Head And Lower Extremities Injury Prevention Research In Car To Pedestrian Impact

For lacking of effective protection measures, pedestrian always becomes to bethe most vulnerable road users, and leads to high frequency. As accidents statisticaldata indicates that head and lower extremities are the most commonly injury parts.Therefore， extensive researches on head and lower extremities protection have beencarried out by vehicle safety experts and researches both home and abroad.This paper analysed the influence of the front structure of a car on pedestrian’shead and lower limbs injury, and the corresponding protection measures wereresearched.The Finite Element Theory and LS-DYNA software were used to develop theimpact models between adult or child head impactor and the front structure of a car,and the impact models were validated through tests. On this basis, the influence ofthe materials and thickness of the hood inside and outside as well as the materialcharacteristics and distribution of the damping rubber on the risk of head injury wasanalysed; then, the transition zone of the hood and fenders was improved to make thehead protection performance better.The Multi-body Theory and MADYMO software were applied to establish thethree typical facet models which were used to develop the impact models with theadult and child pedestrian model. Under the different front structures and speeds, theresponse time of the different height pedestrian impact with car was calculated todefine the application scope of the pop-up hood on vehicle types and speeds; apop-up hood was conceptually designed, whose head protection performance wasassessed by simulation methods.Simple impact models were developed to analyse the energy absorptionefficiency of the three materials which are commonly used to mold the energyabsorber; then, the appropriate material was chose to design the energy absorber andthe lower stiffener, and experimental design and multi-objective genetic algorithmwere applied to optimized the structure.The study results showed: When the impact location located on the “non-hard-point” area, the HIC increases as the increasing thickness of the hood inside andoutside, while the intrusion was contrary; the influence of the materialcharacteristics on the HIC and low-level natural frequencies was greater than that ofthe damping rubber spreading method. On the premise of modal requirements aremet, the damping rubber with small young’s module should be used, and the more the dispersion of rubber is, the better the head protection performance is.Considering the pedestrian kinematics response time and the protection of differentheight pedestrian, sedan is more suitable to equipped with pop-up hood rather thanMPV and SUV, and on vehicle speed,the application scope of pup-up hood should beset up from20km/h to50km/m. The energy absorption efficiency of thermoplastic isthe highest, reached78.4%, in the three energy absorber materials. After thestructures were optimized, the combined using of the lower stiffener and the energyabsorber which is a double-layer structure that made up of foam and thermoplasticcould decrease the injury risk of the lower extremities.