Browsing by Subject "Fracture"
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Item A Materials Science Driven Pattern Generation Solution to Fracturing Computer Generated Glass for Films and Games(2014-08-11) Monroe, David CharlesBelievably and realistically fracturing computer generated glass for visual effects has been previously solved through various methods such as algorithmic approaches, utilizing texture maps, or finite element analysis. These solutions can achieve some believable results but often at the cost of one or more of the following: simulation time, preparation time, art directability, consistency with materials science research, or the requirement of creating or utilizing fixed assets or maps. In this thesis I present a novel method that draws from the appropriate literature and focuses on quickly generating accurate fracture patterns. The method takes inputs such as the artist?s animation of an impact and desired object properties, and outputs fracture patterns used for breaking objects apart based on input values, materials science literature, and fracture mechanics. After determining all of the fracture pattern variables such as the number of radial and concentric cracks, the artist is able to override the computed parameters to retain control and art directability. Implementation of this method was performed using MAXScript, the built-in scripting language for Autodesk 3ds Max. The result is a computationally fast and mechanically accurate tool while retaining art directability to fulfill film storyboards or game design.Item A Novel Model for Fracture Acidizing with Important Thermal Effects(2013-12-05) Lyons, JohnFracture acidizing is a well stimulation technique used to improve the productivity of low-permeability reservoirs, and to bypass deep formation damage. The reaction of injected acid with the rock matrix forms etched channels (that depend on injection rate, mass transport properties, formation mineralogy, reaction chemistry of the acid, and temperature) through which oil and gas can then flow upon production. The use of a model that can effectively describe fracture acidizing is an essential step in designing an efficient and economical treatment. Several studies have been conducted on modeling fracture acidizing, however, most of these studies have not accounted for the effect of variation in acid temperature (by heat exchange with the formation and the heat generated by acid reaction with the rock) on reaction rate and mass transfer of acid inside the fracture. In this study, a new fracture acidizing model is presented that uses the lattice Boltzmann method for fluid transport and takes into account these temperature effects. The lattice Boltzmann method incorporates both accurate hydrodynamics and reaction kinetics at the solid-liquid interface. This method is also well known for its capability to handle re- active transport in complex geometries. This enables the method to model realistic fracture shapes, on a pore-scale level, and predict the shape of the fracture after acidizing. Results of carbonate fracture dissolution with and without the thermal effects are presented. It is found that including thermal effects alters the predicted shape of the fracture after acidizing.Item Analysis of Impedance Response in Lithium-ion Battery Electrodes(2013-12-04) Cho, SeongkooA major amount of degradation in battery life is in the form of chemical degradation due to the formation of Solid Electrolyte Interface (SEI) which is a passive film resulting from chemical reaction. Mechanical degradation in the form of fracture formation due to diffusion induced stress can aggravate the aging of the electrode. These mechanisms of deterioration are primary contributors on limiting the durability of Lithium-ion battery (LIB). In addition, an composition of insertion materials such as active material, additive, and binder as well as active particle?s morphological heterogeneity can influence solid-state transport, electronic conductivity and hence, battery performance. In this study, virtual 3-D microstructures of LIB electrodes with intercalation particles are designed to describe the influence of microstructure on effective electrical conductivity and the electrochemical impedance. The technique of digital stochastic modeling has been employed for the generation of electrode microstructures consisting of active material, binder, conductive additive and electrolyte. Physicochemical properties for each of the constituent phases have been duly accounted for. Mathematical models have been developed to characterize the electrochemical impedance of LIB electrode. In this work, we demonstrate the coupling of electrode microstructures to the solid state diffusion impedance response in LIB electrodes. This model considers not only the effect of heterogeneity in active particle size on the diffusion impedance response, but also the effect of electrical conductivity, interfacial surface area of the active materials, and volume fraction of the active materials in the porous electrode on the impedance response. In addition, the impact of the morphology of the active materials on the diffusion impedance response through utilization of the characteristic diffusion length of active particles and a Sauter mean particle size has been demonstrated. In order to show the effect of chemical degradation on the impedance response with focus on aging, the Li-ion diffusion inside an active particle is considered along with SEI. Finally, mechanical degradation induced increase in impedance is analyzed by coupling diffusion induced fracture with impedance. These approaches are envisioned to offer a virtual impedance response probing framework to elucidate the influence of electrode microstructural variability