The intrinsic complexity of the human head and brain lies within the non-uniformity of their constitutive components in terms of shape, material, function, and tolerance. Due to this complexity, the directionality of impact, when the head is exposed to an assault, is a major concern as different responses are anticipated based on the location of impact. The main objective of the study was to show that while most studies propose the injury criteria as based on the kinematical parameters, the tissue-level brain features are more substantiated injury indicators. Accordingly, a finite element (FE) approach was employed to elucidate the injury-related behavior of the head for front, back, and side impacts against a rigid wall. To this end, a 50th percentile FE head-neck model, including most anatomical features, was used. The kinematics of the head in terms of the linear acceleration, as well as the biomechanical response of the brain at the tissue level in terms of intracranial pressure (ICP) and maximum local shear stress, were evaluated as the main injury criteria. Ls-Dyna, a transient, nonlinear, and explicit FE code, was employed to carry out all the simulations. To verify the influence of impact directionality, identical boundary conditions were enforced in all impact scenarios. While brain responses showed similar patterns in all three directions, different peak values were predicted. The highest peak values for the local shear stress, ICP gradient, and the center mass linear acceleration of brain were observed for the frontal impact. These threshold values are of great significance in predicting injuries such as diffuse axonal injury (DAI) resulting from the shear deformation of brain axons. It is believed that directionality considerations could greatly help to improve the design of protective headgears which are considered to be the most effective tools in mitigating a TBI.

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