Simplified Modeling And Collision Analysis Of Automotive Body Structure At Conceptual Design Stage

The conceptual design is the early stage of the automobile body design,meanwhile,the design and optimization of the automobile body need to be completed under the premise of satisfying the performance of the whole automobile.The detailed model of the automobile body with shell elements needs a long modeling period,which is not suitable for the application in the conceptual design stage.However,the simplified model with thin-walled beam elements has obvious advantages in modeling time,model modification,collision optimization,etc.Therefore,it is important to establish an accurate simplified model with beam elements in the conceptual design stage.Analyzing the static and dynamic characteristics of the simplified model,modifying and optimizing the model are of great significance to shorten the research and development cycle and improve the automobile body performance rapidly.Firstly,a dummy rigid body model for frontal simulation collision is established,which defines the analytical calculation model between the automobile body structure and the dummy.The automobile model is represented by the mass and the appropriate stiffness.By deriving the equation of motion of the multi-rigid model,the MATLAB program is written to solve the implicit differential equations,and the frontal collision characteristics of the model are obtained.Secondly,the mechanical properties of beam element sections required to establish a thinwalled beam element automobile body model are derived,including section area,centroid,bending moment of inertia and torsional moment of inertia.Among them,according to the differential equation of the torsional stiffness of solid arbitrary section beams,the focus is on the solution of the torsional moment of inertia of thin-walled sections.According to the thin film analogy solution of the torsion problem,the balance equation of the torque on the crosssectional area and the shear force flow,and the geometric equations of the shear stress and the torsion angle are derived to obtain a unified calculation formula of the torsional moment of inertia of any number of cells.The finite element method is used to extract the plastic characteristics of the thin-walled beam element,and the thin-walled beam elements are used to establish a simplified model of the automobile body.Finally,the frontal collision of the dummy multi-rigid model,the frontal collision of the front longitudinal beam of the automobile and the simplified model of the body-in-white automobile are established.Compare the deformation mode,deformation displacement,velocity curve,acceleration curve and energy curve with the detailed model with the shell elements,and verify the calculation efficiency.Simultaneously,a collision optimization of the front longitudinal beam of the automobile body is carried out,and the optimal design combining the response surface and the genetic algorithm is proposed.The cross-sectional area of the front longitudinal beam is optimized under the constraints of axial crush displacement,section thickness and section length.The research results show that the beam element model has a considerable degree of computational accuracy compared with the detailed model,and has an absolute advantage in computational efficiency,which can meet the engineering requirements at the conceptual design stage of the automobile body.Compared with the finite element dummy model,the multi-rigid dummy model has better consistency in the frontal collision condition,and the modification speed of the model is faster,and the damage level of the dummy can be quickly evaluated at the conceptual design stage of the automobile.The optimized front longitudinal beam greatly reduces the cross-sectional area under the constraint condition and achieves the purpose of weight reduction.