Development and Numerical Optimization of an Innovative Adhesion Model in the Railway field

The simulation of the railway braking under degraded adhesion conditions is very important since it affects both safety and interoperability issues of the railway network; unfortunately a realistic adhesion law is not easy to be defined and implemented because of the complex and non-linear behaviour of the adhesion coefficient. The presence of contaminants drastically reduces the available adhesion coefficient between the rolling surfaces of wheel and rail producing a limitation of the tangential forces that can be exchanged on the contact patch. Particularly under degraded adhesion conditions very high slidings occur and they usually produce a high dissipation of energy which has a cleaning effect on the rolling surfaces (i.e. the contaminants are removed), that allows to partially recover the adhesion coefficient. In this work this energetic criteria has been studied and the authors propose the implementation of an innovative adhesion law to the simulation of railway multibody models, with 3D multi-point contact algorithms. A benchmark case, the braking of a coach with WSP system is simulated and compared with experimental data available from testing; the new adhesion law permits to match the experimental reference results and to carry out simulated braking tests, with working WSP system, that comply with the current regulations.