and underlying electrochemical and transport interactions.Item Analysis of the effects of carbonate mounds on associated stratal geometry and fracture development, Sacramento Mountains, New Mexico, USA(2016-12) Tinker, Nathan Scott; Janson, Xavier; Zahm, Christopher Kent; Kerans, Charles; Fisher, William LThe objective of this research is an integrated structural‐stratigraphic analysis of compaction‐related fracturing in carbonate mounds and associated cover strata. The influence of early-cemented carbonate mounds on subsequent sediment deposition (such as creation of hard substrates and topographic relief) is relatively well-understood. The effect of early-cemented carbonate mounds during burial, however, has not been studied in detail. Early marine cementation of mounds enhances mechanical rigidity, which reduces mound compaction during burial as compared to less-resistant sediments surrounding and overlying the mound. This rigidity difference facilitates differential compaction of sediments overlying the mound, which are warped over the inflection point created by the mound topography. This study hypothesizes that there is a measurable increase in fracture intensity associated with differential compaction above early-lithified carbonate mounds. Thus, this work analyzes and quantifies the effects of differential compaction on stratal geometry, mechanical stratigraphy, and fracture development in Mississippian strata overlying carbonate mounds which are well-exposed in the Sacramento Mountains in southeast New Mexico. Methods employed in this study are drawn from structural geology, sedimentology, petrography, and remote sensing in an effort to adequately determine facies, examine fracture characteristics (e.g. size, orientation, and intensity), and to better understand which process(es) most directly control those characteristics (e.g. host rock facies type, diagenesis, bed thickness, mound proximity, mound size). Innovative methods of outcrop characterization such as high-resolution gigapan photography and unmanned aerial vehicle (UAV) photography were combined with photogrammetric techniques to create photo-realistic 3D outcrop models. The resulting models enabled a cost-effective, more detailed, less-distorted, and more comprehensive interpretation compared to previous methods, and improved understanding of the relationship between stratigraphy, rock mechanical evolution, and structural deformation in carbonate mound systems. Field work documented facies, stratal geometries, folds, faults, and fracture sets which validated observations and characterizations made using high-resolution field photographs and 3D outcrop models. Results of this work show that paleotopographic relief which has been early lithified (in this instance, Mississippian carbonate mounds) directly controls fracture development and overlying stratal geometry, in that there is a significant increase in tension fracture (mode 1) intensity above pre-existing rigid structures and over-steepening of bed dips beyond an expected and reasonable angle of repose. Additionally, this work outlines a multi-stage tectonostratigraphic sequence of the development of the stratigraphically complex Teepee Mound assemblage based on field observations of facies, fractures, stratal geometries, and diagenetic effects (e.g. cementation, compaction, and chertification), which includes new evidence of late-Mississippian tectonic compression. This result emphasizes the importance of understanding both syndepositional and post-depositional processes in outcrop characterization. Specifically, syndepositional processes establish the original mechanical stratigraphy and control the formation and propagation of early mechanical discontinuities, which in turn set up the fabric of weaknesses preferentially utilized by later fracture development. Post-depositional mechanical and diagenetic processes alter mechanical stratigraphy and rock brittleness, and thus influence fracture propagation through time.Item Analytical modeling of a fracture-injection/falloff sequence and the development of a refracture-candidate diagnostic test(Texas A&M University, 2006-08-16) Craig, David PaulFracture-injection/falloff sequences are routinely used as pre-frac well tests to estimate reservoir pressure and transmissibility, but the current interpretation methods are limited to analyzing specific and very small portions of the pressure falloff data. To remove the current limitations, new analytical fractureinjection/ falloff models are developed that account for fracture propagation, fracture closure, and after fracture closure diffusion. A fracture-injection/falloff differs from a conventional injection/falloff sequence in that pressure during the injection is sufficient to initiate and propagate a hydraulic fracture. By considering fracture propagation as time-dependent storage, three new models are presented for a fractureinjection/ falloff sequence in a well in an infinite slab reservoir with a single vertical fracture created during the injection and with variable fracture and wellbore storage as follows: ?? Equivalent propagating-fracture and before-fracture-closure storage with constant after-fractureclosure storage. ?? Time-dependent propagating-fracture storage, constant before-closure storage, and constant afterclosure storage. ?? Time-dependent propagating-fracture storage, constant before-closure storage with linear flow from the fracture, and constant wellbore storage and skin with after-closure radial flow. When a fracture-injection can be considered as occurring instantaneously, limiting-case solutions of the new fracture-injection/falloff models suggest the observed pressure difference can be integrated to generate an equivalent pressure difference if the rate