Computational investigation of the α-γ phase transformation in 1,3,5-trinitroperhydro-1,3,5-triazine

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Josyula, Kartik
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2018-05
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Electronic thesis
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ENG
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Mechanical engineering
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Abstract
Using thermomechanical properties of γ-RDX, we studied the anisotropic constitutive response of single crystals of α- and γ-RDX using a crystal plasticity-based continuum model. The slip system activation and the extent of plastic slip observed in γ-RDX explain the experimental observations on the anisotropic shock sensitivity of RDX. The results indicate that modeling of γ-RDX is important in understanding the shock sensitivity of RDX. Next, we studied the α-γ phase transition under hydrostatic loading using SB potential. The phase transformation was observed for temperatures beyond 350 K. The simulations show the abrupt changes in volume, the molecular energy terms of the SB potential, and the wag angles of the molecules that are associated with the phase transition. We also hypothesize that the angle energy might play an important role in the ability of the SB potential to simulate α-γ phase transition. Further, we developed a thermodynamically consistent level set approach based on regularization energy functional to capture α-γ phase transformation in single crystal RDX under shock loading. The reinitialization scheme used in our approach leads to an embedded regularization flux within the level set equation so that additional reinitialization step is not required. The level set approach is shown to compare well with the velocity extension method in capturing the phase interface position. It is also shown to capture the characteristics of the shock-induced α-γ phase transformation for loading along (100) crystal orientation such as relaxation behind the phase interface and the finite time required for the phase transformation to complete.
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May 2018
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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