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 L4: Continuum and Multiscale Modeling II |
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Chair: Mel Baer, Sandia National Laboratories Room: Fairmont Orchid Hotel Plaza II |
Wednesday, June 27, 2007 8:00AM - 8:15AM |
L4.00001: Mesoscale and Continuum Calculations of Wave Profiles for Shock-Loaded Granular Ceramics Tracy Vogler, John Borg A significant challenge in the multi-scale modeling approach is the validation of simulations performed at the various length scales considered. Recently, mesoscale modeling of the compaction of granular ceramics has been performed as part of a multiscale modeling approach. Through small adjustments to the model parameters, good agreement between the Hugoniot response for the experiments and simulations was obtained. Here, we evaluate the performance of the mesoscale model in predicting experimental velocity histories obtained with VISAR. In particular, we explore its ability to capture correctly the process of wave attenuation. For comparison, we will also examine the ability of continuum models such as the P-alpha and P-lambda models to correctly predict the wave profiles. The consideration of attenuating waves provides a means of validation not previously considered for these mesoscale simulations. [Preview Abstract] |
Wednesday, June 27, 2007 8:15AM - 8:30AM |
L4.00002: 2D Mesoscale Simulations of Projectile Penetration into Sand R.D. Teeter, S.K. Dwivedi, C.W. Felice, Y.M. Gupta Physical Phenomena governing projectile instabilities during penetration of granular media (e.g. sand) are not well understood. To gain insight into projectile -- granular media interactions, 2-D mesoscale simulations were performed to examine projectile penetration into sand targets with explicit representation of sand grains and representative porosities. The computational procedure used to generate a mesoscale representation of a sand target is presented with emphasis on an energy minimization technique for grain placement and modified Voronoi tessellations to enforce desired grain size and geometry. Simulated sand targets are shown to reproduce grain size distributions and porosities as large as 30{\%} in close agreement with input parameters. Further, initial results from 2D mesoscale simulations, using the ISP-TROTP code, of normal impact of ogive shaped impactors at 0.5 km/s, 1.0 km/s, and 1.5 km/s impact velocities show that heterogeneous deformation in a frictionless granular media can cause deviation of projectile motion from normal direction indicating projectile instability during penetration. Efforts to achieve an improved description of granular media are underway. Work supported by DOE and AFOSR. [Preview Abstract] |
Wednesday, June 27, 2007 8:30AM - 8:45AM |
L4.00003: Determination of simple constitutive models for DEDF glass using penetration-velocity data from ballistic experiments Gordon Johnson, Timothy Holmquist Constitutive models for brittle materials such as glass can be very complex as they are dependent on strains, stain rates, pressures, temperatures, damage and other parameters. There may also be significant (pressure-dependent) strength after failure such that the constitutive response is much different for intact material and failed material. A great number of laboratory tests are required to develop a comprehensive constitutive model. Another approach is to develop simple models using penetration-velocity data obtained from ballistic experiments. Here, various functional forms of simple models (with a limited number of constants) are used to (computationally) match the penetration velocity over a range of impact velocities. This allows for the determination of the most important parameters and it provides an approximation of the stresses that occur during penetration. This paper presents constitutive models for high-density DEDF glass. They are based on penetration-velocity data reported by Behner et al. (Proceedings of the 22$^{nd}$ International Symposium on Ballistics, Vancouver BC, Canada, November 2005) for gold rods impacting DEDF glass at impact velocities from 400 to 2500 m/s. [Preview Abstract] |
Wednesday, June 27, 2007 8:45AM - 9:00AM |
L4.00004: Multiscale Modeling of Shocked Ceramics Ruqiang Feng, Jianbin Zhu Under shock compression, polycrystalline ceramics may undergo mesoscopically heterogeneous inelastic deformation via transgranular slip or twinning in some grains. Although polycrystal modeling, which accounts for crystal anisotropies and grain-to-grain topological variations and permits implementation of crystal plasticity models of interest, may be used to analyze such a deformation, the size affordable is too small to run wave propagation simulations needed to extract material properties from a plate impact experiment. To address this issue, we have developed a multiscale modeling technique, in which a Voronoi polycrystal is embedded in a homogeneous matrix of the size proper for simulating the experiment. The polycrystal model considers nonlinear crystal elasticity and microplasticity by limited slip systems. The matrix model uses the mean stress response predicted by elastic polycrystal simulation and a strength model combining the Drucker-Prager plasticity with a prescribed limiting strength. Two parametric optimizations are pursed iteratively. One is to optimize the matrix parameters to match the simulated wave profile with the measurement. The other is to optimize the polycrystal parameters to match the triaxial stress-strain curves volume-averaged over the polycrystal to those of the matrix. The technique has been applied to analyze the inelastic deformations of shocked alumina and silicon carbide. The results will be presented for demonstration. [Preview Abstract] |
Wednesday, June 27, 2007 9:00AM - 9:15AM |
L4.00005: ABSTRACT WITHDRAWN |
Wednesday, June 27, 2007 9:15AM - 9:30AM |
L4.00006: Mesoscale Calculations of Shock Loaded Granular Ceramics John Borg, Tracy Vogler Mesoscale hydrodynamic calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. From these calculations both bulk material characteristics such as stress and density, as well as local characteristics such as compaction wave thickness and rise time have been obtained and compared to experimentally obtained data in order to assess the viability of the computational method. A parametric study has been conducted in order to assess the sensitivity of the computationally derived characteristics to micro material properties such as strength, particle morphology, and particle size distribution. A discussion as to the shortcomings in the mesoscale modeling technique, as well as, future considerations is included. [Preview Abstract] |
Wednesday, June 27, 2007 9:30AM - 9:45AM |
L4.00007: 2D Mesoscale Simulation of Shock Response of Dry Sand in Plate Impact Experiments L. Pei, R.D. Teeter, S.K. Dwivedi, Y.M. Gupta The one-dimensional approach with a homogenized continuum model used in the literature to derive the shock Hugoniot of sand from plate impact experimental data neglects heterogeneous deformation and cannot incorporate mesoscale phenomena. We present a 2D mesoscale simulation approach to probe the shock response of dry sand with the main objectives to identify important mesoscale phenomena and the role of inter granular friction. The in-house code ISP-SAND was used to generate sand with desired grain size distribution and porosity. The explicit finite element code ISP-TROTP was used to simulate plate impact experiments of assumed configurations. The deformation of individual sand grains was modeled by non-linear mean stress volume compression relation with an assumed mean stress dependent yield strength. The results show heterogeneous deformation with finite lateral velocity and regions of stress concentrations in the sand sample. The effects of grain size distribution, porosity and friction between grains are discussed by comparing the particle velocity profiles at the window interface. Work supported by DOE and AFOSR. [Preview Abstract] |
Wednesday, June 27, 2007 9:45AM - 10:00AM |
L4.00008: Numerical Simulation of Impact Effects on Multilayer Fabrics Eric Fahrenthold High strength fabrics provide lightweight impact protection and are employed in a wide range of applications. Examples include body armor for law enforcement and military personnel and orbital debris shielding for the International Space Station. Numerical simulation of impact effects on fabric protection systems is difficult, due to the complex woven structure of the fabric layers and the typical application of fabrics in a multilayer configuration. Recent research has developed new particle-element methods for the simulation of impact effects on multilayer fabrics, applicable over a wide range of impact velocities, for use in body armor and orbital debris shielding applications. [Preview Abstract] |
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