| Human cranium Composite modeling, and brain movability, during head impact, have been addressed.;An equivalent, homogenized, composite material model has been utilized to represent the three layered cranium as a single layer system; The equivalent material properties can be formulated systematically with confidence. The discrete materials are assumed linear, elastic, and isotropic/anisotropic. Thus, the resultant equivalent material is anisotropic. The numerical results have shown that a single layer cranium of homogenized material properties provided almost the same accuracy of brain stresses and pressures as a three layered cranium of discrete material properties. This investigation indicated that layered cranium models of discrete material properties (existing or still incoming) neither increase accuracy for desired intracranial variables nor reduce computational cost.;The brain movability has been modeled first time by using sliding interface techniques; using a new 3D 50th percentile finite element head model that presents the essential anatomy of cranium and intracranial contents. The sliding interfaces totally separated the brain and cerebrospinal fluid (CSF); this allowed more realistic brain motion within cranial cavity compared to brain-CSF/cranium coupled head models (in most existing head models). Brain responses from a sliding brain-CSF model has been compared with a coupled brain/CSF model in frontal impact simulations. Brain pressure histories at 4 locations compared favorably with experimental and computational results. The deformation and stress fields, from the two models, were significantly different in important intracranial locations. There were several times up to one order difference in magnitude for resulted stresses between the two models. The sliding brain/CSF model predictions not only matched injury evidences in clinics but also reflected geometry effects on brain responses. In an occipital impact simulation, high stress contours occurred in the dorsal part of the brainstem, corpus callosum, and the vicinity of the ventricles; This suggested an occipital impact could cause deeper intracranial content injuries. In conclusion, the brain movability is a critical variable to correctly evaluate the brain dynamic responses during impact. So, it has to be accounted for in future head models. |
