Modeling of Human Brain Tissues and Head Injuries Induced by Blast and Ballistic Impact

The use of body armor and combat helmets has reduced fatalities from explosions and ballistic attacks. However, frequent use of improvised explosive devices and continuing efforts to reduce the weight of each combat helmet have increased the risk of ballistic-impact and blast-induced traumatic brain injuries among soldiers. The objective of this dissertation research project is to develop predictive constitutive and computational models to be used in head injury diagnosis and to aid in the development of new combat helmets that can mitigate non-penetrating head injuries. A transversely isotropic visco-hyperelastic constitutive model is provided for soft tissues, which accounts for large deformations, high strain rates, and short-memory effects. The presented model is tested for a range of strain rates and for multiple loading scenarios based on available experimental data for porcine and human brain tissues. Using this constitutive relation, a finite element model of a helmet/head assembly is developed to study non-penetrating TBI. The effects of constitutive models and blast directions on finite elements simulations of blast induced TBI are investigated. Further, the effectiveness of combat helmets against non-penetrating TBI induced by blast and ballistic impacts is studied. Two types of combat helmets are considered: the advanced combat helmet (ACH) and the enhanced combat helmet (ECH). Spatial distributions and temporal variations of the intracranial pressure and stress components obtained in the simulations reveal significant differences in brain tissue responses to different constitutive models and blast directions. It is found that these combat helmets provide some level of protection against non-penetrating TBI and that the level of protection is higher for the ECH than the ACH