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 Z3: Particulate, Porous and Composite Materials VII |
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Chair: William Proud, Imperial College London, Joseph Bass, University of Texas Room: Grand G |
Friday, June 19, 2015 11:15AM - 11:30AM |
Z3.00001: Micron scale molecular dynamics simulation of shocks in low density structures Tomas Oppelstrup, Jim Glosli, David F. Richards, Erik Draeger, Liam Krauss Engineered porous materials, such as solid foams and nano-structured materials, present novel structural and functional materials in previously inaccessible ranges of strength-density and surface to volume ratios. Shock responses reveal strength and phase-diagram data for materials under extreme conditions. Shocking or ramp compression of porous materials in particular can result in very complex behavior. Besides exhibiting shock- and sound-waves through the dense regions, crush-up of the material can result in ejection of fast particles and liquid jets through the material. Thus shocks in porous materials is a multiphase phenomenon with several energy transport mechanisms. Understanding the interplay between these mechanisms is important for more accurate interpretation of experimental shock data and better macroscopic modeling of shock response of porous materials. To characterize the asymptotic behavior of shocks in porous materials, we performed micron scale molecular dynamics simulations of shocking of copper foams and truss structures. We will present simulation results and analysis of different modes of energy transport. Note: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Friday, June 19, 2015 11:30AM - 11:45AM |
Z3.00002: Enhanced densification, strength and molecular mechanisms in shock compressed porous silicon J. Matthew D. Lane, Tracy J. Vogler In most porous materials, void collapse during shock compression couples mechanical energy to thermal energy. Increased temperature drives up pressures and lowers densities in the final Hugoniot states as compared to full-density samples. Some materials, however, exhibit an anomalous enhanced densification in their Hugoniot states when porosity is introduced. We have recently shown that silicon is such a material, and demonstrated a molecular mechanism for the effect using molecular simulation. We will review results from large-scale non-equilibrium molecular dynamics (NEMD) and Hugoniotstat simulations of shock compressed porous silicon, highlighting the mechanism by which porosity produces local shear which nucleate partial phase transition and localized melting at shock pressures below typical thresholds in these materials. Further, we will characterize the stress states and strength of the material as a function of porosity from 5 to 50 percent and with various porosity microstructures. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Friday, June 19, 2015 11:45AM - 12:00PM |
Z3.00003: Porosity evolution at high strain rates: atomistic simulations, dislocation analysis, and constitutive modeling Eduardo Bringa, Carlos Ruestes, Joaquin Rodriguez Nieva, Diego Tramontina, Yizhe Tang, Marc Meyers Mimicking shock compression experiments, our molecular dynamics simulations explore the mechanical response and plasticity effects under uniaxial high strain rate compression (10**7/s to 10**9/s) for Au and Ta single crystals with a collection of spherical nanovoids, with a radius of 3-4 nm, resulting in an initial porosity of {\%}-10{\%}. Dislocation analysis was used to evaluate and quantify the evolution of plasticity. The evolution of dislocations configuration and densities were predicted and successfully compared to an analysis based on Ashby's concept of geometrically-necessary dislocations. The temperature excursion during plastic deformation was used to estimate the mobile dislocation density. The results obtained are compared with a variety of dislocation-based constitutive models. Plastic activity leads to a decrease in porosity until voids disappear completely. Based on the atomistic simulations, a densification regime was observed in all nanoporous samples studied. With these results, a new strain- based porosity model for metals is proposed for simulations at the continuum scale. [Preview Abstract] |
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