Prediction On Vehicle Rollover Kinematics Posture And Research On Occupant Restraint System Development

As shown in National Highway Traffic Safety Administration(NHTSA),rollover crashes only account for about 2.1% of all crashes but approximately 35% of all fatal crashes in the United States in 2012.Moreover,over 7600 people died in rollover crashes in 2010,69% of whom didn't wear seat belt.Recently,SUV has gained increasing popularity among Chinese while high center of gravity of SUV causes the increase of rollover crashes.However,at present,little attention is paid to the importance of rollover crashes.Only tentative research has been conducted by Chinese researchers.And compulsory laws and standards of injury have not yet been formulated.Therefore,it is important and necessary to develop the China's safety regulations by investigating the rollover and restraint system.Rollover crashes lead to high mortality rates,which can be attributed to the following two reasons.One is that the roof sink causes the decrease of living space.The other is that the lack of efficient restraint system enables occupants to be thrown out from the seats.By adopting the methods of simulation and test,the paper aims to investigate the vehicle rollover kinematics posture and occupant restraint system.Based on the American FWVSS208 and FMVSS216 laws,the simulation models of the roof static crush and skew rolling are established in MADYMO by the methods of finite element and rigid body.The effectiveness of the established simulation models are verified by benchmarking the videos of vehicle rollover tests and simulation results.The curves about the relations between support force and the amount of intrusion are fitted according to the results of the roof static crush model.It is found that the same amount of intrusion provides different support forces at different crushing speeds,and the impact of roof's deformation on support force should be taken into consideration when the postures of rollover are studied.In the simulation model of skew rolling,the dynamic and kinematic responses of the occupant are simulated by the Hybrid III male Dummy.The motion state of the dummy in the crash and the position of the crash between Dummy and vehicle are obtained by analyzing the kinematic posture of vehicle and the motion state of Dummy.The present study conducts dynamic response analysis,and then checks the damage curves of the main parts of Dummy such as head,neck,chest and pelvis to analyze the Dummy's damage mechanism.It is found that Dummy's head,neck,chest and pelvis suffered from serious injuries.Especially,the peak resultant acceleration of the pelvis amounts to 689.98 g,which can result in huge risks of throwing out.Therefore,it is very necessary to develop the occupant restraint system under the rollover.By making Dummy wear seat belt in the model of skew rolling and referring to the injury standards in the FMVSS208,the present study analyzes the Dummy's kinematic and dynamic response.The results of simulation show that peak acceleration of chest decreases to 13.12 g and peak compression amount of chest decreases to 23.51 mm and the peak acceleration of the pelvis decreases to 6.55 g and the peak stress of neck decreases to 1830.74 N.However,the peak acceleration of head rises to 133.98 g.It is concluded that Dummy chest,pelvis and neck have been effectively protected after the restraint of three-point seat belt.Due to the poor effects of side protection of three-point seat belt,Dummy's head and B column collides,which caused serious injury of Dummy.It is hard to protect the occupants efficiently only with seat belt under the condition of rollover.Therefore,it is necessary to develop a safety airbag,which work well with seat belt.In view of the rollover characteristics of long duration and two crushes,a safety air curtain which can be combined with three-point seat belt is proposed and developed on the basis of taking into consideration the side crush protection.The shape of the curtain,the deployment position,the inflation algorithm and the gas mass flow rate are defined with reference to the Dummy's dynamic response relative to the vehicle in the simulation model.A two-stage gas generator with two kinds of trigger modes is firstly proposed and developed,which enables the developed safety curtain to protect the side crush efficiently.It is concluded that the rolling safety curtain can work well with seat belt to buffer the collision between Dummy's head and B column,which can reduce the injury of Dummy's head.The restraint system including the seat belt and safety curtains can protect the occupants efficiently in the process of rollover.