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Strain Response in Insulated Rail Joints. Dan Peltier, Steven Downing, Darrell Socie, and Christopher P. L. Barkan University of Illinois at Urbana-Champaign • Railroad Engineering Program. Background. Typical Failure Mode.

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Strain Response in Insulated Rail Joints

Dan Peltier, Steven Downing, Darrell Socie, and Christopher P. L. Barkan

University of Illinois at Urbana-Champaign • Railroad Engineering Program

Background

Typical Failure Mode

  • Insulated rail joint: used to break railroad tracks into electrically isolated sections
  • Necessary for train detection and rail traffic control
  • With use of welded rail, IJ’s become the only mainline rail joints
  • Joints consist of two rails and two “joint bars”, all held together with a strong, insulating epoxy layer (bolts are of secondary importance)
  • Cyclic high-impact stresses lead to epoxy fatigue failure

Photo courtesy TTCI

Photo courtesy LBFoster

  • Epoxy debonds outward from center of joint
  • Increasing deflections cause wear on insulating materials, allows short circuit to develop

Rail

Epoxy loss and rust between rail and joint bar

Problem statement

Joint bar

  • Insulated joints have the shortest service life of any track components in a heavy-haul environment
  • Current inspection techniques not adequate for detecting failure
  • Need a better way to monitor the health of IJ’s, so that their replacement can be scheduled

Photo courtesy TTCI

NSEL Testing Goals

  • Apply tensile loads to rail ends
    • Simulates thermal stresses normally present in railroad track
    • Relatively easy to model
  • Measure strains at critical locations
    • Test accuracy of finite element model
    • Compare strain response of new joints to failed joint specimens
  • Measure joint’s electrical resistance versus load
    • Determine parameters for an electrical monitoring system
    • Characterize load-related intermittent insulation failures
  • Proof-test prototype smart sensors’ ability to measure strain in rails / joint bars

Project goals

  • Use new wireless sensors (strain gauges, voltmeters) to monitor IJ health without human intervention
  • Identify failing joints based on their physical and electrical responses to load

NSEL Testing Setup

Reaction block

100 kip servo-hydraulic actuator

Reaction block

Load cell

Insulated rail joint

21’

  • 100 kip (tension) design load for all components
  • Both conventional and prototype wireless strain gauges
  • Static, non-cyclic loading
  • Joint length approximately 11’
    • Minimum length at which “new” joints remain serviceable for future use
    • Instrumented joints will be placed in track for further testing

Test area, showing reaction blocks and actuator

Experimental Technique

  • Finite element model of strain response to thermal loads, for both new and degraded joints
  • In-field measurements of electrical voltages across both functional and failed joints
  • In-lab testing of strain response and electrical resistance under longitudinal loads for both new and failed joints
  • Identify signature physical and electrical responses of a failing joint

Acknowledgements

Testing funded by the Association of American Railroads. Test specimens provided by Norfolk Southern, CN, and Portec Rail Products.

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