A study of the phenomenon of wheel climb derailment: Results of basic experiments using model bogies

Abstract

Wheel climb derailment sometimes occurs when a train passes through a steep curve on a railway track at low speeds. The authors conducted experiments on the phenomenon of wheel climb derailment using model bogies and a model track. The Nadal formula (Nadal limit) is used to evaluate the risk of derailment. Because the friction coefficient between the rail and the wheel has a considerable influence on the critical values to be calculated using the Nadal formula, it is inappropriate to evaluate the risk of derailment by using the Nadal formula alone. The risk of derailment can be determined in a straightforward way by measuring the wheel vertical displacement. In this study, to measure the wheel vertical displacement accurately, a high-precision laser displacement sensor was used. The experimental results revealed that a wheel both slips downwards and climbs up simultaneously and that vertical displacement of the wheel occurs when the degree of wheel climb-up exceeds the degree of wheel slip-down. Although the friction coefficient between the rail and the wheel is a primary factor responsible for causing wheel climb derailment, measurement of the friction coefficient is difficult to achieve. Therefore, a model slipping adhesion bogie was used to measure the adhesion coefficient instead of the friction coefficient. The data obtained from the experiments were analysed in order to verify the relationship between the adhesion coefficient and the wheel climb-up behaviour. As a result, it was found that the adhesion coefficient has a major influence on the occurrence of wheel climb derailment.