Nonlinear guided waves for neutral temperature measurement in continuous welded rails: Results from laboratory and field tests

Continuous Welded Rail (CWR) is used in modern rail construction including high-speed rail transportation. The absence of expansion joints in these structures brings about the risk of breakage in cold weather and of buckling in warm weather due to the resulting thermal stresses. The University of California at San Diego (UCSD), under a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, is developing a system for in-situ measurement of the rail Neutral Temperature in CWR. Currently, there is no well-established technique able to efficiently monitor the rail thermal stress, or the rail Neutral Temperature (rail temperature with zero thermal stress), to properly schedule slow-order mandates and prevent derailments. UCSD has developed a prototype (Rail-NT) for wayside rail Neutral Temperature measurement that is based on non-linear ultrasonic guided waves. Numerical models were first developed to identify proper guided wave modes and frequencies for maximum sensitivity to the thermal stresses in the rail web, with little influence of the rail head and rail foot. Experiments conducted at the UCSD Large-scale Rail NT Test-bed indicated a rail Neutral Temperature 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 (TTC) in Pueblo, CO in collaboration with the Burlington Northern Santa Fe (BNSF) Railway. The results of these field tests were very encouraging, indicating an accuracy for Neutral Temperature measurement of 5 F at worst, on both wood ties and concrete ties.