| The lightweight and safe design for automobiles are the key technical means to realize the three major design and development themes of automobiles,namely energy saving,environmental protection and road safety.Lightweight and crashworthiness are two important performances of automobile body that contradict each other and restrict each other,and the lightweight and crashworthiness optimization design of the automobile body is an important constituent part of the lightweight and safe design of the car and the core key technology.As the most critical connection and load-carrying vehicle component,the lightweight and crashworthiness design of the automobile body must be coordinated with the basic performance of the automobile body,which is a typical multi-parameter,multi-constraint and multi-objective complex system engineering problem.How to scientifically carry out the lightweight and crashworthiness optimization design of the automobile body is a very important research topic,research hotspot and difficulty in the current automotive industry.At present,the relevant posted studies mainly concentrated on the lightweight or crashworthiness optimization design for single or small parts of the automobile body structure,while seldomly focused on the systematic lightweight and crashworthiness multi-objective collaborative optimization design for the automobile body as a whole,thus the lightweight and crashworthiness optimization design of the automobile body structure still lacks a systematic design process and method.Secondly,the influence of material cost or other uncertainties on the optimization design results of lightweight or crashworthiness optimization of automobile body structure,is seldomly considered in the reported studies,resulting in the low feasibility and availability of optimization design results.Thirdly,the multi-objective optimization design results are not effectively integrated with multi-criteria decision-making(MCDM)methods,so the selection of multi-objective optimal design scheme often lacks certain theoretical basis.Accordingly,this paper takes a self-owned brand car body as the research object,which was deterministically and nondeterministically lightweight and crashworthiness multi-objective optimized from the component level and body assembly level with the consideration of uncertainties through a combination of the numerical and experimental methods,the sensitivity and contribution based design variable screening methods,the multi-objective experimental design methods,the multi-objective optimization metamodel methods,the multi-objective optimization algorithms and the multi-criteria decision-making methods and the structure-material-performance-cost integrated optimization design method,and thus establishing a complete lightweight and crashworthiness multi-objective collaboration optimization design method for automobile body structure and achieves the sumultaneous improvement of the lightweight and crashworthiness level of the automobile body.It successfully solves some common and key problems in design and development for autobodies,and thus has important theoretical and methodological significance,as well as enormous engineering application value.Main research work and conclusions of the present study are as follows:(1)The research status of lightweight-crashworthiness optimization design of automotive body parts at home and abroad was reviewed,the most popular lightweight and crashworthiness design technologies of automobile body were summarized,some shortcomings of existing research were summarized,and the main research contents of this paper were put forward and the chapters of this paper were carried out.(2)The key theories and methods of multi-objective optimization design,including the multi-objective experimental design methods,the multi-objective optimization metamodel methods,the multi-objective optimization algorithms,especially the multi-criteria decision-making(MCDM)methods seldomly introduced or applied in exsited studies,including the ideal point method(IPM),the entropy-TOPSIS method and the grey relational analysis(GRA),were introduced in detail.(3)The white automobile body FE model was established,which was verified through the combination of numerical and experimental analysis of NVH basic performance of automobile body,and thus the optimization indicators of the automobile body,including the total mass and the NVH basic performance,were extracted.On this basis,the FE model of the whole vehicle was established by using the modular modeling method.Referring to the 2012 version of C-NCAP passive safety regulations,the vehicle 100%-FRB and 40%-ODB frontal impact and MDB side impact were separately established and verified through corresponding vehicle crash tests.The frontal and lateral crashworthiness of the body were then analyzed and thus the automobile body crashworthiness optimization indicators were extracted.(4)Taking the energy-absorbing box,one of the key components of the automobile body,as the research object.Firstly,considering the influence of the uncertainty of the impact angle in the actual vehicle crash condition,the multi-angle impact crashworthiness model of the energy-absorbing box was established and then experimentally verified,thus its intial crashworthiness characteristics were analyzed in detail.Next,in order to further improve its energy absorption potential,the original hollow thin-walled energy-absorbing box was filled with metal aluminum foam,and the influence magnism of four different filling methods on the energy absorption characteristics of the energy-absorbing box were analyzed in detail.On this basis,the optimal aluminum foam-filled energy-absorbing box was selected as the research object.Firstly,the influence of its structural parameters(inner and outer panel thickness,foam density)on its crashworthiness characteristics were analyzed.Then,taking its structural parameters as design variables,the aluminum foam-filled energy-absorbing box was lightweight and crashworthiness multi-objecgtive deterministically optimized and subsequently verified.(5)Taking the aluminum foamed-filled energy-absorbing box as the design object,which was lightweight and crashworthiness multi-objective robust optimized using the 6-Sigma and the proposed Grey-Taguchi multi-objective robust optimization design method respectively in this paper,mainly considering the uncertainties of structural parameters(inner and outer plate thickness,foam aluminum density)or material properties(density,elastic modulus,Poisson’s ratio and yield strength)of the energy-absorbing box.Consequently,a more reliable and robust optimization design of aluminum foam-filled energy-absorbing box was obtained and verified.(6)Integrating the nondeterministic optimal result of the above-mentioned foam-filled energy-absorbing box back to the original automobile body structure,which was then taken as the research objective to be lightweight and crashworthiness deterministically optimized.The details are as follows: Firstly,the automobile body assembly was devided into frontal safety components,side safety components and non-safety components according to the correlation with crashworthiness performance of automobile body,for which the batched lightweight and crash-worthiness multi-objective deterministic optimization design strategy was formulated.Secondly,for the non-safety components,the structure-performance integrated lightweight multi-objective deterministic optimization design was carried out and verified with the consideration of the total mass and the NVH basic performance of automobile body through a combination of the sensitivity analysis method,the RBF metamodel method,the NSGA-II algorithm and the IPM method.Thirdly,for the frontal safety components,the structure-material-performance-cost integrated lightweight and crashworthiness multi-objective deterministic optimization design was carried out and verified with the consideration of the total mass,the NVH basic performance,the frontal crashworthiness performance of the automobile body and the material cost of the frontal safety components through a combination of the contribution analysis method,the RBF-RSM hybrid metamodel method,the MOPSO algorithm and the entropy-TOPSIS method.Next,for the side safety components,the structure-material-performance-cost integrated lightweight and crashworthiness multi-objective deterministic optimization design was carried out and verified with the consideration of the total mass,the NVH basic performance,the side crashworthiness performance of the automobile body and the material cost of the side safety components through a combination of the contribution analysis method and the grey relational analysis(GRA)method.Finally,optimal lightweight and crashworthiness multi-objective deterministic design schemes for the above-mentioned non-safety components and safety components of the automobile body were synthesized,and the final lightweight and crashworthiness multi-objective deterministic optimization design scheme of the automobile body structure was obtained and then validated,thereby establishing the lightweight and crashworthiness multi-objective collaborative deterministic optimization design method for automobile body assembly.The results show that,the automobile body achieves simultaneous improvement of lightweight and crashworthiness levels under the premise of basically guaranteeing the NVH basic performance and material cost.Therefore,in this paper,the lightweight and crashworthiness multi-objective optimization design for the automobile body structure,including the deterministic and nondeterministic optimization design for the key components of automobile body,and the deterministic optimization design for the automobile body assembly,are reasonable and effective,thus establishing a complete and effective set of lightweight and crashworthiness multi-objective collaborative optimization design method for automobible body structure. |
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