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1
Lee, Woong. "Crack deflection and interface cracks in layered composites". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627252.
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McFadyen, Neil B. (Neil Barry) Carleton University Dissertation Engineering Mechanical. "Fatigue crack growth in semi-elliptical surface cracks". Ottawa, 1987.
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Holland, Dominic John Martin. "Cracks and atoms /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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4
Some, Liene. "Automatic image-based road crack detection methods". Thesis, KTH, Geodesi och satellitpositionering, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-189245.
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Pavement crack detection is an important procedure in road maintenanceand traffic safety. Traditionally, the road inventory was performed by field inspection, now it is replaced by the evaluation of mobile mapping system images. The acquired images are still a significant source of temporal condition of thepavement surface. The automatisation of crack detection is highly necessarybecause it could decrease workload, and therefore, maintenance costs. Two methods for automatic crack detection from mobile mapping imageswere tested: step by step pixel based image intensity analysis, and deep learning. The objective of this thesis is to develop and test the workflow for the streetview image crack detection and reduce image database by detecting no-cracksurfaces. To examine the performance of the methods, their classification precisionwas compared. The best-acquired precision with the trained deep learningmodel was 98% that is 3% better than with the other method and it suggeststhat the deep learning is the most appropriate for the application. Furthermore, there is a need for faster and more precise detection methods, and deep learningholds promise for the further implementation. However, future studies areneeded and they should focus on full-scale image crack detection, disturbingobject elimination and crack severity classification.
5
Lawson, Sean. "The Prevalence of Intrapulpal Cracks in 1st and 2nd Mandibular Molars Requiring Non-Surgical Root Canal Treatment". VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3410.
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Few studies have reported the incidence or prevalence of cracked teeth with pulpal involvement. No attempts have been made to evaluate the prevalence or clinical predictors for intrapulpal cracks. The purpose of this study was to investigate the prevalence of intrapulpal cracks in first and second mandibular molars and to determine if clinical findings are predictive for the existence of intrapulpal cracks. First and second mandibular molars (190) requiring non-surgical root canal treatment at the VCU Graduate Endodontic Practice between February 15, 2013 and August 15, 2013 were analyzed retrospectively. Teeth were transilluminated, stained, and inspected for intrapulpal cracks using a dental microscope. Data gathered included: demographics, subjective and objective information regarding the chief complaint to include bite stick test, transillumination, probing depths greater than 4mm, existing restorations, and diagnosis. Chi-square and logistic regression were performed (p<0.05). The prevalence of intrapulpal cracks in first and second mandibular molars combined was 9% (17/190, 95%CI= 5.7% to 13.9%). The prevalence was 7% for 1st molars and 13% for 2nd molars. There was no statically significant difference in the prevalence between first and second mandibular molars. Individual characteristics predictive for the existence of intrapulpal cracks were age, probing depth greater than 4mm, transillumination and a positive Tooth Slooth™ test (all p<0.05). Staining of the pulp chamber after access identified only one of 17 intrapulpal cracks. Staining of the pulp chamber did not significantly increase the ability to identify intrapulpal cracks. Neither diagnosis, sex, nor existing restorations were significant predictors for intrapulpal cracks. Probing depth greater than 4mm, age over 40 and a positive Tooth Slooth™ test were conjointly significant for predicting intrapulpal cracks.
6
Hejman, Ulf. "On initiation of chemically assisted crack growth and crack propagation paths of branching cracks in polycarbonate". Licentiate thesis, Malmö högskola, Teknik och samhälle, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-7790.
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Stress corrosion, SC, in some cases gives rise to stress corrosion cracking, SCC, which differs from purely stress intensity driven cracks in many aspects. They initiate and grow under the influence of an aggressive environment in a stressed substrate. They grow at low load and may branch. The phenomenon of SCC is very complex, both the initiation phase and crack extension itself of SCC is seemingly associated with arbitrariness due to the many unknown factors controlling the process. Such factors could be concentration of species in the environment, stress, stress concentration, electrical conditions, mass transport, and so on.In the present thesis, chemically assisted crack initiation and growth is studied with special focus on the initiation and branching of cracks. Polycarbonate plates are used as substrates subjected to an acetone environment. Experimental procedures for examining initiation and branching in polycarbonate are presented. An optical microscope is employed to study the substrate.The attack at initiation is quantified from pits found on the surface, and pits that act as origin for cracks is identified and the distribution is analysed. A growth criterion for surface cracks is formulated from the observations, and it is used to numerically simulate crack growth. The cracks are seen to coalesce, and this phenomenon is studied in detail. Branching sites of cracks growing in the bulk of polycarbonate are inspected at the sample surface. It is found that the total width of the crack branches are approximately the same as the width of the original crack. Also, angles of the branches are studied. Further, for comparison the crack growth in the bulk is simulated using a moving boundary problem based algorithm and similar behaviour of crack branching is found.
7
Myers, Carol A. "Falling through the cracks". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1995. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23766.pdf.
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8
Bernstorff, Karin Nislev. "Listening through the cracks". Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/14706.
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Kyne is an outsider: a white, Danish girl, living in a country where the majority are blacks and the few whites are English. Her sentiments of belonging and integration are lost when her family's farms are taken away by the dictatorship government in 2004. The country, Zimbabwe, spirals out of control: murder, starvation and chaos becomes the way of life. Kyne and her family are left with nothing. Kyne travels back in time to the bizarre life of her childhood on their farm in Rhodesia during the war in the 1970s. It is a nostalgic yet often horrifying return to her past as she uncovers the strange, sometimes idyllic lifestyle that was once a very normal way of life to her. The story unfolds in a landscape that is both harsh yet beckoning. Kyne confronts her relationships with all those around her beginning with her Danish parents who are determined to continue farming in a land which they call home, even if war threatens their lives. The reader meets Pencil the Cook who allows Kyne into the silent calm of his kitchen, his family, and the secret, adult world in which Kyne will learn of the terrifying reality of war. She describes the workers on the farm who are pulled between loyalty to their employer and to the blacks who seek independence from white rule. Finally, she describes the other white families nearby who are attacked, tortured and killed for attempting to the only way of life they have ever known.
9
Williams, Joshua Marc. "EVALUATION OF FATIGUE CRACK GROWTH SOFTWARE FOR USE ON CRACKS IN COMPLEX GEOMETRIES". MSSTATE, 2009. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04032009-104840/.
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Fatigue-crack growth data for the lower arm of the Apache helicopters scissor assembly is presented from an Army alternate source qualification test. The lower arm model is imported to finite element analysis software to obtain the stress state at a crack location. The stress state and geometry are used in seven fatigue-crack growth cases in NASGRO and AFGROW, with an additional four cases discussed briefly. The results from the fatigue-crack growth routines are compared to the fatigue-crack growth data from the Armys test. One case reproduces the crack growth data prior to breakthrough. Some cases are shown to be more applicable to this configuration than others are. The process of performing fatigue life estimates is discussed. Suggestions are made on the viability of this approach and possible future avenues for development.
