An innovative wheel–rail contact model for railway vehicles under degraded adhesion conditions

The accurate modelling of the wheel–rail contact plays a fundamental role in the railway field since the contact forces heavily affect the vehicle dynamics, the wear of the contact surfaces and the vehicle safety. Concerning the wheel–rail contact, an important open problem is represented by the degraded adhesion. A realistic adhesion model is quite difficult to obtain because of the complex and highly non-linear behaviour of the adhesion coefficient and the presence of external unknown contaminants (the third body); this is especially true when degraded adhesion and large sliding between the wheel and rail contact surfaces occur. In this work the authors present an adhesion model particularly developed to describe degraded adhesion conditions. The new approach will have to be suitable to be employed within the wheel–rail contact models typical of the multibody applications. In other words, the contact model, comprising the new adhesion model, will have to guarantee a good accuracy and, at the same time, a high numerical efficiency to be implemented directly online inside the general multibody model of the vehicles (e.g. in Matlab-Simulink or Simpack environments). The model analysed in the paper is based on some of the main phenomena characterising the degraded adhesion, such as large sliding at the contact interface, high energy dissipation, the consequent cleaning effect on the contact surfaces and the final adhesion recovery due to the removal of external unknown contaminants.