Molecular Dynamics Simulations of the Shock Response of the Energetic Materials Pentaerythritol Tetranitrate and Hexahydro-1,3,5-trinitro-1,3,5-s-triazine PDF Download
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Author: Reilly M. Eason
Publisher:
ISBN:
Category :
Languages : en
Pages : 123
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Book Description
Energetic materials are the key active ingredients in explosive formulations. Understanding the response of energetic materials is vital for the design of safe and reliable explosives. It is a challenge to experimentally study the initial events that lead to detonation in these materials. Classical mechanics based computer simulations are a useful method for the study of these initial chemical and physical events. This research focuses on the shock response of two energetic materials: pentaerythritol tetranitrate (PETN) and hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX). Computer simulations were used to study how the shock response of single crystals of PETN varies based on the orientation of the crystal relative to the shock wave. Thermo-mechanical properties were calculated for the shocks along two different orientations to quantify the difference in response. In RDX, the potential of voids to act as nucleation sites for detonation was studied. The magnitude of energy localization from void collapse as function of shock strength was studied for three different shock strengths.
Author: Reilly M. Eason
Publisher:
ISBN:
Category :
Languages : en
Pages : 123
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Book Description
Energetic materials are the key active ingredients in explosive formulations. Understanding the response of energetic materials is vital for the design of safe and reliable explosives. It is a challenge to experimentally study the initial events that lead to detonation in these materials. Classical mechanics based computer simulations are a useful method for the study of these initial chemical and physical events. This research focuses on the shock response of two energetic materials: pentaerythritol tetranitrate (PETN) and hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX). Computer simulations were used to study how the shock response of single crystals of PETN varies based on the orientation of the crystal relative to the shock wave. Thermo-mechanical properties were calculated for the shocks along two different orientations to quantify the difference in response. In RDX, the potential of voids to act as nucleation sites for detonation was studied. The magnitude of energy localization from void collapse as function of shock strength was studied for three different shock strengths.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 1
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Author: Aaron Christopher Landerville
Publisher:
ISBN:
Category :
Languages : en
Pages :
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ABSTRACT: An understanding of the atomic-scale features of chemical and physical processes taking place behind the shockwave front will help in addressing some of the major challenges in energetic materials research. The high pressure shockwave environment can be simulated using computational techniques to predict mechanical and chemical properties of a shocked material. Density functional theory calculations were performed to investigate uniaxial compressions of diamond and both hydrostatic and uniaxial compressions of TATB and NEST-1. For diamond, we calculated shear stresses for uniaxial compressions in the, and directions and discovered the anomalous elastic regime which is responsible for the significant delay of plastic deformation behind a shockwave. For TATB, the hydrostatic equation of state, bulk modulus, and equilibrium structure were calculated using an empirical van der Waals correction. The principal stresses, shear stresses, and energy change per atom calculated for uniaxial compressions in the directions normal to the {001}, {010}, {011}, {100}, {101}, {110}, and {111} planes show highly anisotropic behavior. A similar study was performed for the newly synthesized energetic material NEST-1 in order to predict mechanical properties under uniaxial compression. From the similarities in the calculated principal stresses for each compression direction we conclude that NEST-1 is likely to exhibit relatively isotropic behavior as compared to other energetic materials. Finally, reactive molecular dynamics of shock-induced initiation chemistry in detonating PETN was investigated, using first-principles density functional theory, in order to identify the reaction mechanisms responsible for shock sensitivities in energetic materials. The threshold collision velocity of initiation for each orientation was determined and correlated with available experimental data on shock sensitivity. The production of NO2 was found to be the dominant reaction pathway in every reactive case. The simulations show that the reactive chemistry of initiation occurs at very short time scales ~10E−13 s at highly non-equilibrium conditions, and is driven by dynamics rather than temperature.
