Vibrational frequency response to impact loading of skull models

More than 73% of soldiers returning from duty are injured by explosive devices. The shock waves generated are believed to cause injury via intracranial pressure and skull flexure. Prior modal analyses of spherical shells as skull substitutes using analytical solutions to the wave equation indicate the impact point and opposite side as areas of intense bending. In this study, finite element models extend modal analyses and applied impulse scenarios for a variety of altered spherical geometries. Holes of differing sizes, the direction of impact, and the presence of water inside were considered. The finite element model matched the analytical modal frequencies within 4%. The discrete modal frequencies are lost as the geometry deviates from the ideal sphere. The frequency response to impact was complex with many participating modal frequencies. The deformation near holes increased as the hole increased in size. Impacts in line with holes increased the minimum to maximum spread by 30% whereas angled impacts caused more pronounced motion near holes. Filling the sphere interior with liquid diverted some load from the shell and decreased the maximum deflections by 80%. Avenues of further research focused on more accurate geometries are discussed.