A 3-D finite element human head model has been developed to study the dynamic response of the human head to direct impact by a rigid impactor. The model simulated closely the main anatomical features of an average adult head. It included the scalp, a three-layered skull, cerebral spinal fluid (CSF), dura mater, falx cerebri, and brain. The layered skull, cerebral spinal fluid, and brain were modeled as brick elements with one-point integration. The scalp, dura mater, and falx cerebri were treated as membrane elements. To simulate the strain rate dependent characteristics of the soft tissues, the brain and the scalp were considered as viscoelastic materials. The other tissues of the head were assumed to be elastic. The model contains 6080 nodes, 5456 brick elements, and 1895 shell elements.

To validate the head model, it was impacted frontally by a cylinder to simulate the cadaveric tests performed by Nahum et. al. (8). Model responses were compared with the measured cadaveric test data in terms of impact force, head acceleration, and coup and contrecoup pressures. Head impact severity from different types of impacts (impact speed, impact mass, and impact location etc.) was evaluated by quantifying intracranial pressure, brain shear stress, and skull von Mises stress. Head Injury Criterion (HIC) was also calculated as an alternate means of impact severity assessment. It was shown that HIC was proportional to the intracranial pressure, shear stress, and skull von Mises stress. Hence, for a direct impact, HIC seems to reasonably reflect impact severity.