A Study On Optimal Design Of Crashworthiness Of B-pillar In Passenger Car Side Impact

B-pillar, as an important assembly of passenger car side configuration, is the main component to withstand the force in the side impact. Its intrusion, intrusion velocity and deformation mode are the main causation of injuries of occupants.So the injury risk of occupants in side impact can be effectively reduced by control of deformation mode of B-pillar in a reasonable way.The thesis aims to optimize the crashworthiness of B-pillar from different aspects by using optimazation methods. At the same time, the protection of occupant's chest is improved by controlling the intrusion and intrusion velocity of B-pillar in the level of the chest region of occupants who sit in the vehicle normally.In the present study, a side impact finite element model was developed and validated. Meanwhile the saftey performance was evaluated in terms of side impact structure. Then, the crashworthiness of B-pillar was optimized from the following three aspects.(1) An improved design of the B-pillar was implemented using the tailor-welded blank structure. The location of weld and thickness of this structure were optimized by using design of experiment method and multi-objective genetic algorithm. A desired deformation mode of B-pillar was finally obtained. Its maximum intrusion was reduced by 10%. The intrusion and intrusion velocity at the middle of B-pillar were reduced by 18% and 12% respectively. The mass was reduced by 18%.(2) In order to improve the efficiency of this optimization, a side impact simplified model was developed from the whole car model. Then the significant degree betweeen the optimization variables and the objectives was assessed by sensitivity analysis. The comprehensive equilibrium method was used to optimize the match of stiffness and strength of B-pillar's components. The optimized results indicated that the intrusion and intrusion velocity at the middle of B-pillar were reduced by 12.3% and 8.5% respectively.(3) The structural optimization, which consists of size and shape optimization, was implemented by using of HyperMesh, HyperStudy and LS-DYNA software. The intrusion velocity at the middle of B-pillar was controlled under 9 m/s while the minimum mass was increased. The intrusion velocity was reduced about 8.5% compared with the former of that. The results indicate that:tailor-welded blank structure with various stiffness used in B-pillar can obtain the desired deformation mode, enhance side impact safety performance. At the same time the mass of vehicle and number of components will be reduced. This is due to the procedure of optimal designing of this structure applied in the study that can effectively balance the requirements of crashworthiness and light-weighting. The match of stiffness and strength of B-pillar has significant influences on its crashworthiness. Meanwhile, the intrusion and intrusion velocity are more sensitive to the factors of material of the components in B-pillar structure than that of thickness. There is a certain amount of reduction of B-pillar's intrusion and intrusion velocity due to the optimization of matching the stiffness and strength. If all the components of side configuration should be included during the optimization process in combination with the use of material more appropriately, the optimization results would be further improved. The structural optimization of B-pillar, which consists of size and shape optimization, can improve the protection of occupants by strengthening or weakening the local stiffness, meanwhile it does not need to change the global design of the B-pillar sturcture.