Bibliographies: 'Crack splitting' – Grafiati (2024)

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Splitting of zero‐offset reflected shear‐waves is measured directly from three‐component finite‐difference synthetic seismograms for media with intersecting vertical crack systems. Splitting is simulated numerically (by finite differencing) as a function of crack density, aspect ratio, fluid content, bulk density, and the angle between the crack systems. The type of anisotropy symmetry in media containing two intersecting vertical crack systems depends on the angular relation between the cracks and their relative crack densities, and it may be horizontal transverse isotropy (HTI), tetragonal, orthorhombic, or monoclinic. The transition from one symmetry to another is visible in the splitting behavior. The polarities of the reflected quasi‐shear waves polarized perpendicular and parallel to the source particle motion distinguish between HTI and orthorhombic media. The dependence of the measured amount of splitting on crack density for HTI symmetry is consistent with that predicted theoretically by the shear‐wave splitting factor. In orthorhombic media (with two orthogonal crack systems), a linear increase is observed in splitting when the difference between crack densities of the two orthogonal crack systems increases. Splitting decreases nonlinearly with the intersection angle between the two crack systems from 0° to 90°. Surface and VSP seismograms are simulated for a model with several flat hom*ogeneous layers, each containing vertical cracks with the same and with different orientations. When the crack orientation varies with depth, previously split shear waves are split again at each interface, leading to complicated records, even for simple models. Isotropic and anisotropic three‐component S-wave zero‐offset sections are synthesized for a zero‐offset survey line over a 2.5-D model of a carbonate reservoir with a complicated geometry and two intersecting, dipping crack sets. The polarization direction of the fast shear wave, propagating obliquely through the cracked reservoir, is predicted by theoretical approximations for effective properties of anisotropic media with two nonorthogonal intersecting crack sets.

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Realize the basic process of fracture analysis in ANSYS. The fore treatment program of crack propagation simulation is compiled by parameterization method of apdl. The calculation and analysis is automatic. ANSYS is well for simulating the structures which contain cracks and bugs. When the parameters are suitable, the propagation of cracks can be simulated well in ANSYS. The different phases of crack propagation are simulated. To compare with the results by theory, perfect the formation process and mechanism of splitting cracks.

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The geometrical shielding produced by intergranular crack-tip branching in the fracture toughness tests of the Fe–V–P alloy is quantitatively assessed particularly with respect to the contribution of crack splitting. This process was evaluated by an identification of secondary intergranular cracks visualized on metalographical samples perpendicular to the fracture surface. The analysis of mixed trans/intergranular fracture revealed no special influence of triple-point branching (splitting) on the total crack tip shielding in cases of such highly spatially tortuous crack fronts. Thus, the previously reported results taking only the effect of crack tip kinking and meandering into account were proved to be correct.

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Abstract Calculations have been made by FEA of strain energy release rates G for a rubber sheet with a small edge crack, subjected to a far-field simple extension. Growth of the crack is considered in both forwards and sideways directions, the latter corresponding to crack splitting or turning. When the imposed extension is large, the value of G at which a small sideways crack will initiate is found to be a substantial fraction, about 60%, of that for further forwards growth. This suggests that crack splitting or turning will occur when the tear strength in the sideways direction is only slightly lower than that for forward growth. However, the value of G for a sideways crack decreases rapidly as the crack grows, indicating that it will stop after a short distance. These conclusions are shown to be in accord with experimental observations of crack splitting in filled rubber compounds and account for the phenomenon of reinforcement by fillers. In particular, they account for the fact that deep edge cracks are less likely to split or turn.

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In order to analysis the splitting property of automotive con-rod steel C70S6, a type of con-rods using this material were manufactured on a domestic production line. Both the fracture and the cracks of the con-rods were observed by SEM, the relationship between the cracks and the grain orientation were analyzed by EBSD. The results show that the fracture of the steel is cleavage fracture and most cleavage planes are {001} , the crack initiation is mainly ferrite or inclusions, and the crack propagation race is along the {001} planes, most microcracks in the vicinity of the main crack induced by the notch can coalesce with it and change its propagation direction, this is the probable formation mechanism of the step-like fracture.

