The Effect of Shock Wave on a Human Head

When a pressure wave of finite amplitude is generated in air by a rapid release of energy, such as high-pressure gas storage vessel or the blast from dynamite, there may be undetected brain injuries even though protective armors prevent the penetration of the projectile. To study brain tissue injury and design a better personnel head armor under blast wave, computational models of human head have been developed. Models with and without helmet are built to quantify the intracranial pressure and shear stresses of head subjected to blast wave. All the models are compared against injury thresholds for intracranial pressure and shear stresses. Overall pressure and shear stress level is highest in model without helmet and lowest in model with helmet having foam layer on inner side of helmet. The results show that helmet reduces the pressure and shear stresses generated in the brain. However this reduction in pressure and shear stresses might not be sufficient to mitigate early time, blast induced, traumatic brain injury. The validated results will provide better understanding of the energy transfer characteristics of blast wave through helmet and the injury mechanism of human head. INTRODUCTION The yearly incidence of traumatic brain injuries (TBI) in the United States has been estimated at 1.4 million people, including 50,000 deaths and 235,000 hospitalizations [1]. The incidence of TBI injuries on the military personnel and civilians have been recently increased due to the tactics of asymmetric warfare, where enemy combatants detonate improvised explosive devices. Recent statistics from the conflict in Iraq shows that several thousand US soldiers have sustained TBI, 69% as a result of blasts [2,3]. The injuries from blast can be broadly divided into primary, secondary and tertiary injuries the details of which can be found elsewhere[4]. TBI has been often linked to traumatic axonal injury, most often referred to as diffuse axonal injury (DAI) [5-6]. The role of brain accelerations in development of diffuse axonal injury have been studied for many years [7-10]. Recently few researchers have shown the role of early time intracranial wave motion in generation of mild TBI [11,12]. They have shown that early time intracranial wave motion can generate significant intracranial pressure, volumetric tension (negative pressure) and shear stresses in the brain which can cause brain disturbance leading to TBI. The effectiveness of protective devices like helmet in reducing pressure, volumetric tension and shear stresses in the brain have been questioned by several researchers [11,13] . The goal of present study is to understand the effectiveness of helmet in mitigating early time blast induced mild traumatic brain injury. Finite element method is used to characterize the effect of shock wave on human head. METHODOLOGY Two dimensional plane strain finite element models of helmet-head under shock loading are studied to compare effectiveness of helmet. Figure 1 describes three comparative models. Model 1 simulates the head (skull and brain) response