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System for in Situ Measurement of Neutral Temperature in Continuous-Welded Rail

Research has been focused on developing a system for in situ measurement of stress in continuous-welded rail to use as a basis for the determination of neutral temperature (NT). Continuous-welded rail is known to break in cold weather and buckle in hot weather because of thermally induced stresses. The need for a reliable technique for determination of NT (rail temperature with zero thermal stress) has been an ongoing challenge for railroads since the advent of continuous-welded rail more than 40 years ago. Railroads need to know the level of stress in the rail to schedule slow-order mandates properly and prevent derailments. A prototype (Rail-NT) was developed for wayside rail NT measurement based on nonlinear ultrasonic guided waves. Numerical models were first developed to identify optimum guided wave modes and frequencies for maximum sensitivity to the thermal stresses in the rail web, with minimal influence of the rail head and rail foot. Experiments indicated a rail NT measurement accuracy of a few degrees. The first field tests of the Rail-NT prototype were performed in June 2012 at the Transportation Technology Center in Pueblo, Colorado, in collaboration with the Burlington Northern Santa Fe Railway. The results of these field tests were encouraging; the tests indicated an accuracy for NT measurement of 5°F at worst on both wood and concrete ties. One of the issues that remains to be investigated is the effect of passing trains on the rail NT measurements.