Condensed-Phase Explosives: Shock Initiation and Detonation Phenomena
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This article is written for the purpose of acquainting the reader with the concept that condensed-phase explosives “detonate” by virtue of shock waveinduced processes. A detonation wave in its simplest form is a steady reactive wave process, with the front of the reactive wave being a shock wave that takes the material to a high pressure/high temperature state in which the chemical reactions start. Chemical reactions develop as a function of time (on nanosecond time scales) and by means of induced sound waves, support the leading shock wave so it is steady. The models that describe this process from a physical standpoint will be discussed in some detail, along with the fluid flow equations, and the equation of state of both the unreacted explosive and the reaction products. Similarly, initiation of detonation must at some point involve shock wave processes. The best understood detonation initiation process involves an input shock wave that starts the chemical reactions and eventually develops into a steady detonation wave, usually on the microsecond time scale. This is called a shock-to-detonation transition (SDT). There are major differences in the transition depending on whether the material is “homogeneous” (e.g., liquid or single crystal) or “heterogeneous” (e.g., composed of granules). Initiation can be started in other ways (e.g., by friction, spark, or flame) which leads to a burning process that sometimes results in a detonation. A burning to detonation process is called a deflagration-to-detonation transition (DDT). This can occur on a hours/minutes/seconds time scale. However, at some point it must involve the development of a shock wave and become a shock initiation. Because of the large difference in timescales, the DDT process is not yet well understood and is not discussed in this chapter. This work will proceed as follows: (1) introduction and brief history, (2) chemical structures and chemical properties of some condensed-phase explosives, (3) conservation relations for shock processes and equation of state of explosives, (4) steady detonation phenomena in one- and two-dimensions (1-D and 2-D) along with detonation properties of some explosives, (5) shock
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S.A. Sheffield and R. Engelke
initiation phenomena of homogeneous and heterogeneous explosives and, finally, (6) summary and possible future developments. This work is meant to be an introductory discussion of shock waves and their involvement with detonation. More detailed developments can be found in several other sources which will be listed in the appropriate sections and in a “Further Reading” portion of the references.
1.1 Introduction In this article we concentrate on condensed-phase high explosives (HE) that do work by a shock-induced chemical energy release (detonation). Primarily because of their initial high mass density and the associated high energy density, liquid and solid materials have a major importance in military and blasting applications. Most of the processes to be described are thought to occur in both condensed-phase and gaseous
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