Towards the Identification of Wheel-Rail Contact Forces

Licentiate thesis, 2010

The accurate determination of the contact forces between rail and wheel is essential in the analysis of different kinds of rolling contact fatigue. As the contact forces cannot be measured directly in the field, one approach is to measure the strain at certain positions of an instrumented wheel. Upon employing signal processing techniques, the forces can be estimated. However, such a scheme typically involves restrictions in terms of the choice of spatial and temporal discretization of the underlying equations of motion or a neglect of the inertia terms. In this work, the vertical contact force is determined by the solution of an inverse problem. A minimization problem is considered in which the time-history of the contact force is sought such that the discrepancy between the predicted and the measured strains is minimized. A particular feature of this formulation is that the discretization of the pertinent state equations in space-time, the sampling instances of the measurements and the parameterization of the sought contact force are all independent of each other. Additionally, a well-established mathematical framework can be exploited to analyze the effect of measurement noise as well as devise suitable strategies for regularization. Moreover, the convergence of the spatial and temporal discretization of the model and the time parameterization of the contact force history are investigated. In the first paper of this work, the proposed strategy is evaluated for a simplified 2D disc with focus on the temporal discretization. In addition, sensitivity to noise and improvements due to proper regularization are investigated. In the second paper, the identification strategy is modified by applying virtual calibration in order to compensate for spatial mesh sensitivity.