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Thiago Bizarria, Ryan Kernes, Riley Edwards
Joint Rail Conference
Knoxville, TN
16 April 2013
Mechanistic Behavior of
Rail Pad Assemblies Printed using Abaqus/CAE on: Mon Dec 10 11:03:19 Central Standard Time 2012
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Slide 2Mechanistic behavior of rail pad assemblies
Outline
• Objectives
• Failure Modes
• Mechanics of Wear
• Preliminary Work and Analysis
• Conclusions
• Future Work
• Acknowledgements
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Slide 3Mechanistic behavior of rail pad assemblies
Objectives
• Analyze the mechanics of rail pad assemblies to support
the development of improved fastening systems
• Quantify pad assembly deformation and displacements
• Investigate the influence of material properties in the
mechanistic behavior of rail pad assemblies
• Make design and material properties recommendations to
enhance the safety and durability of rail pad assemblies
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Slide 4Mechanistic behavior of rail pad assemblies
• Multiple suppliers and designs of concrete crosstie pads since 1980’s.
Rail Pad Assembly Design and Failure Modes
1981 1991 2001+
Adapted from UP Design Requirements and Research Outlook by Chris Rewczuk
Critical Failure Modes
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Slide 5Mechanistic behavior of rail pad assemblies
Fastening System Configuration
Abrasion Frame
Rail Pad
InsulatorClip
Shoulder
• Typically composed by 5 components:
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Slide 6Mechanistic behavior of rail pad assemblies
Failure Modes in Pad Assemblies
Failure Modes:
• Abrasion
• Crushing
• Slippage
• Tearing
Failure Causes:
• Relative displacement between rail pad
assembly and rail seat
• Presence of moisture
• High localized compressive and shear stresses
• Presence of abrasive fines in the rail seat
bearing area
• Large variation in temperature
FMEA Analysis
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Slide 7Mechanistic behavior of rail pad assemblies
Mechanics of Rail Pad Wear Abrasion: process of wearing down by means of friction.
Abrasion
Relative displacement between pad and rail seat; Presence of fines
Loss of thickness; Loss of original geometry; Permanent deformation
Cause by
Results in
Relative Displacement Abrasion Effects
Presence of fines
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Slide 8Mechanistic behavior of rail pad assemblies
Characteristics of Pad Displacements
Types of motion at rail seat surface
• Compressive motion (Poisson’s Effect)
• Rigid body motion
• Internal Shear
Compressive Motion Rigid Body Motion Internal Shear
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Slide 9Mechanistic behavior of rail pad assemblies
Compressive Deformation of Rail Pad Assemblies
Rail PadAbrasion Frame
Component MaterialYoung's
Module (psi)
Poisson's
RatioArea (in
2)
Mass Density
(ln/in2)
Abrasion Frame Nylon 6/6 1090683.8 0.350 38.25 0.0488
Rail Pad Polyurethane 345000 0.394 36.6 0.0368
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Slide 10Mechanistic behavior of rail pad assemblies
Compressive Deformation of Rail Pad Assemblies
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Slide 11Mechanistic behavior of rail pad assemblies
Investigation of Lateral Displacements
• Instrumented pad assembly tested on
Pulsating Load Testing Machine (PLTM)
• High sensitivity potentiometer used to
capture the total displacement of the
abrasion frame
• Lateral load varied from 2,000 lbf to
18,000 lbf
• L/V ratio varied from 0.1 to 0.5
• Imposed dynamic loading at 3Hz
• Potentiometer fixed to the crosstie using a
metal mounting bracket
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Slide 12Mechanistic behavior of rail pad assemblies
Investigation of Lateral Displacements
36 Kips Vertical Load
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Slide 13Mechanistic behavior of rail pad assemblies
Investigation of Lateral Displacements
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Slide 14Mechanistic behavior of rail pad assemblies
Investigation of Lateral Displacements
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Slide 15Mechanistic behavior of rail pad assemblies
Lateral Rail Pad Displacement Test
32.5 Kips
16.25 Kips
La
tera
l D
isp
lac
em
en
t (i
n)
δ
32.5 Kips Vertical Load
0.5 L/V Ratio
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Slide 16Mechanistic behavior of rail pad assemblies
Conclusions • The total displacement of the pad assembly was measurable. The rigid
body motion was the predominant displacement and responsible for
approximately 98% of the total movement
• Pad displacement increases as lateral load increases
• From preliminary results, regardeless the L/V ratio the load is applied, the
rate of change in total displacement is held constant. Further investigation
can confirm if pad displacement is only a function of the lateral load
• Measuring displacements with potentiometers proved to be an efficient
method to acquire such data
• Shoulders are capable to sucessfully restrain the movement of rail pad
assemblies. Depending on how tight they fit on the rail seat area, there is
a considerable variation of the displacement magnitude
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Slide 17Mechanistic behavior of rail pad assemblies
Future Work• Further laboratory testing with different types of pads at different
levels of material degradation
• Field investigation at Transportation Technology Center (TTC) to
measure lateral and longitudinal displacement of rail pad assemblies.
• Comparison between results acquired from laboratory
instrumentation, field testing and FE analysis
• Recommend design improvements and optimized
material properties to support the development of
new fastening system components
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Slide 18Mechanistic behavior of rail pad assemblies
Acknowledgements
• Funding for this research provided by
– National University Rail Center
• For providing direction and resources:
– BNSF Railway: John Bosshart
– Pandrol Track Systems: Bob Coats
– Amsted Rail – Amsted RPS: Jose Mediavilla
– UIUC: Tim Prunkard, Darold Marrow
– For assisting with research and lab work:
– Chris Rapp, Brent Williams, Justin Grassé
• For giving advices on this project:
– Marcus Dersch
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Slide 19Mechanistic behavior of rail pad assemblies
Thank you!
Questions?
Thiago Bizarria do Carmo
University of Illinois at Urbana-Champaign
Department of Civil and Environmental Engineering
Email: [email protected]