Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session Y4: MS: Anisotropy & Orientation-Dependent Behavior |
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Chair: Jason Scharff, MSTS Room: Pavilion West |
Friday, June 21, 2019 9:15AM - 9:30AM |
Y4.00001: The effects of orientation on the shock induced microstructure of single crystal tantalum Glenn Whiteman, Bo Pang, Jeremy Millett, Yu-Lung Chiu, Ian Jones The understanding of a materials response to shock loading (or any other loading regime) requires knowledge of microstructural development during the loading process. Given that many engineering materials have complex microstructures consisting of individual grains of different orientations, textural effects and the possibility of multiple phases, the mechanical response can be cumulative in nature, making the individual aspects difficult to isolate. Matters can be simplified for example by examining the response of single crystals, where many, if not all of these additional features can be eliminated. In this paper, we investigate the microstructural response of single crystal tantalum, orientated in the principal ([100], [110] and [111]) orientations. Recovered samples have been shock loaded and released under full one dimensional strain conditions, using a technique where all three orientations were loaded simultaneously in the same fixture. [Preview Abstract] |
Friday, June 21, 2019 9:30AM - 9:45AM |
Y4.00002: Shock Compression of Molybdenum Single Crystals to High Stresses Tomoyuki Oniyama, Yogendra Gupta, Guruswami Ravichandran To investigate the effect of crystal anisotropy and to elucidate the role of slip systems in BCC crystals, Molybdenum(Mo) single crystals were subjected to shock compression along [100], [111] and [110] directions to various impact stresses up to 190 GPa. The set of impact stresses in this work covers the stress range that is significantly higher than previously studied (12.5GPa). Particle velocity histories and the shock wave velocities were measured using laser interferometry. Along [100] and [111] directions, a two-wave structure, an elastic wave followed by a plastic wave, was observed up to 110 GPa impact stress. Along [110] direction, the two-wave structure was observed only up to 90 GPa impact stress. For all three directions, the elastic amplitude exhibited dependence on the impact stress. The dependence on impact stress was comparable along [100] and [110] directions, and larger along [111] direction. In contrast, at higher impact stresses, only overdriven waves were measured for all orientations. In addition to the experiments, molecular dynamics simulations were carried out to gain insight into the deformation mechanisms. The results of the 90GPa impact simulation revealed the activation of slip systems. This work was supported by DOE/NNSA. [Preview Abstract] |
Friday, June 21, 2019 9:45AM - 10:00AM |
Y4.00003: Dynamic Strength Properties of Single Crystal Iron Sarah A. Thomas, Robert S. Hixson, Brandon M. LaLone, Gerald D. Stevens, William D. Turley The dynamic properties of single crystal metals, including anisotropic dynamic properties, have not been extensively studied. Single crystal metal research is motivated by a need to better understand directional properties and how these properties influence the polycrystalline metal. We chose to study iron because of its relatively high anisotropy ratio of A $=$ 2.34, which causes distinct directional differences in elastic properties. Our ultimate research goal is to examine the dynamic properties of single crystal iron in the three principal orientations: [100], [110], and [111]. We have conducted gas gun experiments in which 1018 cold rolled steel and single crystal iron flyer plates impacted single crystal iron targets in the [100] direction at nominally 300 m/s. The resulting velocimetry plots show elastic yield behavior that is much different than that of polycrystalline iron. The single crystal data show a marked overshoot and subsequent relaxation of the elastic wave, rather than a single yield stress, as seen in polycrystalline iron. The reasons for this difference will be discussed. Additionally, comparisons will be made between yield stresses in dynamic and static experiments. [Preview Abstract] |
Friday, June 21, 2019 10:00AM - 10:15AM |
Y4.00004: Orientation dependent mechanical behavior of shocked AMX602 Mg alloy Scott Turnage, Chad Hornbuckle, Cyril Williams, Kristopher Darling Shock loading provides a means of strengthening beyond the limits of traditional hardening mechanisms in certain alloys. However, while the potential benefits of applying such strengthening mechanisms to lightweight materials are appealing, the effects of shock loading on the residual microstructure and mechanical behavior of complex materials such as ultrafine grained AMX602 Mg alloy have not been thoroughly investigated. To resolve this, samples of ultrafine grained AMX602 Mg alloy are shocked, released, and recovered for microstructural and mechanical analyses. The influence of the high anisotropy of the extruded Mg alloy on the shock deformed structure is probed using electron backscatter diffraction (EBSD), micro-tension testing, and micro hardness testing. Results indicate that significant twinning is observed resulting from shock compression along the extrusion direction. When placed under quasi-static tensile stress, detwinning occurs in both the extrusion and normal directions resulting in a high degree of ductility. [Preview Abstract] |
Friday, June 21, 2019 10:15AM - 10:30AM |
Y4.00005: Pressure-Shear plate impact experiments of Magnesium at high pressures. Suraj Ravindran, Zev Lovinger, Christian Kettenbeil, Michael Mello, Guruswami Ravichandran Magnesium and its alloys are widely used in the aerospace, automotive and defense industries, taking advantage of its high strength to weight ratio. However, these materials show strong anisotropy with its hexagonal close pack structure and texture, which must be understood under desired loading conditions. The experimental investigations probing into the anisotropic behavior of these materials at high pressures and strain rates are limited. In this study, experiments are conducted on extruded commercially pure magnesium and equal channel angular pressed AZ31B using pressure shear plate impact (PSPI) experiments. The strength and the behavior of the materials are measured at pressures up to 15 GPa and strain rates of 10$^{\mathrm{6}}$ s$^{\mathrm{-1}}$. The PSPI experiments enable to measure the materials under unique conditions, loading the material simultaneously in two directions. Different orientations of anisotropy are examined, where, normal compressive stresses are aligned in one direction and shear stresses, probing the material strength, are aligned perpendicular to it. The effect of anisotropy on the behavior of these materials under high pressures and strain rates are discussed and compared with the previous work on these materials. Keywords: Shock, Magnesium, AZ31B, Strength. [Preview Abstract] |
Friday, June 21, 2019 10:30AM - 10:45AM |
Y4.00006: Diamond Single Crystals Shocked to Multi-Megabar Stresses: Anisotropy and Deformation Y. M. Gupta, M. D. Knudson, J. M. Winey Although the shock wave response of diamond at high stresses is of wide-ranging scientific and technical importance, it remains poorly understood. To gain insight into material strength and crystalline anisotropy effects at high stresses, plate impact experiments are underway on diamond single crystals shocked along the [100], [110], and [111] orientations to 400 – 900 GPa elastic impact stress (EIS) using the Sandia Z facility. Thin copper flyers are launched against diamond crystals, backed by quartz or LiF windows, to examine the shock compression and release response. Shock wave transit times in the diamond samples and either shock velocity histories of the optically reflective wave front in the quartz window or particle velocity histories at the diamond/LiF window interface are measured using laser interferometry. Preliminary results reveal two-step waves (elastic-inelastic response), with large elastic waves, to 900 GPa EIS for [110] and [111] diamond. In contrast, single (overdriven) wave profiles were determined at 480 GPa EIS and above for [100] diamond. In addition, the elastic wave amplitudes show significant orientation dependence. Further experiments and the development of a continuum model are underway to understand the strong anisotropy observed at high stresses. [Preview Abstract] |
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