Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session Q5: Phase Transitions IV |
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Chair: William Anderson, Los Alamos National Laboratory Room: Hyatt Regency Constellation F |
Wednesday, August 3, 2005 9:30AM - 9:45AM |
Q5.00001: Micromechanisms of shock-induced twinning and martensitic transformation in bcc metals Luke Hsiung Shock-induced twinning and martensitic transformation in bcc metals and alloys (Ta, Ta-10wt{\%} W and U-6wt{\%} Nb) have been studied using transmission electron microscopy (TEM). The length-scale of domain thickness for both twin lamella and martensite (or omega) phase is found to be smaller than 100 nm. While deformation twinning of {\{}211{\}}$<$111$>$-type is found to occur in Ta when shock-deformed at 15 and 45 GPa, martensitic transformation is found to occur when shock-deformed at 45 GPa. Similar phenomena of nanoscale twinning and martensitic transformation are also found within U6Nb shock-deformed at 30 GPa. Since both deformation twinning and martensitic transformation occurred along the {\{}211{\}} planes in association with high resolved shear stresses, it is suggested that both twinning and martensitic transformation can be regarded as alternative paths for shear transformations occurred in shock-deformed bcc metals. Heterogeneous nucleation mechanisms based upon a dislocation clustering reaction, which causes a localized mechanical instability, are proposed to rationalize the shock-induced twinning and martensitic transformation. [Preview Abstract] |
Wednesday, August 3, 2005 9:45AM - 10:00AM |
Q5.00002: Quantum Molecular Dynamics Simulations of Optical Reflectivity of Shock-Compressed Tin J.D. Kress, L.A. Collins, S. Mazevet Shock-compression experiments have measured the optical reflectivity of tin in an attempt to detect the melting during the release of the strongly shocked material. Recent quantum molecular dynamics (QMD) simulations have been successful at determining the optical properties of warm, dense materials such as shock-compressed deuterium and exploding wires made of aluminum and copper. In this work, we present QMD calculations of the optical conductivity and reflectivity of solid (cold) $\beta$-phase tin, representative of the pre-shock state, and of liquid (warm) tin, representative of a shock-compressed state. Calculated differences in the optical reflectivity between the cold and warm states will be compared with the measurements from shock-compression experiments. [Preview Abstract] |
Wednesday, August 3, 2005 10:00AM - 10:15AM |
Q5.00003: A Multi-Phase Equation of State and A Multi-Phase Steinberg Guinan Strength Model for Tin Geoffrey Cox This paper considers a multi-phase equation of state and a multi- phase strength model for tin in the beta, gamma, and liquid phases. At a phase transition there are changes in volume, energy, and properties of a material that should be included in an accurate model. The strength model will also be affected by a solid-solid phase transition. For many materials there is a lack of experimental data for strength at high pressures making the derivation of strength parameters for some phases difficult. In the case of tin there are longitudinal sound speed data on the Hugoniot available that have been used in conjunction with a multi-phase equation of state to derive strength parameters for the gamma phase, a phase which does not exist at room temperature and pressure. [Preview Abstract] |
Wednesday, August 3, 2005 10:15AM - 10:30AM |
Q5.00004: High temperature dynamic response of alpha- and gamma-uranium. E. Zaretsky, B. Herrmann, D. Shvarts Unalloyed uranium and uranium-based U-0.75{\%}Ti alloy were studied in planar impact experiments with initial sample temperature ranged from 300 to 1050 K. The velocity of the samples free surface was monitored by VISAR. It was found, with aid of the simple wave approximation, that the flow stress of studied materials is composed of two parts: the strain-rate independent part which stays constant up to the onset of alpha-gamma transformation and drops almost four times in gamma-phase, and the strain-rate dependent, viscous, part. The latter is characterized by 20-fold decrease of the dynamic viscosity with heating from room to transformation temperature. This decreased viscosity is inherited unchanged by transformed gamma-phase. The spall strengths of alpha-uranium decreases slightly, about 30{\%}, with its heating towards the transformation temperature and experiences two times drop entering the gamma-phase. The transformation causes similar drop of the uranium shear modulus while its bulk modulus undergoes only 10-{\%} change. [Preview Abstract] |
Wednesday, August 3, 2005 10:30AM - 10:45AM |
Q5.00005: Propagation of Macroscopic Phase Boundary in A Finite Rod with Martensitic Transformation under Dynamic Loading Weiwei Xu, Zhiping Tang Recently, Dai et al[1] studied the propagation of macroscopic phase boundary in a semi- infinitive medium and found some new phenomena. In this article, its propagation along a finite rod is investigated by using a simple mixture model that can describe the mixed phase and reverse transition. Both the shape memory effect (SME) and pseudo-elastic effect (PE) of SMA are considered in the present study. For PE, it is found that under certain loading and boundary conditions, the tension regions can form at different locations of the rod, meaning it may initiate multi-spall. For SME, the functionally graded material (FGM) can formed during the unloading process. By changing the boundary conditions, the fraction distribution of the martensitic phase can be adjusted, suggesting the possibility of producing FGM through a controlled impact loading/unloading process. The general rules of the phase boundary propagation in a finite rod/plate are summarized. [1] Dai X Y et al, Int J Impact Eng, \textbf{30}(2004), 385. [Preview Abstract] |
Wednesday, August 3, 2005 10:45AM - 11:00AM |
Q5.00006: Phase Transition Taylor Test Xinghua Zhang, Yangbo Guo, Zhiping Tang In this article, the Taylor impact test is applied to investigate the dynamic phase transformation behavior of NiTi alloy, which we call it the phase transition Taylor test (PTTT). The symmetry impact configuration is applied in the study at impact velocity range from 47m/s to 175m/s by using a light gas gun facility in this lab. The NiTi alloy is treated in the state of shape memory effect (SME). The shape of the recovered samples is substantially different from that of traditional elastic-plastic Taylor test. The recovered NiTi bar can be divided into three deformation regions from the impact surface: the main deformation region with homogeneous deformation, the gradient deformation region and the elastic region successively, which correspond to the martensitic phase, mixed phase and austenite, respectively. The different deformation regions demonstrate the interaction between the dynamic phase boundary and the rarefaction wave reflected from the free end of the bar. Simulation with the macroscopic phase boundary propagation theory[1]is in good agreement with the experimental measurement. [1] Dai X et al, International Journal of Impact Engineering, 30(4)(2004), 385. [Preview Abstract] |
Wednesday, August 3, 2005 11:00AM - 11:15AM |
Q5.00007: A 3D dynamic constitutive model for stress-induced phase transformation in isotropic material with N transforming phases Yangbo Guo, Zhiping Tang, Songlin Xu In this article, based on the Hayes model for phase transformation[1], a 3D dynamic constitutive model considering deviatoric stress is established to describe the stress-induced phase transformation behavior in isotropic material with N transforming phases. The model includes three parts: the critical criterion of transformation among the N phases; a 3D incremental constitutive equation describing the deformation behavior of the mixture with N phases; and the evolution equation of phase transformation considering the over driving traction and the growing space decrease of the product phase during transformation. The simple 1D models under 1D stress and 1D strain are given respectively. Using the constitutive model established, the phase transformation behavior of TiNi alloy is predicted, the predictions are in good agreement with the experimental results. [1] Hayes D B, J. Appl. Phys. 46(8)(1975), 3438. [Preview Abstract] |
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