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Experiments have been conducted to investigate the crack growth characteristics of 7050-T7451 aluminium plate in L-S orientation. Two loading conditions are selected, i.e. constant amplitude and constant stress intensity factor range (ΔK). The effects of ΔK-levels and stress ratios (R) on crack splitting are studied. Test data shows that crack splitting could result in the reverse of crack growth rate trend with the increasing R ratio at high ΔK-level. The appearance of crack splitting depends on both ΔK and R.

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Laboratory results from sandstone Brazilian splitting tests and uniaxial compression tests based on acoustic emission (AE) monitoring indicated that the acoustic emission parameters analysis method can be applied to analyse the characteristics of acoustic emission and to classify the crack modes in rock materials. It concluded that more than 99 per cent of the whole cracking signals in Brazilian tests were classified as tensile mode, and no shear cracks occurred. And more than 65 per cent of the AE signals in uniaxial tests were tensile-shear crack mode, along with about 30 percent of tensile mode and 5 percent of shear mode, and shear cracks only occurred in the unstable crack extension stages; tensile-shear cracks are the main crack modes in the crack stable extension stage.

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I-II mixed mode fracture under two kinds of load manners was carried out, and it was also simulated by the ANSYS, and the test results and the simulation results were compared and analyzed, and the reasonableness of the model built and the effectiveness of test were verified. The failure process of fracture under the loading could be judged through the development of the crack tip combined with the stress nephogram and strain nephogram when cracks initiation at crack tip, and it provided the basis for the crack damage judgment.

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Crack-free hematite inverse opal photoanodes were fabricated by directly “sewing” the cracks in opal templates, which exhibited record high photo-electrochemical water splitting for pristine nanostructured hematite anodes.

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A universal energy-intensive micromechanism of periodic splitting-rupture (PSR) is revealed which proceeds at the front of the fatigue cracks in metallic materials, providing their steady growth, forming T-shaped crack tip and striated microrelief of the fracture surface. The PSR micromechanism is caused by a critical (prior to fracture) fragmentated structure formed in the area of the crack front where the material is subjected to multiple and increasing plastic deformation. This universal prefracture structure is a final stage of the evolution of the deformational structures emerged in front of the fatigue crack at the stage of stable crack growth in metallic materials with different initial structural states. This is responsible for universality of PSR micromechanism and fatigue striations. Fatigue striations are the traces of extending crack front with T-shaped tip formed during brittle transverse microsplitting along the overstressed boundaries of critical fragmentated structure. Based on 3D finite element modeling of the stress-strain state in front of the cracks with T-shaped tip, it is established that the value and the location of maximum of normalized in-plain stresses (acting in front of crack tip in the plane of crack along the normal to its front) are close or coincide for the cracks of different configuration and different types of tensile load under condition that splitting in the T-shaped crack tip is considerably less than the crack length. Taking into account the PSR micromechanism and asymptotic stress distribution in front of T-shaped crack tip the physically based mathematical model for steady fatigue crack growth is developed along with the techniques for prediction of steady fatigue crack growth in full-scale components under simple and complex loading cycles.

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Doctor of Philosophy
Department of Civil Engineering
Robert J. Peterman
This dissertation describes a testing program to evaluate the bond and splitting propensity characteristics of 5.32-mm-diameter prestressing wires. Prestressing wire reinforcement is used primarily in the production of prestressed concrete railroad ties. Twelve different 5.32-mm-diameter wires were tested in this study in order to measure bonding characteristics of the reinforcement. Establishment of the bond-slip characteristics of these reinforcement at both transfer of prestress (transfer bond) and under flexural loading (flexural bond) is necessary to enable the accurate modeling of these ties using finite elements. Transfer bond and flexure bond of various indent patterns were tested using tensioned pullouts. Specimens of various sizes with single or multiple wires were tested to determine the effects of cover and wire number on bond. Indents were machined on smooth prestressing wires to accurately compare indent geometries. Lateral expansion was tested to determine which wires have higher propensity to cause cracking or splitting. Crossties were instrumented to compare resulting lateral expansion with results found in the laboratory.The results from the testing program showed that the tensioned pullout test was able to be used to predict the transfer length of prisms made with the same reinforcement. The results also showed that the indent geometries were able to be used to predict the splitting of specimens based on the amount of slip the wire had experienced. The testing also showed the importance of concrete cover with the relation to splitting potential.

