A vibration technique for measuring railroad rail stress

Abstract

Longitudinal rail stress, related to constrained thermal contractions and expansions, leads to broken and buckled rails, and consequent service delays and derailments. There is a broad consensus on the need for cost-effective and reliable methods for the measurement of rail stress. Vibration techniques for assessing rail stress, based on the effect of longitudinal force on the free vibrations of beams, have long been proposed. It is well understood that compressive stresses decrease the flexural frequencies, while tensile stresses increase them. Past efforts attempting to use this for measurements of stress in railroad rails have failed due to an inability to control or adequately measure other parameters, most particularly the placement and stiffness of the supports. We are developing a new method in which the influence of support parameters should be minimal. Scanned laser vibrometry measurements of vibration fields, followed by a comparison with guided wave theory for the complex cross section of the rail, promises to allow the stress to be determined with the requisite precision. Here we report on the status of this work. [Work supported by Association of American Railroads and the Transportation Research Board.]