Author: Tracy J. Vogler
Publisher: Springer
ISBN: 9783030230043
Category : Science
Languages : en
Pages : 294
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Book Description
Granular forms of common materials such as metals and ceramics, sands and soils, porous energetic materials (explosives, reactive mixtures), and foams exhibit interesting behaviors due to their heterogeneity and critical length scale, typically commensurate with the grain or pore size. Under extreme conditions of impact, granular and porous materials display highly localized phenomena such as fracture, inelastic deformation, and the closure of voids, which in turn strongly influence the bulk response. Due to the complex nature of these interactions and the short time scales involved, computational methods have proven to be powerful tools to investigate these phenomena. Thus, the coupled use of experiment, theory, and simulation is critical to advancing our understanding of shock processes in initially porous and granular materials. This is a comprehensive volume on granular and porous materials for researchers working in the area of shock and impact physics. The book is divided into three sections, where the first presents the fundamentals of shock physics as it pertains to the equation of state, compaction, and strength properties of porous materials. Building on these fundamentals, the next section examines several applications where dynamic processes involving initially porous materials are prevalent, focusing on the areas of penetration, planetary impact, and reactive munitions. The final section provides a look at emerging areas in the field, where the expansion of experimental and computational capabilities are opening the door for new opportunities in the areas of advanced light sources, molecular dynamics modeling, and additively manufactured porous structures. By intermixing experiment, theory, and simulation throughout, this book serves as an excellent, up-to-date desk reference for those in the field of shock compression science of porous and granular materials.
Author: C. J. Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Book Description
We have carried out density functional based tight binding (DFTB) molecular dynamics (MD) simulation to study energetic reactions of solid Pentaerythritol Tetranitrate (PETN) at conditions approximating the Chapman-Jouguet (CJ) detonation state. We found that the initial decomposition of PETN molecular solid is characterized by uni-molecular dissociation of the NO{sub 2}groups. Interestingly, energy release from this powerful high explosive was found to proceed in several stages. The large portion of early stage energy release was found to be associated with the formation of H{sub 2}O molecules within a few picoseconds of reaction. It took nearly four times as long for majority of CO{sub 2} products to form, accompanied by a slow oscillatory conversion between CO and CO{sub 2}. The production of N{sub 2} starts after NO{sub 2} loses its oxygen atoms to hydrogen or carbon atoms to form H{sub 2}O or CO. We identified many intermediate species that emerge and contribute to reaction kinetics, and compared our simulation with a thermo-chemical equilibrium calculation. In addition, a detailed chemical kinetics of formation of H{sub 2}O, CO, and CO{sub 2} were developed. Rate constants of formations of H{sub 2}O, CO{sub 2} and N{sub 2} were reported.
Author:
Publisher:
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Category :
Languages : en
Pages : 19
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We present a methodology for the efficient calculation of the shock Hugoniot using standard molecular simulation techniques. The method is an extension of an equation of state methodology proposed by J.J. Erpenbeck and is considered as an alternative to other methods that generate Hugoniot properties. We illustrate the methodology for shocked liquid N(sub2) using two different simulation methods: (a) the Reaction Ensemble Monte Carlo method for a reactive system; and (b) the molecular dynamics method for a non-reactive system. The method is shown to be accurate, stable and generally independent of the algorithm parameters. We find excellent agreement with results calculated by other previous simulation studies. The results show that the methodology provides a simulation tool capable of determining points on the shock Hugoniot from a single simulation in an efficient, straightforward manner.
Author:
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Category :
Languages : en
Pages : 17
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Book Description
A theoretical/computational research program to develop methods, simulate complex reactions, and investigate the fundamental chemical dynamics of reactions of nitramine energetic materials occurring under various experimental conditions has been carried out. The focus of the research was on RDX (hexahydro-1,3,3-trinitro-s-triazine), however, the reactions of several related systems were studied. While the goal of the research was to develop accurate models for and a better understanding of the reactions of cyclic nitramines, the work has extended and improved the theoretical and computational methods for treating rate processes in complicated molecules and systems of molecules. Since the goal was realistic simulations of the reaction dynamics, the formulation of accurate potential energy surfaces was a crucial part of the work. We have developed methods for formulating accurate surfaces by using limited amounts of empirical and ab initio results. Classical methods were used in order to realistically treat the full dimensionalities of the systems. Reaction rates were calculated by using classical trajectory simulations, diffusion theory, and Monte Carlo variational transition state theory. Semiclassical methods were developed to treat multidimensional effects in proton tunneling.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
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Book Description
Molecular dynamics simulations of the response of small molecules at a shock front are presented. The simulations are performed in the reference frame of the shock and the results provide a unique insight into the sequence of states through which the material transforms during shock loading. The calculated up-pumping time (time for the translational and vibrational kinetic energy to equilibrate) for small molecules is quite fast, a few picoseconds for butane and about 10 ps for nitromethane. This is somewhat faster than the 100 ps suggested by a recent experiment.