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The design of complex structures demands the prediction of possible fracture-dominant failure processes, due to the existence of unavoidable preexistent flaws and other defects, as well as sharps and cracks. On one hand, the complexity of the structure and the presence of many defects to be accounted for in the modeling can become the computational effort impracticable. On the other hand, it is important to seek the development of a computational framework based on some numerical method to study these problems. A way to overcome the difficulties mentioned, therefore making feasible the analysis of complex structures with many cracks, flaws and other defects, consists of combining a representative mechanical modeling with an efficient numerical method. This is precisely the fundamental aim of this work. Firstly, the Splitting Method is used aiming to build a representative modeling. Secondly, the Generalized Finite Element Method (GFEM) is chosen as an efficient numerical method, in which enrichment strategies of the approximated solution using stress functions in particular can be explored. The GFEM framework also allows avoiding the excessive refinement of the mesh, which increases the computational effort in conventional finite element analysis. In the Splitting Method, a kind of decomposition method, the original problem is subdivided in local and global problems which are then combined by imposing null traction at the crack surfaces. In this work, the Splitting Method was completely programmed in Python language and its use extended to analyze crack propagation including fatigue crack growth. The generated code presents in addition to several features related to Fracture Mechanics concepts, as the computation of the stress intensity factor (mode I and II) trough J Integral. Some examples are presented to depict the propagation of the cracks in multisite damage structures. It is shown that for this kind of problems the enrichment strategy provided by GFEM is essential. Moreover, the final example demonstrates that the computational tool allows for investigation of different possible crack scenarios with a low cost analysis. One concludes about the representativeness and efficiency of the methodology hereby proposed.
O projeto de estruturas complexas demanda a previsão de possíveis processos de ruptura governados por fraturamento, devido à existência de inevitáveis defeitos pré-existentes, como entalhes e fissuras. Por um lado, a complexidade da estrutura e a presença de muitos defeitos a serem considerados no modelo podem tornar a análise inviável devido ao esforço computacional necessário. Por outro lado, é importante procurar desenvolver uma estrutura computacional baseada em métodos numéricos para estudar estes problemas. Um modo de superar as dificuldades mencionadas, portanto tornando possível a análise de estruturas complexas com muitas fissuras e outros defeitos, consiste em combinar um modelo mecânico que seja representativo com um método numérico eficiente. Este é precisamente o objetivo fundamental deste trabalho. Primeiramente, o Método da Partição é utilizado para a construção de um modelo representativo. Em segundo lugar, o Método dos Elementos Finitos Generalizados (GFEM) é empregado por ser um método numérico eficiente, no qual as estratégias de enriquecimento da solução aproximada usando funções de tensão, em particular, podem ser exploradas. A estrutura do GFEM também permite evitar o excessivo refinamento da malha, que aumenta o esforço computacional em análises convencionais nas quais se utiliza o método dos elementos finitos. No Método da Partição, um tipo de método de decomposição, o problema original é subdividido em problemas locais e globais que são então combinados impondo-se a nulidade do vetor de tensões na superfície da fissura. Neste trabalho, o Método da Partição foi completamente programado em linguagem Python® e sua utilização estendida para analisar a propagação de fissuras, incluindo-se a associação do crescimento com a resposta em fadiga. Além disso, o código gerado apresenta diversas características relacionadas aos conceitos da Mecânica da Fratura, como o cálculo do fator de intensidade de tensão (modos I e II) mediante a Integral J. Alguns exemplos são apresentados para ilustrar a propagação de fissuras em estruturas multi-fraturadas. Mostra-se que para este tipo de problemas a estratégia de enriquecimento fornecida pelo GFEM é essencial. Além disso, o exemplo final comprova que a ferramenta computacional permite a investigação de diferentes possíveis cenários de fissuras com uma análise de baixo custo. Conclui-se sobre a representatividade e eficiência da metodologia proposta.

