Research On Lightweight Design Method Of Fatigue Life Such As City Bus Skeleton

Lightweight is the key common technology of traditional bus and new energy bus,and it is one of the important directions of the current development of passenger car industry in the world.The research and application of lightweight technology for passenger cars is the need to realize energy saving and emission reduction,adjusting the industrial structure and improving the ability of independent innovation.The main technologies are structural optimization design,the application of lightweight materials and the implementation of advanced manufacturing processes,etc..With the structure size optimization method as the main stream,the advanced structural optimization design method plays a key role in the field of light weight of the passenger car.In this paper,the lightweight design of bus frame is selected as the research topic.Skeleton structure is the main bearing part of a large city bus,and it must be realized in the premise of ensuring the strength,rigidity and fatigue performance.In the past,only the static stiffness and strength of the size optimization method has certain limitations,it is difficult to achieve the best layout of the material.Therefore,the theory and method of optimization of bus frame structure are put forward.In view of the above requirements,this paper puts forward the theory of lightweight design method of fatigue life and the application of lightweight design for a city bus:(1)Establish the vehicle multi-body dynamics simulation model,as well as the B level road model.The dynamic peak force of the key connection point of the bus in each condition is extracted as the boundary condition of the finite element analysis.The three-dimensional model of the skeleton is established,and the model is simplified,and the finite element model is established,and the finite element analysis is carried out.(2)The condition of finite element results,p-S-N curve of power function formula of logarithmic expression is obtained,and the cyclic load spectrum of frame fatigue calculation,and the establishment of the single mode in the fatigue life of the lightweight model.(3)Taking a passenger car as an example,a case study is made on the case of the lightweight method of the skeleton of the dangerous condition and the fatigue life of the skeleton.Based on the design optimization of the framework of the dangerous conditions,the quality is reduced by 8.84%.The method is based on the whole working condition and other life framework design,which is 11%.(4)The static and dynamic characteristics of the bus skeleton model under the two methods are checked.Based on the maximum stress of the lightweight skeleton model of the dangerous condition,the safety factor is 283 MPa,the safety factor is 1.22,which meets the design requirements;the maximum deformation of the skeleton is less than50 mm,which satisfies the design requirements of the frame stiffness.The minimum fatigue life is 6.21 × 105,less than the bus frame life expectancy,cannot meet therequirements of bus use,and each part of the fatigue life of dangerous point difference of nearly 1,the fatigue life of skeleton uneven distribution of skeleton material is not fully utilized.The performance comparison of the skeleton model of fatigue life under the condition of full load and the lightweight skeleton model based on the dangerous condition is performed.First establish the frame finite element model considering dynamic peak force,through the analysis of the fatigue life of frame model with slow operating conditions the maximum stress is 259 MPa,the safety factor is 1.3,comply with the design requirements;the maximum deformation of the skeleton are less than 50 mm,meet the skeleton stiffness requirements.The five part of the fatigue life of the relative difference is less than 0.5,the skeleton of fatigue life distribution is uniform,the skeleton material utilization rate is better,the fatigue life and the fatigue life of the most dangerous points are less than the condition of fatigue life model the most dangerous point is 9.21×105,greater than the fatigue life of bus passenger traffic requirements meet the expectations.Finally,the modal analysis of the body frame,it is concluded that the natural frequencies of the first 10 order modes of the body frame are all in the range of 5to 12 Hz,and the frequency of the excitation source can be avoided effectively.To sum up,the whole condition of fatigue life optimization method of bus frame optimization design can make better frame lightweight effect at the same time,the framework can achieve better performance level,the skeleton can not only meet the requirements of strength,stiffness and fatigue life of the frame,each part of fatigue life distribution is uniform,the skeleton material utilization rate is more well,the skeleton structure can effectively avoid the excitation frequency.Based on the full operating conditions and other fatigue life of the body frame lightweight analysis method for the passenger light weight has good applicability and value.