Development of a Novel Degraded Adhesion Model for Railway Systems

The accurate modelling of the wheel rail contact plays a fundamental role in the railway field because the contact forces deeply affect the vehicle dynamics, the wear of the contact surfaces and the vehicle safety. Usually, railway dynamic simulations are carried out with multibody software and the numerical performances are a primary concern; therefore, in practice, it is impossible to model the contact by considering the wheel and the rail as generic elastic continuous bodies. Typically, simplified and efficient multibody contact models are characterized by three main logical parts: the contact point detection, the normal problem solution and the tangential problem solution; the latter part includes also the adhesion model. In this work, the authors present an innovative adhesion model particularly developed to describe degraded adhesion conditions. The model proposed in the paper takes into account some important phenomena characterizing the degraded adhesion such as the adhesion recovery in presence of large sliding at the contact interface. This phenomenon is caused by the high energy dissipation at the contact and by the consequent cleaning effect on the contact surfaces due to the friction forces. The final adhesion recovery caused by the removal of external contaminants may deeply affect both the vehicle dynamics and the traction and braking maneuvers and thereby cannot be neglected. The new approach guarantees a good accuracy and, at the same time, a high numerical efficiency and for these reasons it can be implemented directly online (and in real-time) in more general multibody models of railway vehicles.