Effect of microstructure on undrained behaviour of sands

2001 ◽  
Vol 38 (1) ◽  
pp. 16-28 ◽  
Author(s):  
R G Wan ◽  
P J Guo
Keyword(s):  
Phase Transformation ◽  
Mathematical Modelling ◽  
Representative Elementary Volume ◽  
Elementary Volume ◽  
Sand Liquefaction ◽  
Proposed Model ◽  
Undrained Conditions ◽  
Drained And Undrained Conditions

This paper presents a mathematical modelling of the effects of initial fabric on the mechanical behaviour of sand. A stress-dilatancy model that incorporates microstructural aspects of sand is hereby obtained while writing energy conservation for an ensemble of particles over a representative elementary volume at micro- and macro-scales. The resulting stress-dilatancy model, when used within an elastoplastic framework, successfully reproduces certain aspects of sand behaviour that are reflective of its microstructure under both drained and undrained conditions. The role of microstructure in relation to the characterization of steady, quasi-steady, and phase-transformation states is discussed within the framework of the model. Numerical simulations obtained from the proposed model are generally very consistent with experimental observations and provide insightful information.Key words: sand, liquefaction, fabric, dilatancy, constitutive laws, granular materials, plasticity.

Analytical prediction of regular reflection over rigid porous surfaces in pseudo-steady flows

1995 ◽  
Vol 282 ◽  
pp. 219-232 ◽  
Author(s):  
H. Li ◽  
A. Levy ◽  
G. Ben-Dor
Keyword(s):  
Representative Elementary Volume ◽  
Analytical Prediction ◽  
Steady Flows ◽  
Elementary Volume ◽  
Regular Reflection ◽  
Governing Equations ◽  
Balance Equations ◽  
Porous Layers ◽  
Proposed Model ◽  
Porous Surfaces

An analytical model for solving the flow field associated with regular reflections of straight shock waves over porous layers has been developed. The governing equations of the gas inside the porous material were obtained by simplifying the general macroscopic balance equations which were obtained by an averaging process over a representative elementary volume of the microscopic balance equations as originally done by Bear & Bachmat (1990). The analytical predictions of the proposed model were compared to experimental results of Skews (1992) and Kobayashi, Adachi & Suzuki (1993). Very good to excellent agreement was evident.

scholarly journals On the Tortuosity-Connectivity of Porous Materials

2021 ◽  
Author(s):  
Miguel Fenaux ◽  
Encarnacion Reyes ◽  
Jaime C Gálvez ◽  
Amparo Moragues ◽  
Jesus Bernal
Keyword(s):  
Ionic Species ◽  
Transport Equations ◽  
Representative Elementary Volume ◽  
Elementary Volume ◽  
Macroscopic Scale ◽  
Average Speed ◽  
Proposed Model ◽  
Chloride Profiles ◽  
Connectivity Parameter ◽  
Poiseuille Equation

In this work, the transport equations of ionic species in concrete are studied. First, the equations at the porescale are considered, which are then averaged over a representative elementary volume. The so obtained transport equations at the macroscopic scale are thoroughly examined and each term is interpreted. Furthermore, it is shown that the tortuosity-connectivity does not slow the average speed of the ionic species down. The transport equations in the representative elementary volume are then compared with the equations obtained in an equivalent pore. Lastly, comparing Darcy’s law and the Hagen-Poiseuille equation in a cylindrical equivalent pore, the tortuosity-connectivity parameter is obtained for four dierent concretes. The proposed model provides very good results when compared with the experimentally obtained chloride profiles for two additional concretes.

scholarly journals A new hyperelastic model for the multi-axial deformation of blood clots occlusion in vessels

2020 ◽  
Author(s):  
Behrooz Fereidoonnezhad ◽  
Kevin Mattheus Moerman ◽  
Sarah Johnson ◽  
Ray McCarthy ◽  
Patrick McGarry
Keyword(s):  
Mechanical Properties ◽  
Axial Deformation ◽  
Proposed Model ◽  
Nonlinear Stress ◽  
Blood Clots ◽  
Hyperelastic Model

