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Weapons of Mass Destruction (WMD)


Distant Image

Distant Image was a high explosive (HE) test sponsored by the Defense Nuclear Agency. It was detonated on 20 June 1991 on the White Sands Missile Range, NM. The explosive charge consisted of 2,440 tons of ammonium nitrate fuel oil (ANFO). The primary objective of the test was to provide an airblast and ground shock environment for Department of Defense (DoD) sponsored experiments. A secondary objective was to provide a simulated precursor environment for several other experiments.

The simulated nuclear blast and thermal effects of a 4 kiloton weapon were condcuted at Exercise "Distant image", a United States Defense Nuclear Agency sponsored, large scale, high explosive field test. For the first time in this series of large scale synergistic simulation tests, freely reacting, anthropometric manikins were fielded to test the protective properties 0f NBC ensembles. This new experimental set-up performed to design expectations. Fire, caused by the thermal pulse, was extinguished by the blast on the free moving manikins as had previously been observed with tethered manikins. No re-ignition occurred on any of the clothing or equipment.

A study has been made at the Department of Physics and Astronomy, University of Victoria, Victoria, BC of the response of elastic-plastic and brittle circular-cross-section cantilevers when subjected to blast wave loading. It is demonstrated how the deformation or failure of such cantilevers enables them to be used as blast wave gauges. In addition, the deformation of cantilever-type structures can be used to assess the characteristics of accidental explosions.

Two numerical models have been developed to describe the deformation of a dynamically loaded cantilever. Both models assume that the plastic deformation is localized in a region near the fixed end, and that the loading force is a function of the dynamic-pressure time-history and a variable drag coefficient, which depends on the Reynolds number, Mach number and angle of attack of each discretized element of the cantilever.

The first model assumes a rigid-plastic response of the cantilever. It was found that this model accurately described the response of cantilevers made of 50/50 lead/tin alloy. It overestimated the deformation of cantilevers made of more elastic materials when exposed to blast waves from high explosives and in a shock tube.

The second model assumes an elastic-plastic response. The algorithm is based on the premise that the elastic curvature of the cantilever is limited by the plastic yield stress of the material and that as the curvature approaches this limit the cantilever rotates by the amount needed to keep the curvature constant and equal to this maximum. It has been shown that this algorithm minimizes the curvature of the cantilever at the base. This model provided good predictions of the deformation of cantilevers made of aluminum and steel.

The numerical models were evaluated by studying the response of cantilevers exposed to shock waves in a shock tube, and to the blast waves from two explosions of ammonium-nitrate/fuel-oil charges of approximately 2.5 kt. The response to the shock tube flows was recorded by high speed photography which showed good agreement between the observed modes of deflection and those predicted by the elastic-plastic model. The models also provided good predictions of the deformation of a wide range of cantilevers, made of a variety of materials and of different diameters and lengths, when exposed to the free field blast waves.

It is demonstrated how the numerical models can be used to determine the type of cantilever that might be used as a gauge for monitoring the blast wave from an explosion, or for evaluating the deformation of a cantilever exposed to the blast wave from an accidental explosion so as to characterize the explosion.



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