Determination of applied stresses in rails using the acoustoelastic effect of ultrasonic waves

This research develops a procedure to determine the applied stresses in rails using the acoustoelastic effect of ultrasonic waves. Acoustoelasticity is defined as the stress dependency of ultrasonic wave speed or wave polarization. Analytical models are developed that predict the acoustoelastic effect for longitudinal waves, shear waves, Lamb waves, and Rayleigh waves. Using a programming tool, a numerical simulation of the models is generated to obtain the stress dependent curves of wave velocity and polarization of the various ultrasonic waves propagating in rail steel. A comparison of the sensitivity of the acoustoelastic effect is made to determine the feasibility of ultrasonic waves for further study. Rayleigh waves are found to be most sensitive to stress change. Rayleigh waves are generated using ultrasonic transducer and detected using a laser Doppler vibrometer (LDV). The LDV measures the in-plane and out-of-plane velocities. Polarization is defined as the ratio of in-plane and out-of-plane displacements. Initially, polarization is determined for the specimen in unstressed condition. Thereafter, the rail specimen is stressed in a compression testing machine, the experiment repeated, and the polarization determined. Thus, Rayleigh wave polarization is obtained as a function of applied stress. Finally, the change in polarization obtained experimentally is compared with the analytical model.