Mechanical Properties of Microstructural Components of Inorganic Materials

Disertační práce se zabývá studiem strukturních a mechanických vlastností anorganických materiálů. Cílem je nalezení jednotlivých fází ve zkoumaném materiálu a hlavně lokalizace (mechanicky) nejslabšího místa, jeho ovlivnění a následně výroba materiálu o lepších mechanických vlastnostech. Z důvodu velkého množství použitých metod je základní teorie vložena vždy na začátku příslušné kapitoly. Taktéž z důvodu značného množství výsledků jsou na konci kapitol uvedeny dílčí závěry. Práce je rozdělena na tři části, kdy první se zabývá seznámením s možnostmi modelování mikro-mechanických vlastností a provedením experimentů umožňujících posouzení rozsahu platnosti některého modelu. V druhé části je provedeno shrnutí současných možností indentačních zkoušek pro měření mechanických vlastností strukturních složek betonu a praktické zvládnutí metodiky vhodné k užití pro výzkum materiálů zkoumaných domovským pracovištěm. V třetí části je navržena metoda identifikace nejslabších článků struktury anorganických pojiv a její ověření na konkrétním materiálu zkoumaném na domovském pracovišti. V této dizertační práci jsou použity tyto metody: kalorimetrie, ultrazvukové testování, jednoosá pevnost v tlaku, nanoindentace, korelativní mikroskopie a rastrovací elektronová mikroskopie s energiově disperzním spektrometrem. Dílčími výsledky jsou kompletní charakterizace cementových materiálů, upřesnění stávajících poznatků a nalezení optimálního postupu pro charakterizaci. Hlavním výsledkem je inovativní přístup vedoucí k pozitivnímu ovlivnění materiálu.The doctoral thesis deals with study of structural and mechanical properties of inorganic materials. Goal is to find the weakest (mechanically) phases and interfaces of material. By affecting these structures it should be possible consequently produce a material with better mechanical properties. Due to the large amount of used methods the basic theory is discussed always in the beginning of relevant chapter. Similarly, due to the considerable amount of results every chapter includes partial conclusions. The work is divided in three parts. The first deals with the introduction of the possibilities of modeling micro-mechanical properties and performing of experiments that allow assessment of the scope of some model. In second part itis performed an overview of current possibilities of indentation tests for measuring mechanical properties of structural components of concrete and the practical managing of methods suitable for use for materials research examined at our faculty. In third part the method of identifying the weakest points in structure of inorganic binders is proposed and validation on the particular material examined at our faculty is performed. The methods used in this doctoral thesis are: calorimetry, ultrasonic testing, uniaxial compression, nanoindentation, correlative microscopy and scanning electron microscopy with energy dispersive spectrometer. Partial results are a complete characterization of cementitious materials, specification of existing knowledge and finding the optimal procedure for characterization. The main result is an innovative approach that leads to a positive effect on the material.

Impact of anisotropy and fracture density on the approximation of the effective permeability of a fractured rock mass using 2D models

Imperial Users onl

Engineering Curriculum Map 2013-2014

This map displays degree requirements, courses, faculty information, clubs & organizations, and Library resources associated with engineering across the seven Claremont Colleges (7Cs) for the 2013-14 academic year. It was compiled using public information drawn from Colleges websites, course schedules and catalogs, and the Claremont Colleges Library website. This project was completed as part of an IMLS Sparks! Ignition grant in 2013-14

Thermomechanical analysis of rock asperity in fractures of enhanced geothermal systems

Enhanced Geothermal Systems (EGS) offer great potential for dramatically expanding the use of geothermal energy and become a promising supplement for fossil energy. The EGS is to extract heat by creating a subsurface system to which cold water can be added through injection wells. Injected water is heated by contact with rock and returns to the surface through production well. Fracture provides the primary conduit for fluid flow and heat transfer in natural rock. Fracture is propped by fracture roughness with varying heights which is called asperity. The stability of asperity determines fracture aperture and hence imposes substantial effect on hydraulic conductivity and heat transfer efficiency in EGS. Firstly, two rough fracture surfaces are characterized by statistical method and fractal analysis. The asperity heights and enclosed aperture heights are described by probability density function before cold water is pumped into fracture. Secondly, when water injection and induced cooling occurs, the thermomechanical analysis of single asperity is studied by establishing an un-symmetric damage mechanics model. The deformation curve of asperity under thermal stress is determined. Thirdly, deformation of fracture with various asperities on it in response to thermal stress is analyzed by a new stratified continuum percolation model. This model incorporates the fracture surface characteristics and preceding deformation curve of asperity. The fracture closure and fracture stiffness can be accurately quantified by this model. In addition, the scaling invariance and multifractal parameters in this process are identified and validated with Monte Carlo simulation --Abstract, page iii

Mechanisms and conditions of deformation in quartzites from the Cantabrian and west Asturian-Leonese zones, north Spain

