Dynamic response of vehicle and track in long downhill section of high-speed railway under braking condition

The dynamic behaviors of vehicle and track in long and downhill section of high-speed railway are studied under braking condition. A vehicle–track dynamic interaction model is constructed based on two longitudinal vehicle–track interaction models. In the model, the vehicle is considered as a 21-degree-of-freedom multi-rigid body system composed of a car body, two bogies, and four wheels; using the finite-element method, the track is modeled as a Euler beam; the “circular track” method is proposed to reduce the degree of freedom of the model for the simulation of long-distance track; two longitudinal wheel–rail interaction models are considered: the Polach creep theory (suitable for simulating condition of large creep resulting from heavy braking) and the longitudinal rigid-contact theory. The dynamic responses of the substructures during vehicle braking calculated by the models based on the Polach creep model and longitudinal contact model show little difference, but the Polach creep model can fully consider the motion of the wheels and large wheel–rail creep in the braking process and can accurately analyze the wheel–rail interface damage. The results of dynamic interaction between wheel and rail under different conditions suggest that large braking torque will cause some or all of the wheels to slide and then cause the damage of wheel–rail interface. The grade will lead to the increase in braking distance and time and also extend the sliding time of locked wheels, increasing the risk of damage of the wheel–rail interface. The braking torque should be kept below a reasonable value, so that the braking distance and braking time can be as short as possible without the occurrence of wheel sliding along the track. A reasonable braking torque under the dry track and wet track conditions should be 7 and 4 kN m respectively, according to the calculation in this article.