The connection between grain size, porosity, and Biot model parameters

2020 ◽  
Vol 148 (4) ◽  
pp. 2550-2550
Author(s):  
Nicholas P. Chotiros
Keyword(s):  
Grain Size ◽  
Model Parameters ◽  
Biot Model

scholarly journals Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves 

2021 ◽  
Author(s):  
Meghana Ranganathan ◽  
Brent Minchew ◽  
Colin Meyer ◽  
Matej Pec
Keyword(s):  
Grain Size ◽  
Ice Sheet ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Model Parameters ◽  
Localized Deformation ◽  
Ice Shelves ◽  
Fine Grained ◽  
Initiation And Propagation ◽  
Rapid Deformation

<p>The initiation and propagation of fractures in floating regions of Antarctica has the potential to destabilize large regions of the ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the creep and toughness of ice. Here we derive a model for dynamic recrystallization in ice and other rocks that includes a novel representation of migration recrystallization, which is absent from existing models but is likely to be dominant in warm areas undergoing rapid deformation within the ice sheet. We show that, in regions of elevated strain rate, grain sizes in ice may be larger than expected (~15 mm) due to migration recrystallization, a significant deviation from solid earth studies which find fine-grained rock in shear zones. This may imply that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law exponent of n=4 in these regions. Further, we find from existing models that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, we expect that this increase in grain size makes the margins of fast-flowing glaciers less viscous and more vulnerable to fracture than we may suppose from standard model parameters.</p>

Modeling the Densification of FeSi Sintered Magnetic Alloys

2012 ◽  
Vol 727-728 ◽  
pp. 175-180 ◽  
Author(s):  
José Adilson de Castro ◽  
Gilberto V. Concilio ◽  
Daniel Rodrigues ◽  
Livia S. Santomauro ◽  
Marcos Flavio de Campos
Keyword(s):  
Experimental Data ◽  
Grain Size ◽  
Sintering Temperature ◽  
Process Parameter ◽  
Model Parameters ◽  
Important Process ◽  
Sintering Process ◽  
Heating Rates ◽  
Magnetic Alloys ◽  
Sintered Alloys

An important process parameter in FeSi sintered alloys is the sintering temperature. If the sintering temperature can be reduced, the sintering process could be performed in less expensive furnaces. A densification model is here applied to experimental data. The model considers both grain size and density. After the model is applied to experimental data, the acquired model parameters allow the simulation of densification for other situations of temperature and heating rates. The model can be helpful to find suitable sintering temperatures in these alloys.

Simulation of Recrystallization Behavior and Austenite Grain Size Evolution during Hot Deformation of Low Carbon Steel Using the Flow Stress

2011 ◽  
Vol 337 ◽  
pp. 178-183 ◽  
Author(s):  
Jian Wang ◽  
Hong Xiao ◽  
Hong Biao Xie ◽  
Xiu Mei Xu
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Dislocation Density ◽  
Microstructure Evolution ◽  
Hot Deformation ◽  
Process Model ◽  
Model Parameters ◽  
Flow Curves ◽  
Austenite Grain Size ◽  
Average Grain Size

Microstructure evolution can cause changes in dislocation density during hot plastic formation of metals and greatly influence the shape of flow curves. Recrystallization kinetics and average grain size were simulated by the coupled flow stress model describing dislocation development and microstructure evolution. The model for microstructure evolution considered different kinds of recrystallization in the same process rooted from nucleation and grain growth. Flow stress was calculated from the average dislocation density determined by the dislocation density model, which took into account hardening and recovery during the hot deformation process. Model parameters were defined by inverse analysis of flow curves obtained from hot compression tests and were completed through solving a nonlinear least-squares problem with constraints using optimization methods. Finally, the results obtained by the proposed model were compared with experimental results.

scholarly journals Grain-size distribution unmixing using the R package EMMAgeo

2019 ◽  
Vol 68 (1) ◽  
pp. 29-46 ◽  
Author(s):  
Elisabeth Dietze ◽  
Michael Dietze
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Synthetic Data ◽  
Model Parameters ◽  
Size Distributions ◽  
Sediment Sources ◽  
Data Set ◽  
Depositional Processes ◽  
Grain Size Distributions

