The effects of skull thickness variations on human head dynamic impact responses.

Variations in human skull thickness affecting human head dynamic impact responses were studied by finite element modeling techniques, experimental measurements, and histology examinations. The aims of the study were to better understand the influences of skull thickness variations on human head dynamic impact responses and the injury mechanisms of human head during direct impact. The thicknesses of the frontal bone of seven human cadaver skulls were measured using ultrasonic technology. These measurements were compared with previous experimental data. Histology of the skull was recorded and examined. The measured data were analyzed and then served as a reference to vary the skull thickness of a previously published three-dimensional finite element human head model to create four models with different skull thickness. The skull thicknesses modeled are 4.6 mm, 5.98 mm, 7.68 mm, and 9.61 mm. These models were impacted by a cylinder with a mass of 5.23 kg and an initial velocity of 6.33 m/s. Model responses were compared between models in terms of intracranial pressures, head impact accelerations, brain shear stresses, and skull von Mises stresses. It has been shown that the thickness of the skull influenced the dynamic responses of the head during direct impact. As skull thickness increased, skull deformation decreased as the skull absorbed less impact energy. However, this relationship cannot be linearly interpolated to the other parameters such as head acceleration and intracranial pressure responses. Based on model responses to half-sine wave pulses, skull and brain iso-stress curves were constructed for the thicker and thinner skulls. Thresholds for skull fracture and reversible concussion were established for the population represented by these skulls.