Research On Optimization Design Of Skeleton Connection Structure Of A Lightweight Electric Bus

Instead of the traditional welding method with steel thin-walled bar,the lightweight bus body frame is made of light material including aluminum alloy and high strength steel connected by thin-walled bar,which reduces the weight of the bus body frame and saves energy consumption and reduces emissions.However,when aluminum alloy and high strength steel are used at the same time,the structural properties of joints with traditional welded are reduced.In order to ensure that the bus body can achieve the effect of lightweight and improve the strength,stiffness and fatigue performance of the lightweight body frame,this paper starts with the bus body frame joint,and optimizes the structural parameters of the typical T-joint in the body frame to improve the local performance of the bus body.Firstly,the three-dimensional model of the sides and bottom transition joint of the T-bolt connection in the bus body frame is reconstructed,and its finite element model is established.Considering the bolt arrangement way affects the performance of T-joint structure,size of bolt,bolt quantity and distribution of three parameters are selected to combine,14 feasible experimental group are selected to complete the nonlinear quasi static analysis of bolted joints.Then,five design variables those are bolt diameter,center distance between the bolts,the thickness of the connecting part,the area of the ribbed plate of the connecting part and the thickness of the connected aluminum part are introduced for optimizing.The maximum deformation and maximum stress of nodes are selected as indexes.Using25 sets of orthogonal test data are applied,the functional relationship between each index and design variables is established by polynomial regression analysis method.A multi-objective optimization design model is established to minimize the maximum deformation and maximum stress of joints.Adaptive Simulated Annealing(ASA)algorithm was used to solve the optimization model,which could deal with the mixed design variables well.The results show that the optimized bolted connection design reduces the maximum stress by 71.81%,while the maximum deformation changes slightly.Finally,considering that the T-joint involves both heterogeneous materials and homogeneous materials,the thickness matching between the connecting and the connected parts is analyzed.Five thickness variables are selected as the design variables,and the robustness optimization is carried out with the fatigue cycle number and the maximum deformation of the structure as the goals.After optimization,the optimized T-joint is verified and analyzed with the local structure of bus body side.The error between the optimization results and the finite element analysis results is less than 10%.Therefore,the optimal design scheme of T-joint of steel-aluminum body frame of electric bus adopted in this paper is feasible,and can be applied to the body frame.