engleski

Numerical Modeling of Slow and Fast Cookoff

Energetic materials used in ammunition may absorb heat energy from surrounding environment or heat source, leading to its chemical decomposition and explosion. This phenomenon is commonly termed as thermal cookoff. Possibilities of such events are of great concern among explosives’ community in terms of safe and controlled usage of explosive devices. Many theoretical, experimental, and simulation studies have been reported in the past few decades exploring the physics of thermal cookoff events spanning over various thermal, chemical and mechanical processes. The effects of heat transfer and quasi-static mechanics dominate during the initial phases of any cookoff event. Accurate modeling of non-linear heat transfer phenomena during this phase requires material properties accounting for temperature variation, decomposition, phase transformation, etc. and models for surface-to-surface radiation in enclosures and condensed phase chemistry. In this work, the development of a two-dimensional reactive heat transfer code COMEX is described which can model various thermal insult scenarios associated with explosives. The code predicts the transient temperature distribution, the time to ignition, and the location of ignition. The code uses the Crank-Nicholson scheme on the finite difference method and has a built-in self-adjustable time step, criteria for automatic detection of ignition point, various reaction rate models (single-step and multi-steps) and reaction rate integrators, composition- and temperature-dependent thermal properties, and post-processing capabilities. Using different boundary conditions, one can model slow- and fast cookoff scenarios. It was found that the heating rate affects the transient effects significantly which in turn affects the location of ignition and the resulting response. Calculation results are discussed and compared with available literature experimental data for several explosives, as well as with the results of calculation from other heat transfer codes

explosives ; thermal initiation ; slow cook-off ; fast cook-off ; reactive heat conduction ; energy balance equation ; numerical modeling

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