Experimental biomechanical investigation of surrogate headforms equipped with Patka helmet against high-velocity ballistic impact

Abstract

High-velocity bullet impact (velocity: 700 ± 15 m/s) is a significant concern during asymmetric warfare. Ballistic helmets for high-velocity bullet impact and associated biomechanical responses of the headforms are actively sought. Further, data on the performance of ballistic helmets against high-velocity impact are not available in the literature. Toward this end, we have evaluated the performance of Patka (helmet) against high-velocity bullet impact. Patka was mounted on various headforms to assess the perforation of the Patka by the bullet and to measure various biomechanical parameters such as back face deformation (BFD), head kinematics, brain simulant pressures, and neck loads. Bullet impact in front and oblique (30° right to the sagittal axis) orientations were considered. Our results suggest that the Patka was effective in mitigating the high-velocity bullet impact. Perforation of the Patka by the bullet was not observed. BFD in the witness material was negligible (<1 mm). Measured head kinematics and brain simulant pressures were comparable to the quantities typically reported during low- and medium-velocity bullet impacts. Further, most of the biomechanical responses, except angular acceleration and neck force, were below 50% injury risk for mild traumatic brain injury (mTBI). Despite these encouraging trends, the shattering of bullets into fragments was also observed. These fragments traveled a considerable distance at reasonable velocities. This work provides unique insights regarding the performance of Patka and associated biomechanical responses of the headforms against high-velocity bullet impact, with implications in the design and evaluation of futuristic ballistic helmets. TERMINOLOGIES Ballistic threat level: Ballistic threat levels are defined based on the impact velocity of the bullet. Different types of bullets are proposed to achieve the desired impact velocities corresponding to different ballistic threat levels. Ballistic helmet: Ballistic helmet is a type of protective headgear designed to protect the wearer head from potentially fatal impacts during combat operations. Ballistic performance: Ballistic performance of the helmet is evaluated based on the perforation resistance capacity of the helmet and back face deformation (BFD) of the helmet. Back face deformation (BFD): Back face deformation (BFD) of the helmet refers to the localized dent or bulge in the inner layer of the helmet due to ballistic impact. BFD is measured as a depth of indent in the witness material (e.g., Roma Plastilina #1 clay) of the cruciform cavity-based headform. Headform: Headform is a model of the human head replicating a few of the anatomical and material aspects. Headforms can vary in design and complexity based on the intended applications. Patka: Patka is a protective headgear designed to provide ballistic protection to the head against high-velocity threat (impact velocity: 700 ± 15 m/s). Patka is made up of hardened (armour) steel material. Head kinematics: Head kinematics refers to the motion of the head typically measured in terms of linear acceleration and angular velocity. Neck loads: Neck loads refer to the forces and moments experienced by the neck during a static or dynamic event. Brain simulant pressure: Brain simulant pressure is a hydrodynamic pressure generated within the brain simulant.