Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session 1C: Material Microstructure |
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Room: Broadway I/II |
Sunday, June 16, 2019 1:00PM - 1:15PM |
1C.00001: Mode I crack propagation in homogeneous nuclear graphite (symp.) Antoine Cornet, David Eastwood, Neil Bourne, Paul Mummery, Carl Cady, Christoph Rau Because of its unique properties, graphite serves as a structural component and neutron moderator in nuclear reactor for over 40 years, and should continue to play this role in the upcoming fourth generation of power plant. In nuclear graphite, it is known that the strength depends on the length scale probed, and therefore with the level of defect or structure associated. Indeed, the crack path is strongly dependent on the precursor particle shape and density. Thus, nuclear graphite with limited heterogeneity represents an appealing lead to higher performance material. With 4D tomography, we analysed in-situ under load the development of strains in a homogenous graphite during the initiation and the development of a mode I fracture. The structure of this graphite grade (Mersen 2020), consists of a percolating network of porosity channel of about 20 $\mu $m in diameter, with an average grain size of 15 $\mu $m, to be compared to the 2 mm precursor particles in PGA and Gilsocarbon graphite. Assessment of this homogeneous grade is done relatively to Gilscarbon graphite on two relevant quantities: the extension of the process zone, i.e. the plastically deforming zone that will later form the crack tip, and J-integrals, i.e. the quantification of the energy dissipated as the crack propagates. [Preview Abstract] |
Sunday, June 16, 2019 1:15PM - 1:30PM |
1C.00002: On the Role of Texture and Precipitate Orientation in Spall Failure of a Rolled Magnesium Alloy Debjoy Mallick, Suhas Eswarappa-Prameela, Vignesh Kannan, Meng Zhao, Jeff Lloyd, Tim Weihs, KT Ramesh Magnesium alloys are an attractive material system for protection applications owing to their high specific strength and stiffness, but have low ductility in this application. The plastic anisotropy from the low-symmetry HCP crystal structure together with defects in the microstructure, such as voids and second phase particles, may all play roles in spall (dynamic tensile failure at high strain rates). We present a large number of spall experiments on Mg-9Al (wt.\%) thin film specimens performed with a laser-driven micro-flyer apparatus. The Mg-9Al alloy is warm-rolled and processed in two conditions: (a) fully solutionized at 450$^oC$ for 24 hours with no second phase particles and (b) peak aged to generate high aspect-ratio lath precipitates (Mg$_{17}$Al$_{12}$) with thicknesses on the order of nanometers and lengths on the order of microns on the basal plane. The loading direction is varied between the normal-to and transverse-to rolling directions of the specimen in order to interrogate the effects of plastic anisotropy of the matrix material and geometric anisotropy of the precipitates on the spall strength. We compare the experiments to numerical simulations using crystal plasticity and realistic precipitate geometries and spacings from TEM observations. [Preview Abstract] |
Sunday, June 16, 2019 1:30PM - 1:45PM |
1C.00003: Effect of Microstructure on the Dynamic Behavior of UHMWPE Composites Jason Parker, KT Ramesh Ultra-High Molecular Weight Polyethylene (UHMWPE) fiber-reinforced composites are commonly used as a protective material against fragments and projectiles, in part due to the high specific toughness and high longitudinal wave speed of their constituent fibers. UHMWPE composites are inherently difficult to process due to the high viscosity of the thermoplastic matrix and demonstrate a strong sensitivity to processing conditions. The low volume fraction and high viscosity of the matrix can lead to significant porosity. Understanding how porosity affects the dynamic response of these composites and evolves during deformation is important in an effort to model this material. In this study we use a Kolsky bar to dynamically load the composites in out-of-plane compression while simultaneously capturing the deformation history with high speed video. By analyzing the high-speed video, we obtain the complete deformation gradient. Using a finite deformation formulation, we determine how porosity evolves in these composites during loading at several strain-rates and compare our results with post-mortem micro-CT measurements. This work will be used in the development of a constitutive model of the material incorporating microstructure through internal variables. [Preview Abstract] |
Sunday, June 16, 2019 1:45PM - 2:00PM |
1C.00004: Shock Compression of Graphite: Role of Orientational Order on the Graphite to Diamond Transformation (symp) Travis Volz, Y. M. Gupta Past experiments on shock-compressed pyrolytic graphites - having different orientational orders - have shown very different responses below and above the reported transformation stresses. Well-defined two-wave structures, indicative of a rapid phase transformation, were reported for ZYB-grade highly oriented pyrolytic graphite (HOPG) samples. However, two-wave structures were not reported for the less oriented HOPG samples (ZYH-grade) and for as-deposited pyrolytic graphite (PG). The objectives of the present study are to determine if well-defined rapid phase transformation waves are possible in less oriented pyrolytic graphite samples and to better understand the role of orientational order on the phase change mechanisms. To address these objectives, plane shock wave experiments were performed on ZYB-grade HOPG, ZYH-grade HOPG, and PG samples. Using laser interferometry, transmitted wave profiles were measured at the graphite/LiF interface for the different samples. Our results show that rapid, well-defined phase change waves occur in each graphite type examined, regardless of orientational order. In contrast to previous reports, both HOPG grades have similar shock responses above the transformation. However, the PG response is different from both HOPG grades. [Preview Abstract] |
Sunday, June 16, 2019 2:00PM - 2:15PM |
1C.00005: In situ observation of material flow in composite media under shock compression David Bober, Jonathan Lind, Mukul Kumar Internal reverberation, multiphase drag, and particle-particle force transfer determine the rate of compression in a shock loaded particulate composite. Since it is nearly impossible to deconvolve these effects using bulk velocimetry data, it has been difficult to develop models or simulations capable of predicting the outcome of novel compositions or loading scenarios. Instead of trying to solve this difficult inverse problem, we have conducted in situ radiography to directly observe the evolving internal configuration of an impact loaded composite with enough spatiotemporal resolution to build accurate direct numerical simulations. Tracking the motion of individual particles with nanosecond precision reveals how momentum transfer proceeds between the phases. This is complemented by measurements of the flow field in the surrounding polymer. Using dense tungsten particles embedded in a soft/light polymer matrix creates a strong impedance mismatch and a useful model system in which to explore shear mediated effects. These observations make it possible to parametrize a simple shear resistance model for the polymer matrix at the extreme pressures and strain rates encountered. This in turn leads to simulations of the bulk composite that better reproduce conventional velocimetry results. [Preview Abstract] |
Sunday, June 16, 2019 2:15PM - 2:30PM |
1C.00006: Effect of Matrix-Filler Interface Adhesion on the Spall Strength of Particle-Reinforced Polymer Matrix Composites Anton Lebar, Andrew Oddy, Rafaela Aguiar, Oren E. Petel Prior research investigating the spall strength in metal alloys has shown that the presence of secondary phase intermetallics can be a source of spall nucleation. In polymer composites with a reinforcing phase, the particle surfaces can be functionalized to improve the surface adhesion between the matrix and filler at the interface, which has been shown to improve the quasi-static strengths of the materials. In the present study, we apply silanes to modify the surface chemistry of a micron-sized alumina particles to tailor interface adhesion between the alumina filler and an elastomer matrix Sylgard 184. Two silanes were selected to both increase and decrease interface adhesion respectively to further observe the significance of interface adhesion on dynamic tensile strength. Fourier Transform Infrared Spectroscopy was used to quantify these changes in the interface adhesion between the untreated and treated particle composites. The composites were characterized through shock propagation, spall and quasi-static tensile experiments. [Preview Abstract] |
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