Collaborations between Caltech s ASC alliance center and the DP labs

1. Collaborations between Caltech�s ASC alliance center and the DP labs Dan Meiron - Caltech ASC Center ASC PI Meeting San Antonio, TX Feb. 24, 2005

2. 2 Collaborations between Caltech ASC center and DP labs LLNL AX Division � collaboration on compressible turbulence and mixing (this talk) LLNL AX Division � collaboration on the mixing transition in Rayleigh-Taylor flows (Dimotakis, Cook) LLNL DTED � collaboration on solid-fluid interaction (Hoover, Meiron) LLNL CMS � collaboration on multiscale modeling of spall (Ortiz, Becker) LLNL CMS � collaboration on quasicontinuum approach (Bulatov, Ortiz) LLNL � collaboration on MD simulation of R-M instability (Goddard, Zybin, Bringa) LANL � collaboration on multiscale modeling of materials using phase field modeling (Koslowski, Ortiz) LANL � collaboration on Ferroelectrics (Strachan, Goddard) LANL � collaboration on subgrain structures and laminates (Beyerlein, Ortiz) LANL - Simulations of Thermal Decomposition of Polydimethylsiloxane Polymer (Kober, Goddard) LANL Validation of ReaxFF vs. ab initio MD by studying nitromethane thermal decomposition (Strachan, Goddard) Sandia Materials � collaboration on electronic structure code Sequest (Goddard, Schulz) Sandia - collaboration on AMR techniques (Ray, Steensland)

5. Phase-field dislocation dynamics

6. Phase-field dislocation dynamics

7. Phase-field dislocation dynamics

8. Phase-field dislocation dynamics

9. Equal Angular Channel Extrusion

12. 12 Current capability � Limitations Calculations so far have been based on cohesive elements/laws Replace cohesive model by: Porous plasticity and damage localization model (K. Weinberg, A. Mota and M. Ortiz, JCM, submitted). Strain-localization elements (Yang, Mota and Ortiz, IJNME, to appear).

13. 13 Spall � Engineering model - Validation

14. 14 Spall � Engineering model � Assumptions Need estimates of: Elastic energy, EoS Plastic dissipation Kinetic energy Nucleation kinetics Coarsening kinetics �

15. Quasicontinuum 2 Dislocation Dynamics Computed shear stress as a function of the shear angle. On the loading curve, ($\tau_l$,$\theta$), three main regimes, separated by yield points, can be clearly discerned: i) stage I corresponding to elastic loading, ii) stage II corresponding to primary dislocation glide and Lomer-Cottrell junction formation, and iii) stage III corresponding to secondary dislocation glide, cross-slip and stress saturation. The recovery behavior of the material, ($\tau_u$,$\theta$), is gradual and accompanied by the corresponding dislocation density reduction. The area encircled by both curves represents the net plastic work.} Incipient partial dislocation structures generated on the planes of maximum RSS occurring at $45^\circ$ to the shear direction at a shear angle and stress of $6.9^\circ$ and $4.3$~GPa, respectively, corresponding to the first yield point. Atoms belonging to a partial dislocation or a stacking fault can be seen in red and orange, while atoms part of the original void are shown in green/gray} Dislocation structures corresponding at the onset of stage III. Lomer-Cottrell locks forme by reaction of the initial leading Shockley partials. The Lomer-Cottrell harden the primary slip planes, which become inactive. Shear loops are subsequently emitted on secondary slip planes driven by the attendant stress rise.} Final dislocation structures at the end of stage III of the loading phase. The dominant features are large $\small{\frac{1}{6}}\langle112\rangle$ partial dislocation loops growing on $\{111\}$ planes. Other features, such as jogs and cross-slipped sections, are also observed in the figure. Computed shear stress as a function of the shear angle. On the loading curve, ($\tau_l$,$\theta$), three main regimes, separated by yield points, can be clearly discerned: i) stage I corresponding to elastic loading, ii) stage II corresponding to primary dislocation glide and Lomer-Cottrell junction formation, and iii) stage III corresponding to secondary dislocation glide, cross-slip and stress saturation. The recovery behavior of the material, ($\tau_u$,$\theta$), is gradual and accompanied by the corresponding dislocation density reduction. The area encircled by both curves represents the net plastic work.} Incipient partial dislocation structures generated on the planes of maximum RSS occurring at $45^\circ$ to the shear direction at a shear angle and stress of $6.9^\circ$ and $4.3$~GPa, respectively, corresponding to the first yield point. Atoms belonging to a partial dislocation or a stacking fault can be seen in red and orange, while atoms part of the original void are shown in green/gray} Dislocation structures corresponding at the onset of stage III. Lomer-Cottrell locks forme by reaction of the initial leading Shockley partials. The Lomer-Cottrell harden the primary slip planes, which become inactive. Shear loops are subsequently emitted on secondary slip planes driven by the attendant stress rise.} Final dislocation structures at the end of stage III of the loading phase. The dominant features are large $\small{\frac{1}{6}}\langle112\rangle$ partial dislocation loops growing on $\{111\}$ planes. Other features, such as jogs and cross-slipped sections, are also observed in the figure.

17. Large-scale atomistic simulation of shock instabilities in materials

18. 18 Simulations of Thermal Decomposition of Polydimethylsiloxane Polymerin collaboration with Ed Kober at LANL

19. 19 Validation of ReaxFF vs. ab initio MD by studying nitromethane thermal decomposition Work conducted at Los Alamos National Laboratory T-division Conducted by Si-ping Han Mentored by Dr. Alejandro Strachan Supported by a Seaborg Institute Summer Fellowship Objective Validate Reax against ab initio MD results for NM thermal decomposition Results Quantitative agreement on pressure and temperature curves, reaction time scales and initial reactions with ab initio MD results reported in Manaa et al., J Chem Phys, vol 120, number 21, 10146 Found CH3NO2 ? CH3ONO transition state with same geometry as predicted in Nguyen et al., J. Phys. Chem. 107, 4283 Extended calculation to wider range of conditions and longer time scales than Manaa et al work