Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session T1: ME.3 Inelastic Deformation, Fracture, and Spall VIII |
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Chair: Sunil Dwivedi, Georgia Institute of Technology Room: Grand Ballroom III |
Thursday, July 11, 2013 9:15AM - 9:30AM |
T1.00001: ABSTRACT WITHDRAWN |
Thursday, July 11, 2013 9:30AM - 9:45AM |
T1.00002: Modeling the Plastic Response of Single Crystals to High Strain Rate Deformation Curt Bronkhorst, Benjamin Hansen, Irene Beyerlein, Ellen Cerreta, Darcie Dennis-Koller A new metallic single crystal model based upon statistical average dislocation interactions is presented. This model includes motion of dislocations becoming drag-limited rather than thermally activated, requiring a physical transition in the average dislocation motion with strain-rate. Based upon the dislocation dynamics work of Wang, Beyerlein, and Lesar, plastic deformation evolution is based on statistical dislocation populations and the evolution of those populations. Three main dislocation populations are considered: 1) glissile dislocations ($\rho _{\mathrm{M}})$; 2) glissile dislocations, which currently do not move referred to as ``pile up'' ($\rho_{\mathrm{P}})$, and 3) sessile dislocations ($\rho_{\mathrm{D}})$. Mobile dislocations ($\rho _{\mathrm{M}})$ move through the crystal and are blocked by obstacles, react and annihilate, react and become sessile, or exit the region. The motivation to model the distribution of dislocation velocities is used to create the simplest distribution of two populations moving at two velocities. Results of single-crystal tensile simulations using the new model at various rates are compared to copper experiments. The key findings are: 1) a single-crystal model capable of transitioning from low to high strain rates, and 2) prediction of the transition from thermally activated to drag-dominated strain rates. Further investigation is easily adaptable in the model. [Preview Abstract] |
Thursday, July 11, 2013 9:45AM - 10:00AM |
T1.00003: The release of shear stress in metals under dynamic loading Rade Vignjevic, Neil Bourne Metals under shock loading relieve shear stress by slip after. This work focuses on the types of loading where a metal initially responds entirely elastically and plasticity with deformation mechanisms developing over time and determined by the material's state and microstructure. Finite kinetics in shock is mirrored in several commonly observed responses including elastic precursor decay and the measurement of shear stress histories during load. FCC and BCC metals have different kinetics, with those of BCC metals slower. A model, under development, is implemented here to depict the behaviour observed by assigning a finite time to the return of the state point from the quasi equilibrium yield surface to the equilibrium yield surface. This delays the softening of the material and reproduces observed response in the weak shock regime. The model is based on the assumption that formation and self-organisation of dislocation structures at various scales maximises dissipation rate (minimize the free energy) in the material. Initial validation of the model is performed on tantalum by comparing stress histories under shock and shock-less loading with experimental data in order to assess its ability to reproduce experimentally observed features. [Preview Abstract] |
Thursday, July 11, 2013 10:00AM - 10:15AM |
T1.00004: Response of FCC and BCC Metals to High-Amplitude Dynamic Compression Marc Meyers, Bruce Remington, Brian Maddox, Eduardo Bringa, Hye-Sook Park, Chia-Hui Lu The experimentally observed response of FCC and BCC metals to high-amplitude compressive waves is compared with analytical predictions using constitutive models based on dislocations and twinning and with molecular dynamics simulations. In FCC metals (Cu and Ni), the predictions of dislocation densities from a homogeneous nucleation model are close to those of molecular dynamics simulations. Both are orders of magnitude higher than experimentally observed residual dislocation densities. MD calculations predict a drastic decrease in dislocation densities upon unloading, bringing the values in agreement with measurements. For BCC metals (Ta), on the residual densities are close to predictions of Orowan dislocation multiplication. Due to the much higher Peierls-Nabarro stress, the MD simulations predict much lower dislocation densities than in FCC metals subjected to similar pressures. At higher amplitudes, both FCC and BCC metals experience extensive twinning. The threshold pressure for twinning is successfully modeled by constitutive model based on a critical shear stress for twinning, at the imposed strain rate and temperature. Research funded by UCOP/UC Labs Program. [Preview Abstract] |
Thursday, July 11, 2013 10:15AM - 10:45AM |
T1.00005: Phase transformations coupled to deformation processes Invited Speaker: Turab Lookman Phase transformation processes have a substantial impact on the inelastic and damage response of materials. Yet, our understanding of how different loading conditions affect volume fractions of transformed phases, microstructure and transformation pathways is very much in its infancy. With an emphasis on distilling single crystal physics that can, in principle, be incorporated into higher length scale models, I will discuss how recent atomistic simulations on Ti are beginning to provide insights into transformation pathways and the interplay of phase transformations and deformation processes. These simulations are complemented by shock experiments on Zr, Ti together with characterization studies at the Advanced Photon Source. [Preview Abstract] |
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