Strain Response in Insulated Rail Joints
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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


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


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


  • 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


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