Static Dielectric Breakdown Strength of Condensed Heterogeneous High Explosives

Lee, R. J.

doi:10.21236/ada191035

Cited by 3 publications

(1 citation statement)

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“…At ambient temperatures, it is difficult for lightning to penetrate polymer-bonded explosives (PBX) because the PBX's breakdown electric field is quite a bit higher than the air breakdown field [11]; TATB's breakdown strength is 5.75 kV/mm (almost a factor of 2 greater than air breakdown strength) and PBX9502's breakdown strength is 40 kV/mm. As a worst-case, an electrical arc is assumed to penetrate through the explosive with a cylindrical symmetry around the arc.…”

Section: Introductionmentioning

confidence: 99%

TATB Sensitivity to Shocks from Electrical Arcs

Chen

Warne

Jorgenson

et al. 2019

Propellants Explo Pyrotec

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Use of insensitive high explosives (IHEs) has significantly improved ammunition safety because of their remarkable insensitivity to violent cook‐off, shock and impact. Triamino‐trinitrobenzene (TATB) is the IHE used in many modern munitions. Previously, lightning simulations in different test configurations have shown that the required detonation threshold for standard density TATB at ambient and elevated temperatures (250 C) has a sufficient margin over the shock caused by an arc from the most severe lightning. In this paper, the Braginskii model with Lee‐More channel conductivity prescription is used to demonstrate how electrical arcs from lightning could cause detonation in TATB. The steep rise and slow decay in typical lightning pulse are used in demonstrating that the shock pressure from an electrical arc, after reaching the peak, falls off faster than the inverse of the arc radius. For detonation to occur, two necessary detonation conditions must be met: the Pop‐Plot criterion and minimum spot size requirement. The relevant Pop‐Plot for TATB at 250 C was converted into an empirical detonation criterion, which is applicable to explosives subject to shocks of variable pressure. The arc cross‐section was required to meet the minimum detonation spot size reported in the literature. One caveat is that when the shock pressure exceeds the detonation pressure the Pop‐Plot may not be applicable, and the minimum spot size requirement may be smaller.

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Section: Introductionmentioning

confidence: 99%

TATB Sensitivity to Shocks from Electrical Arcs

Chen

Warne

Jorgenson

et al. 2019

Propellants Explo Pyrotec

View full text Add to dashboard Cite

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Piezoelectric response of energetic composites under an electrostatic excitation

Shin

Zhou

2021

Journal of Applied Physics

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Several high-explosive (HE) crystals are known to be piezoelectric. However, no systematic study has been carried out on how this effect can be utilized. In this paper, we report the results of an analysis on the response of composites consisting of HE crystals and a polymeric binder under electrostatic excitation. The HE crystals considered are 1,3,5-trinitroperhydro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, pentaerythritol tetranitrate, and ammonium perchlorate. To explore avenues for enhancing the piezoelectric effect, the binder of the composites is taken to be piezoelectric polyvinylidene fluoride. The focus is on the distributions of induced electric field vector and mechanical stress in the microstructures. The effects of crystal–binder volume fraction, HE crystal size, and dielectric constants of the HE crystals are investigated. To further explore the effect, microparticles of lead zirconate titanate piezoelectric ceramic are introduced to some microstructures. For the HE crystals considered here, a coupled electromechanical analysis shows that the microstructural heterogeneities can enhance the local electric fields to as high as 1.34 times the applied E-field, causing the dielectric breakdown field strength of the overall composite to be much lower than the breakdown strengths of the constituents in the microstructure. In addition, the induced stress levels just prior to dielectric breakdown are well below the yield strengths of the respective constituents. As such, controlled dielectric breakdown, rather than mechanical damage, should primarily be used to facilitate hotspot formation, ignition, and chemical reaction. The likelihood of local dielectric breakdown within the HE crystals is systematically quantified as a function of applied electric field, microstructural attributes, and constituent behavior. To gauge the effect of the direct piezoelectric effect, one material case is also subjected to mechanical excitation in the form of compression. Under an applied external stress, the results show that the direct piezoelectric effect can lead to local yielding and thereby serve as a hotspot generation mechanism. On the other hand, the induced E-field is weak and unlikely to serve as a practical or efficient means of effecting hotspots within an energetic material. The analysis points out that simultaneous application of electrostatic excitation and mechanical excitation can also be considered.

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