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 Y4: Phase Transitions VI: Advances |
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Chair: Saryu Fensin, Los Alamos National Laboratory, Brad Steele, University of South Florida Room: Grand H |
Friday, June 19, 2015 9:15AM - 9:30AM |
Y4.00001: Kinetics of $\alpha $ to $\omega $ structural transition in zirconium Nenad Velisavljevic, Matthew Jacobsen, Stanislav Sinogeikin, Dmitry Popov Zirconium (Zr), along with the other group IV-B transition metals titanium (Ti) and hafnium (Hf), has been widely investigated at high P-T conditions. Initial interest in Zr may have been driven in part by need to understand structural stability at conditions that these materials could experience in a wide range of commercial applications. Multiple studies demonstrate that, at elevated pressure, these metals and their alloys undergo a structural transition from hexagonal close-packed ($\alpha )$ phase to another hexagonal ($\omega )$ phase. Subsequently, $\alpha $-$\omega $ transition has been investigated in detail -- results indicate that the $\alpha $-$\omega $ boundary is significantly influenced by sample purity, experimental conditions (e.g. hydrostatic vs. uniaxial compression), loading conditions (e.g. shock vs. slower ``static'' loading), etc. Early measurements also indicate that kinetics at the onset of $\alpha $-$\omega $ transition may play a significant role in establishing the phase boundary and thus must be fully investigated to gain a more comprehensive understanding of behavior of Zr at high P-T. Ongoing advances in large scale x-ray sources and detector and instrumentation technologies have made investigations of transition kinetics over broader P-T and compression/strain rate conditions possible. Using DAC coupled with piezoelectric and/or gas membrane loading, $\alpha $-$\omega $ transition in Zr was investigated as a function of compression (P-jump) rate. Relevant results, as well as broader impacts regarding $\alpha $-$\omega $ transition mechanism, will be presented. [Preview Abstract] |
Friday, June 19, 2015 9:30AM - 9:45AM |
Y4.00002: Analysis of shock induced depolarization and current generation in ferroelectric ceramics Vinamra Agrawal, Kaushik Bhattacharya Ferroelectric generators are used to generate large magnitude current pulse by impacting a polarized ferroelectric material. The impact causes depolarization of the material and at high impact speeds, dielectric breakdown. The current or voltage profiles obtained vary depending on the loading conditions. In this study, we explore the large deformation dynamic response of a ferroelectric material. Using the Maxwell's equations, conservation laws and the second law of thermodynamics, we derive the governing equations for the phase boundary propagation as well as the driving force acting on it. We allow for the phase boundary to contain surface charges which introduces the contribution of curvature of phase boundary in the governing equations and the driving force. This type of analysis accounts for the dielectric breakdown and resulting conduction in the material. Next, we implement the equations derived to solve a one dimensional impact problem on a ferroelectric material under different electrical boundary conditions. The constitutive law is chosen to be piecewise quadratic in polarization and quadratic in the strain. We solve for the current profile generated in short circuit case and for voltage profile in open circuited case. [Preview Abstract] |
Friday, June 19, 2015 9:45AM - 10:00AM |
Y4.00003: Shock loading and release behavior of silicon nitride Nobuaki Kawai, Taiki Tsuru, Naoto Hidaka, Xun Liu, Tsutomu Mashimo Shock-reshock and shock-release experiments were performed on silicon nitride ceramics above and below its phase transition pressure. Experimental results clearly show the occurrence of elastic-plastic transition and phase transition during initial shock loading. The HEL and phase transition stress are determined as 11.6 GPa and 34.5 GPa, respectively. Below the phase transition point, the reshock profile consists of the single shock with short rise time, while the release profile shows the gradual release followed by more rapid one. Above the phase transition point, reshock and release behavior varies with the initial shock stress. In the case of reshock and release from about 40 GPa, the reshock structure is considerably dispersed, while the release structure shows rapid release. In the reshock profile from about 50 GPa, the formation of the shock wave with the small ramped precursor is observed. And, the release response from same condition shows initial gradual release and subsequent quite rapid one. These results would provide the information about how phase transformation kinetics effects on the reshock and release behavior. [Preview Abstract] |
Friday, June 19, 2015 10:00AM - 10:15AM |
Y4.00004: ABSTRACT WITHDRAWN |
Friday, June 19, 2015 10:15AM - 10:30AM |
Y4.00005: Shock-induced phase transition of Tin: experimental study with velocity and temperature measurements Camille Chauvin, Zakaria Bouchkour, Fr\'ed\'eric Sinatti, Jacques Petit To investigate polymorphic transition and melting on release of Tin, experiments under shock wave compression have been carried out from 10 GPa to 44 GPa with both velocity and temperature measurements. Interface Sn/LiF velocity has been recorded using PDV measurement technique and interface Sn/LiF temperature has been performed thnks to an optical pyrometer appropriate to detect low and high temperature (respectively under 1000 K and upper 1000 K). While PDV measurements are common and accurate, temperature remains often imprecise due to the lack of knowledge of the emissivity of the sample. Nevertheless, temperature profiles show singularities particularly during phase transition, not visible on velocity profiles. The use of an emissive layer at the interface Sn/LiF allows to estimate an accurate temperature measurement which can be compared to our numerical calculations. The profiles of velocity record and radiance record are in a good agreement in chronometry and display the polymorphic transition and the melting on release of Tin. This presentation will discuss the evidence of phase transitions on temperature measurements, the complementarity with velocity data and the advantages of an emissive layer. [Preview Abstract] |
Friday, June 19, 2015 10:30AM - 10:45AM |
Y4.00006: Interaction between shock front and free surface Haibo Hu, Jidong Yu, Luoxia Cao, Yongtao Chen, Guiji Wang, Gang Wu, Meizhen Xiang, Jun Chen, Manling Sui, Zhenxi Guo, Bo Xiao The interaction of shock front with the free surface and its influence on the formation of heterogeneous phase transition percentage distribution in the near surface region is studied in a serial of experiments. The specimen of $\Phi $8mmx0.8mm, $\Phi $8mmx0.6mm pure iron is impacted by magnetically-driven copper flyer to create shock wave with steady amplitude of 5GPa-80GPa and shock front rising time of 10$^{\mathrm{0}}$ ns -10$^{\mathrm{2}}$ ns. The velocity profile of shock wave bearing the phase transition characteristics and release wave information is measured on free surface. The recovery specimen is given to metallographic analysis to reveal the ever happened dynamic phase transition percentage of iron in the near surface region. It is predicted by the phase field simulation that a near free surface layer of several $\mu $m thickness without phase transition will remain independently on the loading intensity and shock front duration in iron while the results of the MD simulation indict extra strong dependence of temperature on shock front duration in near free surface layer. [Preview Abstract] |
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