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EFFECTS OF WHEEL/RAIL CONTACT PATTERNS andCONTACT PATTERNS and VEHICLE PARAMETERS on LOADED CAR HUNTINGLOADED CAR HUNTING
Nicholas Wilson, Huimin Wu, Harry Tournay, Curtis UrbanNicholas Wilson, Huimin Wu, Harry Tournay, Curtis UrbanTransportation Technology Center, IncPueblo, CO, USA
MARTS Chicago September 2009 - 1© Transportation Technology Center, Inc., a subsidiary of the Association of American Railroads, 2009
Background
In 2006, failures of primary suspension adapter pads were reported on a particularwere reported on a particular type of grain car:
Loaded high capacity (286k )lbs) grain hoppers
Truck hunting: loaded hunting is unusualhunting is unusualM-976 trucks with improved tracking Routes with specific rail wear patterns and tighter gage
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p2®
gage
Primary Suspension Adapter PadsP l d i lPolymer pads improve axle steering, reduce W/R forces and rolling resistancegLoaded Hunting motions appeared to cause failures:
P i i dPrimary suspension padsIf a pad does fail, it is typically only 1 out of 8typically only 1 out of 8 in a car
Constant contact sidecontact side bearings (CCSB)
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p3®
Initial Lateral Stability (Hunting)Tests
50 mph Tests performed at TTC
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p4®
Initial Lateral Stability (Hunting)Tests
Tests performed at TTC
Wheel Loaded Hunting Threshold SpeedWheel Profile
and Conicity
Empty ~ Standard Pads
Loaded Hunting Threshold Speed
Summer Standard
Pads
Winter Standard
PadsStiffer Pads
Standard Steel
Adaptersy Pads Pads Adapters
Wornλ>0.6
65 mph 47.5 mph 55.5 mph 65 mph 70 mph
KRλ>0.2
80 mph 65 mph 75 mph 80 mph
AAR1Bλ 0 05
>80 mph 75 mph 80 mph 80 mphλ>0.05
p p p p
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p5®
Initial Hunting Test Conclusions
Loaded car hunting a function ofCar body mass and inertial propertiesHigh W/R Conicity
Worn wheelsWorn rail profile in straight track
Adapter pad stiffness
Loaded car hunting also a function of:Center plate friction
Steel center plates reduced hunting Side bearing friction restraint
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p6®
Grain Car Wheel Wear and Effects on Conicity
96,000 miles160,000 mile
Relatively low wear in this
New AAR-1B 35,000 milesregion
Higher wear in this tread region
Conicity (λ)Average Conicity, RTT 34 Rail
0.796 000 ilConicity (λ)
on TTCI Hunting t t
0.4
0.5
0.6
nici
ty
New AAR-1B
96,000 miles
test zone
0
0.1
0.2
0.3
Con Avg
Max
Min35,000 miles
160,000 miles
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p7®
00 40 80 120 160 200
Mileage (*1000)
High Conicity W/R Contact Conditions
Increased conicity on tangent track after ~ 160,000 kmTangent rail head profiles:Tangent rail head profiles:
Certain new rail sections New Rail
Tight gauge
New Rail
“Flattened” crowns &
Fl t thFlow to the gauge corner Flat railhead &
plastic flow
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p8®
Wheel / Rail Profiles
Average Wheel Flange Width
36m)
Accelerated initial flange wear
34
35
36ng
e Width
(mm
330 50 100 150 200 250
Mileage (*1000)
Flan
Associated ith
1mm gap
New AAR1-B WheelAssociated with initial mismatch & 2-point contact
≅12 mm RRD
Worn rails from 2 degree, 4, degree,
between new wheel & worn high rail in curves
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p9®
and 6 degree curveshigh rail in curves
Wheel / Rail Profiles
Average Wheel Flange Width
Reduced flange wear after ~ 50,000 miles
34
35
36
eW
idth
(mm
)
33
34
0 50 100 150 200 250
Mileage (*1000)
Flan
ge
g ( )
Associated with single point contact & a largepoint contact & a large radius differential generated on the high
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p10®
rail in curves
W/R Conicity as a Function of Mileage, Car and Truck ArrangementTruck Arrangement
Car/Truck typesGen I: Grain car with steel adapterssteel adaptersGen II: Grain car with polymer adaptersCoal: Coal car with steelCoal: Coal car with steel adaptorsCoal HD: Coal car with polymer adapters
Root causes for differences are still unknown but suspected to be a function of:
Curving ability
