A NEW WHEEL-RAIL CONTACT MODEL FOR RAILWAY DYNAMICS João Pombo, Jorge Ambrósio and Miguel Silva IDMEC – Instituto Superior Técnico Av. Rovisco Pais, 1049-001 Lisboa, Portugal e-mail: {jpombo,jorge,miguelsilva@dem.ist.utl.pt} ABSTRACT The guidance of railway vehicles is determined by a complex interaction between the wheels and rails, which requires a detailed characterization of the contact mechanism in order to permit a correct analysis of the dynamic behavior. The kinematics of guidance of the wheelsets is based on the wheels and rails geometries. The movement of the wheelsets along the rails is characterized by a complex contact with relative motions on the longitudinal and lateral directions and relative rotations of the wheels with respect to the rails. A generic wheel-rail contact detection formulation is presented here in order to determine online the contact points, even for the most general three dimensional motion of the wheelset. This formulation also allows the study of lead and lag flange contact scenarios, both fundamental for the analysis of potential derailments or for the study of the dynamic behavior in the presence of switches. The methodology is used in conjunction with a general geometric description of the track, which includes the representation of the rails spatial geometry and irregularities. In this work the tangential creep forces and moments that develop in the wheel- rail contact area are evaluated using alternatively the Kalker linear theory, the Heuristic nonlinear model or the Polach formulation. The discussion on the benefices and drawbacks of these methodologies is supported by an application to the dynamic analysis of the bogie of the railway vehicle. Keywords: Spatial Curves, Contact Point Detection, Creep Forces, Stability Critical Speed. 1. INTRODUCTION The formulation of the wheel-rail contact problem is a complex task which has been the subject of several investigations that presented different solutions for the problem. Several authors [1-5] studied the contact forces between the wheel and the rail during the dynamic motion and, as a result of their investigations, several computer routines are now available for the calculations of the tangential forces at the contact point given the normal force and the relative velocities between the bodies [1-10]. Although the literature offers solutions for the problem of contact mechanics, detailed descriptions of the surfaces in contact and of the kinematics of the bodies, are required to make use of such solutions. Because the wheel and the rail have profiled surfaces, the prediction of the contact point location online is not simple, especially when the most general three-dimensional motion of the wheelset with respect to the rails is considered. In this work, the computational implementation of an appropriate methodology for the accurate description of each rail, in the general case of a fully three-dimensional track, is discussed. The track geometry is described by shape preserving splines and adopts Frenet frames that provide the appropriate track referential at every point. The complete