10
Hannes, Dave. "Growth of cracks at rolling contact fatigue". Thesis, KTH, Hållfasthetslära (Avd.), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33659.
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Rolling contact fatigue is a problem encountered with many machine elements.In the current report a numerical study has been performed in order to predictthe crack path and crack propagation cycles of a surface initiated rolling contactfatigue crack. The implementation of the contact problem is based on theasperity point load mechanism for rolling contact fatigue. The practical studiedproblem is gear contact. Different loading types and models are studied andcompared to an experimental spall profile. Good agreement has been observedconsidering short crack lengths with a distributed loading model using normalloads on the asperity and for the cylindrical contact and a tangential load on theasperity. Several different crack propagation criteria have been implemented inorder to verify the validity of the dominant mode I crack propagation assumption.Some general characteristics of rolling contact fatigue cracks have beenhighlighted. A quantitative parameter study of the implemented model hasbeen performed.Utmattning med rullande kontakter är ett ofta förekommande problem för många maskinelement. I den aktuella rapporten utfördes en numerisk studieför att förutsäga sprickvägen hos utmattningssprickor som initierats i ytan vidrullande kontakter. Implementeringen av kontaktproblemet bygger på asperitpunktlastmekanismen för rullande kontakter. Studien av kontaktproblemetär tillämpad till kugghjul. Olika belastningstyper och modeller studeradesoch jämfördes med profilen hos en experimentell spall. Bra överensstämmelseobserverades för korta spricklängder när en modell med fördelad belastninganvänds för en belastningstyp där en normalbelastning agerar på asperiten ochvid cylindriska kontakten och en tangentialbelastning införs på asperiten. Olikakriterier för spricktillväxt implementerades för att verifiera giltigheten av antagandetatt mode I spricktillväxt är dominant. Några generella kännetecken avutmattningssprickor med rullande kontakter framhävdes. En kvantitativ parameterstudie för den implementerade modellen utfördes.
11
Donohoe, C. J. "Corrosion fatigue of a high strength low alloy steel". Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322985.
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12
Nikolic, Mijo. "Rock mechanics, failure phenomena with pre-existing cracks and internal fluid flow through cracks". Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0043/document.
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Cette thèse aborde le problème de la rupture localisée dans les roches, qui caractérise un grand nombre d'applications dans le domaine du génie civil, tels que la rupture du barrage, effondrement des fondations, la stabilité des excavations ou les tunnels, les glissements de terrain et les éboulements. Le risque de rupture localisée devrait être mieux appréhendé pour mieux l'éviter. La rupture localisée dans les roches est généralement caractérisée par une une rupture soudaine et quasi-fragile sans avertissement sous forme de grandes déformations et visibles avant la rupture elle-même. Cela se produit également sous l'influence des hétérogénéités matériels, des fissures existantes et d'autres défauts initiaux.Les trois nouveaux modèles numériques, intégrant les mécanismes de ruptures localisées, l'hétérogénéité de la roche et des fissures existantes et d'autres défauts, sont présentés dans cette thèse. Le premier modèle propose une représentation en 2D de roche composite à deux phases, où la phase solide représente la roche intacte et la faible phase indique les défauts initiaux. Le deuxième modèle représente l'extension du modèle précédent vers un espace 3D, où est considéré un ensemble complet de mécanismes de ruptures en 3D. Les propriétés hétérogènes sont considérées ici par une distribution aléatoire en accord avec la variation statistique de Gausse. Ce modèle est également utilisé pour l'analyse de la roche intacte par spécimens possédant des écarts de formes géométriques qui influencent la résistance à la compression uni-axiale. Le troisième modèle est un modèle en 2D, traitant l’interaction volumétrique entre un fluide et la structure sous l’influence de l’écoulement du fluide à travers le milieu de la roche poreuse.L'approche des lattices discrètes est choisie pour construire un cadre général pour les trois modèles, où les cellules de Voronoï représentent les grains de roche tenus ensemble par les poutres de Timoshenko comme des liens de cohésion. La cinématique améliorée est caractérisée par l'approche intégrée des discontinuités comme un supplément à la cinématique standard de liens cohérents. Cela sert pour la propagation de la macro fissure dans tous les modes de ruptures et de leurs combinaisons, entre les grains de la roche. La formation de la zone du processus de rupture suivie par des microfissures coalescentes, précédant la rupture localisée, est aussi considérée dans les modèles. L’écoulement du fluide est régi par la loi de Darcy, tandis que les conditions de couplage obéissent à la théorie de poroélasticité de Biot.Les résultats des modèles numériques ont été vérifiés par des exemples de la littérature dans le cas des modèles en 2D. Le modèle en 3D a été validé suite aux résultats expérimentaux effectués sur 90 échantillons de roches, où sont considérées de légères déviations géométriques des spécimens.La présentation de ces modèles, ainsi que leurs aspects de mise en œuvre sont présentés en détail. L’approche avec une discontinuité intrinsèque et le caractère local des améliorations nécessaires à la simulation des discontinuités de déplacement orientent vers la condensation statique des degrés de liberté améliorés sont efficacement intégrés dans l’architecture des éléments finisThis thesis deals with the problem of localized failure in rocks, which occurs often in civil engineering practice like in dam failure, foundation collapse, stability of excavaations, slopes and tunnels, landslides and rock falls. The risk of localized failure should be better understood in order to be prevented. The localized failure in rocks is usually characterized by a sudden and brittle failure without warning in a sense of larger and visible deformations prior to failure. This happens also under the strong influence of material heterogeneities, preexisting cracks and other defects.The three novel numerical models, incorporating the localized failure mechanisms, heterogeneity of rock and preexisting cracks and other defects, are presented in this thesis. First model deals with 2D plane strain two-phase rock composite, where stronger phase represents the intact rock and weaker phase initial defects. Second model represents the extension of the previous model towards the 3D space, where full set of 3D failure mechanisms is considered. Heterogeneous properties are taken here through the random distribution and Gauss statistical variation of material properties. The latter model is also used for the analysis of intact rock core specimens geometrical shape deviations influencing the uni-axial compressive strength. Third model is a 2D, dealing with volumetric fluid-structure interaction and localized failure under the influence of fluid flow throughthe porous rock medium.The discrete beam lattice approach is chosen for general framework for three models, where Voronoi cells represent the rock grains kept together by Timoshenko beams as cohesive links. The enhanced kinematics characterized for embedded discontinuity approach is added upon standard kinematics of cohesive links. This serves for the macro crack propagation in all failure modes and their combinations, between the rock grains. The fracture process zone formation followed by micro-cracks coalescence, preceding the localized failure, is considered as well. Fluid flow is governed by a Darcy law, while coupling conditions obey Biot's theory of poroplasticity. The results of the numerical models were verified by the benchmarks available from literature in 2D case. The 3D model was validated against the experimental results conducted on 90 rock specimens, where even slight geometrical deviations of specimens are considered.Presentation of these models, as well as their implementation aspects are given in full detail. Embedded discontinuity concept and the local nature of enhancements required to capture the displacement discontinuities leads to the very efficient approach with static condensation of enhanced degrees of freedom and technique that can be efficiently incorporated into finite element code architecture
13
Patel, Surendra Kumar. "Experimental And Numerical Studies On Fatigue Crack Growth Of Single And Interacting Multiple Surface Cracks". Thesis, Indian Institute of Science, 2000. https://etd.iisc.ac.in/handle/2005/276.
