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Group DX-1, Detonation Science and Technology
Los Alamos National Laboratory, P952
Los Alamos, NM 87545
Abstract-
Under some circumstances a solid explosive behaves benignly when heated; in
others a violent reaction ensues that, depending on the particulars, can
transit to detonation. Existing thermal explosion models treat the
decomposing material as a continuum mixture. With sufficiently accurate
kinetics such models can predict with reasonable accuracy the time to thermal
explosion and the point in the charge where reaction runs away. Simple
models have also captured the basic coupling between heat release and
mechanical motion to show how an initially quiescent material can
spontaneously cook-off to detonation. However, recent observations of the
cook-off process have revealed a previously unappreciated degree of
structure. For example, if a decomposing HMX grain is quenched and then
examined, one sees a network of "worm holes" created by the combustion
products in escaping the interior. On the macroscopic scale, sequences of
photographs of thermal runaway in a confined explosive tablet show luminous
fast cracks just proceeding explosion. Part of the acceleration appears to
stem from the increase in burning surface area due to multiple branching of
these flame-loaded cracks. The late stages of explosion remain unresolved,
but forensic evidence suggests that in some cases transition to detonation
does indeed occur. It is becoming clear that the traditional continuum
mixture ideas are inadequate to address the question of reaction violence;
consequently, our current emphasis is to better isolate the essential dynamic
phenomena for detailed study.
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