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p11®
Curving abilityVehicle stability
W/R Conicity as a Function of Rail Profiles for a Particular Grain Car RouteParticular Grain Car Route
Analysis of conicity for 108 axles on 25,000 measured rail profiles from 19 miles of tangent track
s Conicity ≅ 0 1s Conicity ≅ 0 1
asur
ed R
ails Conicity ≅ 0.1
Rails producing lower conicityas
ured
Rai
ls Conicity ≅ 0.1
Rails producing lower conicity
age
of M
ea Conicity ≅ 0.4Rails producing higher conicity
conicity
Mainly dueage
of M
ea Conicity ≅ 0.4Rails producing higher conicity
conicity
Mainly due
Perc
enta Mainly due
to worn wheels
Perc
enta Mainly due
to worn wheels
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p12®
Percentage of Exception (Wheels) Percentage of Exception (Wheels)
Tangent Track W/R Conicity Summary
New AAR-1b wheels produce low conicity on all rail profiles
Rail profile pair from the high conicity group
Rail profile pair from the low
i irail profiles
Rails with a low rail shoulder produce lower conicities
conicity group
Rail profile pair from the high produce lower conicities,
high shoulder gives high conicity
conicity groupRail profile pair from the low conicity group
Conformal contact tends to produce low conicity λ = 0.05
Flattened rails, gauge flow and narrow gauge produce
λ > 0 35
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p13®
high conicities λ > 0.35
Tangent Track W/R Conicity Summary (cont.)
Tight gauge is highly correlated to high conicity in tangent track
57
30
60
90
eeda
nce
of W
heel
s (%
)
56.356.456.556.656.756.856.957
Gag
e (in
)
Conicity Exceedance Wheelset % Gage Spacing inches
012200 12220 12240 12260 12280 12300 12320 12340 12360 12380 12400
Distance (feet)
Exce
5656.156.2
High conicity was found on only 10% of trackRail grinding to relieve reduce flattened rails, relieve the gauge corner and remove metal flow in thethe gauge corner and remove metal flow in the gauge corner could reduce conicityA more conformal new wheel profile could change
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p14®
the rapid initial wear pattern of new wheels
Truck Hunting and Warp Dynamics
Loaded hunting tests revealed:
Predominantly in-phasePredominantly in-phase motion (warp) of the wheelsets & truck bolsterbolsterLittle longitudinal deflection of the adapter padsadapter padsDependence on moments due to the adapters / adapter pads & truck rotation on stability
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p15®
Truck Warp Test Results
A tiff 140 klb i / d A tiff 12 5 klb i d
High warp restraint similar to previous tests
Warp stiffness reducedby factor of about 11 due
Avg. stiffness = 140 klb-in/mrad Avg. stiffness = 12.5 klb-inmrad
similar to previous testsof the same truck typewhen friction wedges
to friction saturationwith large wedge motionsfrom combined body
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p16®
have little motion from combined bodyvertical/lateral motions
NUCARS ® simulations to evaluate W/R forces and effects of Carbody and Suspension Parameterseffects of Carbody and Suspension Parameters
40 000 lbs40,000 lbs net lateral axle force
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p17®
W/R Forces due to Loaded Hunting
NUCARS® simulations of loaded grain car hunting show potential for very high W/R forcesL N tLarge Net Axle L/V ratios could
t kcause track panel shift
Large truckside L/V could causecould cause gauge widening and rail rollover
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p18®
rail rollover
Progression to Loaded Car Hunting
Accelerated wheel wear occurs in curves as a result of a “mismatch” between the high rail profile & that on tangent tracktangent track
2-point contactHigh rail “conditions” the wheel of a car making flangeHigh rail conditions the wheel of a car making flange contact to a conformal profile
“Conditioning” results in high conicity, especially onConditioning results in high conicity, especially on particular sections of tangent track
New rail of particular section“Flattened” rail with material flow to the gauge cornerSections of track with tight gauge
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p19®
Progression to Loaded Car Hunting (cont.)