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Design based on damage tolerance concepts has become mandatory in high technology structures. These concepts are also essential for evaluating life extension of aged structures which are in service beyond originally stipulated life. Fracture analysis of such structures in the presence of single or multiple three-dimensional flaws is essential for this approach. Surface cracks are the most commonly occurring flaws and development of accurate methods of analysis for such cracks is essential for structural integrity evaluation of newly designed or aged structures. The crack fronts of these surface flaws are usually approximated mathematically to be of either part-elliptical or part-circular in geometry. In this thesis, some of the issues related to fatigue crack growth of single and multiple surface cracks are studied in detail. Here emphasis is given to the development of simple and accurate post-processing techniques to estimate stress intensity factors for surface cracks, development and/or implementation of simple numerical methods to simulate three-dimensional single and multiple cracks in fatigue and their experimental verification.
Modified virtual crack closure integral (MVCCI) technique for estimation of strain energy release rates has been improved (chapter II) to deal with curved crack front and unequal elements across the crack front. The accuracy of this method is evaluated and presented in this chapter for certain benchmark surface flaw problems. The improved MVCCI is used in the investigation of interaction between multiple surface cracks in three-dimensional solids. The interaction effects are studied for both interacting and coalescing phases as observed to occur in the growth of multiple surface cracks. Extensive numerical work is performed to study the effects of various parameters such as aspect ratio, thickness ratio, interspacing on the interaction factors. These solutions are used in formulating empirical equations to estimate interaction factors. This facilitated the development of a simple semi-analytical method to study fatigue crack growth of multiple cracks.
The growth of surface cracks under fatigue loading in the finite width specimens of an aero-engine superalloy has been studied experimentally (presented in chapter III). Four configurations for single semi-elliptical cracks are considered. Fatigue crack growth is simulated by two models viz. two degrees of freedom and "multi degrees of freedom with ellipse fit'. These models are sometimes referred to as semi-analytical models as the crack growth is predicted by numerical integration combining Paris equation with an empirical form of stress intensity factor solution. In order to use two degrees of freedom model for fatigue crack growth prediction of semi-elliptical cracks, empirical solution for the Ml range of geometric parameters for stress intensity factor is required for the considered
configurations. The available Newman-Raju solution is useful for this purpose within a limited range of surface crack length to width (c/W) of the specimen. Based on the present finite element results, the empirical equations are developed for extended values of c/W. It is well understood that the fatigue prediction for two-dimensional crack can be improved by inclusion of crack closure effects. Usually, in semi-analytical models for growth of surface cracks under fatigue loading, the crack closure is included as a ratio of crack closure factor at surface and depth locations of semi-elliptical crack. In the present work, this ratio for the considered material of specimens is obtained by an experimental study. The difference in characteristics of preferred propagation path between semi-elliptical crack in a finite width plate and a wide plate is clearly brought out.
Current crack growth predictions for most of the structures are based on the presence of only a single crack. However, in structures several cracks may initiate simultaneously within a stress critical zone and may interact depending upon their geometry, spatial location, structure geometry and mode of loading. In this work various configurations of twin semi-elliptical cracks have been studied by experiments. The beachmarks created on the specimens during experiments are used in the investigation of crack shape progression during fatigue. A three degrees of freedom crack growth model for interacting and coalescing cracks has been proposed. The experimentally determined crack shape and lives have been compared with the corresponding values from numerical simulation.
The correlation of experimental results with numerical predictions was carried out through improved MVCCI for eight-noded brick elements. This has worked well in the configurations analysed. However, it is known in literature that there are benefits of using 20-noded singular elements. There could be special situations where the regular elements could fail, and singular elements could be essential. For this purpose, further development of MVCCI were carried out using 20-noded quarter-point elements (presented in chapter IV). Also a novel technique of decomposed crack closure integral (DCCI) was developed (presented in chapter V) for both regular and singular elements to represent the variation of MVCCI more accurately along the crack front.
It is well known that quarter-point elements at crack front produce the required singularity at the crack tip and give accurate stress distribution with fewer degrees of freedom than conventional elements. Thus to develop more efficient post-processing tools, the MVCCI expressions are formulated for 20-noded singular quarter-point element for various assumptions regarding stress and displacement distributions in the elements across the crack front. A comprehensive study is presented (chapter IV) on MVCCI for 20-noded singular brick element including various simplified expressions for three-dimensional part-through cracks in pure and mixed-mode state of deformation of fracture. The developed MVCCI expressions are also valid for 15-noded quarter-point Penta elements. The reduction in model size can further be obtained if 12-noded three-dimensional singular element is employed at the crack front and eight-noded elements are used away from the crack front. The MVCCI expressions are also developed for 12-noded singular element and their accuracy is evaluated by numerical solutions.
Presently, MVCCI, estimates the average stress intensity factor at the center of each element along the crack front. In this thesis, a Decomposed Crack Closure Integral (DCCI) is formulated to represent an assumed variation of stress intensity factor along the crack front in each element. The DCCI is formulated for 8-noded brick, 20-noded conventional brick and 20-noded singular brick elements. The numerical examples presented here deal with three-dimensional problems of patch repair technology and part-through cracks. The technique showed a major advantage for the patch repair problems where SIF variations along the crack front are of significance and large mesh sizes are computationally expensive. This along with MVCCI for 12-noded and 20-noded singular elements formed a part of the work on development of accurate and effective post-processing tools.
It is expected that the present work will be helpful in damage tolerance design and assessment of aerospace structures and the experimental work performed as a part of this thesis will enhance confidence in the damage tolerance analysis.
The thesis is concluded in chapter VI presenting the contributions of this thesis and projecting future lines of work possible in this area.
14
Patel, Surendra Kumar. "Experimental And Numerical Studies On Fatigue Crack Growth Of Single And Interacting Multiple Surface Cracks". Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/276.
