Research And Optimization Of Crashworthiness Of Vehicle Side Structure

Safety design for automotive side impact is one of the most important projects of safety design.In order to protect the occupants in the side impact accident,the most effective way is to absorb and dissipated collision energy by the bending deformation of the body structure which can reduce or avoid transferring collision energy to occupants through the invasion of the body structures.Through the summary of research status at home and abroad,it can be found that the research on the safety performance of side impact by using the CAE technology has important practical significance.At first,based on the finite element model for the whole car,the speed curve is obtained.The whole process of side impact is studied and the two factors which play an important role in the side impact safety are analyzed:the velocity at the end time of collision between dummy and car body and the collision timing.Based on the simplified model of side impact,what should be done to control the two factors mentioned above are to ensure that the collision force F between the MDB and the car should be as large as possible,the contact force F_bbb between the door trim and dummy should be as small as possible,the gap H between the door trim and dummy should be as large as possible.Intrusion,intrusion velocity and energy absorption characteristics are selected as the evaluation index to evaluation the crashworthiness of the structure at the design stage of the body structure without occupant restraint system.Then,based on the finite element of three point bending test,combined with the bending theory about the thin-walled.rectangular beam established by T.H.Kim et al,the thin-walled.rectangular beam is taken as the research object.The effect of material and geometric parameters on the bending behavior of the thin-walled beam under transverse load are studied.It have been found that for the material with strong strain hardening,the plastic limit strain will be higher which means the ability to absorb the bending energy is stronger.For the welding edge position design,the shape of the weak parts of the vehicle side structure should be designed to be close to the double-hat beam.For the aspect ratio of the section,the growth of the aspect ratio leads to the decrease of the moment of inertia which results in the decrease of the resistance to bending deformation.For the design of the plate thickness,if it is too large,it is not conducive to the structure complete deformation which causes waste of thickness and quality.So the selection of plate thickness should be based on actual demands.Finally,the multi-objective optimization design of B-pillar is carried out.On the basis of Latin hypercube test design method and adaptive response surface method,the thickness of the inner plate,the stiffening plate,reinforcing member of B-pillar and the height of reinforcement are multi-objective optimized.The optimal solution is obtained by using Hyperworks and LS-DYNA.The optimization of the other side of the structure is to add support frame to the weak parts of the threshold beam and to properly extend and widen the joints between the B-pillar and threshold beam.Based on the simulation,the velocity curve and the occupant survival space before and after the optimization are compared and the validity and reliability of the optimization design are verified.Under the premise of light weight design,the optimization objective of improving the crashworthiness of side structure of vehicle is realized.