN and (b) P=80 kN.

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