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Design based on damage tolerance concepts has become mandatory in high technology structures. These concepts are also essential for evaluating life extension of aged structures which are in service beyond originally stipulated life. Fracture analysis of such structures in the presence of single or multiple three-dimensional flaws is essential for this approach. Surface cracks are the most commonly occurring flaws and development of accurate methods of analysis for such cracks is essential for structural integrity evaluation of newly designed or aged structures. The crack fronts of these surface flaws are usually approximated mathematically to be of either part-elliptical or part-circular in geometry. In this thesis, some of the issues related to fatigue crack growth of single and multiple surface cracks are studied in detail. Here emphasis is given to the development of simple and accurate post-processing techniques to estimate stress intensity factors for surface cracks, development and/or implementation of simple numerical methods to simulate three-dimensional single and multiple cracks in fatigue and their experimental verification.
Modified virtual crack closure integral (MVCCI) technique for estimation of strain energy release rates has been improved (chapter II) to deal with curved crack front and unequal elements across the crack front. The accuracy of this method is evaluated and presented in this chapter for certain benchmark surface flaw problems. The improved MVCCI is used in the investigation of interaction between multiple surface cracks in three-dimensional solids. The interaction effects are studied for both interacting and coalescing phases as observed to occur in the growth of multiple surface cracks. Extensive numerical work is performed to study the effects of various parameters such as aspect ratio, thickness ratio, interspacing on the interaction factors. These solutions are used in formulating empirical equations to estimate interaction factors. This facilitated the development of a simple semi-analytical method to study fatigue crack growth of multiple cracks.
The growth of surface cracks under fatigue loading in the finite width specimens of an aero-engine superalloy has been studied experimentally (presented in chapter III). Four configurations for single semi-elliptical cracks are considered. Fatigue crack growth is simulated by two models viz. two degrees of freedom and "multi degrees of freedom with ellipse fit'. These models are sometimes referred to as semi-analytical models as the crack growth is predicted by numerical integration combining Paris equation with an empirical form of stress intensity factor solution. In order to use two degrees of freedom model for fatigue crack growth prediction of semi-elliptical cracks, empirical solution for the Ml range of geometric parameters for stress intensity factor is required for the considered
configurations. The available Newman-Raju solution is useful for this purpose within a limited range of surface crack length to width (c/W) of the specimen. Based on the present finite element results, the empirical equations are developed for extended values of c/W. It is well understood that the fatigue prediction for two-dimensional crack can be improved by inclusion of crack closure effects. Usually, in semi-analytical models for growth of surface cracks under fatigue loading, the crack closure is included as a ratio of crack closure factor at surface and depth locations of semi-elliptical crack. In the present work, this ratio for the considered material of specimens is obtained by an experimental study. The difference in characteristics of preferred propagation path between semi-elliptical crack in a finite width plate and a wide plate is clearly brought out.
Current crack growth predictions for most of the structures are based on the presence of only a single crack. However, in structures several cracks may initiate simultaneously within a stress critical zone and may interact depending upon their geometry, spatial location, structure geometry and mode of loading. In this work various configurations of twin semi-elliptical cracks have been studied by experiments. The beachmarks created on the specimens during experiments are used in the investigation of crack shape progression during fatigue. A three degrees of freedom crack growth model for interacting and coalescing cracks has been proposed. The experimentally determined crack shape and lives have been compared with the corresponding values from numerical simulation.
The correlation of experimental results with numerical predictions was carried out through improved MVCCI for eight-noded brick elements. This has worked well in the configurations analysed. However, it is known in literature that there are benefits of using 20-noded singular elements. There could be special situations where the regular elements could fail, and singular elements could be essential. For this purpose, further development of MVCCI were carried out using 20-noded quarter-point elements (presented in chapter IV). Also a novel technique of decomposed crack closure integral (DCCI) was developed (presented in chapter V) for both regular and singular elements to represent the variation of MVCCI more accurately along the crack front.
It is well known that quarter-point elements at crack front produce the required singularity at the crack tip and give accurate stress distribution with fewer degrees of freedom than conventional elements. Thus to develop more efficient post-processing tools, the MVCCI expressions are formulated for 20-noded singular quarter-point element for various assumptions regarding stress and displacement distributions in the elements across the crack front. A comprehensive study is presented (chapter IV) on MVCCI for 20-noded singular brick element including various simplified expressions for three-dimensional part-through cracks in pure and mixed-mode state of deformation of fracture. The developed MVCCI expressions are also valid for 15-noded quarter-point Penta elements. The reduction in model size can further be obtained if 12-noded three-dimensional singular element is employed at the crack front and eight-noded elements are used away from the crack front. The MVCCI expressions are also developed for 12-noded singular element and their accuracy is evaluated by numerical solutions.
Presently, MVCCI, estimates the average stress intensity factor at the center of each element along the crack front. In this thesis, a Decomposed Crack Closure Integral (DCCI) is formulated to represent an assumed variation of stress intensity factor along the crack front in each element. The DCCI is formulated for 8-noded brick, 20-noded conventional brick and 20-noded singular brick elements. The numerical examples presented here deal with three-dimensional problems of patch repair technology and part-through cracks. The technique showed a major advantage for the patch repair problems where SIF variations along the crack front are of significance and large mesh sizes are computationally expensive. This along with MVCCI for 12-noded and 20-noded singular elements formed a part of the work on development of accurate and effective post-processing tools.
It is expected that the present work will be helpful in damage tolerance design and assessment of aerospace structures and the experimental work performed as a part of this thesis will enhance confidence in the damage tolerance analysis.
The thesis is concluded in chapter VI presenting the contributions of this thesis and projecting future lines of work possible in this area.
15
Khushefati, Waleed Hassan Ahmed. "Healing of cracks in concrete". Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/7201.
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16
Harrison, David John. "Eddy-current imaging of cracks". Thesis, University of Surrey, 1985. http://epubs.surrey.ac.uk/847494/.
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As a consequence of metal fatigue, cracks can develop and grow in operational aircraft. Periodic inspections must be made in order to detect and repair them before they reach a dangerous length. Cracks which grow from holes are a significant problem for aircraft since the wings and fuselage can contain many thousands of fasteners, or rivets. Since it is impractical to remove them all, inspection must be made with them installed. Research into the application of eddy currents to this problem has led to the development of a scanning procedure in which a small coil is moved around the circumference of the fastener while its impedance is repeatedly measured at different positions. This set of data constitutes an image which can be analvsed using pattern recognition techniques to identify the presence of a crack. A self-contained automated instrument has been built on these principles. It incorporates a microprocessor which controls all aspects of the systems operation, including analysis and display of results. Tests show that it can detect the presence of simulated radial cracks as small as 0.2 mm long beneath the heads of fasteners. The natural extension of these ideas leads to the concept of eddy-current imaging in which a 3D picture of a defect is reconstructed from measurements of the surface magnetic field. The feasibility of implementing this, using techniques such as tomography, is discussed.
