Performance Analysis Of Bolt Connection Structure For Levitation Chassis Of High-speed Maglev Vehicle

High-speed maglev vehicle has many advantages such as high speed,low energy consumption,low noise and high ride comfort.It is one of the important development directions of rail transit technology in China.As one of the core bearing components of high-speed maglev vehicle,the structural reliability of levitation chassis plays a decisive role in the operation safety of maglev vehicle.In order to meet the requirements of lightweight,the levitation chassis of maglev vehicle is made of aluminum alloy.However,the weldability of aluminum alloy is poor.The bolt connection structure with wire thread insert is mainly used between the core bearing components.This thesis takes the bolted connection structure of the high-speed maglev vehicle levitation chassis as the research object,adopts the dynamic-structural strength co-simulation method,focuses on the static strength and fatigue reliability of the bolted connection structure with wire thread insert.And the method for rapid analysis and verification of bolted connection structures with wire thread insert is explored from the perspective of numerical simulation analysis.Firstly,the influence of wire thread insert on bolt connection structure was analyzed.The three-dimensional model and finite element model of bolt connection structure with wire thread insert and without wire thread insert were established.Through finite element analysis.The magnitude and distribution of thread stress of the bolt connection structure without wire thread insert and after adding wire thread insert were obtained.The results showed that the wire thread insert can greatly improve the mechanical condition of bolt connection structure.After installing the wire thread insert,its maximum stress of internal thread was reduced by about 40%,and that of external thread was reduced by about 10%.Therefore,analyzing the performance of bolt connection structure of levitation chassis,the favorable influence of wire thread insert must be considered.It is necessary to carry out solid modeling to further analyze the performance of bolted connection structure.Secondly,the hybrid model of levitation chassis was established.According to the principle of finite element modeling and the structural characteristics of the levitation chassis of highspeed maglev vehicle,the overall finite element model of the levitation chassis was established.Using the top-down method,the levitation chassis structure was established based on the overall finite element model of the levitation chassis,and the accuracy of the substructure was checked.Considering the influence of wire thread insert,contact nonlinearity and material nonlinearity,the fine finite element modeling of the bolted connection structure of the air spring mounting seat of the levitation chassis was carried out.A hybrid model of super element and ordinary elementis was composed of substructure and refined finite element model of bolt connection structure of air spring mounting seat.Then,the static strength analysis of bolted structure was carried out.According to the actual operation of maglev vehicle,the relevant working conditions for the static strength analysis of bolt connection structure of levitation chassis air spring mounting base were formulated,and the load corresponding to the corresponding working condition was obtained by dynamic simulation analysis.The bolt connection structure of levitation chassis air spring mounting seat was analyzed by using the hybrid model of levitation chassis.The results show that the maximum stress of the bolt connection structure of the air spring mounting seat occurs in the vertical curve condition.Except for the bolt thread,the structural stress is less than its yield stress,which meets the service requirements.The stress at the bolt thread exceeds its yield stress,and plastic deformation occurs,the maximum equivalent plastic strain becomes 0.47%.Under the action of pre-tightening force and external load,slight plastic deformation at the thread is a normal phenomenon,which does not affect the normal use of the bolt.Lastly,the fatigue strength of bolted structure was analyzed.Three operating conditions of maglev vehicles were formulated,and the fatigue load spectrum of levitation chassis under corresponding working conditions was obtained by dynamic simulation analysis method.The time course of stress and strain of the bolted structure was obtained by using the method of transient dynamics.Combined with the rain flow counting method and the fatigue calculation software nCode,the fatigue strength of the bolts was evaluated by the local stress-strain fatigue analysis method,and the fatigue strength of the other bolted structures was evaluated by the nominal stress approach.The analysis shows that the minimum life of the bolt connection structure of the levitation chassis air spring mounting seat is at the internal thread of the first tooth on the inner cavity lining plate,and the equivalent life is 1.332×107 km.The results show that the static strength and fatigue strength of the levitation chassis air spring mounting seat connecting bolt structure meet the service requirements at the speed level of 600 km/h.