Enhanced Acoustic Birefringence Method For Measuring Longitudinal Rail Stress
Analogic Engineering, Inc. is developing a portable instrument for determining Rail Neutral Temperature (RNT) by measuring rail stress using Acoustic Birefringence (AB). This work builds on 2016/2017 FRA-funded research that demonstrated a linear relationship between AB and longitudinal rail stress based on our test instrument that is able to perform accurate, repeatable AB measurements on the complex rail shape. 2017 lab results were consistent with the research goal of RNT error < 5° F.
The 2019/2020 project goal is to verify performance on in-situ rail under field conditions, and develop prototype equipment for extended field testing and validation. A year-2 option planned for 2020-2021 includes testing additional rail samples to determine if families of calibration constants can be applied to related rail types (e.g., by profile, year, batch, etc.) to allow RNT measurements on any rail without needing a prior stress-free reference measurement.
PROJECT STATUS, 2020 - November 2019 testing at TTCI on the instrumented High-Tonnage Loop verified a linear relationship between AB and rail stress for in-situ rail. No problems were encountered with transitioning from the lab environment (where the rail samples were hydraulically loaded to simulate thermally-induced stress) to the field environment where the stress was induced by the daily temperature cycles of the constrained rail. No problems were caused by other differences between the lab rail conditions and field rail conditions, such as rail fastening, location in a curve, the shape of the running surface, surface work-hardening, etc. After calibrating to the TTCI strain gauge data, the rail stress measured using AB closely followed the TTCI strain gauge data throughout two days of testing within an average error of 1.9 KIPS, equivalent to a RNT error of 0.7° F. Additional tests on sample rails, equipment improvements and prototype development are underway.
This work is funded by U.S. Department of Transportation Federal Railroad Administration, Robert Wilson, Ph.D., PE - FRA Project Manager
