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 E5: Phase Transitions II |
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Chair: John Maw, Atomic Weapons Establishment Room: Renaissance Ballroom D |
Monday, June 27, 2011 4:00PM - 4:15PM |
E5.00001: Laser shock-induced melting and fragmentation in metals Didier Loison, Thibaut de Resseguier, Andre Dragon, Emilien Lescoute, Michel Boustie, Laurent Berthe Full or partial melting under shock compression or upon release following a shock wave and subsequent fragmentation in the melted state are still essentially open questions in most metals. We present laser shock experiments performed on tin and aluminium, to pressures ranging from about 60 to 250 GPa. Diagnostics include Photonic Doppler Velocimetry (PDV) measurements of the free surface velocity, transverse observations of the expanding cloud of droplets sometimes referred to as ``micro-spall,'' and soft recovery of such droplets within a low density gel. Multi-phase equations of state are used to infer the evolution of the thermodynamic state along shock propagation distance, accounting for the decay of the loading pressure pulse, and for the presence of mixed regions in the phase diagrams. Experimental observations are interpreted on the basis of hydrodynamic simulations of laser-matter interaction and shock response involving similar multi-phase equations of state. [Preview Abstract] |
Monday, June 27, 2011 4:15PM - 4:30PM |
E5.00002: Modeling high strain rate viscoplastic deformations combined with phase changes Gilles Roy, Frank Montheillet Metallic materials submitted to high strain rates upon dynamic loading can undergo phase changes induced by strains, stresses, and/or temperature increase associated with self-heating. Various mechanical and metallurgical assumptions have been proposed and implemented in numerical codes to deal with such complex interactions. In order to assess their respective influences, a simple nearly analytical model was developed and applied to the classical sphere expansion test carried out on a two-phase strain hardening, strain rate and temperature sensitive material. In this paper, classical homogenization assumptions are compared for deriving the overall material flow stress. Strain hardening transfer upon phase transformation is accounted for. Finally, the respective weights of the various contributions to the work rate, associated with stored energy, self-heating, and phase change, are analyzed. [Preview Abstract] |
Monday, June 27, 2011 4:30PM - 4:45PM |
E5.00003: Lagrangian Hydrocode Performance with a Multiphase Equation of State for Tin Bradley Plohr An advanced multiphase equation of state for Tin has been developed by C.~Greeff, E.~Chisolm, and D.~George. We investigate the behavior of this equation of state in a standard Lagrangian hydrodynamics code. Our focus is on (a)~shocking to liquid and (b)~releasing to a liquid-solid mixture. [Preview Abstract] |
Monday, June 27, 2011 4:45PM - 5:00PM |
E5.00004: Shock Induced Phase Transitions in Polymeric Nitrogen William Mattson, Radhakrishnan Balu The reported density functional molecular dynamics simulations are of a shock travelling through $\sim $4,000 atoms arranged in the equilibrium cg-N configuration equilibrated at T = 250K, P = 1 atm. Atoms within a small segment of the material given an extra velocity consistent with various desired flyer plate impact velocity. The resulting atomic trajectories show a number of complex behaviors including a phase transition to a previously unseen phase, spontaneous defect formation, and chemical reactions. The stability of the shock and the unusual properties of the above phenomena will be discussed. [Preview Abstract] |
Monday, June 27, 2011 5:00PM - 5:30PM |
E5.00005: Colloidal Nanocrystals: A Model System for the Study of Phase Transformations Since 1950 Invited Speaker: Shock waves provide a means of rapidly compressing a condensed phase sample and studying the resulting structural changes. However, shock studies to date have focused on bulk materials, in which multiple uncorrelated nucleation events lead to complex transformation kinetics. An individual nanocrystal, by comparison, can transform completely with $\sim $10ps following nucleation of the daughter phase, reducing the likelihood that a second nucleation event will occur during the transformation time. In a diamond anvil cell, the wurtzite to rocksalt phase transformation in CdSe nanocrystals, for example, has been shown to follow simple first-order kinetics. The slow, ensemble kinetics observed in those experiments, however, obscured the dynamics within each nanocrystal. Rapidly compressing a nanocrystalline sample using a laser-driven shock wave, the pressure around each nanocrystal can rise on a timescale comparable to that for a sound wave to traverse the crystal. Shock experiments on nanoscale materials therefore have the potential to elucidate aspects of the transformation mechanism inaccessible to further quasi-static diamond anvil cell measurements behavior of CdSe nanocrystals under shock stresses of 2--3.75 GPa has been studied. Above 3 GPa a near-complete disappearance of the first excitonic feature and broadening of the low-energy absorption edge were observed, consistent with a wurtzite to rocksalt structural transformation. The transformation pressure was reduced relative to hydrostatic compression in a diamond anvil cell, and the rate increased, attributed to shock induced shear stress along the reaction coordinate. The especially rapid rate observed for a 3.75 GPa shock suggests multiple nucleation events occurring in each particle. [Preview Abstract] |
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