Mechanical thrombectomy can be significantly affected by the mechanical properties of the occluding thrombus. In this study we provide the first characterization of the volumetric behaviour of blood clots. We propose a new hyperelastic model for the volumetric and isochoric deformation of clot. We demonstrate that the proposed model provides significant improvements over established models in terms of accurate prediction of nonlinear stress-strain and volumetric behaviours of low and high haematocrit clots. We perform a rigorous investigation of the factors that govern clot occlusion of a tapered vessel. The motivation for such an analysis is two-fold: (i) the role of clot composition on the in-vivo occlusion location is an open clinical question that has significant implications for thrombectomy procedures; (ii) in-vitro measurement of occlusion location in an engineered tapered tube can be used as a quick and simple methodology to assess the mechanical properties/compositions of clots. Simulations demonstrate that both isochoric and volumetric behaviour of clots are key determinants of clot lodgement location, in addition to clot-vessel friction. The proposed formulation is shown to provide accurate predictions of in-vitro measurement of clot occlusion location in a silicone tapered vessel, in addition to accurately predicting the deformed shape of the clot.

scholarly journals On the Tortuosity-Connectivity of Cement-Based Porous Materials

2021 ◽  
Vol 11 (13) ◽  
pp. 5812
Author(s):  
Michiel Fenaux ◽  
Encarnacion Reyes ◽  
Jaime C. Gálvez ◽  
Amparo Moragues ◽  
Jesús Bernal
Keyword(s):  
Ionic Species ◽  
Transport Equations ◽  
Representative Elementary Volume ◽  
Elementary Volume ◽  
Macroscopic Scale ◽  
Average Speed ◽  
Proposed Model ◽  
Chloride Profiles ◽  
Connectivity Parameter ◽  
Poiseuille Equation

In this work, the transport equations of ionic species in concrete are studied. First, the equations at the porescale are considered, which are then averaged over a representative elementary volume. The so obtained transport equations at the macroscopic scale are thoroughly examined and each term is interpreted. Furthermore, it is shown that the tortuosity-connectivity does not slow the average speed of the ionic species down. The transport equations in the representative elementary volume are then compared with the equations obtained in an equivalent pore. Lastly, comparing Darcy’s law and the Hagen–Poiseuille equation in a cylindrical equivalent pore, the tortuosity-connectivity parameter is obtained for four different concretes. The proposed model provides very good results when compared with the experimentally obtained chloride profiles for two additional concretes.

Microstructural and Microchemical Characterization of Nickel Sulfide Inclusions in Plate Glass

1991 ◽  
Vol 49 ◽  
pp. 962-963
Author(s):  
J. Cooper ◽  
O. Popoola ◽  
W. M. Kriven
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
Glass Matrix ◽  
Nickel Sulfide ◽  
Plate Glass ◽  
Thermal Expansion Mismatch ◽  
Volume Increase ◽  
Β Phase ◽  
Microchemical Characterization

Nickel sulfide inclusions have been implicated in the spontaneous fracture of large windows of tempered plate glass. Two alternative explanations for the fracture-initiating behaviour of these inclusions have been proposed: (1) the volume increase which accompanies the α to β phase transformation in stoichiometric NiS, and (2) the thermal expansion mismatch between the nickel sulfide phases and the glass matrix. The microstructure and microchemistry of the small inclusions (80 to 250 μm spheres), needed to determine the cause of fracture, have not been well characterized hitherto. The aim of this communication is to report a detailed TEM and EDS study of the inclusions.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

Consideraciones en torno a la reducción solipsista

1970 ◽  
Vol 11 ◽  
Author(s):  
Natalia Carolina Petrillo

ResumenEn el presente trabajo se intentará mostrar que la fenomenología no conduce a una postura solipsista. Para ello, se caracterizará en qué consiste el solipsismo. Luego, se intentará refutar a lo que se ha de llamar “solipsismo metafísico” y “solipsismo gnoseológico”, con el objetivo principal de poner de manifiesto el fundamento de motivación para la salida de la ficción solipsista.Palabras claves:Phenomenology – solipsim – empatía - HusserlAbstractWith the aim of showing that phenomenology does not lead in solipsism, I will first attempt a characterization of it. Then, I will attempt a refutation of the so-called “metaphysical” and “epistemological” solipsisms. Finally, the nature and role of Husserl´s solipsistic fiction is examined, and the grounds that motivate the overcoming of this standpoint are disclosed.key wordsFenomenología – solipsismo - empathy – Husserl

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