Clearance joints and friction models for the modelling of friction damped railway freight vehicles

All mechanisms have mechanical joints with clearances and imperfections, either for functional reasons, enabling compliances and damping, or undesired, due to the extra cost resulting from high-precision machining, causing impacts and wear. In the suspensions of freight railway vehicles, joints with clearances are lined with friction surfaces and are used as the main mechanism of damping. Modelling friction-damped railway suspensions requires the selection and tuning of normal and tangential contact models. However, it is not clear how the selection of the contact models and their parameters influences the dynamics of the suspensions and, ultimately, the vehicle dynamics. This work presents and discusses the effect of different tangential contact models on the dynamic response of the vehicle and its sensitivity to the Stribeck velocity. The tangential contact models discussed in this context include the Amontons–Coulomb and Bengisu–Akay static friction models and the Gonthier dynamic friction model. In a multibody framework, a friction-damped locomotive is modelled using clearance joints to model the suspension mechanical contact pairs, which in turn are used to assess the impact of friction models and parameters on the vehicle dynamics. The results of this study suggest a visible influence of the friction models on the dynamic performance of the locomotive while negotiating curve transitions, where the friction state in the contact surfaces shifts from stiction to sliding. The results also highlight the importance of the Stribeck velocity. In contrast, when the vehicle operates in straight tracks or in curves with constant radius, the dynamics are almost unaffected by variations on friction models. This work shows that clearance joints are suited to model friction mechanisms, in particular, friction-damped suspensions of railway vehicles. The selection of the friction models and Stribeck velocity must be judicious as it can strongly influence the vehicle dynamic response, mainly in the curve transitions of railway tracks with small radii.