The Railway Technical Research Institute (RTRI) has investigated the characteristics of the creep force between wheel and rail when a wheel starts to climb the rail. A vehicle running test was also carried out, then the wheel/rail contact force and wheelset behaviors were measured from the beginning of flange climbing to derailment. From these test results, the following were clarified.

(1) The total creep force in the flange contact area of outer rail and wheel is always saturated. The longitudinal creep force increases as the wheel climbs higher, while the lateral creep force that will cause derailment decreases in relative terms (Fig. 1). Simulation models for creep forces were improved by using these test results. It was confirmed that the results of simulation analysis such as wheel load, lateral force, angle of attack and height of wheel flange climbing agreed with the data measured in the running test (Fig. 2). This simulation makes it possible to accurately estimate the height of flange climbing under various conditions of track and train operation.

(2) In the field test, the attack angle of wheelset was measured when the flange of outer wheel was in contact with the rail gauge corner by a newly developed on-board measuring instrument. The obtained data show that the angle of attack decreases as the wheel climbs approximately 10 mm, and then increases as the wheel climbs further (Fig. 3).

(3) When flange climbing starts, there is a definite relationship among three indexes, the derailment quotient, ratio of off-loading on the outer rail side wheel and ratio of lateral force to wheel load on the inner rail side (Fig. 4). Derailment tends to occur with increases of frictional coefficient between wheel and rail, which is related to the ratio of the lateral to vertical force on the inner rail side wheel.

(4) The data of friction coefficient measured on commercial lines show that the value tends to be smaller when relative humidity is high and the number of axles passing per time unit is small (Fig. 5). In track sections where trains do not run frequently, it may be appropriate to evaluate running safety by assuming a small friction coefficient between wheel and rail.
  Based on the results above described, we plan to propose appropriate criteria and a method to more accurately evaluate the running safety against derailment. This study was subsidized by the Ministry of Land, Infrastructure and Transport.