Wheel‐Rail Interaction Fundamentals

1 1 Wheel rail Interaction FundamentalsKevin Oldknow, , Part 1 The Wheel / rail Interface Anatomy and Key Terminology The Contact Patch and Contact Pressures Creepage and Traction Forces Part 2 Vehicle Steering and Curving Forces Wear and Rolling Contact Fatigue Part 3 The Third Body Layer, Traction/Creepageand Friction Management Frequency Domain Phenomena: Noise and CorrugationsThis three part session will provide an introduction to several fundamental aspects of vehicle track Interaction at the wheel/ rail interface3 Part 1 The Wheel / rail Interface Anatomy and Key Terminology The Contact Patch and Contact Pressures Creepageand Traction Forces4(Very) Basic Vehicle Running Gear Anatomy Wheels Wheelsets Axleboxes Suspension Frame5(Very) Basic Track Anatomy rail Crossties (Sleepers)

2 Tie Plates Fasteners / Spikes & Anchors Ballast Subballast Subgrade6 Tangent Curve Spiral high rail Low rail Superelevation(aka Cant) rail CantRecalling a few track geometry Wheel / rail Interface and Key TerminologyField SideGage SideBack of Flange (BoF)Flange FaceFlange RootAncillaryTreadGage FaceGage CornerMid GageBall / Crown / Top of rail (TOR)Back to Back Wheel SpacingTrack Gage8 The Wheel / rail Interface and Key Terminology ( Low rail Contact) Lightly Worn Heavily Worn9 The Wheel / rail Interface and Key Terminology ( high rail Contact) Lightly Worn Heavily Worn10 The Contact Patch and Contact Pressures Prep Question: What is the length of contact between a circle and a tangent line?

3 11 The Contact Patch and Contact Pressures Question #1: What is the area of contact between a (perfect) cylinder and a (perfect) plane? Question #2: Given Force and Area, how do we calculate pressure? Question #3: If a cylindrical body (~wheel) is brought into contact with a planar body (~ rail ) with a vertical force Fand zero contact area, what is the resulting calculated pressure?12 HertzianContact HertzianContact (1882) describes the pressures, stresses and deformations that occur when curved elastic bodies are brought into contact.

4 Contact Patches tend to be elliptical This yields paraboliccontact pressures Contact theory was subsequently broadened to apply to rolling contact (Carter and Fromm) with non elliptical contact and arbitrary creepage(Kalker; more on this )PavgPo=3/2 Pavg13 Creepage, Friction and Traction Forces Longitudinal Creepage The Traction CreepageCurve Lateral Creepage Spin Creepage Friction at the Wheel rail Interface14 Why is creepageat the Wheel/ rail Interface important? Creepageat the wheel rail interface is fundamentally related to all of the following (as examples): Locomotive adhesion Braking Vehicle steering Curving forces Wheel and rail wear Rolling contact fatigue Thermal defects Noise Corrugations 15 What does Longitudinal Creepagemean?

5 16 What does Longitudinal Creepagemean?.. The frictional contact problem (Carter and Fromm, 1926) relates frictional forces to velocity differences between bodies in rolling contact. Longitudinal Creepagecan be calculated as:R VV17 Free Rolling1 wheel circumferenceIn free rolling, a wheel would rotate 100times to travel a distance of (Longitudinal) Creepage1 wheel circumferenceDriving TorqueAt 1% positivecreepage, a wheel would rotate 101times to travel a distance of (Longitudinal) Creepage1 wheel circumferenceBraking TorqueAt 1% negativecreepage, a wheel would rotate 99times to travel a distance of vs.

6 Sliding FrictionThey are notthe same!creep:R VVR(radius) (rotational speed )V(forward velocity)V(sliding velocity)N(normal load)N(normal load)f(friction force)= f(creep) simply Nf(friction force) simply Nfriction force shown as acting on wheel for positive creepfriction force shown as acting on block for positive sliding velocity : coefficient of (sliding) friction21 The Traction CreepageCurve NLongitudinal CreepageCreep Force (Traction) N22 Lateral creepageImagine pushing a lawnmower across a steep , but when does this occur at the WRI?

