Self-consistent modeling of the influence of texture on thermal expansion in polycrystalline TATB

Abstract

This paper presents a modeling approach for simulating the anisotropic thermal expansion of polycrystalline (1,3,5-triamino-2,4,6-trinitrobenzene) TATB-based explosives which utilizes microstructural information including the porosity, crystal aspect ratio and processing-induced texture. A self-consistent homogenization procedure is used to relate the macroscopic thermoelastic response to the constitutive behavior of single-crystal TATB. The model includes a representation of the grain aspect ratio, porosity and, crystallographic texture attributed to the consolidation process. A quantitative model is proposed for describing the evolution of the preferred orientation of basal planes in TATB during consolidation and an algorithm constructed for developing a discrete representation of the associated orientation distribution function. Analytical and numerical solutions using this model are shown to produce textures consistent with previous measurements and characterization for isostatically and uniaxially ‘die-pressed’ specimens. Predicted thermal strain versus temperature results for textured specimens are shown to be in agreement with corresponding experimental measurements. Results from these simulations are used to identify qualitative trends. Key conclusions from this work include the following. Both porosity and grain aspect ratio have an influence on the thermal expansion of polycrystal TATB, considering realistic material variability. The preferred orientation of the single-crystal TATB [0 0 1] poles within a polycrystal gives rise to pronounced anisotropy of the macroscopic thermal expansion. The extent of this preferred orientation depends on the magnitude of the deformation and, consequently, is expected to vary spatially throughout manufactured components much like the porosity. The modeling approach presented here has utility toward bringing spatially variable microstructural features into macroscale system engineering models.

Using Neutron Diffraction to Investigate Texture Evolution During Consolidation of Deuterated Triaminotrinitrobenzene (d-TATB) Explosive Powder

“…Schwarz et al [11] developed a phenomenological model by assuming that shear-driven slip is accommodated on the graphitic (001) planes of the material such that TATB crystals align with the direction of maximum shearing strain during compaction. However, the predicted preferred orientation of (001) using this assumption is inconsistent with published results for uniaxial pressing [8,12]. As noted by Sintubin et al [44], crystal plasticity-based theories may not be justified for explaining the texture evolution of such materials and that it is likely necessary to refine models such as that of March to allow for rigid-particle interactions.…”

“…As noted by Sintubin et al [44], crystal plasticity-based theories may not be justified for explaining the texture evolution of such materials and that it is likely necessary to refine models such as that of March to allow for rigid-particle interactions. Here we apply the approach followed by Luscher et al [12] and Buechler et al [15] using March [16] theory to model the TATB powder-to-pellet compaction process.…”

“…Because of the pronounced anisotropic properties of TATB particles in combination with the non-random crystallographic texture of pressed aggregates, the latter exhibit anisotropic thermomechanical properties [8,11,12]. Understanding and ultimately predicting the crystallographic texture of TATB-based explosives and its influence on thermomechanical properties is critical for interpreting experimental data obtained from specimens of a variety of processing techniques, since they often have different texture.…”

“…For example, the uniaxial thermal strain of a non-textured specimen would be lower than for a die-pressed specimen measured in the pressing direction (cf. [12]). …”

“…However, this method results in an alignment of the (001) poles in an axisymmetric ring inclined 45 • from the pressing direction. Recently, Luscher et al [12] and Buechler et al [15] applied the March [16] theory to model the TATB powder-to-pellet compaction process at the mesoscale for uniaxial die pressing and for a more general engineered component, respectively. That model results in a realignment of TATB (001) poles with the direction of smallest (i.e., most compressive) principal stretch; for uniaxial compression this results in (001) alignment directly along the pressing direction.…”