Nonequilibrium molecular dynamics (MD) simulations show that shock-induced void collapse in copper occurs by emission of shear loops. These loops carry away the vacancies which comprise the void. The growth of the loops continues even after they collide and form sessile junctions, creating a hardened region around the collapsing void. The scenario seen in our simulations differs from current models that assume that prismatic loop emission is responsible for void collapse. We propose a new dislocation-based model that gives excellent agreement with the stress threshold found in the MD simulations for void collapse as a function of void radius.

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ALE3D is a finite element arbitrary Lagrange-Eulerian hydro code with thermal transport and chemical reactions. In order to consider problems of aging a species diffusion capability was added. Species diffusion is the process whereby species move under potential flow from one location in the system to another. The diffusion method needed to work with element-centered concentrations. In order to fit within the ALE3D scheme, the method also needed to work on an arbitrarily connected hexahedral mesh. Since the rate of species diffusion is usually slow compared to other processes, it an explicit method is sufficient. Finally, the method must conserve total species concentration. Three separate finite volume algorithms were developed. These methods share the following characteristics: species fluxes of mass and energy are defined at each face. A second order predictor corrector scheme is used, with the ratio between the corrected mass flux and the predicted mass flux being used to define an accuracy time step constraint. The courant like diffusivity constraint is used for the stability constraint. Examples are shown.

We have utilized SPME GC/MS to monitor the degradation of syntactic polysulfide in the presence of Viton A at elevated temperature. This approach allowed the identification of products from two distinct degradation mechanisms. Small-scale laboratory experiments of this type are directly applicable to gas sampling for enhanced surveillance.

In this report, we present the use of temperature programmed reaction/decomposition (TPR) in the isoconversion mode to measure outgassing kinetics and to make kinetic prediction concerning hydrogen release from the polycrystalline LiH/LiOH system in the absence of any external H{sub 2}O source.