17
Romero, Victor. "Spiraling Cracks in Thin Sheets". Paris 6, 2010. http://www.theses.fr/2010PA066660.
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Cette thèse étudie la rupture de plaques élastiques fragiles dans deux configurations qui conduisent à une propagation en spirale : soit à la suite d’étirement provoqué par le contact avec un indenteur qui pousse toujours sur la même lèvre de la fissure, soit en tirant une languette perpendiculairement au plan de la plaque. Dans le premier cas, on étudie expérimentalement la réponse élastique du système, et on prédit les conditions pour la propagation, ainsi que la direction, à partir du critère du maximum du taux de restitution de l’énergie. En suivant ces résultats, une propagation en spirale logarithmique est alors prédite, ce qui est confirmé par les expériences. Malgré un chargement mécanique différent, la deuxième expérience se ramène à un problème très similaire, avec cependant un taux de croissance de la spirale logarithmique plus faible. Ce processus de rupture à croissance exponentielle a fait l’objet d’un dépôt de brevet pour l’ouverture facile d’emballage. Dans les deux expériences, on observe cependant que la forme des spirales est perturbée de façon similaire par l’anisotropie des propriétés du matériau. Une extension du modèle est proposée pour tenir compte de ces effets.
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Wang, Lehua. "Elastoplastic analyses of multiple cracks in thin sheets, and of elliptical cracks in 3D bodies". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/11781.
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Mohammad, Noor. "Desiccation Cracking Behaviour in Thin Bentonite Layers". Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/22231.
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This thesis investigates the behaviour of desiccation cracks in thin bentonite layers under different conditions (initial water content, layer thickness, temperature and mixtures with kaolinite). For this, a comprehensive series of experiment was conducted as well as some theoretical models were developed. The theoretical model was developed based on the critical cracking thickness following the principles of linear elastic fracture mechanics (Chapter 4). This model was then used in the following chapters and validated with the experimental investigations. Also, hydraulic properties of the cracked soil mass were modelled and the effects of cracks on hydraulic conductivity and water retention properties were shown. In the experimental investigations, firstly, the combined effects of initial water content and layer thickness were studied in a phase diagram to observe the behaviour of desiccation cracks (Chapter 5). It was found that critical cracking thickness could be an important factor in distinguishing cracked and non-cracked samples in the phase diagram. Characteristics of cracks (crack density, total crack length, average crack length and crack width) increase with increasing layer thicknesses as well as initial water contents. The effects of temperature (Chapter 6) and mixtures of bentonite-kaolinite (Chapter 7) on desiccation cracking were investigated in the phase diagram developed in Chapter 5. At higher temperatures, the critical thickness of a clay layer ould be decreased. Results of bentonite-kaolinite mixture demonstrated that the phase boundary shifted to increase the critical thickness of the clay layers of mixtures containing less bentonite (i.e. more kaolinite). Crack morphology was also affected by the change in temperatures and properties of the mixtures. In summary, this study shows some understanding of desiccation cracking behaviour and could provide insights for better design of clay liners, which often at risk of desiccation problem.
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Mürk, Annely. "Optimization of inelastic plates with cracks /". Online version, 2006. http://dspace.utlib.ee/dspace/bitstream/10062/1226/5/murkannely.pdf.
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Broman, Elisabeth. "Cracks in the Spirit of Community". Licentiate thesis, KTH, Industrial Economics and Management, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1781.
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Cracks in the Spirit of Community is a study of a Swedishtrade union in a period of change. Increasingly, traditionaltrade unions´ work based on collective solutions has comeinto question, and the customer perspective of trade unionactivities is becoming more prominent. At the same time, ageneration of mainstay trade union supporters at ourcountry´s workplaces are approaching retirement age. Howdo these - now ageing - children of Sweden´s"people´s home" hand over our society´s institutionsand pass on its traditions to a new generation? Is there a riskthat knowledge will be lost? And is anyone in the newgeneration ready to receive this knowledge?
A systematic and structured dialogue with participants fromSif, Sweden´s leading white collar union, helped developthis complex of problems. The work focused on the interactionbetween people to build up a community of understanding, whichwas at the core of earlier trade union tradition. Broadeningthe present pattern of action allows more long-term trends tobe traced. A disregard for matters of common concern, andunstated dissension, cause cracks in the spirit of community,cracks that undermine the power of collective action inpolitical matters. This dissertation poses complex questionsabout democracy, participation and common responsibility.
The case study was carried out as a series of dialogueseminars with a carefully-selected group of people from Sif.The dialogue seminar method was developed to bring to the foretacit knowledge in skills research. By focussing onvalue-based, shared human knowledge, the dissertation puts tothe test a new application of the dialogue seminar method. Thisstudy illustrates a shift from common interests to individualinterests. It points out general trends in the development ofour society - a trade union member, an employee and a citizenis often one and the same person.
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Schulze, Bert-Wolfgang, Alexander Shlapunov i Nikolai Tarkhanov. "Green integrals on manifolds with cracks". Universität Potsdam, 2000. http://opus.kobv.de/ubp/volltexte/2008/2577/.
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We prove the existence of a limit in Hm(D) of iterations of a double layer potential constructed from the Hodge parametrix on a smooth compact manifold with boundary, X, and a crack S ⊂ ∂D, D being a domain in X. Using this result we obtain formulas for Sobolev solutions to the Cauchy problem in D with data on S, for an elliptic operator A of order m ≥ 1, whenever these solutions exist. This representation involves the sum of a series whose terms are iterations of the double layer potential. A similar regularisation is constructed also for a mixed problem in D.
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Mohamed, Alhade Abdossllam. "Monitoring cracks in a rotating shaft". Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=186894.
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Condition monitoring of rotating shafts is gaining importance in industry due to the need to increase machine reliability and decrease the possible loss of production due to machine breakdown. In this work, the use of vibration signals for the detection of a crack within a shaft was investigated. The research involved the measurement of vibration signals during laboratory tests on a long rotating shaft rig. The focus of the experimental work was on the effect of cracks on the dynamics and the initiation and growth of cracks in the shaft. Measurements were taken from the shaft system both with simulated cracks (notches) cut at 45° and 90° to the shaft axis and with real propagating cracks initiated by a pre-crack cut. All defects were located at the mid- point along the shaft. The vibration responses and stresses were measured for different depths of crack. The vibration responses of the three different defects were compared using PSDs of the data to identify the change in position and magnitude of the peaks in the spectrum under each defect. Experiments to study the effect of defect depth at different shaft rotation speeds were also carried out. Finally, a shaft with a breathing crack (continuously opening and closing as the shaft rotates) was also studied experimentally, with the crack growing under normal steady state operating conditions. After completing the experiment work, the shaft was broken and the type of fracture studied. The results for both simulated and actual crack growth showed that vibration frequencies decreased as a crack progressed, indicating the possibility of using the vibration signal for crack detection. A significant relationship was found between the stage of crack growth and the vibration results. A finite element (FE) model was constructed to explore the relationship between the natural frequencies and crack depth and position along the shaft and to explain and validate the results of the experimental work. The FE model showed similar trends to the experimental results and also allowed the effect of different crack positions to be explored. The PSD data was fed into an artificial neural network after a feature extraction procedure was applied to significantly reduce the quantity of data whilst at the same time retaining the salient information. Such an approach results in a considerably reduced training time for the network due to the reduced complexity. The proposed scheme was shown to successfully identify the different defect levels. This method greatly enhances the capacity of an automated diagnostic process by linking increased capability in signal analysis to the predictive capability of the artificial neural network.