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We investigate multiple crack evolution under quasi-static conditions in an isotropic linear-elastic solid based on the principle of minimum total energy, i.e. the sum of the potential and fracture energies, which stems directly from the Griffith’s theory of cracks. The technique, which has been implemented within the extended finite element method, enables minimisation of the total energy of the mechanical system with respect to the crack extension directions. This is achieved by finding the orientations of the discrete crack-tip extensions that yield vanishing rotational energy release rates about their roots. In addition, the proposed energy minimisation technique can be used to resolve competing crack growth problems. Comparisons of the fracture paths obtained by the maximum tension (hoop-stress) criterion and the energy minimisation approach via a multitude of numerical case studies show that both criteria converge to virtually the same fracture solutions albeit from opposite directions. In other words, it is found that the converged fracture path lies in between those obtained by each criterion on coarser numerical discretisations. Upon further investigation of the energy minimisation approach within the discrete framework, a modified crack growth direction criterion is proposed that assumes the average direction of the directions obtained by the maximum hoop stress and the minimum energy criteria. The numerical results show significant improvements in accuracy (especially on coarse discretisations) and convergence rates of the fracture paths. The XFEM implementation is subsequently applied to model an industry relevant problem of silicon wafer cutting based on the physical process of Smart-CutTM technology where wafer splitting is the result of the coalescence of multiple pressure-driven micro-crack growth within a narrow layer of the prevailing micro-crack distribution. A parametric study is carried out to assess the influence of some of the Smart-CutTM process parameters on the post-split fracture surface roughness. The parameters that have been investigated, include: mean depth of micro-crack distribution, distribution of micro-cracks about the mean depth, damage (isotropic) in the region of micro-crack distribution, and the influence of the depth of the buried-oxide layer (a layer of reduced stiffness) beneath the micro-crack distribution. Numerical results agree acceptably well with experimental observations.

