Computer modal analysis of skull deformation caused by impact to the head

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1. Materials and MethodsAn experiment was done using a physical skull model of FRP and a dry cadaver skull. The intracranial space of a skull model was filled with distilled water and pressure gauges were installed in the frontal and occipital regions of the skull model to measure intracranial pressure change. Accelerometers were installed in the several points of each skull, for example, frontal, parietal, temporal and occipital regions etc. Each skull was suspended by strings turning upside down and impact was given to the median occipital region of each skull by a hammer with a force transducer. Impact force of the hammer and accelerations at the several points of the skull were measured. These signals were Fast Fourier transformed and the frequency response function was computed which gave the transfer function, defined as the ratio between measured response and force in the frequency domain. By these transfer function, curve fitting was done and a mode shape was identified with modal analysis using a personal computer, H-P 9000 model 310M system.2. ResultsThe mode shape of the skull model was almost as same as the one of the cadaver skull. Immediately after impact, there occurred the inbending in both the frontal and occipital regions of the skull and the outbending in both the parietal and temporal regions. Next there occurred the reverse deformation in each region. After that, there did these deformations repeatedly and decreasingly.In the physical skull model, the positive peaks in intracranial pressure were recorded in both the frontal and occipital regions immediately after impact, next negative one were done. After that, these peaks occurred repeatedly and decreasingly. This intracranial pressure change, which showed a positive and negative peak repeatedly, corresponded to a mode shape of skull deformation.