Coupled phase transformation, chemical decomposition, and deformation in plastic-bonded explosive: Models

Abstract

Articles you may be interested inChanges in mobility of plastic crystal ethanol during its transformation into the monoclinic crystal state A continuum thermomechanochemical model of the behavior of a plastic-bonded explosive ͑PBX͒ 9501 formulation consisting of the energetic crystal octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ͑HMX͒ embedded in a polymeric binder is developed. Our main focus is on the study of the ␤ ↔ ␦ phase transformations ͑PTs͒ in crystalline HMX under a complex pressure-temperature path. To reproduce the pressure-temperature path, in particular during heating of PBX inside of a rigid cylinder, the ␤ ↔ ␦ PTs in HMX are coupled to chemical decomposition of the HMX and binder leading to gas formation, gas leaking from the cylinder, elastic, thermal, and transformational straining as well as straining due to mass loss. A fully physically based thermodynamic and kinetic model of the ␤ ↔ ␦ PT in HMX crystal is developed. It is based on a suggested nucleation mechanism via melt mediated nanocluster transformation and the recently revealed growth mechanism via internal stress-induced virtual melting. During the nucleation, nanosize clusters of the ␤ phase dissolve in a molten binder and transform diffusionally into ␦ phase clusters. During the interface propagation, internal stresses induced by transformation strain cause the melting of the stressed ␦ phase much below ͑120 K͒ the melting temperature and its immediate resolidification into the unstressed ␦ phase. These mechanisms explain numerous puzzles of HMX polymorphism and result in overall transformation kinetics that is in good agreement with experiments. Simple phenomenological equations for kinetics of chemical decomposition of the HMX and the binder are in good correspondence with experiments as well. A continuum deformation model is developed in two steps. The geometrically linear ͑small strain͒ theory is used to prove that the internal stresses and macroscopic shear stresses are negligible. Then a large strain theory is developed under hydrostatic loading. The developed continuum thermomechanochemical model is applied in the accompanying paper ͓V. I. Levitas, B. F. Henson, L. B. Smilowitz, D. K. Zerkle, and B. W. Asay, J. Appl. Phys. ͑submitted͔͒ to modeling the heating of PBX inside of a rigid cylinder.

The Microstructural Evolution in HMX Based Plastic-Bonded Explosive During Heating and Cooling Process: an in situ Small-angle Scattering Study

“…The S v can reflect the microstructural changes of HMX-PBX during the heating process. Upon thermal loading, the initial voids could be filled by the binder because of the decrease in the binder viscosity [20,21]. The melt temperature of the F 2314 binder is about 97 °C [22], so the dramatic decrease of the S v at temperatures higher than 100 °C is mainly attributed to the filling of the initial voids by the F 2314 binder.…”

Surface-Induced Phase Transformations: Multiple Scale and Mechanics Effects and Morphological Transitions

“…Finding ways to control Á (e.g., by changing the composition or the surrounding of the surface layer) will allow one to control the surfaceinduced phenomena and nanostructures. For example, -PT at the surface of the occurs at e in the presence of nitroplastiziers only [8]. The revealed low sensitivity of surface nanostructure to the driving force, within some range, may also have practical importance.…”

A diffuse interface approach to phase transformation via virtual melting

“…Such large stresses relax through formation of melt, and they may also form cracks and voids. (Levitas et al, 2007b(Levitas et al, , 2006a The proposed solid-solid PT through virtual melt results in sixteen theoretical predictions which match experimental studies qualitatively and quantitatively. (Levitas et al, 2006a Figure 1.2: Almost all symbols representing experimental data obtained at LANL and LLNL using three different methods are within a band obtained using Eq.…”

“…(Menikoff and Sewell, 2002) In the case of HMX, mesoscale modeling techniques are used to provide better understanding of phase transformation (PT) process between the polymophs of HMX that helps us to develop protocols for handling and disposal of HMX-based explosive materials and munitions. (Levitas et al, 2007b) Crystalline structure of organic nitramines including HMX are studied using ab initio technique. (Dzyabchenko et al, 1996;Lewis et al, 2000) Lattice parameters of HMX over 0 < P < 7.5GPa…”

“…(Gump and Peiris, 2005;Karpowicz and Brill, 1982) In contrast to phenomenological models, the models that are based on the physical mechanisms are much more reliable outside their calibration range. (Levitas et al, 2007b) We have used a mesoscale modeling technique and developed a Ginzburg-Landau model to study β − δ reconstructive PT and possible formation of virtual melt (Levitas et al, , 2004(Levitas et al, , 2006b) under complex thermomechanical paths.…”