Interplay of explosive thermal reaction dynamics and structural confinement

Abstract

Explosives play a significant role in human affairs; however, their behavior in circumstances other than intentional detonation is poorly understood. Accidents may have catastrophic consequences, especially if additional hazardous materials are involved. Abnormal ignition stimuli, such as impact, spark, friction, and heat may lead to a very violent outcome, potentially including detonation. An important factor influencing the behavior subsequent to abnormal ignition is the strength and inertia of the vessel confining the explosive, i.e., the near-field structural/mechanical environment, also known as confinement (inertial or mechanical). However, a comprehensive and quantified understanding of how confinement affects reaction violence does not yet exist. In the research discussed here, we have investigated a wide range of confinement conditions and related the explosive response to the fundamentals of the combustion process in the explosive. In our experiments, a charge of an octahydrotetranitrotetrazine-based plastic bonded explosive (PBX 9501) was loaded into a gun assembly having variable confinement conditions and subjected to a heating profile. The exploding charge breached the confinement and accelerated a projectile down the gun barrel. High bandwidth pressure and volume measurements were made and a first-law analysis was used to obtain enthalpy and power from the raw data. These results were then used to quantify reaction violence. Enthalpy change and power ranged from 0−1.8 kJ and 0−12 MW for 300 mg charges, respectively. Below a confinement strength of 20 MPa, violence was found to decline precipitously with decreasing confinement, while the violence for the heaviest confinement experiments was found to be relatively constant. Both pressure and pressurization rate were found to have critical values to induce and sustain violent reaction.

Pre-ignition confinement and deflagration violence in LX-10 and PBX 9501

“…These observations are consistent with results observed by others, where violence in heated PBX 9501 increased by three orders of magnitude as burst pressure in a pressure vessel was varied from $5-20 MPa. 26 The difference in the initiation location, in turn, can be explained by the differences in the binders of these two explosives. As previously described, 9 Viton, the binder in LX-10, is thermally stable and has a large coefficient of thermal expansion at temperatures 100 C and above.…”

Cookoff

“…Now we will address the question of how to quantify the violence from a given explosion and how such violence might be controlled. Further details of the work presented in this section can be found in [54] and [64]. Any explosive subjected to a given time at temperature will undergo both mechanical and chemical changes, and these changes may substantially modify the performance of the explosive and the behavior during a cookoff event.…”

Dynamic damage and non‐shock ignition behavior of polymer bonded explosive under lower velocity impact

“…Polymer-bonded explosives (PBXs) possess high energy, low susceptibility to mechanical damage, excellent mechanical and processing properties, and are widely used in modern military, aerospace, deep well prospecting and other fields [1]. In scenarios such as transportation and storage, minor impacts (such as dropping, collision, friction) on PBX can lead to accidental ignition [2][3][4], which in turn can cause accidents resulting in casualties and economic losses. Therefore, it is important to study the accidental ignition of explosives under lower velocities impacts.…”