were constant. Consequently, a fractureinjection/ falloff sequence can be analyzed with constant-rate, variable-storage type curves. The new fracture-injection/falloff theory is also extended to allow for a fracture-injection in a reservoir containing an existing conductive hydraulic fracture. The new multiple-fracture fracture-injection/falloff model forms the basis of a new refracture-candidate diagnostic test that uses characteristic variable-storage behavior to qualitatively diagnose a pre-existing fracture retaining residual width and to determine if a preexisting fracture is damaged. A quantitative analysis methodology is also proposed that uses a new pressure-transient solution for a well in an infinite-slab reservoir producing through multiple arbitrarilyoriented finite- or infinite-conductivity fractures.Item Analytical-Numerical Methodology to Measure Undamaged, Fracture and Healing Properties of Asphalt Mixtures(2012-08-29) Koohi, Yasser 1980-Unlike in laboratory compacted asphalt mixtures, the distribution of viscoelastic properties in field layers is not uniform because of nonuniform air void distribution and aging. Therefore, characterization of field specimens is more challenging compared to that of laboratory compacted specimens. Formerly, characterization of field asphalt mixtures was based on binder tests which are useful but do not represent the properties of the asphalt mixtures because binder is only a component in the asphalt mixture. This study uses linear viscoelastic theory and numerical modeling to obtain the undamaged and damaged viscoelastic properties of both laboratory made and field compacted asphalt concrete. Additionally, it uses fracture mechanics principles to find the fracture and healing properties of aged asphalt specimens. The analytical models presented in this research have been successfully verified by testing the actual field specimens of different ages. The model developed in this dissertation is suitable to track the viscoelastic, fracture and healing properties of the field specimen with time and depth. The test protocols and analytical models described in this study can be used for the development of reliable performance models for field-aged asphalt layers.Item Characterization and modeling of mixed-mode I+III fracture in brittle materials(2015-12) Pham, Khai Hong; Ravi-Chandar, K.; Landis, Chad M; Liechti, Kenneth M; Mear, Mark E; Marder, Michael PMixed-mode I+III fracture in brittle materials presents spectacular, scale-independent pattern formation in nature and engineering applications; and it is one of the last remaining puzzles in linear elastic fracture mechanics. This problem has received much attention in the literature over the past few decades both from experiments and analysis, but there are still open challenges that remain. Specifically, the existence of a threshold ratio of mode III to mode I loading below which fragmentation of the crack front (formation of daughter cracks) does not occur and the length scale associated with the spacing of the fragments when they do occur are still under debate. The continued growth of cracks under remote mode I + III loading is also of interest; it is observed that in some cases the fragmented cracks coalesce, while in others they maintain their independent development. We approach this problem through carefully designed experiments to examine the physical aspects of crack initiation and growth. This is then explored further through numerical simulations of the stress state that explore the influence of perturbations on the formation of daughter cracks. We show that a parent crack subjected to combined modes I+III loading exhibits fragmentation of the crack front into daughter cracks without any threshold. The distance between the daughter cracks is dictated by the length scale corresponding to the decay of the elastic field; this decay depends on the characteristic dimension of the parent crack from which the daughter cracks are nucleated. As the daughter cracks continue growing, they coarsen in spacing also through elastic shielding. As the daughter cracks grow farther, the parent crack, pinned at the original position, experiences increased stress intensity factor and the bridging regions begin to crack and the parent crack front advances towards the daughter cracks. This establishes a steady state condition for the system of parent crack with equally spaced daughter cracks to continue growing together. Finally, direct numerical simulation of crack initiation and growth is explored using a phase-field model. The model is first validated for in-plane modes I + II through comparison to experiments, and then used to explore combined modes I + III in order to study the above mechanism of mixed-mode I + III crack growth.Item Comparison of fatigue analysis approaches for predicting fatigue lives of hot-mix asphalt concrete (HMAC) mixtures(Texas A&M University, 2006-08-16) Walubita, Lubinda F.Hot-mix asphalt concrete (HMAC) mixture fatigue characterization constitutes a fundamental component of HMAC pavement structural design and analysis to ensure adequate field fatigue performance. HMAC is a heterogeneous complex composite material of air, binder, and aggregate that behaves in a non-linear elasto-viscoplastic manner, exhibits anisotropic behavior, ages with time, and heals during traffic loading rest periods and changing environmental conditions. Comprehensive HMAC mixture fatigue analysis approaches that take into account this complex nature of HMAC are thus needed to ensure adequate field fatigue performance. In this study, four fatigue analysis approaches; the mechanistic empirical (ME), the calibrated mechanistic with (CMSE) and without (CM) surface energy measurements, and the proposed NCHRP 1-37A 