Abstract. The analysis of grain-size distributions has a long tradition in Quaternary Science and disciplines studying Earth surface and subsurface deposits. The decomposition of multi-modal grain-size distributions into inherent subpopulations, commonly termed end-member modelling analysis (EMMA), is increasingly recognised as a tool to infer the underlying sediment sources, transport and (post-)depositional processes. Most of the existing deterministic EMMA approaches are only able to deliver one out of many possible solutions, thereby shortcutting uncertainty in model parameters. Here, we provide user-friendly computational protocols that support deterministic as well as robust (i.e. explicitly accounting for incomplete knowledge about input parameters in a probabilistic approach) EMMA, in the free and open software framework of R. In addition, and going beyond previous validation tests, we compare the performance of available grain-size EMMA algorithms using four real-world sediment types, covering a wide range of grain-size distribution shapes (alluvial fan, dune, loess and floodplain deposits). These were randomly mixed in the lab to produce a synthetic data set. Across all algorithms, the original data set was modelled with mean R2 values of 0.868 to 0.995 and mean absolute deviation (MAD) values of 0.06 % vol to 0.34 % vol. The original grain-size distribution shapes were modelled as end-member loadings with mean R2 values of 0.89 to 0.99 and MAD of 0.04 % vol to 0.17 % vol. End-member scores reproduced the original mixing ratios in the synthetic data set with mean R2 values of 0.68 to 0.93 and MAD of 0.1 % vol to 1.6 % vol. Depending on the validation criteria, all models provided reliable estimates of the input data, and each of the models exhibits individual strengths and weaknesses. Only robust EMMA allowed uncertainties of the end-members to be objectively estimated and expert knowledge to be included in the end-member definition. Yet, end-member interpretation should carefully consider the geological and sedimentological meaningfulness in terms of sediment sources, transport and deposition as well as post-depositional alteration of grain sizes. EMMA might also be powerful in other geoscientific contexts where the goal is to unmix sources and processes from compositional data sets.

scholarly journals Effects of the Grain Size on Dynamic Capillary Pressure and the Modified Green–Ampt Model for Infiltration

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Yi-Zhih Tsai ◽  
Yu-Tung Liu ◽  
Yung-Li Wang ◽  
Liang-Cheng Chang ◽  
Shao-Yiu Hsu
Keyword(s):  
Grain Size ◽  
Capillary Pressure ◽  
Dynamic Effect ◽  
Pressure Head ◽  
High Flow ◽  
Model Parameters ◽  
Wetting Front ◽  
Grain Sizes ◽  
Cumulative Infiltration ◽  
Capillary Pressures

Darcy-scale capillary pressure is traditionally assumed to be constant. By contrast, a considerable gap exists between the measured and equilibrium capillary pressures when the same moisture saturation is considered with a high flow rate, and this gap is called the dynamic effect on the capillary pressure. In this study, downward infiltration experiments of sand columns are performed to measure cumulative infiltration and to calculate the wetting front depth and wetting front velocity in sands with different grain sizes. We estimate the equilibrium capillary pressure head or suction head at the wetting front using both the classical Green–Ampt (GAM) and modified Green–Ampt (MGAM) models. The results show that the performance of MGAM in simulating downward infiltration is superior to that of GAM. Moreover, because GAM neglects the dynamic effect, it systematically underestimates the equilibrium suction head in our experiments. We also find that the model parameters α^ and β of MGAM are affected by the grain size of sands and porosity, and the dynamic effect of the capillary pressure increases with decreasing grain size and increasing porosity.

scholarly journals Weakly Imposed Symmetry and Robust Preconditioners for Biot’s Consolidation Model

2017 ◽  
Vol 17 (3) ◽  
pp. 377-396 ◽  
Author(s):  
Trygve Bærland ◽  
Jeonghun J. Lee ◽  
Kent-Andre Mardal ◽  
Ragnar Winther
Keyword(s):  
Finite Element ◽  
Finite Element Methods ◽  
Linear Elasticity ◽  
Discrete Systems ◽  
Model Parameters ◽  
Incompressible Limit ◽  
Biot Model ◽  
Finite Element Approximations ◽  
Consolidation Model ◽  
Biot’S Consolidation

AbstractWe discuss the construction of robust preconditioners for finite element approximations of Biot’s consolidation model in poroelasticity. More precisely, we study finite element methods based on generalizations of the Hellinger–Reissner principle of linear elasticity, where the stress tensor is one of the unknowns. The Biot model has a number of applications in science, medicine, and engineering. A challenge in many of these applications is that the model parameters range over several orders of magnitude. Therefore, discretization procedures which are well behaved with respect to such variations are needed. The focus of the present paper will be on the construction of preconditioners, such that the preconditioned discrete systems are well-conditioned with respect to variations of the model parameters as well as refinements of the discretization. As a byproduct, we also obtain preconditioners for linear elasticity that are robust in the incompressible limit.

