Modelling Friction Stick-Slip in Heavy Haul Draft Gears

Despite the well-known variability of friction conditions in friction damping systems it is often assumed by necessity that ‘typical’ friction conditions exist in all friction components in a larger system. Following some surprising results in laboratory tests of friction type draft gears modelling of stick slip behaviour has been attempted. The modelling of friction and wedge geometry was carried out as in earlier studies [1–4]. A maximum force criterion was used to model the point at which slip occurred. As it was expected that large dynamical system will usually mask effects from one or two connections exhibiting different friction behavior, the effects were simulated on a large heavy hail train system. It was found that if the stick-slip behaviour was possible in the force range, then the system could be significantly affected, with in-train forces being doubled in the case presented. The case, however, overstates the problem, as it would be very unlikely that such stick-slip behaviour would exist in all connections. The implications are discussed.