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 R2: TMS: Mesoscale Simulation |
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Chair: Cole Yarrington, SNL Room: Grand Ballroom II |
Thursday, June 20, 2019 9:15AM - 9:30AM |
R2.00001: A hybrid mesoscale-continuum method to model laser shock loading and spall failure at the mesoscales Sergey Galitskiy, Avinash Dongare A hybrid atomistic-continuum approach combining molecular dynamics (MD) simulations with a two-temperature model (TTM) is utilized to model spall behavior of single crystal and nanocrystalline (pc) Al systems induced by ultrafast laser irradiation. The TTM is combined with a mesoscale modeling method, to extend the capability of the MD/TTM simulations to the mesoscales while retaining atomic scale mechanisms that determine microstructure evolution. The mesoscale capability is obtained using a quasi-coarse-grained dynamics (QCGD). The QCGD/TTM simulations are able to model the laser energy absorption by conduction electrons, electron-phonon coupling, heat generation and transfer, melt dynamics, and defect nucleation and evolution behavior. The scaling relationships for QCGD/TTM simulations are developed for various levels of coarsening and enable the investigation of the evolution of microstructure (defects), temperature and pressure at the length and time scales of experiments. The capability of QCGD-TTM approach is demonstrated by modeling effect of system size on the laser shock loading of pc Al films with system sizes of up to 2 $\mu $m and an average grain size of 0.5$\mu $m. The results suggest that the shock wave propagation and spall failure is determined by the size of the system wherein phenomena such as no-spall, void nucleation and collapse and spall failure are observed. The pressure wave propagation, dislocation density evolution behavior and the mechanisms of void nucleation and growth will be presented. [Preview Abstract] |
Thursday, June 20, 2019 9:30AM - 9:45AM |
R2.00002: Simulated diffraction of laser compressed textured polycrystals from Crystal Plasticity FEM. Philip Avraam, John Foster, Emma Floyd, Andy Comley, Steve Rothman, Simon Case, James Turner Dynamically compressed polycrystalline material can exhibit grain-level strain heterogeneity, and grain-rotation leading to texture evolution. These features are, in principle, measurable using in-situ X-ray diffraction techniques, and contain valuable information about the lattice-level mechanisms involved in dynamic plasticity. The interpretation of these patterns can be difficult except in cases of highly idealised texture. Simulated diffraction from crystal plasticity finite element (CP-FEM) modeling is utilised here to interpret complex features seen in experimental diffraction patterns on laser compressed polycrystalline metals of general texture. [Preview Abstract] |
Thursday, June 20, 2019 9:45AM - 10:00AM |
R2.00003: 3D Micromechanical Simulation of PBX Composites David Walters, Darby Luscher, John Yeager Previous research studied the constitutive response and interface strength of a bonded bicrystal system containing two HMX explosive grains bound with a HTPB polymer binder by performing FE simulations on real geometry imaged with micro Computed Tomography ($\mu$CT). The parameters generated from this past study were successfully applied to 2D mesoscale simulations of $\mu$CT imaged HMX-HTPB polycrystal samples. Presently, the mechanical response of PBXs containing a Nitro-Plasticized Estane (NPE) binder with similar microstructural geometry to the HMX-HTPB polycrystal samples were studied. Imaging of a HMX-NPE bicrystal sample allowed for simulation of the new material pairing. However, imaging using $\mu$CT techniques on the new polycrystal samples was difficult due to the decrease in contrast between the HMX grains and the NPE binder. Mesoscale polycrystal simulations utilizing a single $\mu$CT imaged microstructure were performed on a 3D SVE comparing the delamination behavior and macroscale mechanical response of both HMX-HTPB and HMX-NPE PBXs. This technique shows the ability to virtually explore the mechanical response of a range of hypothetical materials that share common microstructural geometric characteristics in addition to studying numerically altered geometries. [Preview Abstract] |
Thursday, June 20, 2019 10:00AM - 10:15AM |
R2.00004: Analysis of Plate Impact and Hopkinson Bar Experiments for RDX Single-Crystals Francis Addessio, Darby Luscher, Nisha Mohan, Marc Cawkwell, Ben Morrow, Chris Meredith, Kyle Ramos Thermomechanical constitutive models have been developed for interpreting experiments for single-crystals of RDX. The models are developed for the large deformation of materials and including the effects of nonlinear elasticity, plastic slip, phase transformations, and brittle damage. The constitutive models are based on the multiplicative decomposition of the deformation gradient and they have been applied to both plate impact and recent Split Hopkinson Pressure Bar (SHPB) experiments. For the plate impact experiments, pressures below and above the 3.8 GPa a to $\gamma$ transformation pressure were accessed. Free energies have been developed for the a and $\gamma$-polymorphs of RDX that provide the driving force for the transformation in our simulations. A phenomenological thermal activation model was employed to model the plastic slip. Crystal orientation and thickness were considered and good agreement with the experimental data was obtained. A constitutive model that combines anisotropic linear elasticity, plastic slip, and brittle damage was developed to understand recent SHPB experiments on oriented RDX single crystals. A finite number of discrete cracks were included to model damage evolution. Crack growth but no nucleation processes were included in the model. The effects of plastic slip and crack friction were investigated systematically. Good accord with the measured stress-strain curves was obtained during the failure of the samples. [Preview Abstract] |
Thursday, June 20, 2019 10:15AM - 10:30AM |
R2.00005: An anisotropic thermodynamically consistent elastoviscoplastic model of HMX under quasi-isentropic compression. Xinjie Wang, Yanqing Wu, Fenglei Huang, Weijia Hu An anisotropic thermodynamically consistent elastoviscoplastic model for $\beta $-HMX is developed to analyze the anisotropic thermomechanical responses under isentropic compression loading. The model considers anisotropy, nonlinear elasticity, and dislocation-based plasticity. The calculated results agree well with isentropic compression experimental wave profiles of (011) and (010) oriented HMX single crystals at pressures up to 12 GPa. The model can well capture the isentropic elastic limit, stress relaxation and steeper plastic wave speed in thick samples. Nonlinear elasticity by both pressure-dependent elasticity tensor and the complete equation of state is responsible for the transition from isentropic wave to shock wave. Pure isentrope is decoupled from quasi-isentrope which is commonly measured by isentropic compression experiments. Distinct detailed mesoscale dislocation activities on seven slip systems were analyzed. Anisotropic temperature rises contributed by pressure-volume work and dislocation based plasticity work were obtained and the effect of heat conduction was analyzed. Results provide insights into understanding the shock formation and predicting ignition sensitivity of explosives at the mesoscale. [Preview Abstract] |
Thursday, June 20, 2019 10:30AM - 10:45AM |
R2.00006: Connecting ordered meso-structures with the system's dynamic response under complex dynamic loading John Borg, Alex Dawson, Dinc Erdeniz, John Moore, Somesh Roy, Simcha Singer, Ron Coutu The aim of this work is to better understand the dynamic behavior of polyester resin and crystalline sucrose systems. Ordered systems were constructed and interrogated in order to characterize the system's meso-structure. These structures were investigated using microscopy and SEM; the resulting images were digitized in order to import them as initial conditions for hydrocode simulations. These same systems were experimentally interrogated under complex dynamic pressure-shear loading. Photon doppler velocimetry (PDV) probes were located at interesting features of the meso---structure, such as interfaces and voids. The resulting experimental and simulated response is presented and compared. [Preview Abstract] |
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