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La perméabilité influe indirectement sur la durabilité des structures en béton. Elle gouverne le taux de pénétration des agents agressifs, responsables de dégradations, sous un gradient de pression. Ce travail a pour but l’étude des interactions entre l’ouverture des fissures et le transport des fluides dans le béton, soumis à un essai Brésilien de traction indirect par fendage. Cette étude est composée de deux parties : une numérique et une expérimentale. La première concerne la modélisation des matériaux hétérogènes, tels que le béton, et met en évidence ses deux particularités : l’aspect multiphasique du matériau et la propagation 3D de fissures. Ainsi, nous proposons un couplage entre l’ouverture de fissure et la perméabilité au gaz selon un modèle hydromécanique à l’échelle mésoscopique. L’objectif de la deuxième partie expérimentale est de fournir des données pour des modèles numériques et de les valider ainsi. Ce travail est réalisé sur des éprouvettes de mortier avec 3 différents tailles de granulat, soumises au transfert de gaz au cours du chargement par l’essai Brésilien. Le modèle numérique mésoscopique, employé dans cette étude, est basé sur une approche tridimensionnelle pour représenter l’hétérogénéité du matériau et les mécanismes de rupture du béton. Ce modèle considère le béton comme un matériau bi-phasique où les granulats sont fondus dans la pâte du ciment. Afin de pallier aux hétérogénéités du matériau et l’emploi du maillage non-adaptatif, une faible discontinuité a été introduite dans le premier enrichissem*nt de la cinématique. Le deuxième enrichissem*nt de la cinématique introduite ici est la discontinuité du déplacement (forte) afin de représenter l’ouverture de la fissure (champ du déplacement discontinu). Le modèle hydromécanique représente le transport du fluide (gaz) dans le béton par l’intermédiaire de la loi de Darcy pour la section non fissurée (porosité) et par la loi de Poiseuille pour la section fissurée (flux laminaire). Dans ce modèle, une interaction entre l’ouverture de fissure, obtenue par le modèle mécanique (mésoscopique), et la perméabilité du gaz est considérée. Le travail expérimental effectué est présenté pour la validation du modèle hydro-mécanique numérique proposé. Les résultats de simulations numériques sont en accord avec des travaux expérimentaux et théoriques précédents
Permeability is a parameter that may indirectly influence the durability of concrete structures by governing the rate of penetration of aggressive substances responsible for degradation under a pressure gradient. The aim of this thesis is to study the interaction between the crack opening and the transfer of fluids in concrete of the Brazilian splitting tensile test (BSTT). Herein, the influence of aggregates size and volume fraction on hydro-mechanical properties of concrete is investigated. This study consists of two parts: the numerical and the experimental one. The first one focuses on the meso-scale modeling of a heterogeneous material like a concrete, which may be characterized by two features: multi-phase behavior and 3D crack propagation. The numerical study deals therefore with the coupling between crack opening and gas permeability according to a developed hydro-mechanical model at a meso-scale. The objective of the second, experimental part, is to provide data for numerical models and to validate the latter. This work is carried out on mortar specimens with 3 different aggregate sizes, submitted to gas transfer during a BSTT. The numerical meso-scale model is based upon a 3D lattice approach to represent the heterogeneity of the material and the failure mechanism of concrete. This model considers concrete as a two-phases material in which aggregates melt within a cement paste. Because a non-adapted meshing process was used to mesh the microstructure, a weak discontinuity was introduced in the first enhancement of the kinematics. The second enhancement of kinematics introduced here is the displacement discontinuity (strong) to represent crack opening (discontinuous displacement-field). The hydro-mechanical model represents the transport of fluids (gases) through the concrete, depending on Darcy's law for a uncracked section (porosity) and Poiseuille's law for a cracked section (laminar flow). In this model, the interaction between the crack opening, obtained from the mechanical model (meso-scale), and the gas permeability is investigated. The experimental work is presented for the validation of the hydro-mechanical model. The numerical results show good agreement with some previous experimental and theoretical studies

