Development of a Computational Model to Visualize Air Flow Into Surrogate Ballistic Wounds

Abstract

In addition to the direct mechanical damage that takes place during a ballistic injury, the formation of the temporary wound cavity creates a suction effect capable of introducing debris, particles, and bacteria from the environment into the wound track. This introduction of bacterial contamination into the wound can give rise to infections which may delay healing or result in more serious problems. Various authors have conducted controlled ballistics experiments placing bacterial contamination on the surface of ballistics gelatin targets to study the effect of parameters such as projectile caliber and speed on the distribution of bacteria along the permanent cavity. The results reported in the literature showed that bacteria were present along the entire surrogate wound track. Understanding the contribution that the formation of the temporary cavity has on the number and distribution of bacteria along the surrogate wound requires the development of experiments to visualize the flow of air during the transient phase of target deformation and the use of numerical simulations to predict variables associated with the flow of air, like pressure-time histories along the projectile path, that cannot be directly measured during experiments. This paper discusses the development of a finite element model using ANSYS Autodyn for the simulation of a small caliber projectile traveling at moderate speeds penetrating a soft tissue surrogate target made of ballistics gelatin. The model uses a Coupled Eulerian-Lagrangian formulation and discretization scheme, which allows for the analysis of not only the deformation of the solid bodies, but also of the flow of air into the wound track. For model validation, the numerical results are compared to spatial data extracted from high speed video recorded during experiments matching key model parameters. Comparisons of the numerical and experimental results indicate that the model is providing reasonable results for the deformations and overall air flow. The predicted pressure dynamics within the simulated wound track clearly suggest that areas of partial vacuum exist within the cavity, which is consistent with the suction effect mentioned by several researchers.