2002 Pavement Design Guide (MEPDG) were comparatively evaluated and utilized to characterize the fatigue resistance of two Texas HMAC mixtures in the laboratory, including investigating the effects of binder oxidative aging. Although the results were comparable, the CMSE/CM approaches exhibited greater flexibility and potential to discretely account for most of the fundamental material properties (including fracture, aging, healing, visco-elasticity, and anisotropy) that affect HMAC pavement fatigue performance. Compared to the other approaches, which are mechanistic-empirically based, the CMSE/CM approaches are based on the fundamental concepts of continuum micromechanics and energy theory.Item Constraining fracture permeability by characterizing fracture surface roughness(2010-12) Al-Johar, Mishal Mansour; Sharp, John Malcolm, 1944-; Ketcham, Richard A.; Cardenas, Meinhard B.Open and connected fractures, where present, control fluid flow and dominate solute transport. Flow through fractures has major implications for water resource management, underground waste repositories, contaminant remediation, and hydrocarbon exploitation. Complex fracture morphology makes it difficult to quantify and predict flow and transport accurately. The difficulty in usefully describing the complex morphology of a real fracture from a small 3-D volume or 2-D profile sample remains unresolved. Furthermore, even when complex fracture morphology is measured across three-dimensions, accurate prediction of discharge remains difficult. High resolution x-ray computed tomography (HXRCT) data collected for over 20 rock surfaces and fractures provide a useful dataset to study fracture morphology across scales of several orders of magnitude. Samples include fractured rock of varying lithology, including sandstone, volcanic tuffs and crystalline igneous and metamorphic rocks. Results suggest that the influence of grain size on surface roughness is not readily apparent due to other competing variables such as mechanics, skins and coatings, and weathering and erosion. Flow tests of HXRCT-scanned fractures provide real discharge data allowing the hydraulic aperture to be directly measured. Scale-invariant descriptions of surface roughness can produce constrained estimates of aperture variability and possibly yield better predictions of fluid flow through fractures. Often, a distinction is not made between the apparent and true fracture apertures for rough fractures measured on a 2-D topographic grid. I compare a variety of local aperture measurements, including the apparent aperture, two-dimensional circular tangential aperture, and three-dimensional spherical tangential aperture. The mechanical aperture, the arithmetic mean of the apparent local aperture, is always the largest aperture. The other aperture metrics vary in their ranking, but remain similar. Results suggest that it may not be necessary to differentiate between the apparent and true apertures. Rock fracture aperture is the predominant control on permeability, and surface roughness controls fracture aperture. A variety of surface roughness characterizations using statistical and fractal methods are compared. A combination of the root-mean-square roughness and the surface-to-footprint ratio are found to be the most useful descriptors of rock fracture roughness. Mated fracture surfaces are observed to have nearly identical characterizations of fracture surface roughness, suggesting that rock fractures can be sampled by using only one surface, resulting in a significantly easier sampling requirement. For mated fractures that have at least one point in contact, a maximum potential aperture can be constrained by reflecting and translating a single surface. The maximized aperture has a nearly perfect correlation with the RMS roughness of the surface. These results may allow better predictions of fracture permeability thereby providing a better understanding of subsurface fracture flow for applications to contaminant remediation and water and hydrocarbon management. Further research must address upscaling fracture morphology from hand samples to outcrops and characterizing entire fracture networks from samples of single fractures.Item Contribution to the Study of Fracture in Amorphous Polymers: Experiments and Modeling(2011-02-22) De Castro, AnthonyGlassy polymers are extensively used to make all kinds of structural components. Polymers, such as epoxies, are often chosen as matrices in polymer matrix composites (PMC). Ever since the 1960s, these types of composites have been gaining importance in aerospace and automotive advanced applications due to their high sti ness and weight saving potential. In order to provide clues on the dependence of the fracture behavior upon the stress triaxiality, a series of tensile tests on epoxy (Epon862) round notched bars were carried out at NASA Glenn Research Center. Using state-of-the-art non-contact dig- ital image correlation measurement technique, the mechanical quantities of interest were extracted in order to understand how the fracture behavior responds when sub- jected to various levels of stress triaxiality induced by varying the notch radius of the specimens. E ects of aging on the fracture behavior were also investigated. A physics-based macromolecular constitutive model that accounts for temperature and pressure sensitivity as well as small-strain softening and large-strain hardening was used to model the deformation behavior. Good correlation between experiments and numerical simulations was achieved. To predict fracture, a pressure-sensitive model motivated by previous work is introduced. Based on the experimental and numerical results, the relation between the mean strain to failure versus the stress triaxiality was de ned and