Research On Key Issues Of Train Collision Dynamics

In order to solve the nonlinear problems of train collisions, the theory of train collision dynamics is constructed. Three topics are studied in depth, including the nonlinear problems of carbody materials, time integration algorithms of nonlinear vibration systems and modelling of train collision dynamics, etc.Firstly, the theoretical framework of the train collision dynamics is described. The research scope, the research contents and the research method of the train collision dynamics are indicated in the framework. The appropriate vehicle models and track models are summarized in the theory. Moreover, various time integration methods are given according to the form of equations of motion.Secondly, the nonlinear problems of carbody materials are studied by means of a series of material tests. The dynamic stress-strain curves of the carbody materials are obtained by employing dynamic impact tests. The dynamic constitutive models of the 5083H111 aluminum alloy, the Q235 steel, the Q345 steel and the HC340/590DP dual-phase steel are built based on the Cowper-Symonds model and the Johnson-Cook model. In addition, the strain rate effect and the influence of strain rate effect on an energy dissipation device are studied and analyzed. The results show that the 5083-H111 aluminum alloy is endowed with negative strain rate sensitivity at low strain rates, and possesses the feature of negative and then positive strain rate sensitivity in the range of medium-low strain rates. The practical absorbed energy of the structure made of 5083-H111 alloy is less than that of the same structure designed in terms of the quasi-static stress-strain curve. The strain rate effect of the alloy can't be ignored.Moreover, the corrected explicit method of double time steps (CEMDTS) and the acceleration explicit method which possess the highest second-order accuracy are proposed on the basis of the assumption of accelerations and the Taylor's formula. The generalized multi-step explicit method with higher accuracy is developed by means of the inductive method. The generalized multi-step explicit method can be third-order accurate or higher. Moreover, the stability, numerical dissipation, numerical dispersion and accuracy of the proposed methods are analyzed in a linear vibration system. The results show that the CEMSTS and the acceleration explicit method (?=1, ?=?) are conditionally stable, and the stability interval is ?t? (0,2/?) in undamped systems. The algorithms possess the characteristic of critical stability. The stability interval decreases with the increasing damping ratio. The generalized multi-step explicit method is endowed with the similar stability. The proposed methods possess the identical properties of the numerical dissipation and dispersion. The numerical dissipation is zero, and the numerical dispersion is identical to that of the central difference method. In contrast to the other algorithms, the proposed methods are endowed with good stability, medium accuracy and the highest computational efficiency in nonlinear systems.Finally, a vehicle moving-track model of the longitudinal plane and a 3D vehicle moving-track model are developed. A comprehensive dynamic model of the train collision is further integrated on the basis of the vehicle moving-track model of the longitudinal plane and the 3D vehicle moving-track model. The models of couplers and anti-climbing energy-absorbing devices are applied to connect the adjacent vehicle models. The effect of different algorithms on the vibration response is studied in nonlinear vehicle systems. In addition, the influence of different vehicle models and track models on the dynamic response of vehicle collisions is investigated by employing the vehicle track models mentioned above. Furthermore, the dynamic model of the train collision are adopted to deeply study the overriding phenomenon of train collisions, the critical speed of overriding and the vehicle parameters having influence on overriding. The results manifest that the precise integration method and the standard Runge-Kutta method (RK4) are applicable to the nonlinear vehicle systems with a few degrees of freedom and a high requirement of accuracy. The Zhai method and the CEMDTS are appropriate for the nonlinear vehicle systems with a large number of degrees of freedom, medium accuracy and high computational efficiency. When only the longitudinal collision is considered, the vehicle moving-track model of the longitudinal plane and the 3D vehicle moving-track model possess the identical response in the longitudinal plane. Moreover, the relationship of the wheel rise height and the speed is nonlinear. The wheel rise height is tiny when the collision speed is far bellow the critical speed of overriding. If the collision speed is close to the critical speed of overriding, the wheel rise height may increase in exponential order. The wheel rise height increases with the increase of the collision speed, the collision mass and the height of the center of mass. In contrast, it decreases with the increasing vertical stiffness of the secondary suspension. The collision speed has the largest influence on the wheel rise height, followed by the collision mass and the height of the center of mass. The behavior of the car bodies and the couplers for the active train and the passive train is regular in the processes of train collisions. The attitude of car bodies and couplers has mirror reflection symmetry with respect to the collision interface.