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Stoll, Anke. "Mechanical analysis of environmentally assisted cracks". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542978.
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Alizadeh, Hassan. "Closure of three-dimensional fatigue cracks". Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425128.
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Dowell, John P. "Thermal Cracks in Diesel Engine Crankshafts". Case Western Reserve University School of Graduate Studies / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=case1093747466.
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Shawkat, Salman, i Ragheed Hussain. "Concrete Cracks in Swimming Pool Basins". Thesis, KTH, Byggnadsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208349.
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Majority of the swimming facilities in Sweden are facing some form of renovation or total substitution. The report analyses cracks in two different public bath facilities namely Eriksdalsbadet and Enskedehallen. The text also discusses different solution strategies for cracks in concrete. The aim with this thesis is to discuss how facility managers can extend the service life of these facilities by taking measures against the crack damages. Since renovation can be expensive, it is important to study cracks early on when they appear. This thesis also emphasizes on how important it is to add resources for preventing cracks, already during casting. Resources should also be added for maintaining the basins, managing repair methods for all types of cracking problems. This thesis is more of a generalized study for cracks in concrete, however it concludes with taking a more specific approach by discussing the problems in swimming basins. Causes of cracks, different types of cracks and evolution of cracks are studied and discussed with emphasis on the structural damages that can occur. With pictures taken and analyzed from the two facilities and a visitation with a experienced concrete investigator from CBI, this thesis concludes with a decision to immediately take repair actions against cracks that are shown in the report. The report discusses two perspectives, one where the authors of the thesis discusses solutions derived from information given in the report, and the other perspective is derived from guided inspection with consultant from CBI.Neris projektet
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Karlsson, David. "Analysis of Three-Dimensional Cracks in Submodels". Thesis, Linköping University, Department of Management and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8105.
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A common technique to evaluate load paths in complex structures is to perform FE-calculations with relative large elements. This procedure gives no information regarding stress concentrations at e.g. holes or radius but this phenomenon can later on be investigated in details with local individual submodels. Displacements is taken from the global model and used to analyse stress concentrations and crack driving parameters in the submodel.
Today, the crack controlling stress intensity factors are in general cases obtained from handbook solutions of elementary cases. This method requires engineering judgements in a conservative manner and one way to improve the solution is to model the crack in its correct surroundings in a local three-dimensional submodel.
This master thesis is focused on the development of an automated support for analysing three-dimensional cracks in submodels. The results from a global Nastran model can be imported to Trinitas and used for a more accurate stress and fatigue life analysis in a local model. Here a three-dimensional crack tip subdomain can be generated inside an eight point brick volume. The crack tip subdomain is specially designed and adjusted for accurate determination of stress intensity factors along the crack front. For example, all points are adjusted with respect to the brick volume and the crack size, triangular wedge elements are applied around the crack tip, the midpoints for these elements are moved to quarter points and the crack front is curved. The crack tip subdomain is validated against several reference cases and shows sufficiently good results with respect to the stress intensity factor.
Finally, the automated crack tip subdomain generation is applied to a geometrically complex part of a main wing carry-through bulkhead of a fighter aircraft in order to show the applicability of the procedure in an industrial environment.
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Moro, Nicole M. "Skipping the cracks a history in poetry /". Diss., Online access via UMI:, 2005.
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Steadman, David Lawrence. "Growth-arrest behavior of small fatigue cracks". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/11731.
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Xue, Yibin. "Three dimensional interface cracks in anisotropic bimaterials". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17273.
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von, Aulock Felix W. "Bubbles, Crystals and Cracks in Cooling Magma". Thesis, University of Canterbury. Geological Sciences, 2013. http://hdl.handle.net/10092/7880.
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Ascent of magma results in drastic drops of pressure and temperature during eruption. Exsolution or dissolution of water changes the physical and chemical properties of the magma and can promote or inhibit the formation of bubbles, crystals and cracks. The microstructural relations between bubbles, crystals and cracks are important records of processes immediately before and during volcanic eruptions and during deposition of volcanic products. This is an integrated study of analyses, conceptual and numerical models of textural relations, and water distribution patterns of natural and experimentally altered samples.
Synchrotron Fourier transform infrared spectroscopy and focal plane array detectors open new possibilities for the analysis of the spatial distribution of volatiles in volcanic rocks. New ways of sample preparation, measurements and data analyses helped to create water distribution maps with spatial resolutions that are close to the diffraction limit (~3 μm). In order to constrain eruptive processes and mechanisms of lava emplacement, I describe textural features in volcanic glasses including bubbles, flow bands of crystals or bubbles, spherulites and different generations of cracks. In experiments, bubbles were grown under isobaric conditions, at one or two cooling steps, their textures were described and volume changes tracked. Water distribution patterns in the glass around the textures were described and categorized, and where possible, diffusion modeling was used to infer temperature- and timescales of formation.
Rocks that are quenched within short periods of time after bubble growth preserve negative gradients of water toward the bubble margins. These gradients are generally not observed if the sample is kept at high temperatures for extended periods. If, however, a second step of cooling is added, water may be re-dissolved into the surrounding melt, which may lead to the complete resorption of bubbles. A conceptual of water redistribution during bubble resorption or collapse is used to interpret water heterogeneities across linear flow banding. These heterogeneities can be caused by shearing of bubbly magma, leading to collapse, degassing and resorption of water into the melt, creating a bubble free melt. Anhydrous spherulitic crystals grow both above and below the glass transition temperature (Tg) redistributiong water into the surrounding melt. Below Tg, cracks form and are successively hydrated by magmatic water from crystal growth or by meteoric water at temperatures far below Tg. The hydrated perlitic cracks in the samples of this study formed at elevated temperatures and are distinct from cracks formed at ambient temperatures without hydrated margins.
This study shows that the heterogeneous distribution of water in volcanic rocks preserves the complex and non-linear degassing and cooling history of eruptive products. The timescales and temperatures discovered here provide new ways to interpret textural observations, water distribution patterns and signals of shallow volcanic unrest.
