Study of Air Flow Into Ballistic Wounds Using Flow Visualization Experiments and Numerical Simulations

Abstract

A common type of battlefield injury involves high speed fragments of different sizes and shapes hitting the human body, particularly the extremities. Gaining a better understanding of the mechanisms involved in those injuries can result in better strategies for providing medical care. One aspect that still requires additional research is the contamination of ballistic wounds. Studies published in the open literature have shown that in perforating projectile wounds airborne debris such as skin, cloth, and soil particles are introduced into the wound by either the projectile or by the suction created due to the formation of the temporary wound cavity. These debris can transport bacteria resulting in infection, delayed wound healing, or other complications. The amount of suction and ultimately the bacteria distribution in ballistic wounds can vary depending on parameters such as projectile velocity, caliber, mass, and location of injury. Numerical models can be used to study the influence of various parameters on the suction effect but experimental data is needed to validate the simulation results. This paper presents an experiment developed to provide an initial evaluation of numerical models of the air flow and suction effect in perforating projectile wounds. The experiment used rectangular prism (cuboid) targets made of ballistic gelatin which is a common soft-tissue surrogate material used in ballistic research. These targets were shot with 11.43 mm (0.45 in) caliber round lead projectiles fired from air rifles at approximately 230 m/s. The air flow into the temporary cavity of the tissue surrogate targets was visualized using a vapor curtain placed at the projectile entry location. A high speed digital camera captured the movement of the vapor curtain and the formation of the temporary wound cavity during the tests. To simulate the experiment, a Coupled Eulerian-Lagrangian (CEL) model was run using Abaqus/Explicit. In the model, the mechanical behavior of the soft-tissue surrogate target was represented using a hyper-elastic constitutive relation. A small pre-made cylindrical channel was added to the targets to avoid using techniques such as element erosion or considering material failure when modeling the passage of the projectile through the material. Qualitative and limited quantitative results from the model were compared with the results from the laboratory tests.