it was shown that the fracture response of the material is strongly a ected by the level of stress triaxiality.Item Development of a novel orthopedic microfastener(Texas A&M University, 2007-04-25) Agnihotri, Mukul MukundOver the last decade, biodegradable screws and plates have received wide acceptance over metallic fasteners for orthopedic fracture fixation. A biodegradable fastener would gradually "disappear" during healing of a fractured bone or tissues, therefore avoiding a secondary operation to remove that fastener. When using a metal fastener, the current approach requires manual threading on a large bone fragment for fixation. This technique is difficult when it is required to fixate a small bone fragment. This study puts forth the development of a threadless, polymer based orthopedic fastener for small fragment fixation which would provide stability and interfragmental compression to the fracture site. The fastener was designed with ratchets on its surface, which deflect during insertion into the drilled hole in the bone and subsequently stiffen to hold the bone fragments in place due to interference. The head of the fastener was developed analogous to a Belleville washer which deflects during insertion of the fastener and subjects the bone fragments to interfragmental compression. Finite element analysis (FEA) was conducted to design the fastener profile and assess its performance. The push-in and pull-out forces predicted by FEA were comparable to the experimental results for the prototype of the microfasteners. The push-in force was found to increase with increasing insertion depth and radial interference. The force required to initiate pull-out was maximum and was reduced with reducing fastener bone contact. An analytical model was proposed to explain the fastener bone interaction. It was found to be in good agreement with the FEA and experimental results at low levels of interference.Item Dynamic response of metal-polymer bilayers subjected to blast loading(2012-12) Albrecht, Aaron Berkeley; Ravi-Chandar, K.; Landis, Chad; Liechti, Kenneth; Mear, Mark; Marder, MichaelThe use of compliant coatings, in particular polyurea, for improved blast protection of structures has been reported recently in the literature. The goal of this research is to develop a comprehensive understanding of the reasons for improved performance of coated structures through experimentation and correlation with simulation. The different factors influencing the response of an elastomer coated ductile metal subjected to a blast load have been examined and quantified. First, dynamic strain localization in the metal is a precursor to ductile failure; this was characterized for the metal of interest with and without the polymer coating. Experiments with the expanding ring/tube and experiments have demonstrated that for Al 6061-O and Al 3003-H14, the localization strain is unaffected by both deformation rate and the polymer coating; however, two important effects of the coating have been explored. First the additional mass of the coating provides an inertial resistance. Second, the flow resistance of the polymer provides continued dissipation of energy even after the metal has yielded potentially preventing failure in the metal, or at least containing fragments. These effects were examined for two different types of polymers – polyurea, an elastomer and polycarbonate, a thermoplastic shear yielding polymer. It is shown that these two effects can be used to tailor the coating to optimize blast protection of the bilayer system. In order to take advantage of this optimization, the constitutive behavior of the elastomer coating must be determined at strain rates and loading conditions that are experienced in the blast loading; these strain rates are in the range of 1000 to 10,000 per second. This has been accomplished through a hybrid method that combines measurements with numerical simulations to extract the constitutive response of the material. The strain rate dependent behavior of polyurea for rates in the range of 800-8000 per second has been determined by measuring the spatio-temporal evolution of the particle velocity and strain in a thin strip subjected to high speed impact loading that generates uniaxial stress conditions and comparing this with numerical simulations of the one-dimensional problem using the method of characteristics. A similar scheme to track the particle velocity and strain during the axisymmetric deformation of a membrane subjected to high speed loading has also been developed; this requires two projections of the deformation to be obtained in order to facilitate the measurement of axial and kink waves in the membrane. The finite volume method is adapted for simulations of these dynamic uniaxial and axisymmetric problems with a view towards simulating shock waves that are expected to form in some loading conditions. The hybrid method is used once again to characterize the constitutive response. The axisymmetric experiments have demonstrated the inability of the uniaxial models for both polyisoprene rubber and polyurea to completely capture their behavior during a more complex loading, and left a need for further work on characterizing the dynamic constitutive response of these polymers.Item Effect of electro-mechanical loading in metallic conductors(2010-12) Gallo, Federico Guido; Ravi-Chandar, K.; Mear, Mark E.; Satapathy, Sikhanda S.; Liechti, Kenneth M.; Landis, Chad M.The development of high powered electro-magnetic devices has generated interest in the effect of combined electromagnetic and mechanical loading of such structures. Materials used in high-current applications – aluminum alloys and copper – are subjected to heat pulses of short duration (in the range of a few hundred microseconds