High Speed Rail IDEA Project 30 [Completed (IDEA)]
Vibration Measurements of Rail Stress
Project Data
Staff Responsibility:
Chuck Taylor
A reliable, low-cost, easy-to-use technology for measuring longitudinal stress in rail continues to be a highpriority objective for both freight and passenger rail operators. The effects of thermal expansion and contraction and train forces can produce tremendous stress in rail; especially long strings of welded rail. Various rail-anchoring systems are used to prevent these stresses from pulling or pushing the rail out of alignment, or breaking it. These stresses can occasionally exceed the capabilities of the anchoring system and/or the strength of the rail, resulting in rail breaks or buckling, which continue to be significant causes of derailments and train delays.
This project and a follow-on project (HSR-48) evaluated “vibro-elastic” methods for measuring longitudinal stress in rails. This concept is based on the known sensitivity of bending vibrations to contained longitudinal stress. The rail is excited at a specified frequency using an electromagnetic shaker. A laser vibrometer that is scanned along the rail is used for dynamic displacement measurements to determine the frequency and wavelength of the resulting rail vibrations. The resulting wavelength, along with the rail rigidity (which can be determined by the rail dimensions and modulus) can be used to determine contained longitudinal load. The results of this concept exploration project were sufficiently promising that a follow-on project (HSR-48) was conducted to improve the prototype system and test it in the field.
