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Pore Collapse (pore + collapse)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Microplane constitutive model for porous isotropic rocks

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2003
k P. Ba
Abstract The paper deals with constitutive modelling of contiguous rock located between rock joints. A fully explicit kinematically constrained microplane-type constitutive model for hardening and softening non-linear triaxial behaviour of isotropic porous rock is developed. The microplane framework, in which the constitutive relation is expressed in terms of stress and strain vectors rather than tensors, makes it possible to model various microstructural physical mechanisms associated with oriented internal surfaces, such as cracking, slip, friction and splitting of a particular orientation. Formulation of the constitutive relation is facilitated by the fact that it is decoupled from the tensorial invariance restrictions, which are satisfied automatically. In its basic features, the present model is similar to the recently developed microplane model M4 for concrete, but there are significant improvements and modifications. They include a realistic simulation of (1) the effects of pore collapse on the volume changes during triaxial loading and on the reduction of frictional strength, (2) recovery of frictional strength during shearing, and (3) the shear-enhanced compaction in triaxial tests, manifested by a deviation from the hydrostatic stress,strain curve. The model is calibrated by optimal fitting of extensive triaxial test data for Salem limestone, and good fits are demonstrated. Although these data do not cover the entire range of behaviour, credence in broad capabilities of the model is lend by its similarity to model M4 for concrete,an artificial rock. The model is intended for large explicit finite-element programs. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Numerical modelling of hydro-mechanical behaviour of collapsible soils

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008
L. M. Costa
Abstract This paper presents a numerical simulation of the response of unsaturated soil under different loads, with special attention devoted to the phenomenon of pore collapse during wetting. A coupled hydro-mechanical formulation, implemented in the computational code CODE_BRIGHT, is first presented. Then the model is applied to assess material parameter from laboratory tests and to simulate, as boundary value problems, new and appealing in situ tests designed in the Federal University of Pernambuco. The soil considered is a collapsible soil located in the semi-arid region of the northeast of Brazil. Two situations are analysed: (i) the soil is initially at its natural water content and then flooded at some determined stress level, (ii) the soil is previously flooded and then loaded. Comparison between output results of numerical simulations and experimental data shows a very good agreement, which validate to some extent the proposed experimental procedure and the model formulation. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Biomedical Materials: Nanoporous Biodegradable Elastomers (Adv. Mater.

ADVANCED MATERIALS, Issue 2 2009
2/2009)
The mechanical properties and degradation rate of elastomers can be tailored with nanoporosity. The elastomers described in this study by Guillermo Ameer and co-workers (p. 188) are based on citric acid and are biocompatible. The nanopores also facilitate the entrapment and slow release of macromolecular therapeutics. The inside cover depicts the nano- and microarchitecture of the elastomer prior to pore collapse. [source]

Experimental dehydration kinetics of serpentinite using pore volumometry

JOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2007
S. LLANA-FÚNEZ
Abstract A series of dehydration experiments was carried out on both intact rock and cold-pressed powdered samples of serpentinite at temperatures in the range 535,610 °C, 100,170 °C above the onset of the breakdown temperature of 435 °C. Pore water pressures near 120 MPa were servo-controlled using a pore volumometer that also allowed dehydration reaction progress to be monitored through measurement of the amount of evolved water. Effective hydrostatic confining pressures were varied between 0 and 113 MPa. The reaction rate of intact specimens of initially near-zero porosity was constant up to 50,80% reaction progress at any given temperature, but decreased progressively as transformation approached completion. Water expulsion rates were not substantially affected by elevation of effective pressures that remained insufficient to cause major pore collapse. An Arrhenius relation links reaction rate to temperature with an activation enthalpy of 429 ± 201 and 521 ± 52 kJ mol,1 for powdered and intact specimens, respectively. Microstructural study of intact specimens showed extensive nucleation beginning at pre-existing cracks, veins and grain boundaries, and progressing into the interior of the lizardite grains. Extrapolation of these data towards equilibrium temperature provides an upper bound on the kinetics of this reaction in nature. [source]