A Table-top Blast Driven Shock Tube

Abstract: The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer which explodes when impacted by the firing pin. The firearm barrel acts as the shock tube,
and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

Keywords: shock tube, rifle primer, blast pressure, blast injury, traumatic brain injury I. Introduction The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries.[1][2][3] Compression-driven and blast-driven shock tubes of varying dimensions have been used to apply blast waves to test subjects and materials. Currently employed shock tube designs suffer from several drawbacks for studying blast-related traumatic brain injury and blast wave transmission, reflection, and absorption in candidate armor materials. Compressed air driven shock tubes exhibit significant shot to shot variations in peak pressure,[4] produce positive pressure durations longer than typically encountered from real threats (antipersonnel mines, hand grenades, improvised explosive devices),[5][6] and often fail to accurately represent the Friedlander waveform of free-field blast waves.[3] Explosive driven shock tubes produce more realistic pressure-time profiles, but their operation requires facilities, liability, and personnel overhead for storing and using high explosive materials. In addition, equipment and personnel need to be isolated from the large mechanical and electromagnetic waves caused by detonation.[1][2] Both air driven and explosive driven shock tubes typically have diameters too large to facilitate isolating exposure to a single anatomical area (head/thorax/abdomen) to isolate injury mechanisms and study wave propagation in animal test subjects and are unwieldy for tissue and cellular level experiments. This paper presents design and characterization of a table-top shock tube that employs firearm primers containing milligram quantities of high explosive and using the firearm barrel as the tube. Unlike existing shock tube designs, this design can apply shock waves with realistic blast wave profiles to small areas of a test subject or candidate armor material. II. Method Rifle primers work by the impact detonation of between 10 and 40 mg of a high-explosive mixture (usually a combination of lead styphnate and lead azide in modern primers), which then ignites the propellant charge.[7] A firearm loaded with a primed cartridge case without any gunpowder or projectile has all the essential elements of an explosive driven shock tube whose blast wave emerges from the muzzle after the primer is detonated by the firing pin. Here, a bolt action rifle chambered in .308 Winchester with a 55.9 cm long barrel is used for the test platform. Tests on large rifle primers employ R-P (Remington) brass cartridge cases with the pockets uniformed and the flash hole deburred. With the method described, this rifle forms a shock tube with a diameter of 7.82 mm. Tests on small rifle primers employ the Lapua Palma cartridge case featuring a small rifle primer pocket. Primers are obtained separately from the cartridge cases and loaded using standard cartridge reloading equipment. Before loading, primer masses are determined with a resolution of 1 mg on an Acculab VIC-123 scale. Blast pressure measurements employ pressure transducers (PCB 102B and PCB 102B15) placed coaxially with the rifle barrel directly facing the muzzle with no separation between the end of the 1

A Table-top Blast Driven Shock Tube References: [1] M.D. Alley, B.R. Schimizze, S.F. Son, NeuroIma