to a few milliseconds); immediately following or along with such heat pulses, these materials are also subjected to large mechanical forces. In previous work reported in the literature, ejection of material from the vicinity of preexisting defects such as cracks, notches or discontinuities have been observed resulting from short-duration high-intensity current pulses; after a series of pulses, permanent deformation and weakening of intact material has also been reported. But a lack of complete understanding of the effects of short duration current pulses hinders the assessment of the reliability of such conductors in high energy applications. Therefore, an investigation was undertaken to examine the behavior of electromagnetically and mechanically loaded conductors. This work investigates the effects of short-duration, high-current-density pulses in combination with viii mechanical loading. The aim is to develop a theoretical model to describe the resulting mechanical response. The model is to provide a characterization of the possible effects of thermally-induced plastic strains on metals loaded beyond or just below their yield strength or below the critical stress intensity factor. In the experiments reported here, two types of specimens, undamaged and damaged, were subjected to combined electromechanical loads. Undamaged specimens were used to observe thermally-induced plastic strains - strains not caused by an increase in mechanical loading, but rather resulting from the reduction of yield strength and post-yield stiffness due to the increase in temperature. The experiments were conducted such that it would be possible to develop a model that would conclusively account for the observed material behavior. The second sets of specimens were weakened a priori by the introduction of a crack in order to study the influence of such crack-like defects on the electrical and mechanical fields, and to produce a safe design envelope with respect to the loading conditions. Failure was found to occur due to melting triggered by joule heating; a quantitative criterion based on current concentration and heat accumulation near the crack tip has been developed based on these experimental results.Item Effect of in-plane voiding on the fracture behavior of laser sintered polyamide(2011-12) Leigh, David Keith; Bourell, David Lee; Beaman, Joseph J.Laser Sintering, a method of additive manufacturing, is used in the production of concept models, functional prototypes, and end-use production parts. As the technology has transitioned from a product development tool to an accepted production technique, functional qualities have become increasingly important. Tension properties reported for popular polyamide sintering materials are comparable to the molded properties with the exception of elongation. Reported strains for laser sintered polyamide are in the 15-30% range with 200-400% strains reported for molding. (CES Edupack n.d.) The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are studied. Methods to quantify decreased mechanical properties are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture.Item Effective fracture geometry obtained with large water sand ratio(2009-05-15) Kumar, AmrendraShale gas formation exhibits some unusual reservoir characteristics: nano-darcy matrix permeability, presence of natural fractures and gas storage on the matrix surface that makes it unique in many ways. It?s difficult to design an optimum fracture treatment for such formation and even more difficult is to describe production behavior using a reservoir model. So far homogeneous, two wing fracture, and natural fracture models have been used for this purpose without much success. Micro seismic mapping technique is used to measure the fracture propagation in real time. This measurement in naturally fractured shale formation suggests a growth of fracture network instead of a traditional two wing fractures. There is an industry wise consensus that fracture network plays an important role in determining the well productivity of such formations. A well with high density of fracture networks supposed to have better productivity. Shale formations have also exhibited production pattern which is very different from conventional or tight gas reservoir. Initial flow period is marked by steep decline in production while the late time production exhibits a slow decline. One of the arguments put for this behavior is linear flow from a bi-wing fractured well at early time and contribution of adsorbed gas in production at late time. However, bi-wing fracture geometry is not supported by the micro-seismic observation. A realistic model should include both the fracture network and adsorbed gas property. In this research we have proposed a new Power Law Permability model to simulate fluid flow from hydraulically fractured Shale formation. This model was first described by Valko & Fnu (2002) and used for analyzing acid treatment jobs. The key idea of this model is to use a power law permeability function that varies with the radial distance from well bore. Scaling exponent of this power law function has been named power law index. The permeability function has also been termed as secondary permeability. This work introduces the method of Laplace solution to solve the problem of transient and pseudo steady-state flow in a fracture network. Development and validation of this method and its extension to predict the pressure (and production) behaviour of fracture network were made using a novel technic. Pressure solution was then combined with material balance through productivity index to make production forecast. Reservoir rock volume affected by the fracture stimulation treatment that contributes in the production is called effective stimulated