Ballistic helmets – Their design, materials, and performance against traumatic brain injury

Protecting a soldier’s head from injury is critical to function and survivability. Traditionally, combat helmets have been utilized to provide protection against shrapnel and ballistic threats, which have reduced head injuries and fatalities. However, home-made bombs or improvised explosive devices (IEDs) have been increasingly used in theatre of operations since the Iraq and Afghanistan conflicts. Traumatic brain injury (TBI), particularly blast-induced TBI, which is typically not accompanied by external body injuries, is becoming increasingly prevalent among injured soldiers. The response of personal protective equipment, especially combat helmets, to blast events is relatively unknown. There is an urgent need to develop head protection systems with blast protection/ mitigation capabilities in addition to ballistic protection. Modern military operations, ammunitions, and technology driven war tactics require a lightweight headgear that integrates protection mechanisms (against ballistics, blasts, heat, and noise), sensors, night vision devices, and laser range finders into a single system. The current paper provides a comparative study on the design, materials, ballistic and blast performance of the combat helmets used by the U.S. Army based on a comprehensive and critical review of existing studies. Mechanisms of ballistic energy absorption, effects of helmet curvatures on ballistic performance, and performance measures of helmets are discussed. Properties of current helmet materials (including Kevlar® K29 and K129 fibers, and thermoset resins) and future candidate materials for helmets (such as nano-composites, thermoplastic polymers, and carbon fibers) are elaborated. Also, experimental and computational studies on blast-induced TBI are examined, and constitutive models developed for brain tissues are reviewed. Finally, the effectiveness of current combat helmets against TBI is analyzed along with possible avenues for future research.