The characterisation of a shock tube system for blast injury studies

Abstract

In recent decades, improvised explosive devices have been one of the main causes of injuries due to blast effects to military personnel as well as civilians. Such injuries are very complex, with multiple types of injuries happening at once. To understand the nature of such injuries, it is important to be able to re-create the blast waves, isolating their different time-dependent effects (e.g. initial accelerations by shock waves, ballistic impacts, etc.). The shock tube is a versatile apparatus that can generate these elements of blasts in laboratory environment. The project aims to deepen the current understanding about the shock tube by characterising it over a range of conditions such as diaphragm breakage, and to measure the evolution of the pressure generated. Then, based on these characterisations, additional adjustments and adaptors are introduced to adapt the performance of the shock tube to specific purposes, especially blast injury and mitigation studies. Experiments were per- formed on an air-driven shock tube system with Mylar and aluminium diaphragms of various thicknesses, and with different lengths of driver section. Single-diaphragm and double-diaphragm configurations were employed, as were open or closed tube configurations. The arrangement was designed to enable high-speed photography and pressure measurements. Overall, the results from the shock tube are highly reproducible, and show that diaphragm burst pressure is the most influential factor on the output pressure pulses. The diaphragm burst pressure is shown to be linearly related to its thickness in the range studied. Com- paring single and double diaphragm systems, both produce similar effects but the latter provides more control over the generation of blast waves. The output blasts were also characterised against different locations, orientations and sizes of sample mountings. The thesis also reports studies on interactions between produced blast waves and various structures, for both biological sample mounting and blast mitigation purpose. It shows that the shock tube system can allow studies of blast effects on biological samples (e.g. osteoblast and Schwann cell cultures), and blast mitigating properties of different materials and structures (e.g. perforated sheets, reticulated foams). Finally, a computational fluid dynamic simulation for the blast generation in the shock tube has been developed, which gives reasonable agreements with experimental data. Improved versions of the simulation will be coupled with structural program to model interactions between blast waves and different geometries and materials.