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Refratários são materiais com microestrutura heterogênea constituída de uma fração grosseira, os agregados, e de uma fração mais fina, a matriz, em que ambas exercem papéis fundamentais nas propriedades dos refratários, sendo a resistência ao dano por choque térmico, uma das mais importantes. Para avaliar essa questão crítica dos refratários há necessidade de se conhecer bem seu comportamento à propagação de trinca, principalmente quando submetido a uma tensão. Porém, devido à complexidade da estrutura desses materiais, o comportamento das regiões à frente e atrás da ponta da trinca sempre foi muito discutido, só que essa discussão sempre fez uso de modelos e simulações computacionais, já que é prevista uma zona de processo, em que diferentes mecanismos podem absorver energia aumentando a resistência à propagação da trinca principal. Nesta tese foi proposto o estudo experimental do comportamento da propagação de trinca em refratários, visando entender os mecanismos de resistência à propagação de trinca e o caminho das trincas propagantes, utilizando o método da cunha para propagação estável da trinca, que é o mais adequado para essa classe de materiais. Para isso foram utilizados, dois refratários distintos: tijolo e concreto, ambos de alta alumina. No tijolo, para visualização do caminho da trinca propagante após o ensaio, o caminho da trinca foi infiltrado com cola instantânea para garantir a integridade da mesma, a fim que amostras pudessem ser preparadas para análise de imagens em microscópio eletrônico de varredura. Devido à dificuldade dessa preparação, e de só ser possível observar a trinca após a propagação, um microscópio digital passou a ser utilizado in loco ao ensaio. Esse estudo foi realizado com o concreto, sendo possível associar o comprimento da trinca com a curva carga-deslocamento. A fim de complementar o estudo do processo de fratura, a técnica de emissão acústica (EA) passou a ser utilizada nos ensaios de propagação de trinca, já que quando um material é submetido a uma carga e as trincas se desenvolvem, há liberação de energia de deformação do material, sendo possível capturar os dados de energia dos sinais gerados pela propagação. Sendo assim foi possível correlacionar resultados de energia de fratura, início e tamanho de trinca com as curvas carga-deslocamento, carga-tempo, e inclusive, com a contagem de sinais acumulada-tempo, que foi complementar na estimativa da zona de processo completa, ou seja, os fenômenos produzidos atingiram o estado estacionário. A região em que se encontra o final da zona de processo coincide com o fim do regime estacionário, que é onde a trinca atravessa o corpo de prova. Dessa forma, mostra-se com essa tese, que o corpo de prova utilizado para a propagação estável de trinca pelo método da cunha, nas dimensões atuais, são suficientes para o desenvolvimento de todos os mecanismos de resistência à propagação de trinca em refratários.
Refractories are materials with heterogeneous microstructure, consisting of a coarse fraction, aggregates, and a finer fraction, the matrix, in which both play key roles in the properties of the refractory, and the resistance to thermal shock damage, one of the most important. To examine this critical issue of the refractory is no need to be familiar with their behavior to crack propagation, especially when subjected to a stress. The behavior of the regions ahead of and behind the crack tip has been discussed exhaustively, because a process zone was envisaged in which different mechanisms could absorb energy, thus increasing the propagation resistance of the main crack. However, this discussion has always been based on the use of models and computer simulations. The thesis presented here proposes an experimental study of the behavior of crack propagation in refractories, aiming to understand the mechanisms of crack propagation resistance and the crack propagation path, using the wedge splitting method to achieve stable crack propagation. To this end, two different refractory materials were used: brick and concrete, both high alumina. Based on the stable crack propagation test by the wedge method, techniques were sought that would aid in the visualization of crack propagation. In brick, the crack path was infiltrated with instant glue and infiltrated samples were examined by scanning electron microscopy (SEM); however, in addition to proving laborious, the crack was only visible after its propagation. In the case of concrete, this study was performed in loco during the test, using a digital microscope in combination with the acoustic emission (AE) technique. AE is defined as the generation of stress waves stored energy is suddenly released from localized sources within a material subjected to external loads. By means of the fracture energy data and the AE signals, it was possible to observe the entire fracture process and to correlate the results of fracture energy and crack onset and size with the load-displacement and load-time curves, and even the count of signals accumulated over time. This information was complementary to estimate the complete process zone, i.e., the phenomena produced reached the steady state. This study demonstrated that the dimensions of the test specimen used for stable crack propagation by the wedge splitting method suffice for the development of all the mechanisms of crack propagation resistance in refractories.

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The thesis focuses on the computational simulation of wedge splitting test of a concrete specimen by using finite element method. Different levels of numeric model for different notch depth and for different position of support are solved. Depending on the depth of a notch and difference of configuration, the crack paths and responses to an exterior load on a crack mouth opening displacement are evaluated.

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Ultra high performance fibre reinforced concrete (UHPFRC) is a relatively new fibre reinforced cementitious composite and has become very popular in construction applications. Extensive experimental studies have been conducted, demonstrating its superior properties such as much higher strength, ductility and durability than conventional fibre reinforced concrete (FRC) and high performance concrete. However, the material's damage and fracture mechanisms at meso/micro scales are not well understood, limiting its wider applications considerably. This study aims at an in-depth understanding of the damage and fracture mechanisms of UHPFRC, combining microscale in-situ X-ray computed tomography (µXCT) experiments and mesoscale image-based numerical modelling. Firstly, in-situ µXCT tests of small-sized UHPFRC specimens under wedge splitting loading were carried out, probably for the first time in the world, using an in-house designed loading rig. With a voxel resolution of 16.9µm, the complicated fracture mechanisms are clearly visualised and characterised using both 2D images and 3D volumes at progressive loading stages, such as initiating of micro-cracks, arresting of cracks by fibres, bending and pulling out of fibres and spalling of mortar at the exit points of inclined fibres. Secondly, based on the statistics of pores in the µXCT images obtained for a 20mm cube specimen, an efficient two-scale analytical-numerical hom*ogenisation method was developed to predict the effective elastic properties of the UHPFRC. The large number of small pores were first hom*ogenised at microscale with sand and cement paste, using elastic moduli from micro-indentation tests. 3D mesoscale finite element models were built at the second scale by direct conversion of the µXCT images, with fibres and large pores were faithfully represented. The effects of the volume fraction and the orientation of steel fibres on the elastic modulus were investigated, indicating that this method can be used to optimise the material micro-structure. Thirdly, 3D mesoscale finite element models were built for the specimen used in the in-situ µXCT wedge splitting test, with embedded fibre elements directly converted from the µXCT images. The fracture behaviour in the mortar was simulated by the damage plasticity model available in ABAQUS. Finally, 2D mesoscale finite element models were developed to simulate the fracture behaviour of UHPFRC using cohesive interface elements to simulate cracks in the mortar, and randomly distributed two-noded 1D fibres and connector elements to simulate the pull-out behaviour of fibres. This approach offers a link between the fibres pull-out behaviour and the response of the whole composite at the macroscale, thus it can be used to conduct parametric studies to optimise the material properties.

