NOTATION βDecay factor λ X , λ Y , λ Z X, Y and Z dimension length scale factors C 10 , C 01 Temperature dependent coefficients G 0 Short term shear modulus G ∞ Long term shear modulus t Time Abstract: A new 3 dimensional finite element representation of the human head complex has been constructed for simulating the transient occurrences of simple pedestrian accidents. This paper describes the development, features and validation of that model. When constructing the model, emphasis was placed on element quality and ease of mesh generation. As such, a number of variations of the model were created. The model was validated against a series of cadaveric impact tests. A parametric study (a High/Low study) was performed to investigate the effect of the bulk and shear modulus of the brain and cerebrospinal fluid (CSF). The influence of different mesh densities on the models and the use of different element formulations for the skull were also investigated. It was found that the short-term shear modulus of the neural tissue had the predominant effect on intracranial frontal pressure, and on the predicted Von-Mises response. The bulk modulus of the fluid had a significant effect on the contre-coup pressure when the CSF was modelled using a coupled node definition. Differences of intracranial pressure were reported that show the sensitivity of the method by which the skull is modelled. By simulating an identical impact scenario with a range of different finite element models it has been possible to investigate the influence of model topologies. We can conclude that careful modelling of the CSF (depth/volume) and skull thickness (including cortical/ trabecular ratio) is necessary if the correct intracranial pressure distribution is to be predicted, and so further forms of validation are required to improve the finite element models' injury prediction capabilities.

In order to create a useful computational tool that will aid in the understanding and perhaps prevention of head injury, it is important to know the quantitative influence of the constitutive properties, geometry and finite element formulations of the intracranial contents upon the mechanics of a head impact event. The University College Dublin Brain Trauma Model (UCDBTM) [1] has been refined and validated against a series of cadaver tests and the influence of different finite element formulations has been investigated. In total six different model configurations were constructed: (i) the baseline model, (ii) a refined baseline model which explicitly differentiates between grey and white neural tissue, (iii) a model with three elements through the thickness of the cerebrospinal fluid (CSF) layer, (iv) a model simulating a sliding boundary, (v) a projection mesh model (which also distinguishes between neural tissue) and (vi) a morphed model. These models have been compared against a cadaver test of Trosseille [2] and of Hardy [3]. The results indicate that, despite the fundamental differences between these six model formulations, the comparisons with the experimentally measured pressures and relative displacements were largely consistent and in good agreement. These results may prove useful for those attempting to model real life accident scenarios, especially when the time to construct a patient specific model using traditional mesh generation approaches is taken into account.

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