A study of blast wave loading on cantilevers |
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Authors: | AA van Netten JM Dewey |
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Institution: | (1) Department of Physics and Astronomy, University of Victoria, Victoria, B.C. V8W 3P6 Canada , CA |
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Abstract: | A study has been made 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.
Received 23 September 1996 / Accepted 11 November 1996 |
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