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

1.材料与方法采用玻璃钢颅骨物理模型和干燥身体颅骨进行实验。在颅骨模型的颅腔内填充蒸馏水，并在颅骨模型的额区和枕区安装压力计，测量颅内压的变化。在每个颅骨的几个点上安装加速度计，如额区、顶区、颞区和枕区等，用倒挂的绳索悬吊每个颅骨，并用带有力传感器的锤子冲击每个颅骨的枕中区。测量了锤子的冲击力和颅骨多个点的加速度。对这些信号进行快速傅立叶变换，并计算频率响应函数，从而得到传递函数，该传递函数定义为被测响应与力在频域中的比率。利用传递函数进行曲线拟合，并在H-P 9000型310M系统上进行了振型识别。结果颅骨模型的振型与身体颅骨的振型基本一致。撞击后即刻，颅骨的额区和枕区均出现内弯，顶区和颞区均出现外弯。其次，各区域都发生了反向变形。在物理颅骨模型中，在撞击后即刻在额区和枕区记录到正的颅压峰值，然后做下一个负的峰值。此后，这些峰值反复出现，并呈递减趋势。这种反复出现正负峰值的颅内压变化与颅骨变形的振型相对应。

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.