Probabilistic finite element modeling of waste rollover

Stratification of the wastes in many Hanford storage tanks has resulted in sludge layers which are capable of retaining gases formed by chemical and/or radiolytic reactions. As the gas is produced, the mechanisms of gas storage evolve until the resulting buoyancy in the sludge leads to instability, at which point the sludge ``rolls over`` and a significant volume of gas is suddenly released. Because the releases may contain flammable gases, these episodes of release are potentially hazardous. Mitigation techniques are desirable for more controlled releases at more frequent intervals. To aid the mitigation efforts, a methodology for predicting of sludge rollover at specific times is desired. This methodology would then provide a rational basis for the development of a schedule for the mitigation procedures. In addition, a knowledge of the sensitivity of the sludge rollovers to various physical and chemical properties within the tanks would provide direction for efforts to reduce the frequency and severity of these events. In this report, the use of probabilistic finite element analyses for computing the probability of rollover and the sensitivity of rollover probability to various parameters is described

Accuracy issues in modeling superplastic metal forming

The utility of finite element modeling in optimizing superplastic metal forming is dependent on accurate representation of the material constitutive behavior and the frictional response of the sheet against the die surface. This paper presents work conducted to estimate the level of precision that is necessary in constitutive relations for finite element analysis to accurately predict the deformation history of actual SPF components. Previous work identified errors in SPF testing methods that use short tensile specimens with gauge length-to-width ratios of 2:1 or less. The analysis of the present paper was performed to estimate the error in predicted stress that results from using the short specimens. Stress correction factors were developed and an improved constitutive relation was implemented in the MARC finite element code to simulate the forming of a long, rectangular tray. The coefficient of friction in a Coulomb friction model was adjusted to reproduce the amount of material draw-in observed in the forming experiments. Comparisons between the finite element predictions and the forming experiments are presented

Review on laboratory preparation processes of polymer modified asphalt binder

Several previous studies have documented the progress in polymer modified asphalt binder with respect to materials’ types and properties. However, limited or no effort was made to document findings on the laboratory preparation practices of polymer modified asphalt binder. Full and clear disclosure of asphalt blend preparation method is necessary for research continuity, reproducibility, and accurate adaptation by future studies for analogy and reliable conclusions. The laboratory preparation processes of various modified asphalt binders have been reviewed in this study. Factors affecting the optimal mixing of asphalt-polymer blends were summarized. The optimal mixing conditions associated with different asphalt modifiers were documented. Gap in the literature on the current practice for the preparation and reporting of various modified asphalt binder was discussed. Modifiers include styrene butadiene styrene (SBS), polyethylene (PE), waste tire rubber or crumb rubber (CR), ethylene vinyl acetate (EVA), sulfur, polyphosphoric acid (PPA), epoxy, polyurethane, nano-materials, etc. Currently, there is lack of modern innovative approached in the preparation of modified asphalt towards better performance. There is no clear standardized definition of term associated with asphalt binder preparation process. Given the limited and common types of polymers utilized for the modification of asphalt binder, it is possible to standardize the mixing procedure for several polymers. Doing so could ease research continuity and facilitates accurate comparison of new studies with earlier ones

Modeling of deformation behavior and texture evolution in magnesium alloy using the intermediate φ-model

The viscoplastic intermediate ϕ-model was applied in this work to predict the deformation behavior and texture evolution in a magnesium alloy, an HCP material. We simulated the deformation behavior with different intergranular interaction strengths and compared the predicted results with available experimental results. In this approach, elasticity is neglected and the plastic deformation mechanisms are assumed as a combination of crystallographic slip and twinning systems. Tests are performed for rolling (plane strain compression) of random textured Mg polycrystal as well as for tensile and compressive tests on rolled Mg sheets. Simulated texture evolutions agree well with experimental data. Activities of twinning and slip, predicted by the intermediate ϕ-model, reveal the strong anisotropic behavior during tension and compression of rolled sheets