CIEM5311 - LW 2 - Wheel-rail dynamic interactions (2).pdf

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CIEM5311-Week 1
(2023/2024 Q1)
Wheel-rail dynamic
contact/interactions and
consequences
Lecturer: Zhen Yang
Room S2 2.35
[email protected]

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CONTENTS
Part 1: Wheel-rail contact mechanics
•1.1 Introduction
•1.2 Normal contact (Hertzianvs Non-Hertzian)
•1.3 Tangential contact (sliding vs rolling)
Part 2: Wheel-rail dynamic
contact/interactions and consequences
•2.1 Contact vs dynamic interactions
•2.2 Impact
•2.3 Wheel slip/sliding
•2.4 Rolling contact fatigue

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CONTENTS
Part 1: Wheel-rail contact mechanics
•1.1 Introduction
•1.2 Normal contact (Hertzianvs Non-Hertzian)
•1.3 Tangential contact (sliding vs rolling)
Part 2: Wheel-rail dynamic
contact/interactions and consequences
•2.1 Contact vs dynamic interactions
•2.2 Impact
•2.3 Wheel slip/sliding
•2.4 Rolling contact fatigue

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1.1 Intro to wheel-rail contact
•A complex & imperfect link transferring
train load to track

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1.2.1 HertzianContact
Solution is semi-ellipsoidal pressure
distribution on an elliptical contact area,
if the following assumptions stand:
•1. Linear elastic (ε<<R)
•2. Non-conforming (‘1 point’, 2
nd
-order
polynomial)
•3. Half-space (a<<R, a<<l)
•4. Frictionless
Discussion: can we
assume wheel-rail contact
as Hertizancontact?

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1.2.1 Calculate HertzianContact
https://www.tribology-abc.com/sub10.htm(Then ‘elliptic contact’)
Input:
•Material (E=210MPa, r=0.3)
•Geometry (Rw=460 mm, Rr=300 mm)
•Normal load (100 kN)
Output:
•Max pressure
•Contact area shape & size

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1.2.2 Non-HertzianContact
elliptical contact patch
‘egg-shaped’ contact patch
Elastic vs Plastic
•Shape & size
•Pressure amplitude
•Peak pressure position

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1.2.2 Non-HertzianContact
Non-conforming vsConforming

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1.2.2 Non-HertzianContact
Joint wear due to stress concentration
New joint used joint

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Δv
1.3.1 Sliding vs Rolling
Sliding: relative translation velocity between two contact surfaces.
Rolling: motion that combines rotation and translation of one
object with respect to a surface.
v
ω
ωr
ωr
v+ωr
=v-ωr
v

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1.3.2 Creepage
•Creepage(creep ratio) ??????= Δv/ v

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1.3.3 Creepagevs friction force
•Creepage(creep ratio) ??????= Δv/ v
Coefficient of
friction

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1.3.4 Calculate tangential contact
•Numerical (Fastsim, BEM, FEM)
•Analytical (Carter’s, V&J, Strip, etc.)
FEM
BEM

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CONTENTS
Part 1: Wheel-rail contact mechanics
•1.1 Introduction
•1.2 Normal contact (Hertzianvs Non-Hertzian)
•1.3 Tangential contact (sliding vs rolling)
Part 2: Wheel-rail dynamic
contact/interactions and consequences
•2.1 Contact vs dynamic interactions
•2.2 Impact
•2.3 Wheel slip/sliding
•2.4 Rolling contact fatigue

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2.1 Contact vs dynamic interaction
Dynamic effects:
inertia of material elements influence the stress field
because they “flow” through the deforming region

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2.2.1 Impact generation
Joint Squat
Wheel
flat
Switch &
Crossing

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2.2.2 wheel-rail impact load
Normal
load

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2.2.2 wheel-rail impact load
Normal
load
Simulation 1
(elastic & new)
Simulation 2
(plastic & new)
Simulation 3
(plastic & used)

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2.2.3 impact-induced problems
Interface deterioration
Structural degradation
Vibration & Noise

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2.3.1 wheel slip/sliding generation
•Accelerating
•Braking
•Curving
•Contamination (rain,
snow, leaves)

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2.3.2 Slip-induced problems: wear
rail gauge wear wheel tread wear
wheel burn

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2.3.2 Slip-induced problems: squeal
noise

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2.3.3 stick-slip contact during curving

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2.4 Rolling contact fatigue (RCF)
Squat Head Check
Hatfield rail
crash (2000)
https://en.wikipedia.org/
wiki/Hatfield_rail_crash

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Wrap-up
➢Wheel-rail contact & dynamic interactions
➢Hertziancontact (assumptions &
calculations)
➢Sliding vs rolling (creepage)
➢Problems induced by dynamic interactions

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Literature (available on Brightspace)
•[1] Johnson KL. Contact Mechanics:
Cambridge university press; 1985. Chapter 4
Hertz theory
•[2] Yang Z, et. al. Numerical study of wheel-
rail impact contact solutions at an insulated
rail joint. IntJ MechSci. 2018;138-139:310-
22. doi:10.1016/j.ijmecsci.2018.02.025
•[3] Yang Z, et. al. Numerical modeling of
wheel-rail squeal-exciting contact. IntJ Mech
Sci. 2019;153-154:490-9.
doi:10.1016/j.ijmecsci.2019.02.012

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Relevant MSc thesis topics
•Track dynamics under extreme loading
conditions
•Degradation of embedded rail system
under wheel-rail dynamic load
•Performance of ‘anti-impact’ insulated rail
joints
•Dynamic behavior of tracks with hanging
sleepers

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Post-lecture questions
•To be uploaded to Brightspace

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End