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For occupant protection in vehicle crash, several kinds of ATDs (Anthropomorphic Test Devices) and associated injury criteria have been used to evaluate the performance of a vehicle body, restraint systems and other safety devices. Because of the lack of sufficiently validated injury criteria for the lumbar spine, it has been a concern that the effectiveness of some safety features for injury reduction based on the dummy and associated injury criteria may not be reasonably assessed. Therefore, in this study, a human FE model capable of evaluating lumbar spine skeletal injuries was developed. Considering an increasing percentage of the traffic accidents relating to elderly people due to extending span of human life and decreasing birthrate, not only an adult model but also a model that represents lowered tolerance of the elderly was developed. From traffic accident statistics, 35 and 75 years old (y.o.) were defined as the representative ages of adult and elderly populations.

Recently, the global increase of elderly vehicle users has become an issue to be considered in the effort of enhancing safety performance of vehicle restraint system. It is thought that an evaluation tool for the system representing properties of age-specific human body will play a major role for that. In previous research, the authors had developed age-specific component finite element (FE) models for the lower limb, lumbar spine, and thorax representing the adult and elderly occupants. However, the models have not been validated in terms of full body kinematics. It is essential for such models to be validated in terms of full body kinematics in order to ensure validity of the results of the assessment of the safety performance of restraint systems. In the present research, the adult and elderly occupant full body FE models were developed by incorporating the lower limb, lumbar spine and thorax of the adult and elderly FE models established in previous research.

The “Statistical Design Support System” produces a new practical optimal design method. It can be used even on nonlinear behavior. The optimization can be carried out with this system using a small number of calculation results. The authors applied it to the design optimization of the occupant restraint system in order to reduce the injury criteria based on the crash simulation. In line with growing interest and improvements in technology on vehicle safety, it will be necessary to consider some different crash situations simultaneously. The authors made an optimal design taking into account the different collision conditions. This paper describes the effectivity analysis and the optimization.