7 23 Steering in Steady State Curving( Mild Curves)23 Angle of Attack (AoA)24 Steering in Steady State Curving( Sharp Curves)24 Angle of Attack (AoA)25 Steering in Steady State Curving( Very Sharp Curves)25 Angle of Attack (AoA)26 Lateral CreepageAn angle of attack (AoA) of degrees ( Radians) corresponds to a lateral creepageof 1%at the leading quick (sample) Radius, RWheelbase, 2 LAngle of Attack, V 28 Spin CreepageThink of spinning a coin on a , but when does this occur at the WRI?..29 Spin CreepageThe net creepagevector at the wheel/ rail interface is (in general) a combination of longitudinal, lateraland (Free Rolling)Slower (Braking)Faster (Driving)30 The Wheelset and Steering ForcesDisplacement (y)longitudinal creep forcesr0r0rR(> r0)rL(< r0)Conicity ( )longitudinal traction/creepagelongitudinal traction/creepage31 Effective Conicity32 Effective Conicity(Worn Wheels)33 Demonstration*.

8 Steering forces in tangent track* Wheel / rail demonstration rig, images and videos prepared by Josh Rychtarczyk34 Tangent Running and Stability Lateral displacement R mismatch friction forces steering moment Wheelsetpasses through central position with lateral velocity. At low speeds, oscillations decay. Above critical hunting speed , oscillations friction forces35 Questions & Discussion36 Part 2 Vehicle Steering and Curving Forces Wear and Rolling Contact Fatigue37 Curving and Theoretical EquilibriumDisplacement (y)rR(> r0)rL(< r0)38 Demonstration*: Steering forces in curved track* Wheel / rail demonstration rig, images and videos prepared by Josh RychtarczykImportant Concept.

9 Sometimes, forces give rise to creepage( traction, braking, steering) Other times, creepagegives rise to forces ( curving)40 Curving Forces (Two Axle Vehicle, Sharp Curve)40 Angle of Attack (AoA)Trailing Axle, Low rail :R > Requilibrium Posi ve Longitudinal Creepage Longitudinal Creep ForceTrailing Axle, high rail :R < Requilibrium Nega ve Longitudinal Creepage Longitudinal Creep ForceLeading Axle, Low rail :Angle of Attack Primarily Lateral Creepage Lateral Creep ForceLeading Axle, high rail (Tread):Angle of Attack Primarily Lateral Creepage Lateral Creep ForceLeading Axle, high rail (Flange):R >> Requilibrium Posi ve Longitudinal Creepage Longitudinal Creep ForcePlus:Normal force (keeps vehicle on track)Reaction Forces (felt by track)41 Impacts of high Lateral Loads: rail Rollover / Track Spread Derailments42 Impacts of high Lateral Loads:Plate Cutting, Gauge Widening43 Impacts of high Lateral Loads:Wheel Climb 60 65 70 75 80 85 Flange Angle (Degrees)Lateral/Vertical of high Lateral Loads.

10 Fastener Fatigue / Clip Breakage45 Quick Calculation: How can we estimate the lateral forces (and L/V ratios) that a vehicle is exerting on the track?46 Estimating AoAand Lateral Creepagein a Sharp CurveCurve Radius, RWheelbase, 2 LAngle of Attack, V Leading Axle angle of attack: ~ arcsin(2L/R) ~ 2L/R = Rad ( mRad) Lateral Creepageat TOR contact:Vlat/V ~ 2L/R ~ = Example:6ocurve (R = 955 )70 wheelbase (2L = ) TOR= (dry)47 Estimating Low rail L/V and Lateral ForceL/VCreep At high creep L/V ~ At low creep L/V ~ const*creep~1(%)Angle of Attack (AoA) At creep:L/V = _____ 48 How does this compare with simulation results?