Dynamic Modeling And Ultimate Bearing Capacity Analysis Of Box Girder Structure At Train End Under Impact

Along with the economy and technology,in recent years,the train is developing towards lightweight and high speed,which leads to the decrease of overall stiffness and increase of flexibility of the carbody structure.In the process of train collision,when the load borne by the train body exceeds the design load and reaches the ultimate bearing state of the train body structure,it will lead to the collapse and damage of the train body structure.In addition,the dynamic ultimate bearing capacity of the vehicle body structure is larger than the static ultimate bearing capacity.The vehicle body structure design method based on the static ultimate bearing capacity will cause the mass redundancy of the vehicle body structure.Therefore,it is an urgent problem for train designers to reasonably evaluate the ultimate strength of the carbody structure under impact load.Compared with the static ultimate strength research of the carbody structure,the dynamic ultimate strength research of structures needs to consider the effects of structural inertia effect,material strain rate effect and dynamic buckling mode.Due to the complexity of carbody structure,there are many problems in using analytical method and empirical formula to predict structural ultimate strength.Therefore,how to accurately analyze the ultimate strength of vehicle body structure under collision load is of great significance for the safety and lightweight design of train structure.Combining orthogonal Legendre polynomials and coordinate transformation matrix,a modified differential quadrature technique is proposed.By using the discretization way,the perforated plate and tube beam structure are discretized into four quadrilateral elements,and the calculation domain is transformed respectively.Then,the spring component method is used to calculate the coupling boundary stiffness matrix of the discrete structure with perforated plate and tube beam.According to the elastic-plastic stress renewal method,the elastic-plastic numerical calculation model of plate and tube beam structure is established.Finally,the dynamic response and critical buckling load of perforated plate and pipe beam under lateral and axial loads are analyzed and verified by using the numerical model.The results show that the numerical model can meet the dynamic elastic-plastic characteristics analysis of beam plate structure.Based on the modified differential quadrature method,the singularity criterion of stiffness matrix and the elastoplastic constitutive model,the dynamic characteristics of plate,perforated plate and tube beam under dynamic pulse load are analyzed.The effects of initial deflection,compression-shear coupling load,aspect ratio and loading time on the dynamic characteristics and bearing capacities of beam plate structure are discussed.The results show that the initial imperfections,coupling load,aspect ratio and loading time have great influence on the ultimate strength of beams and plates.In addition,the larger the loading time is,the smaller the ultimate bearing capacity of the beam and plate is.When the loading time is larger,the ultimate bearing capacity of structures nearly remains same as the loading time continues to increase.In addition,the influence of opening size and location on the ultimate bearing capacity of perforated plate is discussed.Aiming at the ultimate bearing capacity of beam plate coupled structure under axial compression load,this paper applies spring element to deal with the problem of beam plate coupling to ensure the coordination of beam plate deformation,and studies the dynamic and static ultimate bearing capacities of beam plate coupled structures under axial compression load.The modified differential quadrature method is used to analyze the effects of loading time,edge restricted stiffness,initial deflection,coupling load on the dynamic characteristics of beam plate coupled structures.The results show that the increase in the edge restricted stiffness gradually results in the increase of the dynamic,static ultimate bearing capacities of the beam plate coupled structure under dynamic pulse load gradually,but the dynamic static ratio of the ultimate bearing capacity nearly remains same.In addition,the dynamic characteristic analysis method of beam plate coupling structure under pulse load is verified by experimental method.Compared with the coupling structure of the plate and beam,the box girder of train body section can better reflect the dynamic characteristics of the train under pulse load.The coupling structure of the plate and beam is the basic element of box girder structure.According to the research on the coupling structure of the plate and beam,this paper presents a structural element discretization method,which discretizes the box girder into a series of coupling structures of the plate and beam and analyzes the dynamic response of the box girder structure under dynamic pulse load by using the spring element method.The box girder is affected not only by the external pulse load,but also by the geometry of the box girder section.Therefore,the modified differential quadrature method combined with singularity criterion of stiffness matrix is used to analyze the influence of initial deflection,loading time and tube beam geometric dimension on bearing capacities.It is found that the initial deflection,loading time,aspect ratio and tube beam geometric dimension have affected the dynamic bearing capacities of box girder structures markedly,while the effect of aspect ratio and tube beam position is relatively small.In addition,a series of box girder models are designed to study the ultimate bearing capacity and failure mode of box girder structure under different speeds,and the numerical method is verified.Finally,according to the results of parametric analysis,a fast prediction formula of dynamic ultimate bearing capacity of box girder with initial deformation is proposed.The box girder structure at the end of the train is selected as the optimization design model.Based on the research of dynamic ultimate bearing capacity of box girder structure,the shape and size of the structure are optimized by response surface method,in which the ultimate bearing capacity is the optimization constraints and the lightest weight is the optimization objective.The results show that the mass of the optimized box girder structure is reduced by 19.70%.In addition,finite element method and MDQM are used to verify the optimization results.