High conicity on tangent trackOn sections where higher speeds occurHigh creep forces under load excite the wheelsets
to yaw/warp the truck frameto yaw within the truck frame on soft adapter padsto yaw within the truck frame on soft adapter pads
Wheelset & truck yaw excite particular (longer) car bodies in a yaw-dominated mode (includes roll)y ( )Car body yaw and coupled roll motions saturate the truck wedge system, reducing the warp restraintReduced warp restraint results in resonance between wheelset, truck & car body yaw above certain threshold speeds
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p20®
p
Progression to Loaded car Hunting (cont.)
Truck warp restraint breaks-down almost completelyWheelset hollowing (& conicity) increases as a consequence of the hunting motionLoaded car hunting occurs:
At progressively lower speedsAt progressively lower speedsOn increasingly longer sections of tangent track
Pad failure results together with degradation ofPad failure results together with degradation of constant contact side bearing elements
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p21®
Loaded Car Hunting: Conclusions
Loaded car hunting is a system problem:Only certain car types – many cars with trucks do
hnot huntDepends on truck center spacing, car body inertial characteristics (centers of gravity & moments ofcharacteristics (centers of gravity & moments of inertia associated with high capacity cars for low density bulk products)Wheelset and truck constraints (adapter pad stiffnesses, loss of warp restraint due to friction wedge motion)wedge motion)Track (rail profile mismatch, rail deformation, tight gauge)
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p22®
g g )
Loaded Car Hunting: Conclusions (cont.)
Many types of car with these trucks do not experience loaded car hunting:
N d “ ” h d k iNeed “tune” the car and truck suspension parameters to the specific car body characteristics:
Truck spacing inertial parameters (CG height yawTruck spacing, inertial parameters (CG height, yaw and roll moments of inertia)Wheelset and truck constraints (adapter pad ( p pstiffnesses, truck warp restraint)
Loaded hunting may lead to very high W/R forcesLoaded hunting may lead to very high W/R forcesPossibility for increased risk of track damage and
derailment (Oct 2009 tests will measure forces w/IWS)
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p23®
Way Forward: Standards and Testing
Primary Suspension Pad Durability StandardsAAR MSRP, Volume H, Section 4.3.2
Develop M-976 and Chapter 11 Loaded Hunting Test/Analysis Requirements (2009)
What wheel profile?What car body and inertial parameters? (M-976)What performance criteria?
Loaded Hunting Tests at TTCI (Oct/Nov 2009)g ( )Support development of loaded hunting testsIWS to measure W/R forces while hunting
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p24®
Way Forward: Wheel and Rail Profiles
Rail grinding to relieve reduce flattened rails, relieve the gauge corner and remove metal flow in the gauge corner could reduce conicitythe gauge corner could reduce conicity
A more conformal new wheel profile could change th id i iti l tt f h lthe rapid initial wear pattern of new wheels
A new wheel profile design for freight cars is being evaluated at TTCI to replace the AAR-1bevaluated at TTCI to replace the AAR 1bBased on worn wheel shapesMore conformal to existing rail profiles in curves and g pstraight trackNarrower flange for more gage clearance
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p25®
Way Forward: Car and Truck DesignI di tImmediate:
Replace adapters & pads with standard adaptersConsequent reduction in curving performanceConsequent reduction in curving performance (increased wheel wear & wheel RCF)
Intermediate:Intermediate:Stiffer padsPartial improvement in tracking performance (reduced p g p (wheel wear & wheel RCF)
Long term:Improved freight truck with reduced stiffness pads & increased warp restraintReduced wheel wear & eliminated RCF
© TTCI/AAR, 2009, MARTS Chicago, September 2009 p26®
Reduced wheel wear & eliminated RCF
Thank you for your attention!
Nicholas Wilson
Transportation Technology Center IncTransportation Technology Center Inc.PuebloColoradoUSA
MARTS Chicago September 2009 - 27© Transportation Technology Center, Inc., a subsidiary of the Association of American Railroads, 2009
USA
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