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Mathieson, P. A. R. "Acoustic emissions from fatigue cracks in steels". Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379486.
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Zywicz, Edward. "On elastic-plastic cracks between dissimilar media". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14401.
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Atique, Alvis. "Investigation of desiccation cracks in drying soil". Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=20835.
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This research investigates desiccation cracking behaviour of a fill material from a flood embankment along the Bengawan Solo River in East Java, Indonesia, an area that is prone to extremes in flooding and drying. A detailed study of the previous works on this topic showed the absence of fully-monitored laboratory tests dedicated to desiccation cracking behaviour. This study combined traditional and new techniques to characterise desiccation cracking behaviour in this material in a suite of laboratory tests. Desiccation plate tests were conducted to gain basic knowledge of the cracking behaviour of Bengawan Solo soil and identify the influences of plate shape on test results. Crack initiation, evolution, and final pattern were studied in detail. Results of the experiments showed that plate geometry had minimal effect on cracking behaviour except for the final cracking pattern. Crack initiation and evolution was characterised with a 2D/3D profile laser sensor coupled to a motion controller that allowed scanning of the overall surface of the drying soil. The system developed for this work was used to track the three most relevant variables associated with the behavior of soils during desiccation: volume change, water loss, and evolving crack network morphology. With this new method, the evolution of crack aperture, crack depth, surface contour levels (settlements) and evolution of global volume change were captured in real time, significantly improving upon previous methods for crack monitoring. Finally, the effects of moisture content and dry density on tensile strength during cracking was investigated at two states: reconstituted and compacted. Microstructural investigation illustrated the fabric changes during drying at two states to complement the experimental results for tensile strength. The comparison of tensile strength between reconstituted and compacted state has been found promising and believed to be useful in earthwork construction projects.
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Abdul, Manan Muhamad Saifuildin. "Fracture mechanics analysis of multiple edge cracks". Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1444086/.
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This thesis is concerned with the evaluation of crack propagation in the presence of other cracks within the same two-dimensional body. The parameter known as the Stress Intensity Factor (SIF) is used within Linear Elastic Fracture Mechanics (LEFM) to predict crack propagation rate knowing the appropriate material properties. Unfortunately the number of SIF solutions for multiple cracks is very small especially for real engineering cases. This thesis investigates the use of the SIF weight function for the efficient evaluation of SIFs for two one-dimensional cracks in close proximity to each other. The SIF weight function has proved to be a powerful tool for the evaluation of single cracks however, has not before been used to solve multiple crack problems. The main objective of the thesis is to investigate the mechanics of multiple cracks through an experimental and numerical analysis programme and to develop engineering solutions for prediction of multiple crack behaviour in steels and materials that exhibit LEFM characteristics. A Finite Element (FE) approach was employed to model multiple crack interaction. In addition, the FE model was used to study the non-uniform stress distribution caused by the interaction effect between cracks. Over one hundred FE models were analysed for this study. A major experimental programme was conducted to study the interaction effect between two edge cracks. A total of seven specimens with different crack geometries were completed under fatigue loading in tension. The purpose of this experimental work was to better understand the mechanisms of crack interaction and to provide information for validation of the numerical anlayses. The experimental results show that cracks in close proximity to each other interact to varying degrees depending on relative crack lengths, crack separation and plate width. A novel weight function method was developed in order to predict SIFs of two edge cracks under uniform tension. The crack interaction effect was established using the idea of non-uniform stress distributions along the potential crack plane due to the presence of an additional edge crack. Generally the novel weight function approach shows good results compared to finite element analysis. Finally, further work to explore the wide range of SIFs for multiple cracks using the weight function method is identified and proposed.
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Eriksson, Linus. "Detection of facade cracks using deep learning". Thesis, Mittuniversitetet, Institutionen för elektronikkonstruktion, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-39598.
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Facade cracks are a common problem in the north of Sweden due to shifting temperatures creating frost in the facades which ultimately damages the facades, often in the form of cracks. To fix these cracks, workers must visually inspect the facades to find them which is a difficult and time-consuming task. This project explores the possibilities of creating an algorithm that can classify cracks on facades with the help of deep learning models. The idea is that in the future, an algorithm like this could be implemented on a drone that hoovers around buildings, filming the facade, and reporting back if there are any damages to the facade. The work in this project is exploratory and the path of convolutional neural networks has been explored, as well as the possibility to simulate training data due to the lack of real-world data. The experimental work in this project led to some interesting conclusions for further work. The relatively small amount of data used in this project points towards the possibility of using simulated data as a complement to real data, as well as the possibility of using convolutional neural networks as a means of classifying facades for crack recognition. The data and conclusions collected in this report can be used as a preparatory work for a working prototype algorithm.
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Iyyer, Nagaraja S. "Closure of fatigue cracks at high strains". Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/91124.
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Experiments were conducted on smooth specimens to study the closure behavior of short cracks at high cyclic strains under completely reversed cycling. Testing procedures and methodology, and closure measurement techniques, are described in detail. The strain levels chosen for the study cover from predominantly elastic to grossly plastic strains. Crack closure measurements were made at different crack lengths. The study reveals that, at high strains, cracks close only as the lowest stress level in the cycle is approached. The crack opening was observed to occur in the compressive part of the loading cycle. The applied stress needed to open a short crack, under high strain was found to be less than for cracks under small scale yielding. For increased plastic deformations, the value of σop/σmax is observed to decrease and approaches the value of R. Comparison of the experimental results with existing analysis has been made and indicates the limitations of the small scale yielding approach where gross plastic deformation behavior occurs.M.S.
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Lee, Shi-Wei. "Analysis of Composite Laminates with Matrix Cracks". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45539.
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Analysis of the effects of matrix cracking on composite laminates is a well-known problem which has attracted considerable attention for the past decade. An approximate analytical solution is introduced in this thesis to study this type of problem.
The subjects of primary concern are the degradation of effective laminate properties, such as axial stiffness, Poisson's ratio, shear modulus, and coefficient of thermal expansion, as a function of crack density and the axial stress redistribution due to the existence of matrix cracks. Both transverse cracks (2-D problem) and cross (transverse and longitudinal) cracks (3-D problem) are studied. Results for graphite/epoxy cross-ply laminates are presented and compared to those of other approaches. Some other materials, for instance, glass/epoxy, are also studied. The results and comparisons will appear where appropriate. In general, the agreement between the results of the present analysis and those of other approaches, in particular, the finite element method, is good for the lower crack density. The present study shows that Poisson's ratio may be a good indicator of the degree of damage for a cracked laminate.Master of Science
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Iyyer, Nagaraja S. "Fatigue growth and closure of short cracks". Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/52324.
