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 Z5: Materials V: Microstructure 2 |
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Chair: Rachael Abrahams, Air Force Research Lab, Eglin AFB Room: Regency Ballroom B |
Friday, July 14, 2017 11:15AM - 11:30AM |
Z5.00001: Contrasting the effects of cold rolling on the shock response of typical face centred cubic and body centred cubic metals Jeremy Millett, Daniel Higgins, Glenn Whiteman, Ian Jones, Neil Bourne The response of metals to shock loading is affected by a number of factors, including the unit cell and properties that effect the motion and generation of dislocations such as stacking fault energy and the Peierls stress. In an effort to increase the understanding in this area, we have chosen to investigate the response of two near ideal materials; copper as an fcc and tantalum as a bcc. We have also investigated each material in both an annealed and cold worked to 50{\%} reduction in thickness in an attempt to understand how differences in dislocation density effect response. Measurements have been made using standard diagnostics, including stress gauges and Photonic Doppler Velocimetry as well as analysis of the shocked microstructural and mechanical response through one-dimensional recovery. [Preview Abstract] |
Friday, July 14, 2017 11:30AM - 11:45AM |
Z5.00002: Grain-level microstructural changes in shock-compressed polycrystalline Al: use of multi-frame synchrotron x-ray diffraction Stefan Turneaure, Y. M. Gupta Grain-level microstructural changes were examined in shock-compressed polycrystalline Al samples using multi-frame x-ray diffraction measurements at the Dynamic Compression Sector (Advanced Photon Source, Argonne). Polycrystalline Al samples with different grain sizes were impacted with LiF(100) impactors resulting in impact stresses from 5.5-12.7 GPa. Pulsed x-rays (153.4 ns between pulses) passed through the LiF impactor, the polycrystalline Al sample, and an Al(100) single crystal x-ray window bonded to the rear surface of the polycrystalline Al sample. The x-rays were incident on the target at an angle of 30 degrees to the impact surface. Four x-ray diffraction images were obtained during shock-compression and unloading. Fine grained polycrystalline Al samples (\textless 5 micrometer grains) were initially textured and no changes to the initial texture were observed either during compression or during unloading. For larger grained samples (\textasciitilde 34 micrometer grain size), x-ray diffraction spots from individual grains were observed in unshocked samples. In shock-compressed Al, the diffraction spots from the individual grains grew in size such that they were largely overlapping indicating grain substructure development during shock compression. These experiments demonstrate the ability to examine the time-evolution of grain-level microstructural changes (texture and substructure evolution) in shock compressed polycrystalline materials at the Dynamic Compression Sector. [Preview Abstract] |
Friday, July 14, 2017 11:45AM - 12:00PM |
Z5.00003: An atomistic study of the effect of micro-structure on the HEL evolution in a nanocrystalline aluminum R. Valisetty, A. Rajendran, A. Dongare, R. Namburu This study focuses on the shock precursor decay phenomena in pure aluminum crystals and nanocrystalline aluminum (nc-Al) systems under one dimensional strain condition using large scale molecular dynamics (MD) simulations. For this purpose, two different atom systems are modeled for the nc-Al: 1) 900 {\AA} thick (\textasciitilde 20 million atoms) with grain sizes ({\AA}): 60, 100, 140 and 180, and 2) 5000 {\AA} thick (\textasciitilde 2 billion atoms) with grain sizes ({\AA}): 180, 500, and 1000. The MD simulations considered a plate-on-plate configuration at five impact velocities between 0.7 km/s to 1.5 km/s. The very large MD results (\textasciitilde 100s of terabytes) are modeled using a material conserving atom slicing method, based on averaged stress distributions along the shock fronts. The effects of grain sizes on dislocation evolutions at the HEL are analyzed in terms of precursor decay profiles at various distances along the shock front. The results indicate that the effect of impact velocity on the HEL amplitudes becomes insignificant after the wave propagates certain characteristic distances. However, the grain size significantly influences the material shock strength. By combining HELs determined from MD results with plate impact experimental data reported in literature for pure aluminum, the precursor decay for nc-Al systems was constructed across nano to macro length scales. The construct is based on the assumption that the plasticity is a result of accumulations of defects or dislocations from a very small scale to a large scale of the material. [Preview Abstract] |
Friday, July 14, 2017 12:00PM - 12:15PM |
Z5.00004: Abstract Withdrawn |
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