Experimental Characterization of Wheel-Rail Contact Patch Evolution

[+] Author and Article Information
M. B. Marshall, R. S. Dwyer-Joyce

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

R. Lewis1

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

U. Olofsson, S. Björklund

Department of Machine Design, KTH, SE 100 44 Stockholm, Sweden


Corresponding author.

J. Tribol 128(3), 493-504 (Mar 21, 2006) (12 pages) doi:10.1115/1.2197523 History: Received April 07, 2005; Revised March 21, 2006

The contact area and pressure distribution in a wheel/rail contact is essential information required in any fatigue or wear calculations to determine design life, re-grinding, and maintenance schedules. As wheel or rail wear or surface damage takes place the contact patch size and shape will change. This leads to a redistribution of the contact stresses. The aim of this work was to use ultrasound to nondestructively quantify the stress distribution in new, worn, and damaged wheel-rail contacts. The response of a wheel/rail interface to an ultrasonic wave can be modeled as a spring. If the contact pressure is high the interface is very stiff, with few air gaps, and allows the transmission of an ultrasonic sound wave. If the pressure is low, interfacial stiffness is lower and almost all the ultrasound is reflected. A quasistatic spring model was used to determine maps of contact stiffness from wheel/rail ultrasonic reflection data. Pressure was then determined using a parallel calibration experiment. Three different contacts were investigated; those resulting from unused, worn, and sand damaged wheel and rail specimens. Measured contact pressure distributions are compared to those determined using elastic analytical and numerical elastic-plastic solutions. Unused as-machined contact surfaces had similar contact areas to predicted elastic Hertzian solutions. However, within the contact patch, the numerical models better reproduced the stress distribution, as they incorporated real surface roughness effects. The worn surfaces were smoother and more conformal, resulting in a larger contact patch and lower contact stress. Sand damaged surfaces were extremely rough and resulted in highly fragmented contact regions and high local contact stress.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic diagram of (a) partial reflection of ultrasound at a rough surface contact; and (b) the “spring model” used as a method to determine ultrasonic response of the interface

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Figure 2

Schematic of the ultrasonic pulsing/receiving apparatus and scanning system

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Figure 3

Photograph of contact specimens cut from a worn wheel and rail

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Figure 4

Wheel surface profiles for (a) unused specimen and (b) sand damaged specimen. Displayed on the same horizontal and vertical scales.

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Figure 5

Schematic diagram of the scanning of a wheel/rail contact

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Figure 6

Schematic diagram of the calibration specimens and experimental setup

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Figure 7

Relationship between interfacial stiffness and contact pressure for various wheel-rail specimen pairs. These curves are used to calibrate stiffness maps to produce pressure distributions.

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Figure 8

Ultrasonic contact pressure maps for the unused wheel/rail contact

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Figure 9

The proportion of elastic and plastic contact within the nominal region of wheel-rail contact

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Figure 10

Wheel rail contact at 65kN for (a) unused, (b) sand damaged, and (c) worn specimens

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Figure 11

Schematic diagram showing the contact between (a) worn and (b) unused wheel/rail specimens

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Figure 12

Wheel/rail contact pressure maps at 65kN showing the regions of plastic contact for (a) unused, (b) sand damaged, and (c) worn specimens. Two different color maps are used in the scale to distinguish elastic and plastic contact areas.

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Figure 13

Single (a) and double (b) wheel/rail contacts

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Figure 14

Worn wheel/rail contact pressure maps at 65kN for (a) single contact and (b) double contact

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Figure 15

Applied and measured load comparison; (a) unused specimens and (b) sand damaged specimens

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Figure 16

Numerical contact pressure maps at 80kN for (a) unused specimens elastic case, (b) unused specimens elastic-plastic case, (c) damaged specimens elastic case, and (d) damaged specimens elastic-plastic case

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Figure 17

Unused specimen contact pressure maps for a load of 80kN for (a) ultrasonic measurement, (b) Hertzian smooth elastic, (c) elastic model, and (d) elastic-plastic model

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Figure 18

Damaged specimen contact pressure maps for a load of 80kN for (a) ultrasonic measurement, (b) Hertzian smooth elastic, (c) elastic-plastic model, and (d) elastic model



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