Experimental evaluation of the true intrinsic nonlinearity of rail steel using Rayleigh waves and a new nonlinearity parameter

The paper presents the experimental evaluation of the true intrinsic nonlinearity of a macroscopically pristine rail specimen using non-dispersive Rayleigh waves. A second harmonic is produced in the wave as a result of lattice-anharmonicity that is sensed at different locations on the specimen surface. The spectral amplitudes of the fundamental and generated second harmonics are then used to calculate the intrinsic nonlinearity of rail material using a new amplitude-based nonlinearity parameter. The material nonlinearity of the rail steel evaluated using the experimental measurements and amplitude-based parameter are further compared with that obtained using the nonlinear elasticity equations. It is found that the experimentally obtained nonlinearities are in close agreement with that of the nonlinear elasticity equations that show the effectiveness of the proposed method in measuring the intrinsic nonlinearity of the rail steel. Furthermore, the effect of excitation frequency, number of cycles in tone burst, and selection of the windowing functions in evaluating the intrinsic nonlinearity of rail steel are also investigated. The estimation of intrinsic material nonlinearity may help diagnose the health status of the macroscopically pristine rail specimens in terms of the level of dissolved impurities and their microstructural consistency, before fixing them on a track.