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 H5: Phase Transitions III |
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Chair: Gilles Roy, CEA, France Room: Renaissance Ballroom D |
Tuesday, June 28, 2011 9:15AM - 9:30AM |
H5.00001: An Equation of State for Ti-6Al-4V Geoffrey Cox The alloy Ti-6Al-4V is used extensively in industry, and so an accurate equation of state (EoS) is needed for hydrocode simulations involving this material. An accurate model should include phase transitions, where across a phase boundary discontinuities in energy, density and other properties of the material are seen. Due to the limited data available for the alloy a multiphase EoS is first generated for titanium, before using a scaling method to obtain an EoS for Ti-6Al-4V. However, the final EoS produces a region of instability on the Hugoniot that has not been observed experimentally, and thus further improvements to the model are needed. Recommendations for future study are made, as well as detailing the difficulties faced using the current approach. Also, as an interim measure, a single phase analytic EoS is generated for Ti-6Al-4V which shows good agreement with the data available. [Preview Abstract] |
Tuesday, June 28, 2011 9:30AM - 9:45AM |
H5.00002: Equilibrium Conditions at a Solid-Solid Interface JeeYeon Plohr We derive the thermodynamic conditions necessary for two elasto-plastic solid phases to coexist in equilibrium. Beyond temperature, velocity, and traction continuity, these conditions require continuity of a generalization of the specific Gibbs free energy. We express this quantity in the Eulerian frame, as well as the Lagrangian frame. We also discuss two possible interpretations for the Gibbs free energy, which lead to distinct generalizations, except in the case of inviscid fluids, where they coincide. [Preview Abstract] |
Tuesday, June 28, 2011 9:45AM - 10:15AM |
H5.00003: High-temperature phase transformations. The properties of the phases and their equilibrium under shock loading. Invited Speaker: Introducing the temperature as a variable parameter in shock wave experiments extends essentially the scope of these investigations. The influence of the temperature variations on either high strain rate elastic-plastic response of solids or parameters of the shock-induces phase transformations are not trivial and are not quite clear yet. The technique of VISAR-monitored planar impact experiments with the samples preheated up to 1400 K was developed and used for the studies of the effect of the preheating on the impact response and on the ``dynamic'' phase diagrams of pure metals (U, Ti, Fe, Co, Ag), and ionic compounds (KCl, KBr). The studies show that the increase of the shear strength of the shock-loaded metal with temperature (first reported by Kanel et al. 1996) is typical for pure FCC (Al, Ag, Cu) and some other (Sn, U) metals, and for the ionic crystals. In the metals with BCC lattice (Mo: Duffy and Ahrens 1994, Fe: Zaretsky 2009) such thermal hardening was not found. The abrupt strength anomalies (either yield or spall or both) were observed in a narrow vicinity of the temperature of any, polymorphic, magnetic, or melting, phase transformation. It was found that when a pure element approaches the phase boundary (the line of either first or second order phase transition) the result is a 50-100-{\%} increase of the shear strength of the low-temperature phase. At the same time the presence of a small ($\sim $0.5 {\%}) amount of impurities may lead to a five-fold decrease of the strength as it takes place in the vicinity of the Curie point of Ni. The same technique being applied to the study of the shear stress relaxation (elastic precursor decay) near the transformation line may be useful for understanding the mechanisms responsible of these anomalies. [Preview Abstract] |
Tuesday, June 28, 2011 10:15AM - 10:30AM |
H5.00004: Dynamic behavior of bismuth under shock loading Yuying Yu, Chengda Dai, Ye Tan, Qingsong Wang, Qiang Wang, Hua Tan, Xuemei Li, Jun Li, Jianbo Hu Reverse-geometry impact experiments were performed on a powder gun or a two-stage light gas gun to examine the dynamic behavior of bismuth over the pressure range of 10-60 GPa. The particle velocity profiles were obtained at the bismuth/LiF window interface using DISAR system. A transition from elastic to plastic release structure shown in wave profile indicates that bismuth is in solid state at 15.7 GPa and in liquid state at 30.8 GPa. Results also showed a phase transition occurring on release from the principal Hugoniot both at 13.4 GPa and 15.7 GPa. Combined with the measured projectile velocity and the known Hugoniot for LiF crystal, the shock Hugoniot of bismuth was yield. The obtained Hugoniot data indicate that the $D-u$ curve does have a discontinuity at the particle velocity of $\sim $ 0.9 km/s, which is potentially caused by the shock-induced solid-liquid phase transformation. [Preview Abstract] |
Tuesday, June 28, 2011 10:30AM - 10:45AM |
H5.00005: Study on the Kinetics of $\gamma$ and $\alpha$ Phase Transition in Ce Material Hu Xiaomian, Pan Hao, Dai Chengda, Wu Qiang Cerium has lots of phase transition information because electron jump is easy to occur in this material. In low pressure, the phase transition and constitutive model are coupled and hard to be distinguished by single experiment. The passive confined pressure SHPB test can give the pressure-volume relation under dynamic loading and release including the phase transition character. While the plane impact experiment can give the free surface/window velocity which includes the coupled information of phase transition and constitutive model. By combinational calculation of the two experiments, taking account of the multi-phase equation of state, the phase transition and constitutive model and parameters of Cerium under dynamic loading and release can be respectively obtained. Results indicate that under loading condition the phase transition of Cerium is equilibrium. However under release it is hard to be described and non-equilibrium phase transition course is required. The change of shear modulus after the phase transition can notably influence the release process of Cerium. [Preview Abstract] |
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