Description of the Polach model compared to FASTSIM and CONTACT and a proposal for a variant dedicated to large creepages

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The Polach model is a fast and versatile method for calculating tangential forces in railway dynamics under Hertzian conditions. Although its theoretical basis is well established in the original publications, it lacks expressions of local quantities such as tractions and relative slip velocities. They are given in this article in the absence of spin, within the frame of Kalker's original theory, and compared with CONTACT and FASTSIM with an elliptical normal pressure distribution. As for the extended Polach method dedicated to traction and braking, it is generally no longer possible to associate an expression of these local quantities with the tangential forces. In the limited cases where this is still possible, it is found that the tractions associated with the Polach model are very close to those of extensions of CONTACT and FASTSIM with an elliptical normal pressure distribution. Following this observation, a variant of the Polach method is proposed based on the extension of FASTSIM, providing insight into local quantities in the absence of spin. The principle of this modification could be applied to any approximate method based on Kalker’s simplified theory in order to extend its field of application to large creepages.