Tailoring the Blast Exposure Conditions in the Shock Tube for Generating Pure, Primary Shock Waves: The End Plate Facilitates Elimination of Secondary Loading of the Specimen.

Matthew Kuriakose,Maciej Skotak,Namas Chandra,Anthony Misistia,Aravind Sundaramurthy,Sudeepto Kahali,Firas H Kobeissy

doi:10.1371/journal.pone.0161597

Abstract

The end plate mounted at the mouth of the shock tube is a versatile and effective implement to control and mitigate the end effects. We have performed a series of measurements of incident shock wave velocities and overpressures followed by quantification of impulse values (integral of pressure in time domain) for four different end plate configurations (0.625, 2, 4 inches, and an open end). Shock wave characteristics were monitored by high response rate pressure sensors allocated in six positions along the length of 6 meters long 229 mm square cross section shock tube. Tests were performed at three shock wave intensities, which was controlled by varying the Mylar membrane thickness (0.02, 0.04 and 0.06 inch). The end reflector plate installed at the exit of the shock tube allows precise control over the intensity of reflected waves penetrating into the shock tube. At the optimized distance of the tube to end plate gap the secondary waves were entirely eliminated from the test section, which was confirmed by pressure sensor at T4 location. This is pronounced finding for implementation of pure primary blast wave animal model. These data also suggest only deep in the shock tube experimental conditions allow exposure to a single shock wave free of artifacts. Our results provide detailed insight into spatiotemporal dynamics of shock waves with Friedlander waveform generated using helium as a driver gas and propagating in the air inside medium sized tube. Diffusion of driver gas (helium) inside the shock tube was responsible for velocity increase of reflected shock waves. Numerical simulations combined with experimental data suggest the shock wave attenuation mechanism is simply the expansion of the internal pressure. In the absence of any other postulated shock wave decay mechanisms, which were not implemented in the model the agreement between theory and experimental data is excellent.

Highlights

Exposure to shock waves is identified as the leading cause of Traumatic Brain Injury (TBI) in military personnel [1, 2]
Increased focus on bTBI has resulted in intensified research efforts and a number of groups have opted to use compressed-gas driven shock tubes to study the etiology of blast injury [9,10,11,12,13,14]
We demonstrate conditions inside of the shock tube can be controlled and secondary waves eliminated by careful adjustment of the end plate reflector gap; the specimen is exposed only to a single shock wave with well-defined doi:10.1371/journal.pone.0161597.g001

Summary

Introduction

Exposure to shock waves is identified as the leading cause of Traumatic Brain Injury (TBI) in military personnel [1, 2]. The injuries associated with explosive detonation are classified into four different categories based on their etiology: 1) primary, caused by pure shock waves, 2) secondary, resulting from penetration of fragmentation (shrapnel) and other projectiles into the brain parenchyma, 3) tertiary, originating from impact with other objects, and 4) quaternary, caused by exposure to heat and toxic gases [3,4,5]. It appears mixed type of injuries are expected near the epicenter of a blast, while shock wave is far reaching, compared to the other TBI risk factors associated with explosive blast. There is only a limited understanding of conditions affecting shock wave propagation inside of the shock tube, what crucial differences exist between testing inside versus outside of the shock tube, and how the end-effects affect the shock wave profile and propagation [18, 19]

Methods

Results

Discussion

Conclusion