volume. This represents the extent of fracture network in this case. Barnett shale formation is a naturally fractured shale reservoir in Fort Worth basin. Several production wells from this formation was analysed using Power Law Model and it was found that wells productivity are highly dependent on stimulated volume. Apparently the wells flow under pseudo steady state for most part of their producing life and the effect of boundary on production is evident in as soon as one months of production. Due to short period of transient flow production from Barnett formations is expected to be largely independent of the relative distribution of permeability and highly dependent on the stimulated area and induced secondary permeability. However, an indirect relationship between permeability distribution and production rate is observed. A well with low power law index shows a better (more even) secondary permeability distribution in spatial direction, larger stimulated volume and better production. A comparative analysis between the new model and traditional fracture model was made. It was found that both models can be used successfully for history matching and production forecasting from hydraulically fractured shale gas formation.Item The enriched Galerkin method for linear elasticity and phase field fracture propagation(2015-12) Mital, Prashant; Wheeler, Mary F. (Mary Fanett); Wick, ThomasThis thesis focuses on the application of the discontinuous Galerkin (DG) and enriched Galerkin (EG) methods to the problems of linear elasticity and phase field fracture propagation. The use of traditional and popular continuous Galerkin method (CG) for linear elasticity has posed some challenges. For example, nonphysical stress oscillations often occur in CG solutions for linearly elastic, nearly incompressible materials. Furthermore, CG solutions produce discontinuous stresses at the finite element boundaries which need to be post-processed. Based on the success of the DG methods in solving these challenges, we attempt resolution of the same problems with the yet untested EG method. For phase field fracture propagation, the CG method has been ubiquitously used in the literature. Since the phase field displacement solution is essentially discontinuous across the crack, we hypothesize that the discontinuous DG and EG methods could offer some advantages when applied to the fracture problem. We then perform a comparative analysis of CG, DG and EG applied to the phase field equations to determine if this is indeed the case. We begin by applying a family of DG and EG methods, including Nonsymmetric Interior Penalty Galerkin (NIPG), Symmetric Interior Penalty Galerkin (SIPG), and Incomplete Interior Penalty Galerkin (IIPG) to 2D linear elasticity problems. It is shown that the EG methods are simple and robust for dealing with linear elasticity. They are also shown to converge at the same rates as the corresponding DG methods. A detailed comparison of the performance of NIPG, IIPG, and SIPG is also made. We then propose a novel monolithic scheme with an augmented-Lagrangian method for phase field fracture propagation. We apply CG, DG and EG methods to the scheme and establish convergence in space and time through numerical studies. It is shown that the Newton method used for solving the system of nonlinear equations converges faster for DG and EG than it does for CG.Item Experimental investigation of ASR/DEF-induced reinforcing bar fracture(2011-12) Webb, Zachary David; Bayrak, Oguzhan, 1969-; Zhu, Jinying; Jirsa, James O.Numerous cases of premature concrete deterioration due to alkali-silica reaction and/or delayed ettringite formation have developed within highway infrastructure in the state of Texas over the past two decades. Although experimental research and in-situ load testing on an international scale has indicated that moderate levels of deterioration are unlikely to pose a threat to structural safety, the discovery of reinforcing bar fracture in Japan due to ASR-related expansion has called into question the integrity of heavily damaged structures. A two-part experimental program was conducted at The University of Texas at Austin relating to ASR/DEF-induced reinforcing bar fracture. Work conducted under TxDOT Project 0-6491 included the fabrication and monitoring of four concrete specimens. Methods were employed to simulate a fracture of the transverse reinforcement within the time frame of the study and the applicability of various NDT monitoring techniques to detect bar fracture was evaluated. Furthermore, a number of reinforcing bar samples were tested and analyzed to investigate (1) the development of reinforcing bar cracking due to the bending operation and (2) the progression of cracks after application of an expansive opening force on bars with 90° bends. Research findings and conclusions form a preliminary assessment on the potential for reinforcing bar fracture within affected infrastructure in Texas.Item Experimental Investigation of Propped Fracture Conductivity in Tight Gas Reservoirs Using The Dynamic Conductivity Test(2012-10-24) Romero Lugo, Jose 1985-Hydraulic Fracturing stimulation technology is used to increase the amount of oil and gas produced from low permeability reservoirs. The primary objective of the process is to increase the conductivity of the reservoir by the creation of fractures deep into the formation, changing the flow pattern from radial to linear flow. The dynamic conductivity test was used for this research to evaluate the effect of closure stress, temperature, proppant concentration, and flow back rates on fracture conductivity. The objective of performing a dynamic conductivity test is to be able to mimic actual field conditions by pumping fracturing fluid/proppant slurry fluid into