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In frontal impact, the occupantlbelt interaction is essential to obtain a good simulation of the occupant dynamic behaviour. Nevertheless, current mathematical models do not allow a realistic representation of this interaction to be obtained. Especially they are not adapted to simulate two important phenomena: the chest and pelvis deformation under the belt loading, and the belt sliding on the occupant. This paper deals with a tridimensional finite element model which allows an improved simulation of this interaction. The Hybrid III dummy, restrained by a 3-point retractor belt, was aimed, with a finite element program (RADIOSS). The model consisted of two parts: a deformable part representing, by means of springs and shell elements, the belt system, the thorax and the- pelvis; a rigid part representing, with rigid shell elements, the other components of the system. The belt was simulated by shell elements with a elasto-plastic material law.

Biomechanical studies related to the head have been mainly directed towards the determination of cerebral tolerance to impact in the absence of fracture. However, the frequency of skull trauma producing complex fractures and cerebral lesions linked to these fractures should be taken into consideration. On a human being, impacts under similar mechanical conditons can produce either fatal encephalic lesions without fractures or skull fractures with encephalic lesions if the subject has a different skull morphology. A sample of 146 subjects has been studied to determine the relation between the morphological characteristics of the skulls (weight of the skull cap, thickness, weight of the cranial skeleton…), their mineralization. The mechanical tests were performed on bone fragments (bending and shearing tests). Nine accelerometers were used during the experiments of various types of impacts. The results were computerized. The skull fractures observed (a total of 45) are described.