Abstract: China is seeing to develop the 30 t axle load railway freight car, and according to the schedule, the crossbar set used in K2 and K6 truck in which the axle load are 21 t and 25 t respectively should be used in the 30t axle load truck. Therefore, the influence of the axle load increasing to the service life of the crossbar set would be researched in advance. With the establishment for the dynamic models of three types of railway freight cars, the P64 (21 t axle load), C80 (25 t axle load) and M95 (30 t axle load), the cross bars in the three type of freight car dynamic models are set to 6 degrees of freedom (DOFs), the influences of the axle load on the freight car to the maximum force and average load on the cross bar are studied, and the forces status of the cross bar are also obtained. Farthermore, the influences of other factors such as vehicle operating velocity, curve radius and railway level to the dynamic characteristics of the cross bar are researched. Moreover, in order to predict the influence of the axle load increasing to the service life of the crossbar set, a method to calculate the equivalent loads of the crossbar set is advanced. The calculating measure contains the contribution of the load level and load acting frequency to the equivalent loads. By use of the equivalent loads of crossbar set under the three type of the freight car and the service life of the crossbar set, the service life of the crossbar set under 30 t axle load freight car is predicted. The results show that the service life of the crossbar set under 25 t and 30 t axle load freight car are decreased to 82.6% and 76.2% of the former respectively. The way advanced is a new method to study the influence of the axle load to the structure service life after integrating the vehicle system dynamics and the structural stress, and it is very helpful to solve the similar engineering problems.

Key words: Axle load, Crossbar set, Equivalent load, Railway freight car, Service life, Vehicle system dynamics