| There are around 260,000 child fatalities and 10,000,000 injured in traffic accidents worldwide every year. The safety of children in cars is a significant issue in the world today. The vehicle seat, safety belt and airbags are designed for adults. The injury risk for children is higher than for adults in car collisions. Studies about child occupant safety were started from the 1960s around the world. The European countries as well as U.S. and Japan established regulations for child restraint systems. The child occupant safety researches have been begun in China. The to-be-commented draft of"Restraining Devices for Child Occupants of Power-Driven Vehicles"has been published and will come into effect in the near future. The child restraint systems (CRSs) are designed for children. Unfortunately, there are two major problems associated with the use of CRSs in China. First, the usage rate is rather low. Second, the CRSs are often misused for children in cars. It is very important to study the child occupant protection in China.This thesis aimed at study of the characteristics of child occupant traffic injury epidemiology; analysis of the dynamics responses of children in the accidents; determination of child occupant injury reasons and mechanisms; evaluation of the efficiency of child restraint system under different crashes; improvement of child restraint system design in reliable and effective ways. To this end, child occupant accident data from the CIREN database (from 1996 to 2005), FARS database (from 2000 to 2007) and Changsha traffic police database (from 2001 to 2007) were analyzed statistically, the descriptive statistics and multinomial logistic regression methods were used; the multi-body dynamics and the finite element models were utilized in the accident reconstruction analysis, proposed a method of combining PC-Crash, LS-Dyna and MADYMO softwares to reconstruct the child occupant accident cases, the method was used in the two cases (frontal and side impact cases) selected from the GIDAS database; then employed the multi-body dynamics methods in frontal impact to study the impact of CRSs misuse, constructed PRG, Kriging and RBF neutral network surrogate models to optimize the design parameters of CRS, and the energy efficiency theory was used to analyze the dissipated kinetic energy of child occupant in vehicle impacts. Finally, PSM method was used to construct simulation models in side impacts, the efficiency of protection of booster seat in different impact angles and of side airbag in different uses of restraint system were studied, and RBF neutral network was used to construct the surrogate model to optimize the parameters of side thorax airbag based on the injury protection of child occupant and adult occupant.The statistical results of child occupant accident data from U.S. and China indicated that the small passenger car is the main type of vehicle (the saloon cars are most) involving child occupants, the two vehicles collision is the main type of accident, frontal and side impacts are the most frequent accident configurations, and the children aged from 4 to 8 account for a high proportion among casualties. In addition, the factors associated with the injury risks of the child occupant are impact type, seat position, impact severity, restraint type, the child's age and the use of the restraint system. The injury regions vary with the type of restraint system used.The accident reconstruction results indicated that the rest positions and wheel traces of two cars were comparable with ones in real world accident, the intrusions and deformations of door of the objective car were comparable with that of accident car, the dynamic responses of child dummy reflected well the injury risk of the objective child in crash accident, and the reconstruction method is feasible and effective. In addition, in frontal impact case, the head injury was mainly caused by the impact on the headrest of the reclined front seat, the nonsynchronous motion between head and thorax caused the neck injury. In side impact case, the head injury was mainly caused by the headrest of booster seat and intrusion of door, which resulted in the death of the child occupant. The results from two reconstructions (frontal and side impact cases) indicated that the thorax and abdominal soft tissue organ were injured by webbing of seat belt.The study results of child occupant injury protection in frontal impacts indicated that misuse will reduce the protective effects of CRS and increase the injury risks of child occupant comparing the correct use of CRS. Except for the Kriging model, the optimal values suggested by the surrogates for the objective function PCOMB were smaller than those obtained within the sample. The optimization using the PRG model resulted in the smallest objective function value (the best solution found), a 14.7% improvement over the minimum value of the sample. The RBF neural network model presents the smallest difference between the surrogate estimations for PCOMB and the corresponding values obtained using MADYMO. The use of multiple surrogates has helped identify alternative optimal solutions corresponding to different regions in the design space. In addition, it was concluded that the chest acceleration was not dependent on the ride down energy efficiency but dependent on the energy efficiency absorbed by the belt. The chest acceleration will decrease with the reduced energy efficiency absorbed by the belt. The belts having slack or using built-in booster seat will increase the energy efficiency absorbed by the belt.The study results of child occupant injury protection in side impacts indicated that booster seat will produce some benefits when an axial motion component exists in the objective vehicle. When the axial motion component does not exist or is very small, the booster seat may not provide enough protection for children. A misused child booster seat will not increase injury risks from the side airbag to the head and thorax. A child using the booster seat correctly may receive the protective benefits of the side airbag for head and thorax. Whether a child misuses or uses correctly booster seat, the injury risks of the neck depends on the actual impact situations. The optimal values suggested by the surrogate models for the objective functions were smaller than those obtained from the initial models. Compared to the head resultant acceleration of the child, a 17.9% improvement over the initial value of the initial model was found, and compared to the chest VC value of the adult, a 49.7% improvement over the initial value of the initial model was found. The thorax side airbag can protect not only the adult but also the child effectively after optimization.In recent years, the number of newly registrated passenger cars in China is increasing rapidly. Therefore, the issue of crash safety of child occupants is becoming more and more serious. The characteristics of child occupant traffic injury epidemiology were studied from the macro-perspective. The accident reconstruction was studied from the micro-perspective. The injury protection of child occupants in frontal and side impacts were studied further, in detail. The findings from this study may contribute to the child occupant protection research for passenger car impacts in China.
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