The Analysis Of Strength And Fatigue Properties Based On The Random Vibration For A Steel And Aluminum Frame Of An Electric Bus

With the continuous depletion of the global energy, the deterioration of the environment and the increasingly prominent problem of traffic congestion, the pure electric city bus with the characteristics energy saving and environmental protection comes into the people’s daily life, drawing more people’s attention. And its safety performance, fatigue life and light weight has become the research focus of a large number of research institutions and car enterprises.This paper takes the frame structure of steel-aluminum composite body in a certain type of pure electric bus as the object of study, using the ANSYS to analyze the static strength, modal, random vibration and fatigue life of the frame structure in light of the finite element analysis method, and makes the structure optimization according to the analysis of the static strength at last. Specific research contents are shown as follow:(1) The finite element model of the steel-aluminum composite body frame structure is established. Three-dimensional geometric modularized models of chassis, roof, left-side body, right-side body, the front and rear body in CATIA are established according to the existing drawings and data, and then imported into Hypermesh to establish the finite element model of the steel aluminum composite body structure.(2) Making the static strength analysis of steel aluminum composite body frame structure. Calculating and analyzing the strength and stiffness of steel-aluminum composite body frame structure aiming at five typical conditions of buses in actual operation in detail : bending condition, starting condition, braking condition, right-hand bend condition, and twisting working condition, obtaining the stress and deformation circumstances under various working conditions, and making the corresponding evaluation which leads the improvement direction for optimization.(3) Making fatigue life analysis of steel-aluminum composite body frame structure based on random vibration. Firstly, the modal analysis is carried out to obtain the first 20 natural frequencies and mode shapes of the structure. Making the structural random vibration analysis of based on the modal analysis, getting the power spectral density curve of displacement, velocity and acceleration in the place of maximum deformation and the steel structure and aluminum alloy structural part 1σ stress value in the steel aluminum composite body frame structure at the same time. Finally using the obtained 1σ stress value to calculate the fatigue life of the steel structure and aluminum alloy structure according to three interval method which Steinberg proposes based on Gaussian distribution and Miner linear fatigue cumulative damage rule in order to obtain the fatigue life of the whole frame structure.(4) Optimizing frame structure based on the analysis of the static strength. Based on the results of static strength analysis, the partial structures of body frame are improved according to design experience. On the basis of strength and stiffness guarantee, the structure of the stress and deformation distribution becomes more uniform and achieves the goal of reducing weight of body frame.