The rail pad is the elastic element between the rail and the sleeper that has the role of absorbing the mechanical stresses from the rail and reducing the vibrations and shocks generated by wheel–rail interactions. In this paper, the problem of the influence of the variability of the nonlinear load-deformation characteristic of rail pads (resulting from the manufacturing process) on wheel–rail vibrations is investigated. The limit load-deformation characteristics of a manufactured rail pad and the medium load-deformation characteristic resulting as the arithmetic mean of the two are considered. The nonlinear load-deformation characteristic of the ballast is also considered. All these characteristics are approximated with the help of the bilinear function and are implemented in a track model consisting of an infinite Euler-Bernoulli beam placed on a two-elastic layer continuous foundation with inertial insertion, resulting in a model with an inhomogeneous foundation. The parameters of the inhomogeneous foundation are established from the equilibrium condition under a static load. Wheel–rail vibrations are studied in terms of the contact force and the acceleration of the rail and wheel. The influence of the variability of the elastic characteristics of the rail pad manifests itself in the field of medium frequencies, which amplify or attenuate the vibration levels in certain bands of one-third of an octave.

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The paper focuses on the experimental verification of the results derived from numerical simulations, based on a model of the bogie-track system, where the vertical track irregularities are introduced in the form of a pseudorandom function. This function comes from an original method of synthesizing the vertical track irregularities, depending on the geometric quality of the track and on the velocity. To verify the method, the root mean square (RMS) of the simulated accelerations in the axles and the bogie frame against each axle is compared to the experimental accelerations within the frequency range of wavelengths of the track vertical irregularities from 3 to 120 m. The results have shown a good correlation between the simulated RMS accelerations for a low quality track and the measured RMS accelerations.

The driving wheelset is used in railway traction (locomotives, electric trains, trams, etc.) to support part of the weight of the suspended mass and to drive and brake the vehicle. The dynamics of the driving wheelset/track system is a very important issue in the railway engineering, and this paper is focused on basic features of the frequency response functions which describe the dynamic behavior in the presence of the rolling surfaces harmonic irregularities. To this end, a simple model of the driving wheelset/track system with the range of application limited up to 6-700 Hz is adopted. The driving wheelset model consists of a free-free uniform Euler-Bernoulli beam with three attached rigid bodies, representing the axle, the two wheels and the gear; the distinct feature of this model is the inertial asymmetry. Two independent infinite uniform Euler-Bernoulli beams, each on its foundation including two elastic layers for rail pad and ballast and an intermediate inertial layer for sleepers represent the track model. For simplicity, the moving irregularity model is applied to simulate the interaction between wheels and rails. Numerical simulations show that the driving wheelset/track system has three resonance frequencies, all situated in the frequency range of the evanescent waves in rails. FRF of the driving wheelset/track system have been calculated for left and right wheel/rail pair. The influence of the asymmetric inertia of the driving wheelset and the out of phase between the rolling surface irregularities are evaluated in terms of frequency response functions of the wheel/rail contact force.

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