Deformation mechanisms and conditions have been studied, principally in Ordovician quartzites, from the Cantabrian and West Asturian-leonese zones, north Spain. The quartzites have been strongly deformed at shallow crustal levels during the Variscan orogeny. In the external Cantabrian zone, the dominant mechanism was cataclasis, which occurred both pervasively around large-scale folds by shear on a network of bedding-normal fractures, and as localised deformation along large faults. Solution transfer was confined to grain boundaries. Grain boundary sliding operated in sandstones with porous microstructures, which deformed by small-scale chevron folds. This contrast in deformation modes is shown to be a consequence of different initial microstructures. In the West-Asturian leonese zone ( towards the internal part of the orogen), solution transfer extended along stylolites, and progressively increasing amounts of crystal plasticity became the fold accommodating mechanism. This can be followed by an increase in the intracrystalline extinction angle as grain boundary migration and sub-grain rotation contributed to further dynamic recrystallisation. The late stages of deformation were cataclastic. In all examples of cataclasis, fractures clustered together to form deformation zones of high density fracturing: this is an inherent part of the deformation mechanism, which is interpretted as a localisation phenomenon in response to changed material properties. The changes in mechanisms from the external to internal parts of the orogen correlate with an increase in temperature from 0-2500 to 311 - 411°. Effective confining pressures were from 30 to 7S MPa. and differential stresses from 50 to 300 MPa. These conditions of deformation are linked with the deformation modes to define nine deformation facies; the sequence of facies, the deformation path, is plotted for the four localities studied in detail, and it is suggested that the study area can be subdivided into four sub-areas, each characterised by one path

Characterisation and modelling of natural fracture networks: geometry, geomechanics and fluid flow

Natural fractures are ubiquitous in crustal rocks and often dominate the bulk properties of geological formations. The development of numerical tools to model the geometry, geomechanics and fluid flow behaviour of natural fracture networks is a challenging issue which is relevant to many rock engineering applications. The thesis first presents a study of the statistics and tectonism of a multiscale fracture system in limestone, from which the complexity of natural fractures is illustrated with respect to hierarchical topologies and underlying mechanisms. To simulate the geomechanical behaviour of rock masses embedded with natural fractures, the finite-discrete element method (FEMDEM) is integrated with a joint constitutive model (JCM) to solve the solid mechanics problems of such intricate discontinuity systems explicitly represented by discrete fracture network (DFN) models. This computational formulation can calculate the stress/strain fields of the rock matrix, capture the mechanical interactions of discrete rock blocks, characterise the non-linear deformation of rough fractures and mimic the propagation of new cracks driven by stress concentrations. The developed simulation tool is used to derive the aperture distribution of various fracture networks under different geomechanical conditions, based on which the stress-dependent fluid flow is further analysed. A novel upscaling approach to fracture network models is developed to evaluate the scaling of the equivalent permeability of fractured rocks under in-situ stresses. The combined JCM-FEMDEM model is further applied to simulate the progressive rock mass failure around an underground excavation in a crystalline rock with pre-existing discontinuities. The scope of this thesis covers the scenarios of both two-dimensional (2D) and three-dimensional (3D) fracture networks with pre-existing natural fractures and stress-induced new cracks. The research findings demonstrate the importance of integrating explicit DFN representations and conducting geomechanical computations for more meaningful assessments of the hydromechanical behaviour of naturally fractured rocks.Open Acces

Modeling the spatio-temporal evolution of fracture networks and fluid-rock interactions in GPU : Applications to lithospheric geodynamics

In this thesis, I present the theory and modeling of poro-elasto-plastic rheology coupled to a non-linear diffusion equation with a step increase in permeability at the onset of slip. This theoretical model is implemented in the graphic processing unit (GPU) architecture and programmed using the nVidia CUDA programming language. The numerical models are benchmarked by investigating fracture orientation for the solid-mechanical aspects, and by using the Method of Manufactured solutions for the diffusion part. I find that the GPU platform is ideal for these models because very high resolution simulations can be performed on an explicit finite difference algorithm using a single GPU card, outperforming CPU by a factor of at least five. The inherent problem with these coupled systems is the wide range of time and length scales that needs to be considered, and the advantage of GPU is its inherent parallel architecture that allows to do so. In these models, numerical fractures develop and evolve in response to prevailing far-field stresses, to local stress heterogeneity and pore-elastic stresses resulting from fracture growth, dislocation slip and fluid pressure diffusion within the domain. The numerical models, once benchmarked, are used to understand a variety of important and diverse lithospherical geodynamical problems, including enhanced geothermal systems (EGS), volcano-tectonic interactions and aftershocks. Envisaged future applications include hydro-fracture (’Fracking’), CO2 sequestration, earthquake nucleation and nuclear waste isolation. The potential of this model is far-reaching, and future developments in 3 dimensions will open up countless new avenues of insight and understanding of fluid-rock interactions and lithospheric dynamics

Quantification of flow impairment in faulted sandstone reservoirs.

Abstract unavailable please refer to PD