Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session S3: High Pressure Strength III |
Hide Abstracts |
Chair: Jeremy Millett, Atomic Weapons Establishment Room: Renaissance Ballroom AB |
Thursday, June 30, 2011 9:15AM - 9:45AM |
S3.00001: The development and application of multi-scale materials modeling methods for the prediction of dynamic strength Invited Speaker: It becomes more difficult to simply extract experimental information on the strength of materials under dynamic conditions simultaneously reaching high pressures, temperatures, and strain rates. The difficulty stems from the inability to independently control and extract the pressure, temperature and strain rate dependence under dynamic conditions, the inability to maintain those conditions, and the inability to probe into the volume of a material during an experiment. The observations that are made during dynamic materials experiments tend to be integrated measures of the equations of state and materials strength. As a result, materials experiments reaching dynamic extremes may be better suited to validate and constrain materials strength models and equations of state than they are for actually uniquely determining their forms and coefficients. Conversely, as the dynamic conditions become more extreme they may become more amenable to being investigated with the suite of materials modeling and simulation tools currently available. In studying the dynamic strength of simple ductile metals, molecular dynamics simulations are able to easily simulate the mobility of dislocations when their velocities are on the order of 0.1 m/s and above. The low velocity limit is controlled by the frequency of atomic vibrations, the spacing between atoms, and the limits of strong scaling of molecular dynamics simulations on massively parallel computers. For dislocation densities on the order of 10$^{12}$-10$^{16}$ m$^{-2}$, and lattice spacings on the order of Angstroms, the mobility information becomes relevant for materials experiencing strain rates greater than 10$^{4}$ s$^{-1}$. The typical time scales of dislocation dynamics tools are controlled by the frequency of dislocation collisions, the natural frequencies of a dislocation line segment whose length scales with the spacing between dislocations, and the limits of strong scaling of dislocation dynamics simulations on massively parallel computers. These time scales practically limit dislocation simulations to strain rates greater than 10 s$^{-1}$. Furthermore, the efficiency of these simulations increases with increasing strain rate. When the mobility of the dislocations is obtained by molecular dynamics simulation the strain rate limit from the molecular dynamics simulations apply. The development of the constitutive models for dynamic straining conditions using a multiscale modeling methodology employing ab intitio, molecular dynamics, dislocation dynamics, and continuum finite element methods will be presented. Each modeling method is used to obtain information about material behavior that is sourced at its relevant length scale of applicability. The results obtained with the each simulation method are coarse grained and used as input for all of the simulations applicable at larger length scales. At the end of this chain, a final constitutive model for material strength is constructed for use in general engineering codes used to simulate the behavior of components under dynamic loading conditions. The final form of the model as well as all of its coefficients are determined by the supporting lower length scale simulations so that it can be considered a true numerical prediction of the material's dynamic strength. The predictive quality of the model is assessed by comparing the prediction of engineering simulations with the observations under a variety of loading conditions obtained with gas guns, explosive drives, and laser ramp loadings. [Preview Abstract] |
Thursday, June 30, 2011 9:45AM - 10:00AM |
S3.00002: A multi-scale strength model with phase transformation N. Barton, A. Arsenlis, M. Rhee, J. Marian, J. Bernier, M. Tang, L. Yang We present a multi-scale strength model that includes phase transformation. In each phase, strength depends on pressure, strain rate, temperature, and evolving dislocation density descriptors. A donor cell type of approach is used for the transfer of dislocation density between phases. While the shear modulus can be modeled as smooth through the BCC to rhombohedral transformation in vanadium, the multi-phase strength model predicts abrupt changes in the material strength due to changes in dislocation kinetics. In the rhombohedral phase, the dislocation density is decomposed into populations associated with short and long Burgers vectors. Strength model construction employs an information passing paradigm to span from the atomistic level to the continuum level. Simulation methods in the overall hierarchy include density functional theory, molecular statics, molecular dynamics, dislocation dynamics, and continuum based approaches. We demonstrate the behavior of the model through simulations of Rayleigh Taylor instability growth experiments of the type used to assess material strength at high pressure and strain rate. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (LLNL-ABS-464695). [Preview Abstract] |
Thursday, June 30, 2011 10:00AM - 10:15AM |
S3.00003: Analyzing Strength Effects in Shocks, Backwards and Forwards Bryan Reed, Damian Swift, James Stolken, Roger Minich, Mukul Kumar Extraction of strength information from shock measurements is typically done in two ways: Forward calculation with an assumed strength model and backward calculation of the behavior consistent with the measurement and wave propagation physics. Both approaches can be troublesome when rate-dependent effects are important, and each is subject to its own blind spots. We present results showing significant agreement between the two approaches, using a multiscale strength model for the forward calculation and a general thermodynamic formalism for the backward calculation. The discrepancies are indicative of known limitations of the two approaches, e.g. the parameter sensitivity of LaGrangian integration schemes at late times. The points of agreement between these totally different methods enhance our confidence in both, while the points of disagreement highlight focus areas for future development efforts. [Preview Abstract] |
Thursday, June 30, 2011 10:15AM - 10:30AM |
S3.00004: Shock structure and Riemannian geometry Roger Minich The stress-energy tensor, T$_{\mu \nu }$ is studied for 1+1 dimensional compressive flow. In particular, the convergence and curvature of Riemann characteristics and corresponding shock structure is studied for different symmetries of the stress-energy tensor. The curvature of the Riemann characteristics is related to the trace of the stress-energy tensor, T$_{\mu }^{\mu }$ , and the energy dissipated. Universal constraints on the thermal conductivity are also discussed. The results are compared to both experiment and molecular dynamics simulations. The study suggests that conformal symmetry may play a key role in understanding shock formation and empirical scaling laws. [Preview Abstract] |
Thursday, June 30, 2011 10:30AM - 10:45AM |
S3.00005: A numerical study of the dynamic inelasticity under compression-shear ramp wave loading Jow Ding, C. Scott Alexander, James Asay A new experimental technique has recently been developed at Sandia National Labs to measure the dynamic material strength at high pressures using ``magnetically applied pressure shear (MAPS)'' ramp waves. The objective of this study is to use numerical simulation to gain insight on the inelastic material response to such loading and develop a knowledge basis for further development and improvement of the technique. Two different materials were studied. One was FCC aluminum which was described by a simple viscoplastic model and the other was BCC tantalum described by a dislocation density based model developed in a previous work. The responses of these models to non-proportional compression-shear loading; effects of rate sensitivity, pressure dependence of strength, and wave interaction on shear wave propagation; and the correlation between in-situ inelastic behavior and measured experimental output were investigated and compared with the available experimental data. [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