Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session U3: CM-5: Continuum and Multiscale Modeling of Strength |
Hide Abstracts |
Chair: Peter Gould, QinetiQ Room: Hermitage C |
Thursday, July 2, 2009 11:00AM - 11:30AM |
U3.00001: Mesoscopic studies of shock compression involving structural phase transformations and plasticity Invited Speaker: An outstanding issue in shock compression is to understand the interplay between a moving shock front, evolution of plasticity and strain-induced phase transformations. At low strain rates, the occurrence of yielding can be identified using a suitable yield criterion that has to be a function of both temperature and plastic strain rate. At high strain rates, the plasticity is overdriven by the rapidly advancing shock front and phenomenological rules are typically utilized to describe this regime. The conditions under which the moving shock front can induce structural phase transformations and the distribution of the individual variants of the product phase have been little studied. In this talk we introduce a mean-field Landau model of structural phase transformations, mediated by elastic strains, that also includes phenomenological models of yielding (von Mises-Prandtl-Reuss) and strain hardening that are dependent on temperature and strain rate. Due to high strain rates, the system is not in equilibrium and a Rayleigh dissipative functional is utilized to include the transfer of energy into heat. The resulting heat conduction equation is coupled with both local strains and strain rates and solved concomitantly with the evolution of the microstructure. The complex phase changes are thus driven by strain, strain rate and temperature. The main features of this model are demonstrated on a two-dimensional model system by examining the dynamic propagation of shock induced by a flying impact plate. For a given initial temperature at which the high-symmetry cubic phase is stable, we study the propagation of heat throughout the sample and evolution of the microstructure as a function of the velocity of the impact plate. This simplified model represents a starting point for the development of a mesoscopic framework that will be useful to study complex phase changes induced by inhomogeneously distributed strain, strain rate and temperature. [Preview Abstract] |
Thursday, July 2, 2009 11:30AM - 11:45AM |
U3.00002: An Assessment of Diamond Anvil Cell Measurements of Material Flow Strength Ryan Vignes, Rich Becker, Jeff Florando, Hyunchae Cynn, Mukul Kumar Diamond anvil cell experiments have been used to determine plastic flow strength in ductile metals at high pressure. To gain insight into the experiments and assess how accurately the material's strength at pressure can be determined, finite element simulations of DAC experiments have been performed. In the analyses, constitutive responses were assumed for the diamonds and vanadium test specimen; within the constitutive models, pressure sensitivity of strength was an input parameter. The quantities measured during experiments were extracted from the simulations and analyzed in an identical manner as the experiments to obtain the pressure sensitivity. The computed pressure sensitivity was then compared with the prescribed, input pressure sensitivity, allowing the accuracy and sensitivities of the experimental technique to be evaluated. Recommendations are made to improve accuracy of strength determinations. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Thursday, July 2, 2009 11:45AM - 12:00PM |
U3.00003: Damage development in high purity copper under varying dynamic conditions and microstructural states using Continuum Damage Mechanics Nicola Bonora, Andrew Ruggiero, Luca Esposito The evolution of ductile damage processes in pure metals is strongly dependent on the material microstructure and purity level. Although damage modeling at the continuum scale (CDM) is very attractive, the role of microstructural features, such as grain size, grain boundary type, orientation, purity, etc., is usually not taken into account explicitly in the formulations. A possible simple extension of CDM model formulations can be done through the identification of the dependency of the damage model parameters from these microstructural features. In this work, the correlation of two typical damage parameters, common to several CDM formulations, that are the damage threshold strain, $\varepsilon_{th}$, at which the ductile damage processes are initiated, and the theoretical uniaxial strain at failure, $\varepsilon_{f}$, with material grain size and purity level, has been investigated. Annealed and half hardened pure copper with different grain sizes and different purity grades have been investigated. Successively, these information have been used to predict damage development under different dynamic loadings and stress triaxiality testing conditions such as Hopkinson pressure bar experiment on both smooth and round notched samples, Taylor and Flyer Plate impact tests and to extrapolate the response of different material metallurgical states. [Preview Abstract] |
Thursday, July 2, 2009 12:00PM - 12:15PM |
U3.00004: Defect induced structural-scaling transitions and shock waves evolution in large range of strain rates (experimental and theoretical study) Oleg Naimark, Yuri Bayandin, Marvin Zocher, Dean Preston Statistically based phenomenology allowed formulation of thermodynamic potential and constitutive equations to establish link of defect induced structural-scaling transition, plastic flow and damage-failure transition. Relaxation properties of metals in strain rate range 10$^{3}$ 10$^{10}$s$^{-1}$ were analyzed that allowed interpretation: (i) self-similarity of shock wave profile for different stress amplitudes, mechanism of generation of second ``elastic precursor'' under reloading tests; (ii) mechanism of transition from thermally activated dislocation glide to regime of steady-state plastic wave and overdriven shock. Comparison of MTS-PTW and statistically based models allowed link hardening law, saturation stress and yield stress in thermal activation regime with non-linearity of thermodynamic potential, to propose interpretation of ``singularity gap'' between thermally activated dislocation glide and overdriven-shock regimes. Using 3D New View profilometry data correspondence of defect induced relaxation properties and multiscale correlation in defects ensemble was established for vanadium recovered specimens subject to quasi-static, dynamic and plate impact tests. [Preview Abstract] |
Thursday, July 2, 2009 12:15PM - 12:30PM |
U3.00005: Strength of Shocked Aluminum Oxynitride J. Zhu, R. Feng, D.P. Dandekar Aluminum oxynitride (AlON) is a polycrystalline and transparent ceramic. An accurate characterization of its shock response is critically important for its applications as transparent armor. Shock wave profiles measured in a series of plate impact experiments on AlON [Thornhill, et al., SCCM-2005, 143-146 (2006)] have been reanalyzed using finite element wave propagation simulations and considering an effective strength behavior that is pressure- and time-dependent. The results show a stiffer shock response than that calculated previously using the jump conditions. The material has a Hugoniot elastic limit of 10.37 GPa and sustains a maximum shear stress of 4.38 GPa for shock compressions up to a shock stress of 96 GPa. The mean stress response determined from the simulations displays no sign of phase transformation and corresponds to a linear shock speed-particle velocity relation with a slope of 0.857. These results have been successfully summarized into an AlON material model consisting of compression-dependent nonlinear elasticity, pressure-dependent equilibrium strength, and over-stress relaxation. The wave profiles simulated with the model show very good agreement with the experimental measurements. [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