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New concept of contrecoup lesion mechanism: modal analysis of a finite element model of the head
Published September 09, 1992 by International Research Council on Biokinetics of Impact in Switzerland
A theoretical modal analysis of a finite element model of the human head in its sagittal plane is proposed. The result applications to the crash biomechanics field are presented. For the model validation, this approach allowed us to determine the mechanical properties of the material used to model the subarachnoid space so as to obtain the first natural frequency and mode shape in accordance with the mechanical impedance recorded on the human head in vivo. The main result of our analysis is reached at the mode shape level and in particular with respect to its quasi insensitivity to mechanical properties of the materials involved. This first mode shape reveals a rotation of the brain mass around a point located at the center of a circle which describes the skull contour in the sagittal plane. This motion leads to significant brain stresses at the frontal lobes level and mainly at their interface with the orbital floor. Considering the response of a structure to a blow as a superposition of excited vibration modes, we show how occipital impacts lead to frontal injuries. This result is then illustrated in the temporal field by calculating the brain motions and intracerebral stresses under impact conditions.