Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session Y4: Continuum & Multiscale Modeling VI |
Hide Abstracts |
Chair: Eric Mas, Los Alamos National Laboratory Room: Hyatt Regency Constellation E |
Friday, August 5, 2005 8:00AM - 8:30AM |
Y4.00001: Direct Numerical Simulation of shock propagation in polycrystalline tantalum Invited Speaker: In this presentation, I describe our efforts to model the propagation of intense shock waves in polycrystalline metals with particular focus on tantalum. The main objective is to simulate the shock-response of polycrystalline tantalum accounting for the influence of the anisotropy of elastic and plastic deformation at the grain level as well as at the level of grain interactions, which enables to ascertain the role of these grain interactions in the overall response. The necessary ingredients enabling this type of simulations are described in some detail, including: appropriate nonlinear elastic models of cubic anisotropic behavior under large deformations, the calibration of these models to elastic constants obtained by ab-initio quantum mechanics calculations, their integration with multiscale models of b.c.c. crystal plasticity, the numerical need for especialized shock-capturing methods and, finally, the need for a framework for conducting high-resolution, large-scale calculations of the resulting initial boundary value problem. I will present simulation results corresponding to intense planar shocks propagating in tantalum and comment on our efforts to validate these simulations against experimental data. [Preview Abstract] |
Friday, August 5, 2005 8:30AM - 8:45AM |
Y4.00002: Modelling the Shock Compression of Polycrystalline Metals Simon Case, Yasuyuki Horie A 2D mesh-free particle computational method is used to model the shock compression of polycrystalline metals. The code is evolved from the Discrete Element Method (DEM) code, DM2, developed by Horie et al. It is based on a Molecular Dynamics computational scheme, but with discrete particles representing mesoscale-sized portions of material rather than atoms. The model uses pair potentials to represent effective hydrostatic compression behaviour. However, in the new model the potential is a function of the representative area (volume in 3D) between particles, rather than their radial separation as in the original code. Complementary to the hydrostatic potential is an elastic perfectly plastic shear force, which facilitates the simulation of plastic deformation. A polycrystalline grain structure is computationally grown onto a regular 2D arrangement of particles, and a crystallographic orientation is assigned to each grain on a distributed basis. The heterogeneous deformation properties of the polycrystal are manifested through selection of spatially dependent particle interactions. For example particles adjacent across a grain boundary are given a reduced shear strength, whilst the longitudinal wave speed in each grain is dependent upon its crystallographic orientation with respect to the shock direction. Results of the shock compression reveal a non-planar shock front and a distribution of the shock induced particle velocity in a plane perpendicular to the shock direction, which are qualitatively in agreement with experiment. [Preview Abstract] |
Friday, August 5, 2005 8:45AM - 9:00AM |
Y4.00003: Plasticity and spall in high density polycrystals: modeling and simulation John Clayton The dynamic thermomechanical response of a tungsten alloy is investigated via modeling and simulation. The material of study consists of relatively stiff pure tungsten grains embedded within a more ductile alloy comprised of tungsten, nickel, and iron. Constitutive models account for finite deformation, heat conduction, plastic anisotropy, strain-rate dependence of flow stress, thermal softening, and thermoelastic coupling. The potentially nonlinear volumetric response at large pressures is addressed by a pressure-dependent effective bulk modulus. Our framework provides a quantitative prediction of the total dislocation density, associated with cumulative strain hardening in each phase, and enables calculation of the fraction of plastic dissipation converted into heat energy. Cohesive failure models are employed to represent intergranular fracture at grain and phase boundaries. Dynamic finite element simulations illustrate the response of volume elements of the polycrystalline microstructure subjected to compressive impact loadings, ultimately resulting in spall of the material. Relative effects of mixed-mode interfacial failure criteria, thermally-dependent fracture strengths, and grain shapes and orientations upon behavior are weighed. Spatially resolved profiles of particle velocities at the free surfaces of the volume elements indicate the degree to which the incident and reflected stress waves are altered by the heterogeneous microstructure. [Preview Abstract] |
Friday, August 5, 2005 9:00AM - 9:15AM |
Y4.00004: 2-D Mesoscale Predictions of Local Shock States in Aluminum J.R. Asay, S.K. Dwivedi, Y.M. Gupta Two-dimensional mesoscale simulations of 6061 Al alloy during planar reshock and unloading impact experiments show that the stress state achieved during initial shock loading deviates from 1-D elastic-plastic response. The stress state unloads from an equilibrium yield surface due to mesoscale phenomena such as collapse of micro-voids or local plastic rearrangements to attain lateral stress equilibrium near hard inclusions or hardened grain boundaries. The quasi-elastic longitudinal velocity profiles calculated for reshock or unloading are similar to experimentally measured profiles. Mesoscale heterogeneities causing the observed quasi-elastic response were found, in reducing order of importance, to be hardened grain boundaries, hard inclusions, micro-voids, and grain-to-grain property variation. These phenomena can be quantified through longitudinal and lateral velocity distributions and differences in the lateral stresses along mutually orthogonal directions. The results contrast with 1-D model predictions of uniaxial strain reloading and unloading. Work supported by DOE. [Preview Abstract] |
Friday, August 5, 2005 9:15AM - 9:30AM |
Y4.00005: 1-D Continuum and 2-D Mesoscale Simulations of Plate Impact Spall Experiments S.K. Dwivedi, X.L. Chen, J.R. Asay, Y.M. Gupta 1-D simulations using a continuum fracture model show good agreement of the calculated spall threshold stress and pull-back velocity profiles with plate impact spall data on Al alloys. The calculated mode I critical strain energy release rate, or fracture toughness, was observed to increase over the impact stress range of 4-13 GPa and decreased for higher stresses. The model did not predict a change in slope of the pullback velocity profile observed in several experiments. In contrast, 2-D mesoscale simulations of thinner sample using grain boundary debonding as the failure phenomenon also resulted in free surface profiles similar to that measured experimentally. These simulations showed the observed change in slope, heterogeneous spall planes, and a strong dependence of the velocity profile on mesoscale heterogeneities modeled in terms of grain-to-grain property variation, micro-voids, inclusions, and hardened grain boundaries. The change in the slope of the pull back velocity appears to result from attenuation and dispersion of stress waves produced by secondary spall planes. Work supported by DOE. [Preview Abstract] |
Friday, August 5, 2005 9:30AM - 9:45AM |
Y4.00006: On the presence of the elastic precursor in re-shock experiment: an unorthodox explanation Andrew Ruggiero, Nicola Bonora According to the stress wave theory, for an elastic-plastic material reloading from the shocked state, the expected response should be entirely plastic because the initial compression beyond the HEL should produce a material state on the yield surface. Experiments show the presence of a step anticipating the arrival of the plastic reloading wave, which is commonly recognized as an unexpected ``elastic precursor.'' Several explanations have been proposed assuming that the shocked material is not on the current yield surface. Lipkin and Asay (1977) justify this assumption with the fact that neighboring grains have different slip system orientations and they proposed a model to duplicate the key features of the shock-re-shock experiment; Swegle and Grady (1986) believed that the phenomenon is due to a thermal trapping localized shear deformation regions. Here, a continuum mechanics approach is used to justify the presence of the step and to demonstrate that it is not an elastic precursor. According to the authors interpretation, a justification of this should be found in the non uniform residual plastic deformation distribution along the target thickness caused by dissipative processes during the first compressive stress wave travel. The proposed interpretation of the phenomenon can explain the reason why the initial part of the release and recompression velocity profiles should not be completely centered as confirmed by experimental observations. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700