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The influence of different boundary conditions on the response of the head to impact: a two-dimensional finite element study.

The objective of the present study is to gain a better understanding of the possible importance of skull-brain interface conditions, boundary conditions at the head-neck junction, and brain material properties when modeling the response of the human head to transient loadings. To that end, a two-dimensional plane strain finite element model of a para-sagittal section of a human head has been developed. The model comprises the brain and the skull, with the foramen magnum represented by a force-free opening. The model geometry was obtained from MRI data. The material properties used were adopted from the literature and are homogeneous and isotropic. In all analyses the skull bone was modeled as a linearly elastic material. First, to enable a comparison between simulation results and experiments reported in the literature, the loading conditions, realized in experiments reported in literature, were used as input to the completely linearly elastic model without a kinematic constraint at the head-neck junction. This was done for both rigid coupling and no coupling at the skull-brain interface. Next, various versions of the model were constructed by using different combinations of the following features: linear elastic or viscoelastic brain material properties, different contact conditions at the skull-brain interface, and incorporation of a neck constraint. The results show that both coup and contrecoup pressures are much more sensitive to the type of skull-brain interface condition than to the presence or absence of a force-free foramen magnum. A neck constraint proves to be an important modeling assumption, because of its effect upon the deformation of the brain. The use of different time-dependent deviatoric material parameters for the brain did not significantly change the head's response.