Blast Wave Mitigation

1. Shadowgraphy • Provides a useful qualitative look at the propagation of the blast wave • Allows transparent phenomena i.e. pressure waves, to be made visible due to refracted light • Images captured on high-speed camera Objective: To determine materials best suited for blast wave mitigation within the confines of a helmet. Blast Wave Mitigation Fig 1 Professor Steven Son, Matthew Alley, Stephen Strinka Abstract Brain injuries due to blast waves have contributed an increasing portion of casualties in Iraq and Afghanistan. Current body armor was designed for protection against shrapnel, but is ill-equipped to prevent blast waves from damaging the brain. The purpose of this experiment is to determine suitable materials for disrupting blast waves within the constraints of a helmet. Candidate materials were chosen based on weight, microstructure, and proven capability to inhibit blast waves. The materials were cast into dimensionally uniform samples and subjected to blast waves. Pressures near the explosion and behind the samples were recorded. In addition, high speed shadowgraphy provided a qualitative look at the propagation of the blast wave. An analysis of this data will reveal the best choice in material for blast wave mitigation. The results are still forthcoming, as the experiments are currently underway. Once a material is selected, it will be suggested for use within combat helmets. Purdue University School of Mechanical Engineering • Fig 1 Experimental Setup before • explosion • Fig 2 Explosion Begins • Fig 3 Explosion expands, spherical • blast propagation is visible just • above and below fireball. • Fig 4 Blast contacts and propagates • through the experimental • material • Fig 5 Fireball envelops material, • interfering waves continue past • experimental setup. • Fig 6 Fireball continues to expand, • reaching maximum size • Fig 7 Fireball clears revealing the • material has broken out of the • fixture • All of these occur in the span of milliseconds Fig 2 Blast “Cannon” -Used to direct explosive blast wave toward material • Experimental Method • Generate lethal levels of pressure • with a small amount of explosive • Monitor pressure near blast • Introduce Blast Mitigation Material • to explosive pressure • Monitor pressure behind material • for reduced pressure Fig 8 • Experimental Materials • Materials chosen in attempt to maximize number of density changes • Materials suspended in resins to form uniform test slabs • Materials Include: • Hollow Glass Microspheres (10-179 µm) • Solid Glass Shot(250-425 µm) • Solid Ceramic Microspheres (1-40 µm) • TUFF (volcanic rock) • Others in Research Fig 3 Pencil Gages monitor pressure -10.5” from explosion -20” from explosion, behind material -20” from explosion, exposed The material is placed in test fixture -10.5” from explosive -pressure at this distance calculated to be 50 psi -a blast pressure of 50 psi can be lethal • Motivation: • The Changing Nature of Warfare • Roadside and concealed explosions increasing with use of Improvised Explosive Devices (IEDS) • IEDS responsible for over 60% of casualties in Iraq and 50% in Afghanistan [3] • Hundreds of soldiers returned in last several years with symptoms attributed to Traumatic Blast Injury (TBI) from ongoing studies [4] • Improved body armor has led to improved overall survival rates • Closed brain injuries are outnumbering lethal penetrating injuries [1] • Previous blast studies focused mainly on air filled organs (ear, lung, GI tract) [2] • TBI symptoms: • Insomnia, vertigo, memory deficits [4] • Headaches, swelling in the brain, • speech deficits, cognitive deficits [1] • Concussion, contusion [2] • Blast wave energy transfer results in a multitude of injuries • The greatest amount of energy transferred occurs at density changes in system [5] • For example: bone/tissue interface can experience partial to complete amputation Fig 6 Fig 4 Observed Blast Waves The characteristic idea blast wave (Fig 11) is composed of 2 parts: -A sharp peak pressure, caused by the mass of propagating medium -A brief vacuum follows the peak, air refills the void left by the wave -Experimental Data (Fig 12) matches basic pattern - but interference creates a non-ideal form • Summary of Progress • Have run numerous nonel shots and open air trials for calibration • Assembled test fixture • Composed numerous casts of experimental materials • Established conventions for gage placement, experimental procedure • Started running actual tests. Fig 9 Fig 7 Fig 5 Fig 11 • Goals for the Future • Conduct open air and no filler runs to establish performance baseline • Test all materials molded so far • Continue research for other possible materials • Run trials on actual helmet Fig 10 References Fig 12 [1] S. Okie, "Traumatic Brain Injury in the War Zone," The New England Journal of Medicine, vol. 352, pp. 2043-2047, 2005. [2] D. Warden, "Military TBI During the Iraq and Afghanistan Wars," The Journal of Head Trauma Rehabilitation, vol. 21, pp. 398-402, 2006. [3] C. Wilson, "Improvised Explosive Devices (IEDs) in Iraq and Afghanistan: Effects and Countermeasures," CRS, Ed. Washington, DC: The Library of Congress, 2007. [4] Y. Bhattacharjee, "Shell Shock Revisited: Solving the Puzzle of Blast Trauma," in Science. vol. 319 Washington, DC: AAAS, 2008, pp. 406-408. [5] C. Stewart, "Blast Injuries," CO: USAF Academy Hospital, 2006. Acknowledgements The SURF program is supported by alumni and the following corporations and organizations: • Fig 9 Sample Slab after testing This was composed of 74.07 volume percent hollow glass microspheres embedded in an elastomeric resin. • Fig 10 Same material, note the air vacancies in the material A special thank you is extended to Intel for their continued support of the SURF program, including providing materials for professional development activities.