Modeling of Train-Induced Transitional Wavefields

Transitions in constitutive or cross-sectional properties are at the basis of long-term degradation of railway tracks. Therefore, the study of transitional wavefields excited by moving loads is of paramount importance. The study, reported in this paper, proposes an elementary model of two elastic layers, having a thin plate mounted on top, resting on a rigid foundation and connected at a straight vertical interface. The system is excited by a surface load (i.e., axle load) that crosses the vertical interface, and thus moves from one medium with given material parameters to another. Using a semianalytical solution, the energy flux associated with the transitional wavefield (i.e., the free-field energy flux) close to the vertical interface can be assessed. Initial results show that the flux becomes powerful for load velocities close to the critical velocity or for large contrasts in the material parameters. In addition, the free-field energy flux exhibits peculiar angle dependence; depending on the load velocity and the mentioned contrast, it can be extreme in the horizontal direction, into the layers, or along the vertical interface. Though this study models transitions in a simplified way, it clearly highlights fundamental features of transitional wavefields that should be incorporated in the assessment of track degradation.