| The energy crisis and environmental pollution problems are significant owing to the increasing of vehicle population.Lightweight design is an effective way to handle aforementioned problems.The mass of white body accounts for about 20%-30% of the total vehicle mass,which is an important focus of the vehicle lightweight.At present,the most direct and effective means to achieve lightweight body is to use lightweight materials.Steelaluminium hybrid has become an important development direction of material combination to better balance crashworthiness and lightweight of car body.As a cold joining technology,selfpiercing riveting(SPR)can be used to join same and different materials.The SPR technique has been widely applied in steel-aluminium hybrid body owing to the advantages of the simple process,high connection efficiency and reliable connection strength of joints.However,there are still some problems during the actual engineering application process,such as: How to guarantee the quality of steel-aluminium hybrid SPR forming process under different combinations of material strength and thickness;It is difficult to construct the high precision numerical simulation model of SPR joint;The calculation cost and cycle of the detailed numerical model for SPR joint are high;Lacking of a new body thin-walled structure with consideration of lightweight and crashworthiness from the aspects of structure crushing energy absorption mechanism and material matching design.In order to handle the above problems and promote the application of SPR technique in steel-aluminium hybrid car body,this paper carried out the following specific research work:(1)The evaluation metrics of SPR joinability is proposed by analysing the characteristics of SPR forming process and a process design window of material strength and thickness distribution is constructed,which can provide design guidance for the application of SPR technique in steel-aluminium hybrid materials.A 2D axisymmetric numerical model is constructed based on r-adaptivity method to simulate the SPR forming process.The accuracy of the numerical model is subsequently validated by comparing the cross-sectional shape of SPR joint between test and simulation.An evaluation metrics of SPR joinability is proposed by analysing the typical defects of SPR forming process.The design range of material strength and thickness for joinable SPR joints is obtained by exploring the effects of material strength and sheet thickness on the SPR joinability and process quality indexes.A qualified SPR joint with good connection strength can be obtained based on quality evaluation standard of SPR forming process,and a process design window of material strength and thickness distribution for steelaluminium hybrid SPR is constructed.(2)A novel generation method of detail 3D finite element(FE)model of SPR joints is proposed.The mechanical response and deformation behavior of steel-aluminum hybrid SPR joints under different loading conditions are analyzed,and the failure mechanism of typical SPR joints is revealed.The mechanical properties of the B280 VK high-strength steel and 6063-T6 aluminium alloy are obtained by performing the quasi-static and dynamic uniaxial tension tests.The Johnson-Cook constitutive and failure model of B280 VK steel and 6063-T6 aluminium alloy are constructed,which can provide model support for material failure simulation of SPR joints.The mechanical response of SPR joints under quasi-static and dynamic loadings are compared in detail by experimental tests and the failure mechanism of typical SPR joints is revealed.A novel generation method of detail 3D numerical model of SPR joints is proposed and the FE model of SPR joints is established,which is validated by tests.The total effect generation method is proposed and the relationships between process parameters,process quality indexes and mechanical response of SPR joints are parametrically investigated based on the proposed generation method.The above study results can provide reference for the design of process parameters of steel-aluminum hybrid SPR technique.(3)The equivalent simplified model of self-piercing riveting joint(SPR-ESM)is established by the constrained model of CONSTRAINED＿SPR3＿IWM,and the simulation accuracy of the SPR-ESM under different loading conditions is validated by tests,which can realize the efficient numerical characterization for steel-aluminum hybrid SPR joints under multiple working conditions.The mechanical mechanism of the two constrained models of CONSTRAINED＿SPR3 and CONSTRAINED＿SPR3＿IWM is compared,which can provide theoretical basis for the construction of steel-aluminum hybrid SPR-ESM.The parameter calibration process of SPR-ESM based on CONSTRAINED＿SPR3＿IWM is established,and the parameters of the SPR-ESM are reversed by software of LS-OPT.The mechanical response of shear,peeling and cross-tension SPR-ESM under quasi-static and dynamic loadings are analyzed,and the accuracy of the three SPR-ESM are validated by tests.An interactive window for the CONSTRAINED＿SPR3＿IWM constraint model is created based on Tcl interface provided by Hyper Mesh,which can realize the fast modeling of SPR-ESM.(4)An innovative steel-aluminum hybrid hat-shaped tube with strengthened corner structures(HT-SCS)is proposed,which can considerate the lightweight,crashworthiness and material cost.A theoretical prediction model is developed,which can be directly used to predict the of the mean crushing force(MCF)of the HT-SCS with different material and thickness combination.The accuracy of the theoretical prediction model and numerical simulation model are subsequently validated through axial crushing tests.The Pareto optimal frontiers based on theoretical prediction model and numerical surrogate model are compared by performing multiobjective optimization design for HT-SCS.The application of SPR technique in automobile crash safety is investigated by constructing the FE model of front longitudinal beam based on SPR-ESM,and the crashworthiness performance of the front longitudinal beam before and after optimization is compared. |
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