Piezoelectric response of energetic composites under an electrostatic excitation

Abstract

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.

Molecular Structures, Dipole Moments, and Electronic Properties of β-HMX under External Electric Field from First-Principles Calculations

“…Subsequently, iterative calculations and structural relaxation are performed until the convergence criterion of a maximum total energy of 5 × 10 –6 eV on each atom, a maximum Hellmann–Feynman force of 0.01 eV/Å, a maximum stress of 0.02 GPa, and a maximum displacement of 5 × 10 –4 Å are attained. Although the typical experimental breakdown strength of β-HMX is 10 –3 V/Å, the computational simulations are based on a defect-free perfect crystal structure. As shown in Figure , to induce geometric and electronic structural changes in β-HMX during the calculations, external electric fields at the magnitude of 0.1 order are applied along each of the three directions of β-HMX until the simulations could no longer reproduce the desired changes.…”

Initial Decomposition of DATB Induced by an External Electric Field

“…According to similar studies, 1,24,32 the common extra electric field value can be around 0.1 V/Å magnitude. For experiments, the common breakdown strength of energetic materials such as HMX, RDX, and PETN (pentaerythritol tetranitrate) is around 10 −3 V/Å, 33 which is an objective and common order of magnitude. As a reference, TATB, whose structure is similar to that of DATB, has a breakdown strength of around 5 × 10 −4 V/Å.…”

“…According to similar studies, ,, the common extra electric field value can be around 0.1 V/Å magnitude. For experiments, the common breakdown strength of energetic materials such as HMX, RDX, and PETN (pentaerythritol tetranitrate) is around 10 –3 V/Å, which is an objective and common order of magnitude. As a reference, TATB, whose structure is similar to that of DATB, has a breakdown strength of around 5 × 10 –4 V/Å. , Since there are defects and impurities in the real DATB samples, and our calculation is to simulate the perfect crystal structure, the calculated crystals can withstand a stronger strength of electric fields.…”