Author: Joseph Louis Bass
Publisher:
ISBN:
Category :
Languages : en
Pages : 396
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Book Description
Macroscale, mesoscale, and ab initio models of reacting shock physics are based, in their most general forms, on rate law descriptions of the chemical processes of interest. Reacting molecular dynamics simulations, by contrast, typically employ potential functions (holonomic Hamiltonian methods) to model chemical reactions. An alternative approach to reacting molecular dynamics models the bonding-debonding process using a rate law, resulting in a nonholonomic Hamiltonian formulation. In previous work at macro and meso scales, discrete nonholonomic Hamiltonian methods have been applied to develop very general models of shock impact and fragmentation process. In this dissertation a similar nonholonomic modeling methodology is used, at the molecular scale, to explicitly model transient chemical processes. Note that the chemistry problem is much more difficult, since both dissociation (fragmentation) and the formation of new molecules must be modeled. The result is the first general reacting molecular dynamics formulation which explicitly models chemical kinetics. Simulation results using this method show good agreement with experiment, for energy release and detonation products in two widely used explosives (HMX and RDX). The reacting molecular dynamics simulation results are used to propose reaction mechanisms and species concentration based kinetics models suitable for use in meso and macro scale shock to detonation simulations. Computational modeling of energetic materials is capable of estimating molecular behavior under conditions not amenable to direct experimental measurement. Further development of RMD methods may help to provide a better understanding of energetic material behavior. This in turn may help to develop improved insensitive high energy density materials.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 46
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Book Description
Energetic materials are unique for having a strong exothermic reactivity, which has made them desirable for both military and commercial applications. Energetic materials are commonly divided into high explosives, propellants, and pyrotechnics. We will focus on high explosive (HE) materials here, although there is a great deal of commonality between the classes of energetic materials. Although the history of HE materials is long, their condensed-phase properties are poorly understood. Understanding the condensed-phase properties of HE materials is important for determining stability and performance. Information regarding HE material properties (for example, the physical, chemical, and mechanical behaviors of the constituents in plastic-bonded explosive, or PBX, formulations) is necessary for efficiently building the next generation of explosives as the quest for more powerful energetic materials (in terms of energy per volume) moves forward. In modeling HE materials there is a need to better understand the physical, chemical, and mechanical behaviors from fundamental theoretical principles. Among the quantities of interest in plastic-bonded explosives (PBXs), for example, are thermodynamic stabilities, reaction kinetics, equilibrium transport coefficients, mechanical moduli, and interfacial properties between HE materials and the polymeric binders. These properties are needed (as functions of stress state and temperature) for the development of improved micro-mechanical models, which represent the composite at the level of grains and binder. Improved micro-mechanical models are needed to describe the responses of PBXs to dynamic stress or thermal loading, thus yielding information for use in developing continuum models. Detailed descriptions of the chemical reaction mechanisms of condensed energetic materials at high densities and temperatures are essential for understanding events that occur at the reactive front under combustion or detonation conditions. Under shock conditions, for example, energetic materials undergo rapid heating to a few thousand degrees and are subjected to a compression of hundreds of kilobars, resulting in almost 30% volume reduction. Complex chemical reactions are thus initiated, in turn releasing large amounts of energy to sustain the detonation process. Clearly, understanding of the various chemical events at these extreme conditions is essential in order to build predictive material models. Scientific investigations into the reactive process have been undertaken over the past two decades. However, the sub-[mu]s time scale of explosive reactions, in addition to the highly exothermic conditions of an explosion, make experimental investigation of the decomposition pathways difficult at best. More recently, new computational approaches to investigate condensed-phase reactivity in energetic materials have been developed. Here we focus on two different approaches to condensed-phase reaction modeling: chemical equilibrium methods and atomistic modeling of condensed-phase reactions. These are complementary approaches to understanding the chemical reactions of high explosives. Chemical equilibrium modeling uses a highly simplified thermodynamic picture of the reaction process, leading to a convenient and predictive model of detonation and other decomposition processes. Chemical equilibrium codes are often used in the design of new materials, both at the level of synthesis chemistry and formulation. Atomistic modeling is a rapidly emerging area. The doubling of computational power approximately every 18 months has made atomistic condensed-phase modeling more feasible. Atomistic calculations employ far fewer empirical parameters than chemical equilibrium calculations. Nevertheless, the atomistic modeling of chemical reactions requires an accurate global Born-Oppenheimer potential energy surface. Traditionally, such a surface is constructed by representing the potential energy surface with an analytical fit. This approach is only feasible for simple chemical reactions involving a small number of atoms. More recently, first principles molecular dynamics, where the electronic Schroedinger equation is solved numerically at each configuration in a molecular dynamics simulation, has become the method of choice for treating complicated chemical reactions.
