On the use of a SEBS polymer gel block as a new ballistic target to assess blunt ballistic impacts: Application to a wide range of LLKE projectiles

Abstract

The objective of the present paper is to determine the ability of a transparent polymeric gel, used as a reference material with a mechanical response comparable to that of a human body, to assess less-lethal kinetic energy (LLKE) projectiles. To do this, a consistent measurement method of the dynamic deformation of the gel impacted by a projectile is first of all presented. It relies on high-speed images and image processing routines. Several metrics from the measured gel wall displacement profile are used to investigate experiments. Secondly, repeated impact conditions on various gel blocks confirm that, the proposed material meets the requirements of mechanical consistency, batch-to-batch reproducibility and easy handling. Thirdly, 138 ballistic experiments covering kinetic energies from 10 J up to 300 J are performed, involving commercially available LLKE projectiles of various stiffness. The important dataset is used to perform a statistical analysis through Spearman’s correlation matrix between metrics and projectile parameters. It mainly reveals the need to use a ballistic target to determine the wounding potential of a given projectile rather than kinetic energy density or momentum density. Robust power law mathematical fits describe the relations between three metrics (maximum gel displacement, displacement - rate of displacement-based metric and maximum displaced volume) and kinetic energy density depending on LLKE projectiles’ stiffness. Fourthly, three case reports available in literature and involving LLKE projectiles have been replicated on a gel block. An experimental procedure is proposed based on numerous case reports to give design guidelines in terms of projectile mass, velocity and stiffness. Finally, this original study demonstrates the gel material capabilities to assess LLKE weapons before their field deployment. However, further investigations need to be pursued to propose a relevant injury predictive tool and associated risk curves to law enforcement agencies and regulatory bodies.