scholarly journals Thermal consolidation of porous medium with a rheological kelvin–voigt skeleton

2012 ◽  
Vol 34 (3) ◽  
pp. 17-35 ◽  
Author(s):  
Monika Bartlewska-Urban ◽  
Tomasz Strzelecki
Keyword(s):  
Porous Medium ◽  
Temperature Gradient ◽  
Porous Plate ◽  
Model Parameters ◽  
Vertical Load ◽  
Consolidation Process ◽  
Biot Model ◽  
Thermal Consolidation ◽  
Deformation Tests

Abstract This study presents calculations results of thermal consolidation process of the porous medium with the rheological Kelvin-Voigt skeleton, obtained numerically with the use of Flex.PDE software. The investigated calculation scheme consisted of the porous column filled with a liquid. The vertical load was applied to the top surface of the column through a porous plate allowing the free flow of liquid through this surface. Numerical solution is based on compression of the sample at appropriately defined boundary conditions. The aim of this study was to describe the influence of external load and temperature gradient on the deformation tests progress at different values of three parameters: λ, rs and cv. The results obtained, in the context of further research, can also be used for the determination of the influence of other parameters of the state and model parameters on the process of thermo poroelasticity of Biot model with rheological skeleton.

Computational Simulation of Dynamic Recrystallization and Severe Deformation of AA7075 Alloy

2017 ◽  
Author(s):  
José Luis Hernández-Rivera ◽  
Perla Julieta Cerda Vázquez ◽  
Jose de Jesús Cruz Rivera ◽  
Pedro de Jesús García Zugasti ◽  
Mitsuo Osvaldo Ramos Azpeitia
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Volume Fraction ◽  
Experimental Testing ◽  
Computational Simulation ◽  
Peak Load ◽  
Model Parameters ◽  
Heterogeneous Distribution ◽  
Average Grain Size ◽  
Fourth Pass

The empirical model of dynamic recrystallization (DRX) coupled with DEFORM 3D® software (based on the finite element method (FEM)) was used to predict the microstructural evolution of the AA7075 processed by four passes of equal channel angular pressing (ECAP) at 250° C. The DRX model parameters were taken from the literature. The simulation results showed that the DRX exhibited a heterogeneous distribution from the back to the frontal part of the sample and this heterogeneity markedly diminished in the fourth pass. The recrystallized volume fraction reached 50% in most of the sample in the fourth pass and the average grain size did not show significant changes, going from an initial value of 16.4 μm to 12.5 μm. This latter result was attributed to the fact that DRX occurred partially even for the last pass. Experimental testing of ECAP was conducted by using the same conditions of computational simulation. The validation of model was performed by comparison of average grain size values with those obtained experimentally by means of image analysis applied on micrographs that were acquired by means of optical microscopy (OM). Hardness and peak load values also indicated the occurrence of a partial dynamic recrystallization and recovery.

scholarly journals MEDIUM-TERM MORPHODYNAMIC MODELING OF MIXED MUD AND SAND IN THE

2011 ◽  
Vol 1 (32) ◽  
pp. 65
Author(s):  
Markus Witting ◽  
Christof Wehmeyer ◽  
Hanz Dieter Niemeyer
Keyword(s):  
Grain Size ◽  
Field Measurements ◽  
Model Parameters ◽  
Shear Stresses ◽  
Transport Parameters ◽  
Medium Term ◽  
Mud Transport ◽  
Spm Concentration ◽  
Morphodynamic Modeling ◽  
Qualitative Measurements

A morphodynamic model for the Jadebusen basin based on the current DELFT3D model is established. With morphological information such as qualitative measurements of SPM-concentration (Suspended Particular Matter) and bottom change estimates as well as detailed surveys of a sand pit refilling process the model parameters for cohesive transport (Partheniades 1965) are calibrated. Within a period of 8 month, which is condensed to a representative period of 28 days for the modeling, almost 45% of the initial pit volume was refilled with mud. Despite the lack of specific field measurements a setup of mud transport parameters can be defined, which allows further investigations of sand pit locations in the Jadebusen basin. On major outcome is that critical erosion shear stresses for mud should be spatially varied in order to account for the different consolidation states of the mud fraction. Furthermore the paper addresses the problem of the initial grain size distribution for graded sediment transport. Wadden flat types are characterized based on aerial observations which build the underlying information for a relocation model run.

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