Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session P2: Material Science III |
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Chair: Scott Greenfield, Los Alamos National Laboratory Room: Fairmont Orchid Hotel Amphitheater |
Thursday, June 28, 2007 10:30AM - 10:45AM |
P2.00001: Microstructural Evolution and Phase Stability in Shock-Loaded Tantalum Single Crystals Jikou Zhou, Cheng Saw, Ricky Chau, Luke Hsiung Deformation of tantalum and tantalum alloys has been studied repeatedly in order to understand their constitutive behavior and microstructural stability under dynamic pressure conditions. Shock-induced microstructures including dislocation patterning, deformation twinning, and phase change have been reported in shock-deformed poly-crystalline tantalum, and the strain hardening of post-shocked polycrystalline tantalum was mainly attributed to deformation twinning. However, the underlying mechanisms for shock-induced deformation twinning remain unclear. In this presentation, we report the results of a systematic study, which investigate the microstructural evolution and mechanical properties of shocked tantalum single crystals. Shock impact experiments were carried out in a two-stage gas gun under three different pressures: 25 GPa, 50 GPa and 70 GPa. The effects of crystal orientation and pressure on deformation substructures and mechanical properties are investigated by analyzing shock-recovered samples using x-ray diffraction, nanoindentation, and transmission electron microscopy techniques. This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. [Preview Abstract] |
Thursday, June 28, 2007 10:45AM - 11:00AM |
P2.00002: Fabrication of W-Cu/Mo-Cu functionally graded materials by explosive consolidation Pengwan Chen, Zhiming Jiang, Weiping Shen, Jun Yang, Fenglei Huang Attempts are made to use explosive consolidation to fabricate high quality W-Cu/Mo-Cu FGMs. Tungsten powder with 99{\%}purity and a particle size of 3$\sim$25$\mu$m and molybdenum/copper powder with $\ge $99{\%} purity and a particle size of 74$\mu$m are used as starting powder. A novel technique, called bidirectional underwater shockwave explosive consolidation, is developed. Two water chambers are placed in both sides of the sample. Detonation-generated shock waves are attenuated by the water chambers before acting on the samples. Through adjusting the height of the water columns, the applied pressure can be adjusted. A self-propagating reaction system is used to provide temperature compensation and to enhance consolidation quality. Flash X-ray photography is used to observe the process of explosive consolidation. Various techniques are used to characterize the recovered samples including optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy spectrum analysis, hardness measurement and density measurement. The explosive consolidation methods developed in the paper can be used to other hard-to-consolidate powder materials. [Preview Abstract] |
Thursday, June 28, 2007 11:00AM - 11:15AM |
P2.00003: Comparison of Porter-Gould constitutive model with Compression Test data for HTPB/Sugar Philip Church, Peter Gould, William Huntington-Thresher, Daniel Drodge, William Proud QinetiQ has been developing the physically based QinetiQ Porter-Gould (P-G) model for the mechanical response of PBXs over a number of years and applying to solving real scenarios involving impact and blast. The main difficulty with these models is predicting the intermediate strain rate regime where the relaxation time for the polymer is of the same order as the duration of the Hopkinson bar test. The other main issue is the ability of the model to predict the stress/strain data as a function of temperature up to and through the glass transition temperature. The paper presents predictions from the QinetiQ P-G model compared to quasi-static compression and Hopkinson bar compression test data and discusses the results in terms of requirements for future developments of the model. [Preview Abstract] |
Thursday, June 28, 2007 11:15AM - 11:30AM |
P2.00004: Microstructural Defects in Shocked Nanocrystalline Ni and Ni-W Hussam Jarmakani, Eduardo Bringa, Morris Wang, Chris Schuh, Marc Meyers This mechanisms of defect generation and multiplication in nanocrystalline Ni and Ni-W deformed at very high strain-rates between $\dot {\varepsilon }\sim 10^4\sec ^{-1}$and $\dot {\varepsilon }\sim 10^7\sec ^{-1}$ quasi-isentropically compression via gas-gun and laser methods are investigated experimentally, experimentally, and computationally. Transmission Electron Microscopy (TEM) was used to probe the recovered microstructure for defects (dislocations, stacking faults, twins, etc). As the grain size is decreased and stacking-fault energy is increased, the propensity for twinning is decreased and the critical twinning pressure is increased. An analytical model was developed that determines the critical twinning pressure as a function of grain size and stacking-fault energy. Molecular dynamics (MD) simulations using LAMMPS were performed on nc Ni, and results of the defect substructure are compared with that of TEM. This research effort is funded by grant no. LLNL-B560780. [Preview Abstract] |
Thursday, June 28, 2007 11:30AM - 11:45AM |
P2.00005: Influence of polyethylene molecular conformation on Taylor impact measurements: a comparison of HDPE, UHMWPE, and PEX Carl P. Trujillo, Eric N. Brown, George T. Gray III The current work presents the comparison of the Taylor impact response of three different industrial forms of polyethylene. Specifically, high-density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX) were tested. From quasi-static and intermediate strain-rate compression measurements as a function of temperature (75 to 100C) and strain-rate (10$^{-4}$ to 2600 s$^{-1})$ the responses of UHMWPE and PEX are very similar, whereas HDPE exhibits some differences. The HDPE samples display a significantly higher yield stress followed by a flat flow behavior. Conversely UHMWPE and PEX both exhibit significant strain hardening after yield. Taylor impact experiments are presented as a function of velocity and temperature to probe the dynamic yield behavior and ductile-to-brittle response of these polymers. [Preview Abstract] |
Thursday, June 28, 2007 11:45AM - 12:00PM |
P2.00006: Propagation of strongly nonlinear signals in a two dimensional network of granular chains Chiara Daraio, Vitali F. Nesterenko We report experimental observation of strongly nonlinear signals propagating in a two dimensional system composed of guided granular chains. In this system one of the chains contacts two others to allow splitting and redirecting the solitary-like signal formed by impact on the first chain. The system consists of a double Y-shaped guide in which high- and low-modulus chains of spheres are arranged in various geometries. We observed fast splitting of the initial pulse, rapid chaotization of the signal and sharp bending of the propagating acoustic information. Pulse and energy trapping in the branches was also observed in composite systems assembled from hard- and soft- particles. [Preview Abstract] |
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