Abstract
In the passive automobile safety design, prevention of head injuries of the passengers or pedestrians is very important. However the injury mechanism of a brain subject to impact loads hasn´t been made clear since the experimental or medical data as to the relation between the head injuries and impact loads are quite limited. To study this relation computer simulation is very promising. In this study we developed a very precise human head model using the CT images and validated it and discussed the injury criteria of a human head by comparing several numerical results. The human head model in this research was constructed by the VOXEL approach, where the rectangular plane finite elements were created first using the pixel data in a cross sectional CT (Computed Tomography) image and they were extruded to the vertical direction to make solid elements. 433 pieces of the CT images, which corresponds to 0.6mm pitch, were used and 10 tissues, such as scalp, bone, dura mater, brain, CSF and so on were classified. The original model with 40 million solid elements was reconstructed to the model with 1.22 million elements so that the computational analysis can be finished in a reasonable time by our PC cluster system. In order to validate the developed model, simulation of the cadaver test by Nahum et al. was done. The properties of tissues for a human head model were obtained by referring to some reports. It should be noted that CSF (Cerebro Spinal Fluid) was treated as an incompressive solid material with a very low shear modulus. The calculated results showed good agreement with the experimental ones. It is well known clinically that human brain is frequently injured in the front area rather than the occipital area regardless of the impact position. So a front and rear impact analyses were performed to discuss this tendency. The Von Mises stress became high in the front area in both cases while the absolute value of the pressure became high near the loading position. This result suggests that the brain injury has a closer relation with the Von Mises stress.
Keywords:passive automobile safety design, brain injury, VOXEL approach, CT images, impact analysis