Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session D6: Inelastic Deformations, Fracture and Spall I |
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Chair: Michael Winey, Washington State University, Eugene Zaretsky, Ben-Gurion University of the Negev Room: 8/9/10 |
Monday, June 15, 2015 2:00PM - 2:15PM |
D6.00001: Change of regime of decay of elastic precursor wave in BCC metals Eugene Zaretsky, Gennady Kanel Our studies of decay of elastic precursor wave with propagation distance in five BCC metals, namely V, Ta, Fe, Nb, and Mo show that at propagation distances of about $h* =$1 mm the regime of the decay is changed. At propagation distances smaller than $h*$ the decay is fast and the spatial variation of the elastic wave amplitude $\sigma_{HEL}$ is described by the power function $\sigma_{HEL} =\sigma _{\mathrm{0}}(h$/$h_{\mathrm{0}})^{\mathrm{-\alpha}}$ with $\alpha $ ranged between 0.3 and 0.7 for different metals at different temperatures. Beyond the distance $h*$ the decay is much slower and is characterized by much lower values of $\alpha $, of about 0.1 or less. The stresses $\tau $* at which the transition occurs at room temperature is close to the Peierls stresses $\tau_{P}$ of the studied metals. This allows us to conclude that the change of the decay regime at $\tau $* is caused by the change of the mode of the dislocations motion from the over-barrier glide controlled by the phonon viscous drag above $\tau $* to that controlled by thermally activated generation/motion of the dislocation double-kinks below $\tau $*. The decline of $\tau $* with temperature ($\sim$ 50{\%} over 1000-K interval) agrees with the growing with temperature support of dislocation motion by thermal fluctuation. [Preview Abstract] |
Monday, June 15, 2015 2:15PM - 2:30PM |
D6.00002: Shock-Induced Elastic-Plastic Deformation of Molybdenum Single Crystals A. Mandal, Y.M. Gupta To gain insight into the shock-induced deformation response of Molybdenum (Mo), high purity single crystal samples were shocked along $<$100$>$, $<$110$>$, and $<$111$>$ orientations to a peak stress of 12.5 GPa. Elastic-plastic wave profiles, measured at different propagation distances ranging between 0.3 and 3 mm using laser interferometry, suggest a highly anisotropic time-dependent material response. Initially, the elastic wave amplitude exhibited a large and rapid decay before reaching a threshold stress beyond which no significant decay occurred. The decay rates were larger along $<$100$>$ and $<$110$>$ orientations. The resolved shear stresses on the quasi-static slip systems at the threshold stress are comparable to the reported Peierls stress of screw dislocations in Mo. Numerical simulations, performed using a dislocation-based plasticity model, suggested that quasi-static slip systems are likely operative under shock loading. A good fit to the measured profiles was obtained when a term, representative of dislocation nucleation [Winey and Gupta, J. Appl. Phys. \textbf{99}, 023510 (2006)], was included in the model in addition to regenerative multiplication. A physical justification for the nucleation term will be discussed. Work supported by DOE/NNSA. [Preview Abstract] |
Monday, June 15, 2015 2:30PM - 2:45PM |
D6.00003: Two-Dimensional Imaging Velocimetry of Heterogeneous Flow and Brittle Failure in Diamond Suzanne Ali, Raymond Smith, David Erskine, Jon Eggert, Peter Celliers, Gilbert Collins, Raymond Jeanloz Understanding the nature and dynamics of heterogeneous flow in diamond subjected to shock compression is important for many fields of research, from inertial confinement fusion to the study of carbon rich planets. Waves propagating through a shocked material can be significantly altered by the various deformation mechanisms present in shocked materials. Quantifying the spatial and temporal effects of these deformation mechanisms has been limited by a lack of diagnostics capable of obtaining simultaneous micron resolution spatial measurements and nanosecond resolution time measurements. We have utilized the 2D Janus High Resolution Velocimeter at LLNL to study the time and space dependence of fracture in shock-compressed diamond above the Hugoniot elastic limit. We have imaged the development and evolution of elastic-wave propagation, plastic-wave propagation, and fracture networks in the three primary orientations of single-crystal diamond, as well as in microcrystalline and nanocrystalline diamond, and find that the deformation behavior depends sensitively on the orientation and crystallinity of the diamonds. [Preview Abstract] |
Monday, June 15, 2015 2:45PM - 3:00PM |
D6.00004: Shock Compression and Release of c-axis Magnesium Single Crystals: Time-Dependent Elastic-Inelastic Response Prithachakaran Renganathan, J.M. Winey, Y.M. Gupta To gain insight into the inelastic deformation mechanisms for shocked hcp metals, 0.5 - 4.0 mm thick c-axis magnesium (Mg) single crystals were shocked to peak stresses of 2.6 and 4.2 GPa followed by release. Measured wave profiles, obtained using laser interferometry, show a two-wave elastic-inelastic response. Rapid decay of the elastic precursor and the stress relaxation behind the elastic wave indicate a strongly time-dependent elastic-inelastic response. Several interesting experimental observations are: the distinct peaked structure observed in the release wave; the significant scatter observed in the measured elastic wave amplitude for 0.5 mm thick samples; and the larger elastic wave amplitudes in the lower peak stress (2.6 GPa) experiments compared to the elastic wave amplitudes in the higher peak stress (4.2 GPa) experiments. Numerical simulations, carried out using a time-dependent anisotropic modeling framework, show that wave profiles calculated using a combination of dislocation slip and twinning provide a good match to the measured profiles for c-axis Mg. Efforts to resolve and understand the scatter in the thin sample experiments and the relationship between the elastic wave amplitude and peak stresses are underway. Work supported by ARL and DOE/NNSA. [Preview Abstract] |
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