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Module 6: Train-Track Dynamics

Module 6: Train-Track Dynamics. Module Objectives. Understanding the Rail/Wheel Interface Identifying Force Generators Understanding Force Effects. Train-Track Dynamics. Definition Interaction of forces occurring as train moves over the track structure Lateral Forces Vertical Forces

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Module 6: Train-Track Dynamics

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  1. Module 6: Train-Track Dynamics

  2. Module Objectives • Understanding the Rail/Wheel Interface • Identifying Force Generators • Understanding Force Effects

  3. Train-Track Dynamics Definition • Interaction of forces occurring as train moves over the track structure • Lateral Forces • Vertical Forces • Vehicle Dynamics • Rail & Wheel Profile • Many factors affect these forces • Train Speed & Handling • Train Consist & Placement of Cars, etc.

  4. L/V Ratio • L/V Definition • Effect on Stability • Lateral Forces • Vertical Forces • Wheel/Rail Profile

  5. Lateral Forces • Flanging Force • Centrifugal Force • Frictional Curving Force • Coupler Force • Buff & Draft Force • Truck Hunting • Track Geometry Force

  6. Frictional Curving Force • Difference in Distance Outside Vs. Inside Wheel Rolls in Curve • Effect of Conical Wheel Tread • Generation of Creep Forces • Cause Truck to Steer to Curve Outside • Magnitude of Forces Vs. Wide Gage, Corrugations & Geometry Problems • Importance of Lubrication

  7. Coupler Forces • Position of Coupler Faces in Curves • Long Car Coupled to Short Car • Longitudinal Force Effect • Angularity of Couplers • Torque Applied at Wheel-Rail Interface

  8. Buff & Draft Forces Longitudinal Train Forces Result of Changes in Gradient, Curvature & Speed • Buff - Run-in = Train in Compression - Produces Outward Force on Curve, Increases Vertical Load on Outside • Draft - Run-Out = Train in Tension Produces Inward Force on Curve, Increases Vertical Load on Inside • Train in Simultaneous Buff & Draft -Torque Produced - Force Applied at Coupler Resisted at the Rail Slack 6"/Car 50' Slack/6000' Train

  9. Hunting v s • Caused by: • Empty or lightly loaded cars (though heavy cars can also hunt). • Train speeds above 45 mph. • Dry rail. • Three piece freight car truck. • Roller side bearings. • Tangent track or curvature of 1 degree. • Roller bearing wheelsets. • Worn wheel treads having a hollow appearance over good quality track. • Poor vertical snubbing.

  10. Track Geometry Forces • Lateral Force Result of Changes in Alignment & Gage • Wide Gage > Truck Hunting at High Speeds • Tight Gage > Truck Hunting at Low Speeds • Vertical Force Result of Changes in Cross-level/Superelevation & Profile • Vehicle Rocks About CG • Produces Horizontal Component at Rail because of Shift in CG

  11. Vertical Forces • Vehicle Weight • Unbalanced Elevation in Curves • Car/Locomotive Dynamics • Track Geometry Input • Coupler Forces

  12. Effects of Centrifugal Force OVERBALANCE EQUILIBRIUM UNDERBALANCE Centrifugal Force Centrifugal Force Centrifugal Force Centerof Gravity Centerof Gravity Centerof Gravity Resultant Resultant Resultant Gravity Gravity Gravity Superelevation Superelevation Superelevation + E 3 Amount of = a V Underbalance max 0 . 0007 D V = Maximum allowable operating speed (mph). max E = Average elevation of the outside rail (inches). a = Degree of curvature (degrees). D

  13. Car & Locomotive Dynamics Bounce Increase & Decrease Vertical Loading Speeds > 40 MPH Change in Track Modulus Pitch Varying Vertical Load Transfers End to End Square Joints Wheel Climb & Short Flange Marks Bounce & Pitch Result of Surface Variations

  14. Track Geometry Deviations in Geometry Accentuate Pitch & Bounce • Deviation in Uniform Profile • Mismatched, Bent or Battered Joints • Worn Points/Battered Frogs & Crossing Diamonds • Poor Cross-level • Rock & Roll • Spirals • Warp Forces Suspension Diagonally to Limits • Bind Side Bearings - Trucks Can't Turn

  15. Harmonic Oscillation Rock & Roll • High Center of Gravity Cars & Low Joints at Truck Spacing • Rocking Magnifies Alternate Rocking on Other Rail • Wheel Lift on Successive Joints • Especially Dangerous on Curves • Resonance Occurs at Critical Speed • Critical Speeds Occurs at Multiples of Frequency & Wavelength

  16. Center of Gravity & Oscillation

  17. Longitudinal Coupler Forces • Loaded car coupled to empty car (difference in compression of springs). • Differences in wheel wear, especially with multi-wear wheels. • Inequality of track surface, or sharp vertical curvature. • Vehicle bounce or pitch. • Effects of slack run-in or run-out.

  18. Coupler Forces & Derailments • Time duration of coupler forces • Train consist and makeup • Train handling by crew • Terrain • Geometry of coupled cars

  19. Rail-Wheel Profile New Wheel & Worn Rail New Wheel & New Rail Worn Wheel & New Rail Worn Wheel & Worn Rail

  20. Critical L/V Ratio • L/V = 1.29 wheel may climb new rail. • L/V = .82 wheel lift impending. • L/V = .75 wheel may climb worn rail. • L/V = .64 rail overturn force starts (unrestrained rail may overturn: rail rollover).

  21. QUESTIONS?

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