Dynamic Response and Energy Absorption Characteristics of Auxetic Concave Honeycomb Pad for Ballistic Helmet under Shock Wave and Bullet Impact

Abstract

The non-penetrating deformation of ballistic helmets caused by bullet impact can lead to craniocerebral injuries, and ballistic helmets are unable to provide effective protection against the blast wave. To enhance the protective performance of helmets, this paper proposed a novel pad based on a concave hexagonal auxetic structure, which has a porous internal structure and can contract under uniaxial compression. Numerical simulation was used to study the blunt force and shock wave protection mechanism of auxetic pads, and to analyze the protection effect of different pads on the human head under the two working conditions of 9 mm pistol bullet hitting the helmet and shock wave action. The study results indicated that the auxetic pad absorbed 13.2 J of energy after blunt force deformation of the ballistic helmet shell, and the energy absorption capacity was 424% higher than that of the foam pad; cranial stress was reduced by 44% and peak intracranial pressure was reduced by 35% when the auxetic pad was worn. Under the effect of the shock wave wearing foam pad helmet would still produce 269.3 kPa overpressure in the occipital part, and the auxetic pad could absorb a certain degree of the shock wave which transmitted into the area between the helmet and the head, and effectively avoid the damage caused by the shock wave to the head. The study demonstrated that the auxetic pad has good application prospects, which could provide a reference for improving the protective performance of helmets and reducing traumatic brain injury.