A Study of Safety Performance of Passenger Car and Occupant Injury Protection Technique in Side Impact
|Keywords||Side Impact Biomechanics Head FE Model Airbag Inflatable Curtain Optimization|
Improvements in roads and automobile design have steadily reduced injury and death rates in traffic accidents in all industrialized countries. Nevertheless, automobile collisions are the leading cause of traffic injuries, with an estimated total of 1.2 million cases around the world in 2004 according to world health organization’s latest record. The side collisions of passenger cars are a particularly dangerous form of vehicle accident, because there is not enough space for padding that can absorb energy. Compared to frontal collisions, side ones are more likely to cause casualties. Head and chest injuries in side impacts are very common. Moreover, these types of injuries are usually serious and can lead to death. Such fatalities and the treatment of head and chest trauma from road accidents result in a lot of social and economic costs. Therefore, it is vital to conduct research on the types of injuries, injury mechanisms, injury tolerance, and protective measures.This thesis aims at the study of occupant biomechanical responses in vehicle side impacts, investigation of the head and chest injury mechanics, identification of the relationship between physical parameters and injury, development of protective solutions for reduction of the head and chest injury risks from side impacts. To achieve the objectives mentioned above, the multi-body dynamic method and the finite element (FE) method were used to study the injury biomechanics problem and human protection techniques. The conducted researches is summarized as follows. Firstly, the modeling and validation of an FE head model were carried out based on human anatomical structures. The effect of protective devices in side impacts such as the air curtain was evaluated by using this model. Also the effect of an optimized inner panel as well as the thorax airbag was evaluated with the ES-2 dummy model for improving thorax protection.The entire mesh of the finite element head model, developed previously in Hunan University was improved. Several structures as the corpus callosum, pons, and 3rd ventricle as well as the representation of cerebral spinal fluid (CSF) were improved. The improved FE model of the head was based on anatomical structures of a male adult head. This model consists of the skull with representation of compact and trabecular bones, brain with dura and pia mater, falx cerebri, cerebral cortex, cerebral spinal fluid, cerebellum and brain stem. The model includes 57,043 nodes, 51,728 solid elements and 11,984 shell elements, with an effective mass of 4.36 kilograms. Material parameters of the model mainly come from literature. Based on experimental data from Nahum’s study, the HBM head model was validated regarding force and stress distribution. The results showed that the simulation and experimental results agree well. The model has high biofidelity and can be used in studies on brain injury, particularly once involving investigation of intracranial stress and strain distribution, intracranial pressure and other injury related parameters, as well as in the assessment studies of restraint systems.An FE approach was applied to evaluate the protective efficiency of the air curtain. An occupant head impacting a B-pillar was simulated using the HBM head model and a car model. The validity of this car model was evaluated by using the results from a side crash test performed within C-NCAP. The impact responses of the HBM head impacting an air-curtain were analyzed using calculated injury parameters, including the distribution of von Mises stress, shear stress, coup and contrecoup pressure. These parameters were used for assessment of the injury risk to occupants. Furthermore, an optimization of the safety air-curtain was conducted in terms of the mass flow rate and permeability coefficient by using the DOE procedure. The results show that the HBM is an effective tool for the analysis of the brain injury risk and for the evaluation of the performance of the protective devices.The human chest is also likely to be exposed to serious injuries in side collisions. In the study the FE simulation and optimization methods were used to improve the protection level of the chest in side impacts. The main effort was placed on the optimization of the response of the door trim panel. An FE model of a full scale vehicle to simulate side impacts was developed. The validity of the model was evaluated through a comparison with a side crash test performed within C-NCAP. Considering the crash safety of the car side structure, a sub-structure model of the car side assembly was derived based on the FE model mentioned above. Simulation and optimization of the car side structure were carried out using the response surface method (RSM). The chest injury parameters were calculated in terms of rib deflection criterion (RDC), which was reduced from 52.66mm to 41.02mm. The results of the simulation demonstrated that the duration of optimization using sub-structure model and RSM can be reduced to one fifth, compared with the traditional method of using a full scale model. The injury related parameters such as the RDC were lowered to a level that meets the C-NCAP requirements of occupant protection in side impacts. After optimization of the side structure of the car, enhancements of the chest protection through an additional thorax airbag was further evaluated. The airbag was mounted in the seat and optimization of the thorax airbag was done by a combination of the variable screening technique and the quadratic response surface method. The study was carried out through the following steps: development and validation of a full-scaled car finite element model; coupling of a thorax airbag model; screening sensitive variables and optimizing design. Finally, based on the RDC, the key parameters affecting the thorax airbag’s efficiency were analyzed. It was found that the level where the airbag is installed and the distance between the airbag and passenger are two crucial parameters influencing the safety level. The results from optimizations showed that the RDC could be reduced by 23.1%.Based on the research mentioned above, the multi-body dynamic models and the finite element method are valuable approaches for study impact responses and injury biomechanics of the occupant head and chest in side impact accidents. The developed HBM head model is helpful in development of new protective system, which provided means for assessment of safety performance in new car design.