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 B7: Grain-Scale to Continuum Modeling I |
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Chair: H. Keo Springer, Lawrence Livermore National Laboratory Room: Regency Ballroom F |
Monday, July 10, 2017 9:15AM - 9:30AM |
B7.00001: Direct Numerical Simulations of Microstructure Effects During High-Rate Loading of Additively Manufactured Metals Corbett Battaile, Steven Owen, Nathan Moore The properties of most engineering materials depend on the characteristics of internal microstructures and defects. In additively manufactured (AM) metals, these can include polycrystalline grains, impurities, phases, and significant porosity that qualitatively differ from conventional engineering materials. The microscopic details of the interactions between these internal defects, and the propagation of applied loads through the body, act in concert to dictate macro-observable properties like strength and compressibility. In this work, we used Sandia's ALEGRA finite element software to simulate the high-strain-rate loading of AM metals from laser engineered net shaping (LENS) and thermal spraying. The microstructural details of the material were represented explicitly, such that internal features like second phases and pores are captured and meshed as individual entities in the computational domain. We will discuss the dependence of the high-strain-rate mechanical properties on microstructural characteristics such as the shapes, sizes, and volume fractions of second phases and pores. In addition, we will examine how the details of the microstructural representation affect the microscopic material response to dynamic loads, and the effects of using ``stair-step'' versus conformal interfaces smoothed via the SCULPT tool in Sandia's CUBIT software. [Preview Abstract] |
Monday, July 10, 2017 9:30AM - 9:45AM |
B7.00002: The Effect of Surface Heterogeneities in Exploding Metallic Foils William Neal, Nathaniel Sanchez, Brian Jensen, John Gibson, Mike Martinez, Jonathon Romero, Charles Owens, Denis Jaramillo, Adam Iverson, Carl Carlson, Alex Derry, Paulo Rigg During the electrical explosion of bridge-wires and bridge-foils, the metal bridge undergoes rapid resistive-heating. The metal is rapidly expanded through solid, liquid, vapour and plasma phases. This study uses ALEGRA MHD, a Sandia National Laboratory magneto-hydrocode, to predict the formation of these metallic phases during the explosion process and determine the effects of surface heterogeneities on the spatial distribution of these phases. The simulations are compared against x-ray phase contrast radiographs of electrically exploded bridge-foils. From comparison of these data, it is evident that the meso-structure of the metallic foil dominates the explosion process and is something that should be controlled during the manufacturing processes for detonator designs. [Preview Abstract] |
Monday, July 10, 2017 9:45AM - 10:00AM |
B7.00003: A Continuum Mixture Model for Steady Detonation Using a Multiphase-Based Closure Michael Crochet Continuum mixture models are commonly used to predict the macroscale thermomechanical behavior of energetic materials. These models include evolutionary expressions for mass, momentum and energy conservation, in addition to constitutive relations for equations of state and burn rates. A separate closure relation is also required to obtain a unique solution to the model equations. However, these closure relations are either heuristic in nature, or enforce thermal equilibrium between reactant and product throughout the reaction zone, which has questionable physical merit immediately after ignition. Here, we present a framework for a generalized mixture model closure relation using principles of continuum multiphase modeling. The objective of this work is to determine a closure expression which is valid throughout the reaction process for general mixture burn rates, while enforcing model consistency between the mixture and multiphase formulations. To this end the development of a steady detonation model for the reaction zone is a preliminary step for the characterization of this model closure. Here, a one-dimensional multiphase hydrocode is used to predict the detonation structure of PBX-9501, with the results compared to those obtained from the steady detonation mixture mode [Preview Abstract] |
Monday, July 10, 2017 10:00AM - 10:15AM |
B7.00004: Temperature and Pressure from Collapsing Pores in HMX D. Barrett Hardin The thermal and mechanical response of collapsing voids in HMX is analyzed. In this work, the focus is simulating the temperature and pressure fields arising from isolated, idealized pores as they collapse in the presence of a shock. HMX slabs are numerically generated which contain a single pore, isolated from the boundaries to remove all wave reflections. In order to understand the primary pore characteristics leading to temperature rise, a series of 2D, plane strain simulations are conducted on HMX slabs containing both cylindrical and elliptical pores of constant size equal to the area of a circular pore with a 1 micron diameter. Each of these pore types is then subjected to shock pressures ranging from a weak shock that is unable to fully collapse the pore to a strong shock which overwhelms the tendency for localization. Results indicate that as shock strength increases, pore collapse phenomenology for a cylindrical pore transitions from a mode dominated by localized melt cracking to an idealized hydrodynamic pore collapse. For the case of elliptical pores, the orientation causing maximum temperature and pressure rise is found. The relative heating in elliptical pores is then quantified as a function of pore orientation and aspect ratio for a pore of a given area. [Preview Abstract] |
Monday, July 10, 2017 10:15AM - 10:45AM |
B7.00005: Linking the Grain Scale to Experimental Measurements and Other Scales Invited Speaker: Tracy Vogler A number of physical processes occur at the scale of grains that can have a profound influence on the behavior of materials under shock loading. Examples include inelastic deformation, pore collapse, fracture, friction, and internal wave reflections. In some cases such as the initiation of energetics and brittle fracture, these processes can have first order effects on the behavior of materials: the emergent behavior from the grain scale is the dominant one. In other cases, many aspects of the bulk behavior can be described by a continuum description, but some details of the behavior are missed by continuum descriptions. The multi-scale model paradigm envisions flow of information from smaller scales (atomic, dislocation, etc.) to the grain or mesoscale and the up to the continuum scale. A significant challenge in this approach is the need to validate each step. For the grain scale, diagnosing behavior is challenging because of the small spatial and temporal scales involved. Spatially resolved diagnostics have begun to shed light on these processes, and, more recently, advanced light sources have started to be used to probe behavior at the grain scale. In this talk, I will discuss some interesting phenomena that occur at the grain scale in shock loading, experimental approaches to probe the grain scale, and efforts to link the grain scale to smaller and larger scales. [Preview Abstract] |
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