Technical Reports

Experimental 3-D Residual Stress Measurement in Rails via Thermal Annealing

  • 01
  • Jul
  • 1999
AUTHOR: Federal Railroad Administration
KEYWORDS: heat treatment; interferometry; rail grinding; residual stress; stress relief; thermal annealing
ABSTRACT: This report describes a novel method to determine three-dimensional (3-D) residual stresses in railroad rails. The method uses Moire and Twyman/Green interferometry to measure the deformation of rail slices during a stress relief process which is accomplished by thermal annealing (heat treatment). The rail slices are approximately 1/4 inch thick. Two slices from the same general location on a rail are used in this method. One splice is cut in the transverse plane and another in a 45¬į oblique plane. The 3-D residual stresses are then reconstructed from the deformation measurements by applying basic engineering assumptions and principles. In this report, the thermal annealing method was applied to five different rails to examine the effect of rail grinding on rail performance. Residual stress was used as a measure of performance because it is known to have a strong affect on the occurrence and growth of rail defects. One rail sample was naturally worn. A second rail sample had conformal grinding. Two rails were ground at periodic intervals for two-point contact up to a total accumulation of 178 million gross tons (MGT); one rail was ground at 12.5 MGT intervals and another every 25 MGT. The final rail sample was a brand new rail. Traffic accumulation and rail grinding were performed on the High Tonnage Loop at the Facility for Accelerated Service Testing (FAST) which is located at the Transportation Technology Center (TIC) in Pueblo, Colorado. The results from the residual stress reconstruction indicate that the horizontal tensile stress, which is the stress component most closely related to rail failures, was highest for the naturally worn rail. In the rails with two-point contact, the horizontal tensile stress was found be relatively small, although these rails also had the largest compressive stresses. The horizontal tensile stress component was found to be the smallest in the brand new rail.