Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session D7: Soft Matter II |
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Chair: Dana Dattelbaum, Los Alamos National Laboratory Room: Regency Ballroom F |
Monday, July 10, 2017 2:00PM - 2:15PM |
D7.00001: Modeling pressure-driven assembly of polymer coated nanoparticles J. Matthew D. Lane, K. Michael Salerno, Gary S. Grest, Hongyou Fan High-pressure experiments have successfully produced a variety of gold nanostructures by compressing polymer coated spherical nanoparticles. We apply atomistic simulation to understand the role of the soft polymer response in determining the pressure-driven assembly of gold nanostructures. Quasi-isentropic experiments have shown that 1D, 2D and 3D nanostructures can be formed and recovered from dynamic compression of fcc superlattices of alkanethiol-coated gold nanocrystals on Sandia’s Veloce pulsed power accelerator. Molecular modeling has shown that the dimensionality of the final structures depends on the orientation of the superlattice and the uniaxial loading. We describe the role of coating ligand length and grafting density, on ligand migration and deformation processes during pressure-driven coalescence of the cores into permanent nanowires, nanosheets and 3D structures. The role of uniaxial vs isotropic pressure and the effects of compression along various superlattice orientations will be discussed. Sandia National Laboratories is a multi-mission 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] |
Monday, July 10, 2017 2:15PM - 2:30PM |
D7.00002: The Response of Simple Polymer Structures Under Dynamic Loading. William Proud, Kay Ellison, Su Yapp, Cloe Cole, Stefano Galimberti The dynamic response of polymeric materials has been widely studied with the effects of degree of crystallinity, strain rate, temperature and sample size being commonly reported. This study uses a simple PMMA structure, a right cylindrical sample, with structural features such as holes. The features are added an varied in a systematic fashion. Samples were dynamically loaded using a Split Hopkinson Pressure Bar up to failure. The resulting stress-strain curves are presented showing the change in sample response. The strain to failure is shown to increase initially with the presence of holes, while failure stress is relatively unaffected. The fracture patterns seen in the failed samples change, with tensile cracks, Hertzian cones, shear effects being dominant for different holes sizes and geometries. The sample were prepared by laser cutting and checked for residual stress before experiment. The data is used to validate predictive model predictions where material, structure and damage are included.. [Preview Abstract] |
Monday, July 10, 2017 2:30PM - 2:45PM |
D7.00003: Sound wave propagation within granular packings. Liam Smith, Danyal Magnus, William Proud The propagation of pressure waves in 3-dimensional mono-disperse and poly-disperse samples of soda-lime glass and sand were investigated. Packing density and confining pressure were varied. A preconditioning routine was developed to increase sample consistency. Piezoelectric transducers were used to both produce and record the passing of pressure pulses with time-of-flight and amplitude measurements allowing the analysis of attenuation, hysteresis and sound speeds. Times-of-flight were recorded from first deviations, giving greater repeatability due to the near isotropic propagation of initial wave fronts within packings. Sound speed measurements in mono-disperse packings under increasing pressures showed an initial non-Hertzian response preceding a distinct transition to a Hertzian response at higher confining pressures. A similar response was not observed in poly-disperse packings. Variations in packing dimensions showed a dependency of transition pressure on packing size. [Preview Abstract] |
Monday, July 10, 2017 2:45PM - 3:00PM |
D7.00004: Simulation of Polyurea Shock Response under High-Velocity Microparticle Impact Joshua Gorfain, Christopher Key, David Veysset, Keith Nelson On-going research into the complexities of polyurea behavior under shock loading has led to some breakthroughs in the predictive simulation of how this nominally soft polymer responds under high velocity impact conditions. This work expands upon a previously reported modified pressure-dependent viscoelastic constitutive model for polyurea and its performance under ballistic impact. Specifically, we present recent enhancements to the model including nonlinearites in the Hugoniot and improvements in the high-temperature viscoelastic behavior, which substantially improved accuracy and extended the model’s range of applicable conditions. These improvements are demonstrated through correlation of computations for a suite of normal and pressure-shear plate impact experiments well documented in the open literature. Additionally, microparticle impact experiments were performed on polyurea using a laser-induced particle impact test (LIPIT) technique. High-speed imaging of the impact mechanics revealed elastic particle rebound at low velocity but penetration at high velocity. Simulation of these LIPIT experiments demonstrates good accuracy of the polyurea model under these conditions as well as provides insight into the mechanisms governing the results observed. [Preview Abstract] |
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