Numerical modeling of the thermal expansion of an energetic material

Abstract

Two typos in the last two equations in the appendix have been corrected (changes highlighted in red). This preprint is consistent with the published version. Results unchanged.International audienceThe thermoelastic response of a TATB-based pressed explosive is studied using morphological modeling and a numerical Fourier scheme. First, we characterize the polycrystalline-like microstructure in terms of the (2D) granulometry and covariance functions, measured on SEM micrograph images. The granulometry is found to be close to a Rayleigh distribution. Second, we represent the polycrystal by a modified Johnson-Mehl tessellation with time-varying germination-rate, in order to approach the wide size distribution observed on the SEM images. We find excellent agreement between the numerically optimized model and the real material in terms of granulometry. Third, we compute the thermoelastic response of the microstructure model by means of full-field Fourier-based computations. Each crystal is assigned uncorrelated random orientations. The thermomechanical response of single crystals is provided by the molecular dynamic simulations of Bedrov et al. (2009) and the X-ray diffraction results of Kolb et al. (1979). Macroscopic (uniform) temperature or strain loadings are applied along various directions (tension, shear or hydrostatic). We observe strong internal stresses upon heating, owing to the highly anisotropic thermoelastic response of TATB and random crystallographic orientations in the polycrystal. The largest stress and strain gradients are observed at grain boundaries, enforcing the idea that grain boundary fracture is indeed the irreversible mechanism underlying ratchet growth. As a first attempt to account for the plastic binder, a 4-voxels soft interphase is inserted at grain boundaries. This results in a strong softening effect on elastic macroscopic properties

Structural Defect Evolution of TATB‐Based Compounds Induced by Processing Operations and Thermal Treatments

“…They are not given in Ta ble 3. The cell volumes are comprised between 442.4 and 442.7 3 .T hey do not differ significantly from those determined for the powder (between 442.5a nd 443 A 3 ). The FWHM obtainedo nm olding powders are largert han those obtainedo nt he powders.…”

“…An interpretation basedo nt he fact that the TATB crystal displays an anisotropic mechanical behavior [30] is proposed and thatt winning-like plasticity has been observed in TATB pressed compounds( see for exampleR ef. [3]). Mathew and Sewell calculations [31] also suggestt hat sliding would be easier in the [0 01]c rystallographic directions, compared to the others.…”

“…[1]), or to perform microstructure level simulations (see, for example, Refs. [2,3]). Besides, ag rowing number of modern techniques mayp rovide useful data related to differenta spectsa nd scales of explosives microstructures and their evolutionu nder variousa pplied thermal or mechanical loads.…”

“…TATB is at riclinic crystal, space group P " 1, with two molecules per unit cell. The lattice parameters determinedb y Cady and Larson [ 19] are: a = 9.010 , b = 9.028 , c = 6.812 , a = 108.598, b = 91.828, g = 119.978,a nd the lattice volumei sV = 442,485 3 . TATB powders were synthesized by nitration of 1,3,5-trichlorobenzene and dissolution of the resulting trichloro-trinitrobenzene in toluene.T he solution was heated at 145 8C and gaseous ammoniac was introduced in the reactor.A mination reaction produced TATB and NH 4 Cl.…”

The thermoelastic response of cracked polycrystals with hexagonal symmetry

“…Initially isotropic materials should remain so if micro-cracking results from the application of a nondirectional load, in particular by heating or cooling slowly enough for the temperature field to remain uniform. Such a situation may be encountered in materials made of strongly thermally and elastically anisotropic crystals, such as polycrystalline graphite [17,18], or the energetic material 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) [19,20].…”