Abstract
The problem of train localisation on some part of the railroad is still an open question. Indeed, when electrical systems are used, the train is localised due to variation of an electrical signal: It is the shunt phenomena. But if the wheel-rail contact is insulating enough, the signal intensity is not affected and the train is invisible for the rail operators, and can lead to dramatic accident. Among the several parameters which can be involved, the impact of the brake shoe composition is investigated.
To investigate the shunt phenomena, one focus at the contact between the wheel and the rail accounting for the interfacial layer (called usually third body in tribology [Godet,1984]), composed of debris particles issued from the wheel and the rail but also from brake shoes or external environment. To be able to reproduce this three body contact, numerical simulations based on the discrete element framework (DEM) are performed. Such an approach is able to reproduce the mechanical but also the electrical behaviour of this heterogeneous and discontinuous medium [Renouf, 2008]. Recent works propose to relate the electrical resistance and the electrical noise to the property of such an interface [Zeng, 2016] Nevertheless, as the brake shoes seems have an important role, its composition is a first order parameter and the impact of such heterogeneities should be identified.
For the different models, friction and electrical resistance are measured. Different kinds of stress condition are used corresponding to different load and local shearing. The impact of the brake shoe composition on the different measures will be investigated as well as their ability to oxidation.
Three main limitations are present in this work. The first one concerns the degradation process, which is not yet taking into account (but is in progress). The second one is the wear flows (in the sense of the tribological circuit [Berthier, 1988]) which is not yet introduced in the model. Finally, for the third limitation, the model is not 3D and could lead to large stress values.
Several points appear as new results. The first concern the impact of oxide in the model and especially the competition between mechanical and electrical breakdown. The second one concerns the behaviour of multi-phasic third body layer from a mechanical and an electrical point of view.
The interest of discrete approach for the study of third body flows has been underlined (again). A methodological works has been done to underline the impact of brake shoe composition on the mechanical and electrical behaviour of the wheel rail contact at a local level.
KEYWORDS electrical contact, third body, DEM, shunting, friction.