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A study has been carried out to investigate the growth and closure behavior of short cracks in 2024-T351 aluminum alloy and four different conditions of 4340 steel using through thickness cracks of straight fronts. The experiments were carried out to study the influence of stress level, stress ratio, yield strength and prior austenitic grain A sizes in notched and unnotched specimens. The stereoimaging technique was developed and adapted to obtain crack closing and opening points, and also near tip displacement fields. Experimental results are presented with a general discussion. It was found that long cracks showed good correlation when analyzed in terms of effective stress intensity range. However,correlations were poor for short cracks. lt was found that short cracks show less closure behavior than long cracks. The estimates of initial crack lengths based on linear elastic data were made. These estimates differed significantly from the actual initial crack lengths for completely reversed cycling tests. Suggestions have been made to the equivalent initial flaw size approach and conclusions have been drawn.Ph. D.
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karashi, husain. "The Prevalence, Predictive Factors, and Classification of Intrapulpal Cracks in Maxillary Molars Requiring Endodontic Treatment". VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/4755.
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Diagnosis and treatment of teeth with longitudinal fractures is challenging. Cracks are usually not visible radiographically; they require a thorough evaluation to aid in diagnosis. Patients may be asymptomatic, demanding the dentist rely on clinical findings to make a diagnosis. Early diagnosis of the presence and extent of a crack is essential for the successful management of a cracked tooth. There is limited information in the literature regarding the prevalence or predictive factors of cracks extending into the pulp chamber of teeth. The purpose of this study was to determine the prevalence of intrapulpal cracks in maxillary molars and to identify factors that may aid in diagnosing the existence of a crack. All maxillary molar teeth requiring non- surgical root canal therapy or retreatment at the Virginia Commonwealth University graduate endodontic clinic from June 2016 through December 2016 were included in the study after obtaining patient consent. Teeth were examined visually, transilluminated, stained, and examined microscopically for the presence of an intrapulpal crack. Demographic information, subjective data associated with the chief complaint, objective results of diagnostic testing (percussion, palpation, bite stick test, transillumination, probing depths, existing restorations, and diagnosis) were analyzed using chi-square and logistic regression (p<0.05) to identify associations of these findings with the existence of a crack. A total of 18% (15/82 teeth) of maxillary molars that were evaluated and had endodontic treatment initiated were cracked. There was a significant association between cracked teeth and pain on biting (P<.0001) and with probing depths greater than 4 millimeters (mm) (P < 0.003). Those positive on a tooth slooth test were more likely to have an intrapulpal crack (P<.001) and teeth with a positive transillumination test were also found to be associated with the presence of a crack(P < .001).
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Elgazzar, Hesham, i Viktor Ansnaes. "Concrete Cracks in Composite Bridges : A Case Study of the Bothnia Line Railway Bridge over Ångermanälven". Thesis, KTH, Bro- och stålbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-100831.
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Cracks in the concrete slab of continuous composite bridges are common due to the tensile stresses at the supports. These bridges are allowed to crack as long as the cracking is controlled and not exceeding the design crack width (according to Bro 94 the crack should be injected if they are bigger than 0.2 mm). The Ångermanälven Bridge (railway bridge part of the Bothnia line project) was designed with big edge beams of width 1.2 m, 40 % of the total area of the concrete deck cross-section. During the final inspection cracks larger than the design crack width (0.3 mm according to Bro 94) were observed over the supports.In this thesis the design and the construction procedure of the bridge is studied to clarify the causes of the cracking in the edge beam. The objectives of this thesis were addressed through a literature study of the different types of cracks and the Swedish bridge codes. The expected crack width was calculate according to the same code, using a 2-D FEM model for the moment calculation, and compared with the crack width measured at the bridge.The result of the calculations shows that tensile stress due to ballast and only restraining moment due to shrinkage is not big enough to cause the measured crack width. Shrinkage force and temperature variation effects may have contributed to the concrete cracking in the edge beams. The large cross-section area of the edge beams indicates that it should be designed as part of the slab, taking that into consideration, 1.1 % reinforcement ratio in the edge beams is believed to limit the crack width to the code limits (0.3 mm).
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Potirniche, Gabriel Petru. "FINITE ELEMENT MODELING OF CRACK TIP PLASTIC ANISOTROPY WITH APPLICATION TO SMALL FATIGUE CRACKS AND TEXTURED ALUMINUM ALLOYS". MSSTATE, 2003. http://sun.library.msstate.edu/ETD-db/theses/available/etd-06242003-220551/.
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For the characterization of crack advance in mechanical components and specimens under monotonic and fatigue loading, many engineering approaches use the assumption that the plastic deformation at the crack tip is isotropic. There are situations when this assumption is not correct, and the modeling efforts require additional correction factors that account for this simplification. The goal of this work is to study two cases where the plastic anisotropy at the crack tip is predominant and influences the magnitude crack-tip parameters, which in turn determine the amount of crack advance under applied loading. At the microstructural level, the small crack issue it is a long-standing problem in the fatigue community. Most of the small crack models consider that the plastic deformation at the crack tip is isotropic. The proposed approached for analyzing small crack growth is to perform finite element simulation of small cracks growing in a material that is assigned single crystal plastic properties. The nature of the plastic deformation of the material at the crack tip in the intra-granular regions could be accurately described and used for modeling small crack growth. By employing finite element analyses for stationary and growing cracks, the main characteristics of the plastic deformation at the crack tip, such as plastic zone sizes and shapes, crack-tip opening displacements, crack-tip opening stresses, are quantified and crack growth rates are determined. Ultimately, by using this crystal plasticity model calibrated for different microstructures, important time and financial resources for real experiments for the study of small cracks can be spared by employing finite element simulations. At macroscale, it is widely known that the manufacturing processes for aluminum alloys results in highly anisotropic microstructures, known as textures. The plastic behavior of these types of materials is far from isotropic and even the use of classical anisotropic yield criteria, such as that on Hill (Hill, 1950), is far from producing accurate results for describing the plastic deformation. Two of these anisotropic yield functions are implemented into finite element code ANSYS and stationary cracks are studied in a wide variety of textures. Significant variations of the plastic deformation at the crack due to the anisotropy are revealed.
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Rahman, Md Moshiur. "Experimental and theoretical study of the stress and strain fields around fatigue cracks and plasticity-induced crack closure". Thesis, Open University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.446310.
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Jassal, Kulbir Singh. "Development of potholes from cracks in flexible pavements". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ39100.pdf.
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Garces, Rodriguez Olga. "Influence of cracks on chloride ingress into concrete". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62948.pdf.
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Cook, Daniel Adam. "Monitoring small fatigue cracks using ultrasonic surface waves". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17381.
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Araujo, Jose Alexander. "On the initiation and arrest fretting fatigue cracks". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342243.
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Lang, Christopher Leslie. "Composite patching of fatigue cracks in steel structures". Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2041.
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Lynch, Michael Anthony. "Limit loads of piping branch junctions with cracks". Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399152.
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