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. For the pelvis/lap belt modelling, special attention was given to the iliac spine function and the abdomen deformation effect as well as the belt sliding over the pelvis, essential for the submarining investigation. For the chest/shoulder belt interaction, the whole chest surface was considered as being deformable, in order to take account of its influence on belt sliding. A series of subsystem tests was firstly used to validate the chest and pelvis model:​ a belt loaded by an impactor, the pelvis loaded by a lap belt, the thorax loaded by an impactor and by a shoulder belt. Then the complete model was evaluated by comparing with sled tests, special attention being paid to the submarining. The correlation of analytical predictions with test data is presented.