Effect of confinement during cookoff of TATB

Abstract

Abstract. In practical scenarios, cookoff of explosives is a three-dimensional transient phenomenon where the rate limiting reactions may occur either in the condensed or gas phase. The effects of confinement are more dramatic when the rate-limiting reactions occur in the gas phase. Explosives can be self-confined, where the decomposing gases are contained within non-permeable regions of the explosive, or confined by a metal or composite container. In triaminotrinitrobenzene (TATB) based explosives, self-confinement is prevalent in plastic bonded explosives at full density. The time-to-ignition can be delayed by orders of magnitude if the reactive gases leave the confining apparatus. Delays in ignition can also occur when the confining apparatus has excess gas volume or ullage. Understanding the effects of confinement is required to accurately model explosive cookoff at various scales ranging from small laboratory experiments to large real systems. IntroductionPredicting the response of energetic material during an accident, such as a fire, is important for high consequence safety analysis, even for insensitive high explosives (IHE). The ignition time, the amount of decomposed gas, the thermo-mechanical sensitization of the degraded energetic material (EM) at ignition, burning of the degraded EM, the possible run-up to detonation and subsequent violence is needed for safety assessments. Even if the EM does not thermally ignite, degraded HE at elevated temperatures are more sensitive to shock initiation than pristine HE. For example, the shock sensitivity of the IHE triaminotrinitrobenzene (TATB) at elevated temperature was shown to be similar to room temperature 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) [1]. Predictive models must be able to resolve phenomena across ten orders of magnitude in time from hours to sub-microseconds and six orders of magnitude in space from microns to meters. These models should include robust computational tools with solvers for numerically stiff sets of differential equations using adaptive gridding on massively parallel computers. Constitutive models for the EM should consider coupled thermal, mechanical, and chemical phenomena. Constitutive models for confining materials are also needed at elevated temperatures.In the early stages of a cookoff event, the mechanical response and decomposition gas velocities are slower than acoustic wave speeds and can be determined in a quasistatic manner. During this time, heat transfer, decomposition, and gas generation are coupled. Reaction rates are dependent on temperature and, in some cases, pressure. Disparity in thermal expansion between the confinement and the EM can change heat transfer paths as well as available gas volume. The pressurization rate and the degree of confinement influence the probability of deflagration-to-detonation transition (DDT) in the EM.

LX‐17 Thermal Decomposition‐Characterization of Solid Residues from Cook‐Off in a Small‐Scale Vessel Under Confinement

“…The 0.1 °C/min profile shows little build up, also. Pressure spikes appear in several experiments, concurring with Sandia's Instrumented Thermal Ignition experiments [17] in which cracking was heard. These profiles demonstrate the diverse conditions producing these samples.…”

“…Attempts to characterize volatile decomposition products along with light gases led to the perspective benzo‐furazans and benzo‐furoxans are potentially stepwise formed and are part of the chain of decomposition reactions [6–15]. The overall mechanism was further developed for thermal modeling purposes showing the first part of the decomposition is the loss of water with the formation of mono‐benzo‐furazan (F 1 ), di‐benzo‐furazan (F 2 ), tri‐benzo‐furazan (F 3 ), and ultimately the ring system falling apart [5, 16–19]. This early work has been reviewed recently [20].…”

Towards a heat‐ and mass‐balanced kinetic model of TATB decomposition

“…Solids 2 and 3 were described as furoxans and furazans. Not being autocatalytic, it is fundamentally flawed. The 2014 Hobbs‐Kaneshige model [14] was the first to introduce liquid‐gas equilibrium for water as a pressurization mechanism. This model also specified the initial reaction as F1 specifically as contrasted to a set of furazans and furoxans for the first step.…”

“…Not being autocatalytic, it is fundamentally flawed. * The 2014 Hobbs-Kaneshige model [14] was the first to introduce liquid-gas equilibrium for water as a pressurization mechanism. This model also specified the initial reaction as Given that these models are diverse in structure but can all be tuned to match cookoff data, one must conclude that none are uniquely correct.…”

“…In the middle of the spectrum are global lumped-species models such as those pioneered by Tarver and coworkers and explored by others [11][12][13][14][15][16]. These models are more reflective of underlying classes of chemical reactions (i. e., autocatalytic, sequential, competitive), and the global reaction elements can have different proportional yields for heat and gas.…”