Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session U5: Materials Science III |
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Chair: Naresh Thadhani, Georgia Institute of Technology Room: Renaissance Ballroom D |
Thursday, June 30, 2011 2:00PM - 2:15PM |
U5.00001: Effect of strain rate and dislocation density on the twinning behavior in Tantalum Jeffrey Florando, James McNaney, Mary LeBlanc, Mukul Kumar, Changqiang Chen, Kaliat Ramesh, Kevin Hemker Compression experiments on polycrystalline Ta were conducted at liquid nitrogen temperatures at stain rates ranging from 10$^{-4 }$to 10$^{5}$ s$^{-1}$. In addition, samples were cold-rolled and then tested at liquid nitrogen temperatures to determine the effect of dislocation density on the overall twin fraction. Samples were also pre-strained to induce a range of dislocation densities to see the effect of the initial density on the amount of twinning observed. Recovered samples were characterized using EBSD orientation mapping along with transmission electron microscopy to assess the occurrence of twinning under each test condition. [Preview Abstract] |
Thursday, June 30, 2011 2:15PM - 2:30PM |
U5.00002: Role of stored defects on the mechanical response of shock prestrained HT-9 steel Sara Perez-Bergquist, Ellen Cerreta, George (Rusty) Gray III, Stuart Maloy, Osman Anderoglu HT-9 is a 12Cr-1Mo ferritic/martensitic steel with significant experience as cladding material in fast reactor applications. Recent investigations into precipitation of $\alpha^{\prime}$ in HT-9 steel after irradiation at elevated temperatures suggests that it nucleates at dislocation loops. It is recognized that steel shocked below the peak shock stress for the $\alpha $ to $\varepsilon $ high-pressure phase transformation results in a material with a high density of stored defects. These defects have a profound effect on subsequent mechanical properties and with additional elevated temperature exposure could serve as nucleation sites for the $\alpha^{\prime}$ precipitate. To investigate the possibility of precipitating $\alpha^{\prime}$ at dislocations, HT-9 steel was shocked at a peak pressure of 11 GPa and subsequently annealed at 475\r{ }C for up to 16 weeks. The mechanical response of shock prestrained HT-9 steel was investigated and compared to the mechanical response of the shocked and annealed material. Substructure and texture evolution due to shock loading was examined and mechanical response of shock prestrained HT-9 is rationalized in terms of these observations. [Preview Abstract] |
Thursday, June 30, 2011 2:30PM - 2:45PM |
U5.00003: The Role of the Structure of Grain Boundary Interfaces During Shock Loading Alejandro Perez-Bergquist, Juan Pablo Escobedo, Carl Trujillo, Ellen Cerreta, George Gray In order to understand the role of interface structure during shock loading, and specifically the role of interfaces in damage evolution due to shock, four copper bi-crystal boundaries were studied under shock loading and incipient spall conditions. These boundaries, two 001/111 boundaries and two 001/001 boundaries, were characterized prior to deformation using both electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM) to determine axis/angle pair relationships and grain boundary structure. Samples containing these boundaries were then subjected to incipient spall at 2.5 GPa and shock loading at 10 GPa, respectively, in an 80 mm gas gun. Samples were soft recovered and characterized post-mortem via EBSD and TEM. Preliminary results indicate that typical grain boundaries readily form damage during shock loading but that special boundaries, such as S3 twin boundaries, are resistant to failure. Differences in slip and defect transmissibility across these types of boundaries likely play a role in the failure modes. [Preview Abstract] |
Thursday, June 30, 2011 2:45PM - 3:00PM |
U5.00004: Dynamic Deformation and Fragmentation Response of Maraging Steel Linear Cellular Alloy Adam Jakus, D.A. Fredenburg, T. McCoy, N.N. Thadhani, J. Cochran The dynamic deformation and fragmentation response of 25{\%} dense 9-cell linear cellular alloy (LCA) made of unaged 250 maraging steel, fabricated using a direct reduction and extrusion technique, is investigated. Explicit finite element simulations were implemented using AUTODYN. The maraging steel properties were defined using a Johnson-Cook strength model with previously validated parameters. Rod-on-anvil impact tests were performed using the 7.6mm helium gas gun and the transient deformation and fragmentation response was recorded with high-speed imaging. For purpose of comparison, the response of 25{\%} dense hollow cylinders of same density as the 9-cell LCA was also studied. Analysis of observed states of specimens and finite element simulations reveal that in the case of the 9-cell LCA, dissipation of stress and strain occurs along the interior cell wells resulting in significant and ubiquitous buckling prior to confined fragmentation. In comparison, the simple hollow cylinder undergoes significant radial lipping, eventually producing larger sized, external fragments. [Preview Abstract] |
Thursday, June 30, 2011 3:00PM - 3:15PM |
U5.00005: The condition for dynamic recrystallization of aluminum alloy in shock waves Natalia Naumova, Svetlana Atroshenko, Yuri Mescheryakov, Alexandr Divakov A series of mechanical tests on aluminum alloy samples under uniaxial strain conditions in single and double impact loading regimes showed that dynamic recrystallization in localized shear bands takes place only in the latter case, with the second (additional loading) pulse delayed by 0.5--0.7 $\mu $s relative to the first shock-wave front. It is established that, in addition to well-known conditions ($\gamma \quad \ge $ 3, $\dot {\gamma }\ge $ 10$^{4}$ s$^{-1}$, $T \ge $0.4$T_{m})$, a determining role in the dynamic recrystallization process is played by the nonuniformuty (variation) of particle velocity at the leading front of the compression pulse. [Preview Abstract] |
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