The Research On The Rollover Characteristics Of Passenger Vehicle And The Countermeasures In Rollover Crashes

According to the statistic data of various countries and regions, the proportion which rollover accident accounts for is very low in all vehicle crashes but very high in vehicle occupant fatalities. Therefore, reducing the injuries in rollover crash has a positive effect on reducing the socioeconomic burden. However, the vehicle in rollover crash generally has the multidirectional linear and rotational accelerations. Thus, the vehicle and occupant kinematics in rollover crash are very complex and the rollover associated injury are very hard to be predicted. There are still many problems existing in the research field of rollover safety, such as the contradictory field data analysis, unknown injury mechanisms and tolerance limits and lack of rollover regulation, physical surrogate and numerical simulation models. Based on the review of many literatures, the computational research method which can study the whole rollover accident, the occupant injury responses during the rollover crash and the occupant protection countermeasures in rollover crash event were investigated. The main contents and conclusions are as follows.1. A simulation method which can study the whole rollover accident was proposed by using HVE, LS-DYNA, MADYMO and MADYMO Coupling software. A computational model which considers the kinematic responses of vehicle and occupant during different sub-phases was developed based on this method. The simulation using this model was conducted to validate this method. It is found that the interactions of different sub-phases can be considered and studied together in this simulation method, which has positive effect on understanding the vehicle and occupant kinematics during rollover crash correctly.2. The kinematic responses of vehicle and occupant during tripping phase were studied by conducting the simulations of tripping phase. It is showed that the vehicle tripping track can be seen as a curve and the change of vehicle initial speed has an effect on changing the curvature of this track. The curvature can be increased when the initial speed is reduced because of the reduction of the linear velocity along this track. When vehicle is rotating, the higher initial speed can throw the vehicle further, which results in larger curvature of rotation track.It is also found from the occupant kinematic responses that the occupant kinematic is mainly influenced by the gravity of occupant and the centrifugal forces generated by vehicle steering and rotation during the tripping phase. The occupant has a trend of moving forward, upward and outward during the tripping phase. When the vehicle initial velocity is reduced, the far-side occupant is moved more forward and outward and the displacements of near-side occupant in forward and outward direction is also reduced.3. A detailed FE model of Jordan Rollover System (JRS) was developed by using the2003Ford Explorer FE model developed by the National Crash Analysis Center (NCAC) of the George Washington University. The MADYMO coupling software was used to couple the LS-DYNA FE vehicle model and the MADYMO facet occupant model. The JRS simulation model involving the occupant was validated by the figure results of2000Ford Explorer JRS test, the injury results in a real accident case and the results of unconstrained real rollover (URR) simulations. The effect of the end constraints of JRS test fixture on the vehicle and occupant responses was also investigated by using this model. It is showed that although the end constraints have an effect on the vehicle kinematics, but the difference is not larger than10%. Therefore, the JRS model can basically represent the vehicle kinematics of URR event and the occupant responses of the URR event rolling in passenger side direction.4. Each initial impact parameter of JRS was changed to investigate its effect on the vehicle kinematics and occupant responses during the rollover crashes. It is indicated that the vehicle kinematics is highly sensitive to drop height, roll rate and pitch angle. Therefore, the drop height, the roll rate and the pitch angle should be mainly concerned when designing the vehicle dynamic rollover test. It is also showed that only drop height has an obvious effect on the dummy injury responses but the human is sensitive not only to the drop height but also to the roll rate and the yaw angle. Therefore, the drop height is the most important parameter when designing a rollover test using a dummy and the drop height, the roll rate and the yaw angle are the mainly concerned parameters when designing a rollover test using cadaver.5. The differences between the kinematic and injury responses of dummy and human were compared and analyzed in this paper. It is concluded that the current dummy cannot precisely represent the injury responses of human during rollover crash because of the stiffer dummy body than the human body. The head injury of dummy is less serious than that of human but the neck and chest injuries of dummy are more serious than those of human during a rollover crash. Therefore, how to make the kinematic behavior of dummy during a rollover crash softer is the most important task for developing a special physical surrogate for rollover. Meanwhile, the neck should be the first concerned part when developing a new rollover dummy or redesigning current Hybrid III dummy for improving its performance during a rollover test. Besides that, the human is observed that it is more sensitive to the initial impact parameters than dummy. Thus, more parameters should be considered when designing the rollover test using a cadaver compared with designing the rollover test using a dummy.6. According to the literatures and the simulation results, the cinching latch plate of seat belt has a positive effect on the performance of occupant protection. Two new types of latch plate were developed in this paper. Both of them have many advantages like simple structure, low cost, large applicable scope and stable operation. The validity of this latch plate was verified by conducting physical test. It is indicated from the test results that the device can restrict the mutual movement between shoulder belt and lap belt effectively. Besides that, three roof strengthening methods, such as increasing the yield stress of material, thickening the thickness of sheet and adding inner sheets into the roof structure were simulated to investigate the effect of different roof strengthening methods on the performance of occupant protection.