Adaptation of the semi-Hertzian method to wheel/rail contact in turnouts

A procedure is described in order to assess loads applied on a turnout due to track-train interaction. Co-simulation is used between a finite element method (FEM) model of the turnout and a multibody system (MBS) of the vehicle. Wheel/rail contact forces are computed in the MBS and applied to the rails of the turnout modelled as FEM beams. FEM displacements under the wheel are accounted in the MBS in the next time step. A modification has been applied to the semi-Hertzian (SH) method used to assess wheel/rail forces. This adapted SH method is designed to take in account the relative flexibility of the components of the turnout, like the stock rail and the switch rail. Such parts have their own degree of freedom and may in some extent behave independently: the proposed method takes it in account in the contact search. The co-simulation has been first used in a referenced case-study. 2 TRACK MODEL 2.1 Description of the FEM model A view of the ANSYS model of the UIC60-760-1:15 turnout is shown in Figure 1. Rails and sleepers are modeled with beam finite elements, here displayed with shapes determined from the section definition. 118 sections are used to define the whole turnout. They are imported from a computer-aided design (CAD) model of the turnout. There are 3 beam elements between 2 successive sleepers. Rail pads are modelled with 6 degrees-of-freedom (dof) spring-dampers (not shown in Figure 1). The ballast is modelled by a viscously damped Winkler foundation. An effective ballast contacting area is assigned under each rail above a sleeper. The value of this area depends of the location in the turnout. For instance, the area is smaller in the crossing zone, where the ballast is less compacted. Dofs are coupled at both ends of the diverging route. The total number of dofs is 56,000. The presented model doesn’t include nonlinearities but could be nonlinear. 2.2 Nodal Loads Wheel loads including moments (see section 3.2) are applied to the rails. For the special case of a two-point contact, with one contact on the stock rail and the other contact on the switch rail, both beams shown in Figure 1 will be loaded by a component of the total wheel load (see section 3.3). Figure 1. Model of the UIC60-760-1:15 turnout – Zoom on sections of the switch and the crossing Figure 2. Distribution of the wheel vertical load Q to the FEM nodes For each wheel, forces and moments are distributed to adjacent nodes around the position of the wheel. Hermitian cubic polynomials are chosen as they are continuously differentiable.