a conductivity cell, and applying closure stress afterwards. In addition, a factorial design was implemented in order to determine the main effect of each of the investigated factors and to minimize the number of experimental runs. Due to the stochastic nature of the dynamic conductivity test, each experiment was repeated several times to evaluate the consistency of the results. Experimental results indicate that the increase in closure stress has a detrimental effect on fracture conductivity. This effect can be attributed to the reduction in fracture width as closure stress was increased. Moreover, the formation of channels at low proppant concentration plays a significant role in determining the final conductivity of a fracture. The presence of these channels created an additional flow path for nitrogen, resulting in a significant increase in the conductivity of the fracture. In addition, experiments performed at high temperatures and stresses exhibited a reduction in fracture conductivity. The formation of a polymer cake due to unbroken gel dried up at high temperatures further impeded the propped conductivity. The effect of nitrogen rate was observed to be inversely proportional to fracture conductivity. The significant reduction in fracture conductivity could possibly be due to the effect of polymer dehydration at higher flow rates and temperatures. However, there is no certainty from experimental results that this conductivity reduction is an effect that occurs in real fractures or whether it is an effect that is only significant in laboratory conditions.Item Fold-related brittle structures and associated strain in a limestone bed of the Carmel Formation, San Rafael Swell, Utah(2015-12) Laciano, Peter Joseph; Marrett, Randall; Cloos, Mark; Ukar, EstibalitzThe San Rafael Swell (SRS) is a basement-cored Laramide uplift located in central-eastern Utah. The SRS is bounded on the east by a 70 km long monocline, a fault-propagation fold, with excellent exposure of sedimentary strata including the Carmel Formation. This monocline is an ideal natural laboratory for studying brittle deformation associated with folding. Qualitative and quantitative observations for brittle structures in a limestone bed near the base of the Carmel Fm. were made in a wide range of bedding dip, curvature, and fold domains. Kinematic data was collected for 2942 structures (1865 veins, 746 stylolites, 314 faults) in 30 locations in order to calculate principal directions of strain. Additionally, data was collected along 71 scanlines at 19 of those locations in order to estimate structure intensities and strain magnitudes. Dekameter-displacement thrust faults, acting as ramps between inferred layer-parallel faults, accommodate orders of magnitude more strain than all other observed brittle structures. These faults are only found in segments of the monocline where bedding dip is high, but curvature is low, which provides strong evidence that limb rotation more strongly controls strain magnitudes than layer bending in the SRS. The trishear model effectively predicts SRS monocline geometry, specifically observed limb thickening, broad, curved hinges, and progressively rotating limb. This is likely due to the dominance of thick, homogeneous rock packages, such as the Navajo Sandstone, in the SRS monocline. In contrast, strain localization within the Carmel Fm. is poorly predicted by trishear: there is strong evidence of flexural slip, and folding induced structure orientations and calculated principal strain directions remain consistent relative to bedding. These strain directions are inconsistent with trishear forward models produced by workers such as Zuluaga et al. (2014) that do not stay consistent relative to bedding. These divergences are likely due to the fact that trishear is a kinematic model that assumes rock homogeneity, while the Carmel Fm. is stratigraphically and mechanically heterogeneous. Because this heterogeneity appears to have a strong effect on strain localization, kink band models likely better estimate strain localization in the Carmel limestone bed as well as other layers in folded heterogeneous strata. The monocline’s interpreted transition from layer-parallel shortening to extension at the steepest locations in the monocline, and thus at most advanced stage of folding, enabled estimation of the dip of the basement fault beneath the SRS as ~30°. This shallow dip contrasts with the steep dip (~60°) assumed for the SRS by Zuluaga et al. (2014) and observed in the Kaibab uplift (Huntoon and Sears, 1975; Tindall, 2000), but is consistent with a recent estimation of 20-40° for the SRS by Davis and Bump (2009) using trishear modeling.Item A fracture mechanics approach to accelerated life testing for cathodic delamination at polymer/metal interfaces(2013-05) Mauchien, Thomas Kevin; Liechti, K. M.This work presents a fracture mechanics analysis of the cathodic delamination problem for the polyurethane/titanium and polyurea/steel interfaces. The nonlinear behavior of both polymers was investigated. The recent Marlow model was used to define the strain energy function of the polymers. Viscoelastic effects of the polyurea were also studied. The Marlow model was associated with a nine-term Prony series. This model was seen to represent experimental data relatively well for a wide range of strain rates both in tension and compression. The driving force for delamination, the strain energy release rate G, is presented for both interfaces. Cathodic delamination data for several temperatures are presented as crack growth rate as a function of crack driving force. The approach recognizes that both temperature and stress can be used as accelerated life testing parameters.
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