Study On Energy Absorption Performance And Structure Optimization Of Carbon Fiber Thin-walled Round Tubes With Varying Thickness Gradient

With the improvement of living standards,more and more people own cars,and the number of car accidents is also increasing.Therefore,car collision safety is one of the issues that researchers focus on.At the same time,environmental pollution and energy shortage are becoming more and more serious,and lightweight is an important means to reduce consumption and emissions,which is of great significance to energy protection and pollution reduction.Using new materials with excellent energy absorption performance and low density to design some new structures can effectively improve the safety of vehicles and reduce the weight of automobiles..Composite materials have developed rapidly due to their advantages such as high specific energy absorption and high specific strength.They are widely used in the fields of aerospace,ships,automobiles and other fields.In some parts,composite materials are used instead of traditional metal materials,which can not only reduce the weight of the structure,but also ensure the safety performance of the structure.Therefore,it is necessary to study the crashworthiness of the composite structure,in which the carbon fiber reinforced plastics(CFRP)is the most potential lightweight material for automobile because of its light weight,high strength and good formability.In this paper,a new kind of thin-walled gradient CFRP structure is proposed.The thickness of the structure is increased in sections.The energy absorption performance of the structure is studied and optimized.The research contents are as follows:1)This chapter introduces the background and research significance of the subject,explains the necessity of vehicle lightweight,describes the energy absorption characteristics of thin-walled materials,and introduces the research status at home and abroad.2)This chapter introduces the finite element theory and related algorithms,introduces the axial crushing failure mode and theoretical model of metal thin-walled tube,and introduces the axial crushing failure mode and failure mechanism of composite thin-walled tube.3)In this section,a quasi-static compression test is performed on a gradient carbon fiber tube and a uniform CFRP tube.The compression results of the two structures are compared to analyze the energy absorption characteristics of a thick gradient CFRP thin-walled tube.The following conclusions are drawn: in the compression process,the CFRP gradient tube absorbs energy in layers,which is more effective.Although the total energy absorbed by the uniform thick tube is higher,its mass is also larger,and the final specific energy is smaller than the gradient tube.Comparing the forcedisplacement curves of the gradient tube and the uniform thick tube,it is found that the characteristic that the thickness of the gradient tube gradually increases makes its safety performance higher.4)In order to reduce the cost of the experiment and shorten the research time,after the experiment is completed,the finite element software Ls-dyna is used to simulate the quasi-static compression experiment of carbon fiber thickness gradient thin-walled circular tubes,Mat-54 material is used in LS-DYNA.According to the experimental results,the simulation material parameters are adjusted to make the simulation results approximate to the experimental results.Then,the parameters are used for collision simulation.The results show that the structure can effectively absorb energy.Then,in order to further discuss the failure mechanism of the gradient tube,the thicknesses of the second and third sections of the gradient tube were exchanged,and the simulation results showed that the gradient tube after the replacement position had better protection for the occupants.5)After the simulation parameters are adjusted,the wall thickness of the tube is used as the design variable,and the maximum energy absorption and minimum mass are used as the optimization goals.The response surface model is used to optimize the design to find a structure with better energy absorption.Pareto is selected after the optimization calculation is completed.A point on the curve is compared with the finite element simulation results to verify.