Study On The Thermal Influence On The Steel-aluminum Clinch-adhesive Connection Structure Of The Car Body

With the increasing of cars in domestic,a series of social problems such as air pollution,traffic congestion,and energy crisis are becoming increasingly serious.It is imperative to reduce the weight of cars.The steel-aluminum hybrid car body structure has obvious advantages in reducing the weight of the car body,and has attracted extensive attention from car companies and universities.Therefore,how to ensure the reliability of the connection of steel and aluminum dissimilar materials parts has become an urgent problem to be solved.The steel-aluminum clinch-adhesive connection technology combines the advantages of clinching bonding and adhesive bonding technology,which can effectively solve the problems of intermetallic compounds and electrochemical corrosion caused by the differences in physical and chemical characteristics of different materials.Under the modern automobile manufacturing system,the body must be coated.However,the thermal expansion characteristics of steel and aluminum materials are quite different.During the coating process,the thermal expansion of the steel and aluminum connected together is different,which will may lead to the deformation of the steel-aluminum clinch-adhesive connection of the car body.It may affect the connection strength and assembly accuracy of the body structure,and may even lead to the failure of the steel-aluminum clinchadhesive connection.Therefore,the thermal influence of the coating temperature on the steel-aluminum clinch-adhesive connection structure of the car body cannot be ignored.This paper relies on the National Natural Science Foundation of China(5177050834): Research on the manufacturing technology and service failure of warm clinch-adhesive joints of steel/aluminum dissimilar materials for body structure,and studies on the thermal influence of the coating temperature on the steel-aluminum clinch-adhesive connection structure of the car body.The main research contents of this paper are as follows:1.Material testing and verification.Q235 steel,5754 aluminum alloy,and DP760 epoxy resin adhesive were selected as the research materials.First,uniaxial tensile tests at different temperatures were carried out to obtain the stress-strain curves of steel,aluminum,and adhesive in the range of 20 ~ 200?.Then,the thermal expansion tests of the materials were carried out,and the linear expansion coefficients of steel,aluminum and adhesive materials in the range of 20 to 200°C were obtained.Finally,the thermal expansion finite element models of the materials were established.The errors between the simulated values and the theoretical values were less than 2%,which verified the accuracy of the three material thermal expansion models,and proved the accuracy of the measured material parameters.2.Thermal expansion test and simulation research of the steel-aluminum clinchadhesive connection structure.First,the thermal expansion test of the steel-aluminum adhesive bonding structure and the clinch-adhesive connection structure at the coating temperature were carried out to obtain the strain values on the surface of the steel and aluminum sheets at 200?.Then,a finite element model of thermal expansion of the steel-aluminum adhesive bonding structure was established.Tie bonding was used to simulate the adhesive bonding of steel and aluminum sheet.The error of the simulation results compared with the test results was less than 10%,which verified the accuracy of the thermal expansion model of the adhesively bonded structure and the rationality of the selected bonding simulation form is shown.On this basis,the Tie bonding connection form was used to establish the thermal expansion finite element model of the steel-aluminum rubber riveted connection structure.The error of the simulation results compared with the test results was less than 10%,which proved the accuracy of the steel-aluminum clinchadhesive connection structure thermal expansion model.Finally,based on the simulation results,the distribution and variation of thermal stress and thermal deformation in the clinch-adhesive connection structure were analyzed.The simulation results showed that under the temperature conditions of the coating process,the thermal stress in the clinch-adhesive connection structure increased rapidly,and the structure warped significantly.After lowering to 20?,there was large residual stress in the clinch-adhesive connection structure,the stress concentration at the neck of the clinchadhesive joint,the edge of the sheets and the adhesive layer were serious,and there was plastic deformation in the structure,indicating that the problem of thermal influence on steel aluminum clinch-adhesive connection structure of the car body cannot be ignored.3.Research on the thermal influencing factors of the steel aluminum clinchadhesive connection structure.Based on the established finite element model of the steel-aluminum clinchadhesive connection structure,the influence of the thickness of the adhesive layer,the elastic modulus of the adhesive,the structural overlap width,the clinching sequence of the metal(aluminum clinching to steel,steel clinching to aluminum),the layout of the clinching points(horizontal layout and vertical layout)on the thermal stress and thermal deformation of the steel-aluminum clinch-adhesive connection structure were studied.The simulation results showed that the thickness of the adhesive layer,the elastic modulus of the adhesive,and the width of the structural overlap had great influence on the thermal stress and thermal deformation of the steel-aluminum clinchadhesive structure.The influence of the clinching sequence of the metal and the layout of the clinching points on the structure was limited.The results of the study provided a reference for improving the thermal influence of the steel-aluminum clinch-adhesive connection structure of the car body.