Experimental and Numerical Studies of Blast, Fragmentation and Thermal Effects Mitigation of Energetic Materials Detonation

Abstract

The detonation of an energetic material (EM) is mainly manifested in the form of blast, fragmentation and thermal effects. These effects are very destructive and cause injuries-being fatal-and structural damage as well. The suppression or attenuation of these effects is a prime focus. The present research is related to the concerted investigations employing lightweight materials capable of mitigating the blast, fragmentation and thermal effects of explosive devices including lighter improvised explosive devices (IEDs). Commercially available shaving foam was characterized and investigated as a potential mitigating material in combination with Kevlar woven fabric, laminated glass fiber reinforced polymer (GFRP), Bakelite, Polyurethane (PU)/expanded Polystyrene (EPS) foams and PU-silica to withstand the impact of blast wave and explosively driven high velocity fragments. Various amounts of C4 explosive (82, 104, 250 and 800 grams) were tested in air and immersed in shaving foam. The shaving foam confinement suppressed the fireball radius by 80% and quenched the afterburning reactions resulting from an EM detonation. About 70% reduction in blast overpressure and 62% reduction in positive impulse were observed for shaving foam confinements weighing 1.0 - 2.05 kg against C4 explosives of 82 - 250 grams. Lightweight protective configurations comprising different combinations of Kevlar woven fabric, laminated GFRP, PU/EPS foams and alumina (Al2O3) tile were tested against blast, fragments and bullet impact. Multi-layer composition of PU-silica and a mixture of PU-silica and alumina powder were also studied. The protective configurations were tested under static detonation of geometrically scaled down 155 mm artillery shell. Fragments weighing up to 4.3 grams with velocities in the range of 961–1555 m/s were produced and impacted the configurations. The Kevlar woven fabric, laminated GFRP and PU foam compositions provided significant absorption and attenuation to impacting fragments. Configurations employing alumina tile were able to resist perforation of 7.62 mm mild steel core (MSC) bullet and also withstood the blast and multiple fragments impact without significant backface signatures (blunt force trauma). Numerical simulations were performed using ANSYS AUTODYN. SPH (Smoothed Particle Hydrodynamics) solver was used for characterization of shell fragmentation. iv Coupled SPH -ALE (Arbitrary Lagrangian-Eulerian) approach was used to simulate the interaction of fragments with protective configurations. A coupled Euler-ALE approach was employed to simulate blast wave propagation in air and loading on protective configurations. The fragments mass, initial velocity and spatial distributions were in good agreement with the experimental findings. The blast wave parameters showed good match of the arrival time and peak pressure values with measured data, however, a discrepancy in incident impulse was observed. On the basis of experimental and simulation studies a model heterogeneous containment system was developed to counter combined blast, fragmentation and thermal effects of energetic material detonation of 1.0 kg bare and 0.6 kg of steel cased TNT equivalent charge. The two layers container provided 97% overpressure reduction as well as contained the high velocity fragments. The novel combination of EPS foam, Bakelite and PU-silica layers provided protection against in contact C4 detonation at the base of the container. The upshot of this research work is that, besides being of academic significance, it provides ample data to design a device to combat terrorism against lighter time bomb/IEDs placed at public places, high profile meeting venues and transportation systems (land, air etc.).