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This thesis has discussed both properties and geometry of concrete slabs used in bridges. It gave understanding on behavior of concrete in both tension and compression zones and how crack propagates in specimens by presenting both theory of fracture and performing concrete tests like tension splitting, uniaxial compression and uniaxial tension tests. Furthermore, it supported experimental tests with finite elements modelling for each test, and illustrated both boundary conditions and loads. The thesis has used ARAMIS cameras to observe crack propagations in all experimental tests, and its first study at LNU that emphasized on Brazilian test, because of importance of this test to describe both crushing and cracking behavior of concrete under loading. It’s an excellent opportunity to understand how concrete and steel behave individually and in combination with each other, and to understand fracture process zone, and this has been discussed in theory chapter. The geometry change that could affect stresses distributions has also described in literature and modelled to give good idea on how to model slabs in different angles in the methodology chapter. Thus, thesis will use finite elements program (Abaqus) to model both experimental specimens and concrete slabs without reinforcement to emphasize on concrete behavior and skewness effect. This means studying both properties of concrete and geometry of concrete slabs. This thesis has expanded experimental tests and chose bridges as an application.

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Thesis (Master of Sciences (Engineering))--Case Western Reserve University, 2010
Department of Materials Science and Engineering Title from PDF (viewed on 2010-05-25) Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

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The theory and application of a variety of methods to solve partial differential equations are introduced in this chapter. These methods rely on representing continuous quantities with discrete approximations. The resulting finite difference equations are solved using algorithms that stress different traits, such as stability or accuracy. The Crank-Nicolson method is described and extended to multidimensional partial differential equations via the technique of operator splitting. An application to the time-dependent Schrödinger equation, via scattering from a barrier, follows. Methods for solving boundary value problems are explored next. One of these is the ubiquitous fast Fourier transform which permits the accurate solution of problems with simple boundary conditions. Lastly, the finite element method that is central to modern engineering is developed. Methods for generating finite element meshes and estimating errors are also discussed.

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Pre-stressed concrete railroad ties must meet requirements during service life. Using pre-stressed wires in concrete members enhances load-carrying capacity of concrete ties. It is important to ensure that pre-stressed forcing is introduced well before rail seat where the high impact load is applied. The required length of wire to fully transfer pretension forcing to concrete member is referred as transfer length. In order to shorten the transfer length, wires with improved indentation are used. As the transfer length is shortened, the high amount of stress concentration at the interface of wire-concrete can lead to longitudinal splitting cracks in concrete railroad ties. Splitting crack can occur either right after de-tensioning or during service life. It has been observed that concrete properties and components can highly affect crack formation and propagation. In this research, the effect of coarse aggregate on the splitting cracks of concrete railroad ties was investigated. To assess the impact of coarse aggregate features on splitting crack performance, fracture toughness test was done on three-point bend prisms. The specimens were made of four different coarse aggregate including crushed aggregate and well-rounded aggregate. It was observed that angularity and coarseness of aggregate increases the fracture toughness of concrete by 20%. Then, the same mixes were used in fabrication of pre-stressed prisms with different cover length to evaluate actual performance of splitting cracks after de-tensioning. The wires were tensioned up to 7000 Ib per wire and de-tensioned when concrete strength of 4500 psi is reached. The results of crack area/length of splitting cracks showed that increasing angularity can significantly improve splitting cracks resistance.

