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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.

It has been difficult to evaluate injuries to the elderly whose body tolerance is lowered due to aging. The objective of this study was to develop human FE models for evaluating skeletal injuries to the lower limb and pelvis of both adult and elderly people. From traffic accident statistics, 35 and 75 years old (y.o.) were defined as the representative ages of adult and elderly population. An existing human FE model for an adult male pedestrian was adopted for the baseline. Femur models were developed first, because there existed most sufficient data of material properties and geometry for the femur. Age-related changes in material properties and geometries of bone were investigated by literature survey, from which average values of Young’s modulus, yield stress/strain and ultimate stress/strain, section areas and cortical bone thicknesses for 35 and 75 y.o. were determined.

In recent years, several kinds of seat systems that aim to reduce cervical spinal injuries in rear impacts, so called ‘whiplash injuries’, have been released by some car manufacturers and seat suppliers in the world. Meanwhile, several kinds of dummies have been developed to be representatives of occupants under such conditions. One of these is the BioRID II equipped with a realistic spine constructed of multiple vertebrae similar to that of a human. It is regarded as the most biofidelic dummy for low speed rear impact. Using this dummy, some typical ‘whiplash protective’ seat systems currently available were dynamically tested to see their performance on injury reduction. From the results of these tests, the design direction to lessen the injury level more efficiently was determined.

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.

Corresponding to the increasing need for the protection of elderly people from traffic accidents, the authors have been developing age-specific human FE models capable of predicting body kinematics and skeletal injuries for younger adult (35y.o.) and the elderly (75y.o.). The models have been developed and validated part by part referring to the literature and then integrated into whole bodies. Validation had been conducted in order of single bones, components and whole body. Whole body kinematics in frontal impact had been validated against the PMHS frontal belt restrained sled tests series, resulting in good biofidelity scores. In this study, the models were validated for lateral impact. The models were validated against several impact tests of body regions from ISO-TR9790 and against recently published full scale lateral sled tests for whole body kinematics. In most cases, the results showed good biofidelity of the models.