A Simplistic Approach to the Shock Initiation of Detonation in Heterogeneous Explosives PDF Download
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Author: Philip M. Howe
Publisher:
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Languages : en
Pages : 25
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Book Description
A model of the shock initiation of heterogeneous explosives is presented. The model is based upon a 'hotspot' ignition mechanism. Choice of the energy density as the independent variable in the problem permits separation of Hugoniot effects from the buildup process, and leads to a critical condition for initiation which is independent of the loading density. The model is found to be consistent with data from the literature on porous tetryl. (Author).
Author: Philip M. Howe
Publisher:
ISBN:
Category :
Languages : en
Pages : 25
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Book Description
A model of the shock initiation of heterogeneous explosives is presented. The model is based upon a 'hotspot' ignition mechanism. Choice of the energy density as the independent variable in the problem permits separation of Hugoniot effects from the buildup process, and leads to a critical condition for initiation which is independent of the loading density. The model is found to be consistent with data from the literature on porous tetryl. (Author).
Author:
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Category :
Languages : en
Pages : 10
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Book Description
We present a new methodology for fitting the x-t shock initiation trajectories of heterogeneous explosives. The technique is motivated by extended detonation shock dynamics (DSD) theory, which suggests a class of simple phase plane generating functions. We choose one theoretically derived equation as an example, and show that it can fit PBX 9501 and 9502 gas gun data in detail. The fitted function comprises the DSD calibration in the initiation regime, and determines the ordinate values of the Pop plot and inert Hugoniot curves. We describe how the underlying extended DSD assumptions are equivalent to those of certain other initiation models. Finally, we examine a scaling law that assumes all PBX's follow the same x-t trajectory when normalized by their respective c-j reaction zone thicknesses [delta]. This assumption allows [delta] to be estimated from the fit, yielding values similar to other estimates.
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Languages : en
Pages :
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The basic processes in the shock initiation of heterogeneous explosives have been investigated theoretically using a model of a cube of nitromethane containing 91 cubic air holes. The interaction of a shock wave with the density discontinuities, the resulting hot spot formation and interaction, and the buildup to propagating detonation were computed using three-dimensional numerical Eulerian hydrodynamics with Arrhenius chemical reaction and accurate equations of state. The basic process in the desensitization of a heterogeneous explosive by preshocking with a shock pressure too low to cause propagating detonation was numerically modeled.
Author: Blaine Asay
Publisher: Springer Science & Business Media
ISBN: 3540879536
Category : Technology & Engineering
Languages : en
Pages : 630
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Book Description
Los Alamos National Laboratory is an incredible place. It was conceived and born amidst the most desperate of circumstances. It attracted some of the most brilliant minds, the most innovative entrepreneurs, and the most c- ative tinkerers of that generation. Out of that milieu emerged physics and engineering that beforehand was either unimagined, or thought to be f- tasy. One of the ?elds essentially invented during those years was the science of precision high explosives. Before 1942, explosives were used in munitions and commercial pursuits that demanded proper chemistry and con?nement for the necessary e?ect, but little else. The needs and requirements of the Manhattan project were of a much more precise and speci?c nature. Spatial and temporal speci?cations were reduced from centimeters and milliseconds to micrometers and nanoseconds. New theory and computational tools were required along with a raft of new experimental techniques and novel ways of interpreting the results. Over the next 40 years, the emphasis was on higher energy in smaller packages, more precise initiation schemes, better and safer formulations, and greater accuracy in forecasting performance. Researchers from many institutions began working in the emerging and expanding ?eld. In the midst of all of the work and progress in precision initiation and scienti?c study, in the early 1960s, papers began to appear detailing the ?rst quantitative studies of the transition from de?agration to detonation (DDT), ?rst in cast, then in pressed explosives, and ?nally in propellants.
Author: F. Zhang
Publisher: Springer Science & Business Media
ISBN: 3540884475
Category : Science
Languages : en
Pages : 407
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Book Description
The fourth of several volumes on solids in this series, the six extensive chapters here are more specifically concerned with detonation and shock compression waves in reactive heterogeneous media, including mixtures of solid, liquid and gas phases.
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Category :
Languages : en
Pages : 9
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Part of the difficulty in developing physically based models of shock initiation which have genuine predictive capability is that insufficient constraints are often imposed: models are most often applied to very limited data sets which encompass very narrow parameter ranges. Therefore, it seems to be of considerable value to examine the rather large existing shock initiation database to identify trends, similarities, and differences, which predictive models must describe, if they are to be of genuinely utility. In this paper, existing open-literature data for shock initiation of detonation of heterogeneous explosives in one-dimensional geometries have been examined. The intent was to identify -- and where possible, isolate -- physically measurable and controllable parameter effects. Plastic bonded explosives with a variety of different binders and binder concentrations were examined. Data for different pressed explosive particulate materials and particle size distributions were reviewed. Effects of porosity were examined in both binderless and particle-matrix compositions. Effects of inert and reactive binders, and inert and reactive particle fills were examined. In several instances, the calculated data used by the original authors in their analysis was recalculated to correct for discrepancies and errors in the original analysis.
