Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session Z2: Detonation and Shock-Induced Chemistry: Hot Spots - Early Dynamics |
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Chair: Will Bassett, University of Illinois at Urbana-Champaign Room: Grand Ballroom AB |
Friday, July 14, 2017 11:15AM - 11:30AM |
Z2.00001: Probing Dynamic Processes in Explosives and Propellants -- Science Issues David Moore Recent experiments on advanced light sources have started to unravel some of the micromechanical behavior of single crystal energetic materials, including void collapse under shock loading and inter-granular failure. These examples just scratch the surface of many extant explosives science issues, which could be elucidated with advanced XFEL-type resources. These include such diverse questions as: How do powders actually compact and what are the spatially and temporally resolved temperature and flow fields generated (especially two-phase flows)? Are there polymorphic effects (if so, how are they spatially distributed)? What are the strain fields during compaction? What happens near surfaces, especially for composite explosives? How is mechanics coupled to chemistry? What are hot spots really? I will provide some history behind these and other questions and point towards how future experiments might be designed to provide some answers. [Preview Abstract] |
Friday, July 14, 2017 11:30AM - 11:45AM |
Z2.00002: 3D Simulations of Void collapse in Energetic Materials. Nirmal Kumar Rai, H.S. Udaykumar Voids present in the microstructure of heterogeneous energetic materials effect the sensitivity towards ignition. It is established that the morphology of voids can play a significant role in sensitivity enhancement of energetic materials. Depending on the void shape, sensitivity can be either increased or decreased under given loading conditions. In the past, effects of different void shapes i.e. triangular, ellipse, cylindrical etc. on the sensitivity of energetic materials have been analyzed. However, most of these studies are performed in 2D and are limited under the plain strain assumption. Axisymmetric studies have also been performed in the past to incorporate the 3D effects, however axisymmetric modeling is limited to only certain geometries i.e. sphere. This work analyzes the effects of various void shapes in three dimensions on the ignition behavior of HMX. Various void shapes are analyzed including spherical, prolate and oblate speheroid oriented at different orientations, etc. Three dimensional void collapse simulations are performed on a single void to quantify the effects void morphology on initiation. A Cartesian grid based Eulerian solver SCIMITAR3D is used to perform the void collapse simulations. Various aspects of void morphology i.e. size, thickness of voids, elongation, orientation etc. are considered to obtain a comprehensive analysis. Also, 2D plane strain calculations are compared with the three dimensional analysis to evaluate the salient differences between 2D and 3D modeling. [Preview Abstract] |
Friday, July 14, 2017 11:45AM - 12:00PM |
Z2.00003: Detonation initiation in atomistic and mesoscopic simulation of porous explosives Semen Murzov, Vasily Zhakhovsky Atomistic simulation of chemical reactions activated by shock compression is feasible at sub-nanosecond timescale, and molecular dynamics simulation indicates that the most energetic reactions accomplish within several tens of picosecond. This is too short time in comparison with microseconds required for experimental shock-to-detonation transition in real solid explosives with pores. Different types of hotspots were found in MD simulation of porous explosive described by AB model. Those types are categorized according to ratios between a characteristic time of reactions, a material motion time and a time of hotspot formation. The characteristic time of reaction is determined in MD simulation of isochoric thermal decomposition at different densities. To transfer such information into macroscopic spatial-time scale a simple model of material decomposition using a local thermodynamic and chemical equilibrium was developed. Consistent MD simulation and hydrodynamics modeling of AB samples by our smoothed particle hydrodynamic code are agreed well. The developed model was utilized in mesoscale modeling of shock-to-detonation transition in real porous explosives. [Preview Abstract] |
Friday, July 14, 2017 12:00PM - 12:15PM |
Z2.00004: Simulation of hot spots formation and evolution in HMX Cheng Wang, Tonghui Yang In order to study the formation and evolution of hot spots under shock loading, HMX explosives were selected as the object of study for the two-dimensional finite difference numerical simulation. A fifth order finite difference weighted essentially non-oscillatory (WENO) scheme and a third order TVD Runge--Kutta method are utilized for the spatial discretization and the time advance, respectively. The governing equations are based on the fluid elasto-plastic control equations. The Mie-Gruneisen equation of state and the ideal gas equation of state are selected to use in the state equation of the solid explosives and gas material. In order to simplify the calculation of the model, the reaction can be considered to complete in one step. The calculated area is [3.0*10$^{\mathrm{-5}}$ m]×[3.0*10$^{\mathrm{-5}}$ m]. The radius is 0.6*10$^{\mathrm{-5}}$ m, and the internal gas is not involved in the reaction. The calculation area is divided into 300*300 grids and 10 grids are selected from the bottom of each column to give the particle velocity $u$ as the initial condition. In the selected grid, different initial velocity 100m/s and 200m/s are loaded respectively to study the influence of hot spot formation and evolution in different impact intensity. [Preview Abstract] |
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