Dry friction modelling by means of the bond graph technique.

Dry friction is present in many engineering situations, in most of them it is damaging therefore it is avoided using lubrication, but in many others is the working principle of the system. Different theories have been developed, during the last five centuries, for studying this kind of friction. The first theory that offered a good explanation to the process was stated by Coulomb (1785). His second law, the friction force is proportional to the normal load between the bodies, enables to define a coefficient of friction CI, thus: F-R = -mu F-N sgn(V) When modelling dry friction using Coulomb's theory, no realistic results appear if the sliding velocity tends to zero. This is due to the step change in the friction force when the sliding velocity changes sign. The most widespread theory nowadays for dry friction, was developed by Bowden and Tabor in 1950, it was called "the adhesion theory of friction". Based on Bowden and Tabor's theory, a model for dry friction has been developed, using the Bond Graph technique. It includes a simulation of the real physical elements that take part in the process. The use of the Bond Graph technique allows clear identification of the processes and elements that are involved in such situations, improving the understanding of the phenomenon. A few Bond Graph elements are used to model the system, each of them representing a clear part of it, in this way the influence of every parameter may be analysed precisely. The performance of the model may be adjusted for different metals and contacting situations with very few parameters, that are obtained from the physical behaviour of the materials involved in the system. Taking into account the low complexity introduced in the system under study, the obtained results are very accurate.