Dynamic Behaviour of Railway Vehicles Using Perfect and Imperfect Mechanical Joints

The use of reliable computer codes and the construction of detailed models are essential to study the dynamic behaviour of railways vehicles for realistic operation conditions. Such studies involve the construction of three independent models: the vehicle model; the track model; and the wheel-rail contact model. In this paper, a methodology is used to create detailed three-dimensional track models, which includes the three-dimensional parameterization of the rails geometry. A generic wheel-rail contact formulation is applied in order to determine the location of contact points and compute the contact forces. A multibody formulation is used to describe the kinematic structure of the rigid bodies and of the joints that make up the vehicle model. The mechanical joints control the relative motion among the bodies, while the springs and dampers introduce internal forces in the system arising from the relative motion of the bodies. In general, dynamic studies involving railway vehicles consider that the mechanical joints of the suspension are perfect. Nevertheless, these joints are not perfect as a result of the tolerances required in the fitting of their components. Moreover, such clearances tend to increase as a result of wear resulting from service usage. Furthermore, many of the mechanical joints used in the suspension of railway vehicles have bushing elements, with nonlinear characteristics, that allow additional degrees of freedom between the bodies. In this work, a methodology for the implementation of realistic joints with clearances and bushings is proposed. This method is used here to evaluate the importance of using such realistic mechanical joints in the vehicle models and to assess the influence that the dimensions and material properties of the compliant elements have on the dynamic behaviour of the railway vehicles.