Effect of oxide on friction of rail-steel roller/plate contact

In railways, when trains run through sharp curves at some low speed, there is a possibility to have wheel climb derailment. Previous researches said that the increase in the friction coefficient between a rail and a wheel is one of the reasons of the derailment. In this study, the variation of friction coefficient with the number of rolling was investigated. In order to identify mechanisms of the variation of friction coefficient with the number of rolling cycles, some surface analyses were conducted. The results of sliding tests showed that the friction coefficient was low as 0.3 below 102 cycles, then it reached the maximum value of 0.6 at 105 cycles. The results of surface analyses suggested that the variation of friction coefficient was caused by the variation of composition of oxide with the number of rolling. If the oxide on the rolling track governs the friction, the increase of friction coefficient with the number of rolling contact can be detected by the measuring the electrical resistance of the oxide made during rolling contact. In order to investigate the relation between electrical resistance of oxide on the rolling track and friction coefficient, the electrical resistance of the oxide on the rolled track was measured. It can be found that friction coefficient was a function of electrical resistance and estimated from the electric resistance.