Numerical Modeling Of Heterogeneous High Explosives

This report contains a numerical algorithm for modeling the detonation and explosion of a heterogeneous mixture of high explosive and small metal particles. The simulation examines a spherical explosive design with a mixture of nitromethane as the high explosive and steel as the metal particles. The algorithm provides a computational model of the detonation and explosion by producing position, velocity, and temperature profiles for the metal particles over time. For the gas phase, the algorithm produces position, velocity, temperature, density, and pressure profiles over time. This is accomplished by taking into account the initial position and velocity profiles for the metal particles, a corresponding particle drag law, appropriate explosive energy and detonation pressure inputs, and a blast wave solution that governs the thermodynamic state of the gas phase. The behavior of the solid particles and gas phase throughout the explosion is simulated by a coupled, two-phase algorithm. The results of the model are compared against experimental data and critiqued on a theoretical level as well. Recommendations and plans for improvements to the algorithm are discussed. This model is intended to provide a sound representation of the detonation as well as insight into the behavior of a heterogeneous explosive.

Major advances, both in modeling methods and in the computing power required to make those methods viable, have led to major breakthroughs in our ability to model the performance and vulnerability of explosives and propellants. In addition, the development of proton radiography during the last decade has provided researchers with a major new experimental tool for studying explosive and shock wave physics. Problems that were once considered intractable – such as the generation of water cavities, jets, and stems by explosives and projectiles – have now been solved. Numerical Modeling of Explosives and Propellants, Third Edition provides a complete overview of this rapidly emerging field, covering basic reactive fluid dynamics as well as the latest and most complex methods and findings. It also describes and evaluates Russian contributions to the experimental explosive physics database, which only recently have become available. This book comes with downloadable resources that contain— · FORTRAN and executable computer codes that operate under Microsoft® Windows Vista operating system and the OS X operating system for Apple computers · Windows Vista and MAC compatible movies and PowerPoint presentations for each chapter · Explosive and shock wave databases generated at the Los Alamos National Laboratory and the Russian Federal Nuclear Centers Charles Mader’s three-pronged approach – through text, computer programs, and animations – imparts a thorough understanding of new computational methods and experimental measuring techniques, while also providing the tools to put these methods to effective use.

The initiation of propagating, diverging detonation is usually accomplished by small conventional initiators. As the explosive to be initiated becomes more shock insensitive, the initators must have larger diameters to be effective. Very shock-insensitive explosives have required initiators larger than 2.5 cm. We have numerically examined the process of initiation of propagating detonation as a function of the shock sensitivity of the explosive using the two-dimensional Lagrangian reactive hydrodynamic code 2DL and the Forest Fire rate to describe the shock initiation process of heterogeneous explosives. The initiation of propagating detonation in shock-insenstive explosives containing triamino trinitrobenzene results in large regions of partially decomposed explosive even when initiated by large initiators. The process has been observed experimentally and reproduced numerically.

Charles Mader, a leading scientist who conducted theoretical research at Los Alamos National Laboratory for more than 30 years, sets a new standard with this reference on numerical modeling of explosives and propellants. This book updates and expands the information presented in the author's landmark work, Numerical Modeling of Detonations, published in 1979 and still in use today. Numerical Modeling of Explosives and Propellants incorporates the considerable changes the personal computer has brought to numerical modeling since the first book was published, and includes new three-dimensional modeling techniques and new information on propellant performance and vulnerability. Both an introduction to the physics and chemistry of explosives and propellants and a guide to numerical modeling of detonation and reactive fluid dynamics, Numerical Modeling of Explosives and Propellants offers scientists and engineers a complete picture of the current state of explosive and propellant technology and numerical modeling. The book is richly illustrated with figures that support the concepts, and filled with tables for quick access to precise data. The accompanying CD-ROM contains computer codes that are the national standard by which modeling is evaluated. Dynamic material properties data files and animation files are also included. There is no other book available today that offers this vital information.

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We performed continuum mechanics simulations to examine the behavior of energetic materials in Ballistic Chamber Impact (BIC) experiments, using an Arbitrary Lagrangian-Eulerian code (ALE3D). Our simulations revealed that interface friction plays an important role in inducing the formation of shear bands, which result in 'hot spots' for ignition. The temperature localization during BIC impact was found to be significant in materials with high yield strength. In those materials, there are multiple locations inside shear bands can achieve temperatures exceeding the threshold temperature for reaction. In addition, we investigated the relevant parameters influencing the pressure profile of a BIC test by numerical analysis from a simple phenomenological model. To our surprise, we found that the peaks of BIC pressure profiles not only can be a result of multi-center chemical reactions, but can also arise from factors associated apparatus configuration.

Papers presented in this publication cover special problems in the field of energetic materials, particularly detonation phenomena in solids and liquids. General subject areas include shock-to-detonation transition, time resolved chemistry, initiation modeling, deflagration-to-detonation transition, equation of state and equation of state and performance, composites and emulsions, and composites and emulsions/underwater explosives, reaction zone, detonation wave propagation, hot spots, detonation products, chemistry and compositions, and special initiation.

Plastic-bonded explosives (PBX) are heterogeneous materials. Nevertheless, current explosive models treat them as homogeneous materials. To compensate, an empirically determined effective burn rate is used in place of a chemical reaction rate. A significant limitation of these models is that different burn parameters are needed for applications in different regimes; for example, shock initiation of a PBX at different initial temperatures or different initial densities. This is due to temperature fluctuations generated when a heterogeneous material is shock compressed. Localized regions of high temperatures are called hot spots. They dominate the reaction for shock initiation. The understanding of hot spot generation and their subsequent evolution has been limited by the inability to measure transients on small spatial (≈ 1 [mu]m) and small temporal (≈ 1 ns) scales in the harsh environment of a detonation. With the advances in computing power, it is natural to try and gain an understanding of hot-spot initiation with numerical experiments based on meso-scale simulations that resolve material heterogeneities and utilize realistic chemical reaction rates. However, to capture the underlying physics correctly, such high resolution simulations will require more than fast computers with a large amount of memory. Here we discuss some of the issues that need to be addressed. These include dissipative mechanisms that generate hot spots, accurate thermal propceties for the equations of state of the reactants and products, and controlling numerical entropy error from shock impedance mismatches at material interfaces. The later can generate artificial hot spots and lead to premature reaction. Eliminating numerical hot spots is critical for shock initiation simulations due to the positive feedback between the energy release from reaction and the hydrodynamic flow.