Elastic and Acoustoelastic Properties of Railroad Rail
The measurement of thermally induced longitudinal forces in railroad rail is an important element in the control of train damage due to rail buckling or other modes of track failure. Acoustoelastic techniques, whereby stresses are inferred from small shifts in the ultrasonic velocity, are attractive because they can sample the stresses on the interior of the rail and because relatively simple instrumentation can be utilized . The effectiveness of acoustoelastic techniques, however, is limited by the degree to which other sources of velocity shifts are present, generally associated with rail-to-rail variations in microstructure. Figure 1 illustrates the problem. Stress is inferred from the shift in velocity from its stress free value, based on a proportionality constant known as the acoustoelastic constant. Errors in the values of either the stress free velocity or the acoustoelastic constant can lead to errors in the predicted stress.