Experimental Measurement of Residual Stress Distribution in Rail Specimens Using Ultrasonic L-CR Waves

Longitudinal critically refracted (L-CR) waves are considered bulk longitudinal waves and penetrate into an effective depth beneath the surface parallel to the material surface. Such L-CR waves can be employed to measure residual stresses because the acoustoelastic effect is the basis for ultrasonic residual stress measurements. This effect is described by the relationship between change of wave travel time and stress applied when such waves propagate in a stressed medium. In this paper, stresses applied in a rail were evaluated by using a developed L-CR probe. With this transducer, it was verified how the difference in the arrival times of the L-CR waves showed a trend as the tensile stresses increased. The acoustoelastic coefficients were calculated using the relationship between the stresses and the travel times, and the residual stresses of the used rails were measured using these coefficients. In addition, the difference in residual stress distribution according to the characteristics of the wheel-rail contact surface was analyzed from the obtained residual stress value. It was concluded that this non-destructive evaluation technique using L-CR waves could be employed for accurate stress measurement of rails because differences in stress applied to the rail can be detected.