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Category :
Languages : en
Pages : 7
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It has long been known that there are fundamental differences between homogeneous and heterogeneous high explosives. The shock initiation behavior of these materials was first described in the literature by Campbell et al, in 1961. Chaiken was also involved in describing this process for liquid nitromethane. Since then, there have been a number of studies which have added considerable incite into the shock initiation/detonation behavior of these materials. We only give a few references here (Refs. 4 - 11) and these should be considered representative; e.g. they do not represent an exhaustive list of references available. Many of these studies were done on homogeneous explosives, most often nitromethane (NM) and include particle velocity gauge measurements, optical temperature measurements, VISAR measurements, as well as streak camera measurements of interfaces. In some cases NM was heterogenized by gelling and adding silica particles. Homogeneous materials are typically liquids or single crystals in which there are a minimal number of physical imperfections (e.g. bubbles or voids) that can cause perturbations in the input shock and the flow behind it. Homogeneous materials viewed with macroscopic probes characteristic of detonation physics experiments appear uniform. Heterogeneous explosives are generally all other types; these are usually pressed, cast, machined, or extruded into the shapes or parts desired. These materials contain imperfections of a variety of types that cause fluid-mechanical irregularities (called hot spots) when a shock or detonation wave passes over them. Such hot spots cause associated space/time fluctuations in the thermodynamic fields (e.g., the pressure or temperature fields) in the material. These thermodynamic variations affect the local chemical-heat-release rate - they produce an average heat-release rate that is a combination of chemistry and mechanics. Hot spots could be the result of voids, shock interactions, jetting, shock impedance mismatches, etc. Shock initiation of homogeneous explosives is due to a thermal explosion that occurs in the material shocked the longest. This reaction produces a reactive wave that grows behind the front and eventually overtakes the front. The reactive wave may grow into what is called a superdetonation before it overtakes the initial shock and settles down to a steady detonation. The shock initiation process in heterogeneous explosives differs a great deal because the hot spots cause early chemical reaction as soon as the shock passing over a region creates them. This causes reactive growth both in and behind the shock front. This leads to a relatively smooth growth of the initiating shock to a detonation, in contrast to the abrupt changes that occur in the homogeneous case. These differences are apparent in both the in-situ reaction wave profiles and the acceleration of the shock front.
Author: J. E. Reaugh
Publisher:
ISBN:
Category :
Languages : en
Pages : 27
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Book Description
The fundamental picture that shock initiation in heterogeneous explosives is caused by the linking of hot spots formed at inhomogeneities was put forward by several researchers in the 1950's and 1960's, and more recently. Our work uses the computer hardware and software developed in the Advanced Simulation and Computing (ASC) program of the U.S. Department of Energy to explicitly include heterogeneities at the scale of the explosive grains and to calculate the consequences of realistic although approximate models of explosive behavior. Our simulations are performed with ALE-3D, a three-dimensional, elastic-plastic-hydrodynamic Arbitrary Lagrange-Euler finite-difference program, which includes chemical kinetics and heat transfer, and which is under development at this laboratory. We developed the parameter values for a reactive-flow model to describe the non-ideal detonation behavior of an HMX-based explosive from the results of grain-scale simulations. In doing so, we reduced the number of free parameters that are inferred from comparison with experiment to a single one - the characteristic defect dimension. We also performed simulations of the run to detonation in small volumes of explosive. These simulations illustrate the development of the reaction zone and the acceleration of the shock front as the flame fronts start from hot spots, grow, and interact behind the shock front. In this way, our grain-scale simulations can also connect to continuum experiments directly.
Author: Pier K. Tang
Publisher:
ISBN:
Category : Explosives
Languages : en
Pages : 15
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Book Description
![Numerical Calculation of Shock-induced Initiation of Detonations. [PBX 9501]. PDF](https://books.google.com/books/content/images/frontcover/7OqVnQAACAAJ?fife=w80-h100)
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Languages : en
Pages :
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The results of some numerical calculations of the impact of steel cylinders and spheres on the plastic-bonded high explosive PBX 9501 are described. The calculations were carried out by a reactive, multicomponent, two-dimensional, Eulerian hydrodynamic computer code, 2DE. The 2DE computer code is a finite difference code that uses the donor-acceptor-cell method to compute mixed cell fluxes. The mechanism of shock initiation to detonation in heterogeneous explosives is best described as local decomposition at hot spots that are formed by shock interactions with density discontinuities. The liberated energy strengthens the shock so that as it interacts with additional inhomogeneities, hotter hot spots are formed, and more of the explosive is decomposed. The shock wave grows stronger until a detonation begins. This mechanism of initiation has been described numerically by the Forest Fire burn model, which gives the rate of explosive decomposition as a function of local pressure. The parameters in the Forest Fire burn model have been developed from experiments where the induced shock approximates a plane wave and are applied, in this case, to a situation where the induced shock is a divergent wave with curvature that depends on the size and shape of the projectile. The calculated results have been compared with results from experiments involving instrumented mock and live high explosives, with projectiles of varying sizes, shapes, and velocities. We find that there is good agreement between the calculated and experimental data.