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Abstract:

<p>Reinforced concrete structures are subjected to several sources of deterioration that can reduce their load-resisting capacity over time. This has significant consequences for the management of infrastructure, leading to high costs of maintenance, repair, strengthening and premature decommissioning. Assessing the residual capacity of structures is challenging but paramount to manage the infrastructure network effectively. Corrosion of the internal steel reinforcement is among the main causes of deterioration in reinforced concrete bridges. The subsequent reduction in steel-to-concrete bond strength is difficult to evaluate with accuracy. There is no unified theory of general validity. Most existing models adopt measures of the level of corrosion as the key parameter to evaluate the bond reduction. In this paper, a different approach is investigated. Corrosion-induced splitting crack widths are used as the fundamental indicator of bond strength reduction, irrespective of the associated degree of steel corrosion. Available experimental results on deformed steel bars embedded in concrete subjected to either natural or accelerated corrosion, with or without transverse reinforcement, are analysed and compared with a different perspective. The analysis indicates that this new splitting crack-based approach can lead to more accurate predictions. This contributes to a better understanding of the fundamental principles underlying bond of corroded reinforcing bars. Enhanced assessment strategies can lead to a reduction of the safety risks, maintenance costs and environmental footprint of the infrastructure network.</p>

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Abstract:

Abstract A case study is presented in which a composite driving shaft of a motor-bike was loaded with different increasing numbers of load-cycles in a pulsating testing machine to reach different stages of damage. For each number of load-cycles an experimental modal analysis was performed by an iterative, global, multi-degree-of-freedom, frequency-domain modal testing technique and the eigenfrequencies and modal damping ratios were identified. From the results it is shown that the damping increases with the number of load-cycles i.e. the state of damage. However, it turned out that a more sensitive indicator for the state of damage is the splitting and shifting of the ‘double’ eigenfrequencies of the bending modes of the driving shaft with the ‘axisymmetric’ circular ring cross section. This fact is shown on the basis of several related experimental data.

APA, Harvard, Vancouver, ISO, and other styles

APA, Harvard, Vancouver, ISO, and other styles

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Sudden concrete failure is due to inelastic deformations of concrete subjected to tension. However, synthesizing nanomaterials reinforcements has significant impact on cement-based composites failure mechanism. Nanomaterials morphology bridges cement crystals as hom*ogeneous and ductile matrix. In this experiment, cement matrix with water to cement ratio of 0.5 reinforced by 0.2–0.6 wt% of functionalized (COOH group) multi-walled and single-walled carbon nanotubes were used. After sonication of carbon nanotubes in water solution for an hour, the cementitious nanocomposites were casted in cylindrical molds (25 mm diameter and 50 mm height). Failure mechanism of cementitious nanocomposite showed considerable ductility throughout splitting tensile test compared to cement mortar. Additionally, the failure pattern after developing the initial crack provided additional time before ultimate failure occurred in cement-based nanocomposites. The evolution of crack propagation was assessed until ultimate specimen failure during splitting-tensile test on cementitious nanocomposite surface. The deformation of cross section from circle to oval shape augmented tensile strength by 50% in cementitious nanocomposite compared to conventional cement mortar.

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Abstract:

The initial damage and fracture zone are determined by the approach of coupling analysis of fracture mechanics and damage mechanics. An optimum fiber content of 0.2% in the asphalt concrete is proposed in comparison of the results obtained from composite theory with that obtained from the splitting tests. Crack growth with number of load cycles and fiber mass fraction of asphalt concrete pavement in which an initial surface crack of 4 cm length is included under cyclic temperature loading (-15°C) is simulated using damage mechanics theorem. By computing fatigue life, a new type of fiber-reinforced asphalt concrete pavement is developed.