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 F4: Inelastic Deformations, Fracture and Spall V |
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Chair: Justin Wilkerson, University of Texas San Antonio Room: Regency Ballroom A |
Monday, July 10, 2017 5:00PM - 5:15PM |
F4.00001: Measuring twinning and slip in shock-compressed Ta from in-situ x-ray diffraction Christopher Wehrenberg, David McGonegle, Marcin Sliwa, Matt Suggit, Justin Wark, Hae Ja Lee, Bob Nagler, Franz Tavella, Bruce Remington, Rob Rudd, Amy Lazicki, Hye-Sook Park, Damian Swift, Louis Zepeda-Ruiz, Andrew Higginbotham, Cindy Bolme A fundamental understanding of high-pressure and high-strain-rate deformation rests on grasping the underlying microstructural processes, such as twinning and dislocation generation and transport (slip), yet simulations and \textit{ex-post-facto} recovery experiments provide conflicting answers to these basic issues. Here, we report direct, in-situ observation of twinning and slip in shock compressed Ta using in-situ x-ray diffraction. A series of shock experiments were performed on the Matter in Extreme Conditions end station at LCLS. Direct laser ablation was used to drive a shock, ranging in pressure from 10-300 GPa, into a Ta sample with an initial (110) fiber texture. The subsequent changes in texture were observed in-situ by examining the azimuthal distribution of the diffraction intensity and found to match twinning and lattice rotation. Measurements of the twin fraction and lattice rotation were used to calculate the equivalent plastic strain from twinning and slip. [Preview Abstract] |
Monday, July 10, 2017 5:15PM - 5:30PM |
F4.00002: Deformation Twinning in Shock Compressed Magnesium Alloys Cyril Williams, Jonathan Ligda Extension \textbraceleft 10-12\textbraceright and contraction \textbraceleft 10-11\textbraceright twins, each with six twinning variants are the most prevalent deformation twins observed in magnesium and magnesium alloys. Twinning plays an important role on the plastic deformation of magnesium and magnesium alloys because they increase the deformation modes available during straining. Therefore, deformation twinning, texture changes, and second phase intermetallic particles were studied under shock compression using AZ31B and AMX602 magnesium alloys, which were mechanically processed via Equal Channel Angular Extrusion (ECAE) and Spinning Water Atomization Process (SWAP) respectively. Results show that twinning, texture changes, and second phase intermetallic particles can strongly influence the mechanical response and consequent failure of these materials. Spall failure in the ECAE processed AZ31B-4E magnesium alloy was dominated by debonding of the matrix magnesium from large Al-Mn-rich intermetallic inclusions after the passage of shock stresses ranging from 1.5 - 4.5 GPa. Whilst failure in the SWAP AMX602 magnesium alloy for the same shock stress range reveals numerous isolated cracks around the spall plane. The spall surfaces of the AMX602 samples were striated possibly due to corrosion of the SWAP powder prior to green-compaction. Mixed-mode failure was observed in both materials possibly due to homogeneous and heterogeneous nucleation, growth, and coalescence of nanovoids and microvoids respectively. [Preview Abstract] |
Monday, July 10, 2017 5:30PM - 5:45PM |
F4.00003: Ballistic behavior of anisotropic metals Jeffrey Lloyd Finite element simulations are used to understand the localization, damage, and failure behavior that occurs during ballistic penetration. Spherical projectiles are launched at low to intermediate velocities against metal targets that possess pronounced anisotropy. Because much of our current understanding of ballistic behavior is rooted in the assumption that metals are well-described by isotropic strength and failure relations, special attention is given to highlight how a material's anisotropy causes its ballistic response to deviate from the idealized isotropic description. Where possible, comparisons are made with spatio-temporal velocity measurements of back-face deformation, as well as with post-mortem features observed in intact and failed targets. [Preview Abstract] |
Monday, July 10, 2017 5:45PM - 6:00PM |
F4.00004: Shock Compression and Release of a-axis Magnesium Single Crystals: Anisotropy and Time-Dependent Elastic-Inelastic Response P. Renganathan, J. M. Winey, Y. M. Gupta To understand the role of crystal anisotropy on shock-induced inelastic deformation in hexagonal close-packed metals, magnesium (Mg) single crystals were subjected to shock compression and release along c- and a-axes to 3.0 and 4.8 GPa elastic impact stresses. Wave profiles, measured using laser interferometry, showed a sharply peaked elastic wave followed by a plastic wave and time-dependent response. Compared with c-axis Mg, the elastic wave amplitudes for a-axis Mg were lower and less attenuation of the elastic wave amplitude was observed. The featureless release wave for a-axis Mg was in marked contrast to the structured features observed for c-axis Mg. Numerical simulations, using a time-dependent anisotropic modeling framework, showed that the wave profiles calculated using either prismatic slip or (10\=12) twinning, individually, do not match the measured a-axis compression profiles but a good match is obtained when both are incorporated together. In contrast, prismatic slip alone provides a reasonable match to the measured release wave profiles. The experimental results and the corresponding simulations for c- and a-axis Mg demonstrate the important role of crystal anisotropy on the time-dependent inelastic deformation response of shocked and released Mg single crystals. [Preview Abstract] |
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