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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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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.
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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.
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CORBANI, SILVIA. "CRACK GROWTH WITH PARTIAL BENDING-INDUCED CRACK CLOSURE". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=23847@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Neste trabalho são investigadas experimentalmente e numericamente as mudanças de geometria em trincas inicialmente passantes submetidas a carregamento remoto de flexão pura induzindo fechamento parcial das faces da trinca. Esse crescimento de trinca pode ocorrer numa variedade de estruturas com defeitos pré-existentes, tais como fuselagens de aviões, cascos de navios, vasos de pressões e pontes metálicas. O carregamento de flexão pura ocasiona regiões de tração e compressão na frente da trinca. É inquestionável que parte das faces da trinca sob compressão fecha independentemente de qualquer mecanismo de fechamento; e outra parte das faces da trinca, por outro lado, sob tração cresce mudando gradualmente de geometria. Após realizar ensaios em corpos-de-prova de aço ASTM A-36, foi observado que tais carregamentos geram uma quina na frente da trinca, que é a transição de uma geometria parcialmente passante e um trecho remanescente da geometria inicial. Para entender a distribuição do fator de intensidade de tensão em tais frentes de trinca, suas geometrias foram reproduzidas em um modelador tridimensional de mecânica da fratura linear elástica, o FRANC3D, acoplado a um programa de análise de elementos finitos (ABAQUS). Com este sistema acoplado, foram executadas análises considerando efeitos não lineares causados pelo contato das faces da trinca sob compressão. Verificou-se a necessidade de propor metodologias para tratamento dos resultados numéricos na quina, obtendo-se predições eficientes das mudanças na geometria da trinca. Contudo, a estimativa de vida, quando se compara taxas de crescimento da trinca obtidas em um corpo-de-prova sob tração cíclica e as taxas em um corpo-de-prova sob flexão com fechamento parcial da trinca, foi melhor reproduzida usando um fator de correção de fechamento da trinca. Adicionalmente, uma série de expressões empíricas normalizadas para geometrias da trinca e fatores de intensidade de tensão são propostas.
This work investigates experimentally and numerically how the front of initially through edge cracks in plate changes after they pass to be remotely fatigue loaded under pure bending to induce partial closure of the crack faces. This type of crack growth problem can occur in a variety of structures with preexisting defects, such as aircraft fuselages, ship hulls, pressure vessels components, and steel bridges. The bending loads induce tension and compression regions along the crack front, with the part of the crack faces that work under compression undoubtedly closed by the load, independently of any other closure mechanism. The part of the crack faces that work under tension; on the other hand, crack grows by fatigue gradually changing its shape. After performing tests on ASTM A36 steel specimens, it was observed that the bending load induces a kink on the crack front, in the transition between the part through crack created on the tension side and initial crack geometry. To understand the distribution of the stress intensity factor along such crack fronts, the measured crack shapes were reproduced in a three-dimensional fracture mechanics modeler (FRANC3D) coupled to a finite element analysis program (ABAQUS). With this coupled system, linear elastic stress analysis simulations were performed considering the nonlinear effects caused by the crack face contact in the compressed region. In particular, methods had to be proposed to treat numerical noise around the kink. The proposed methodology efficiently predicts the observed crack front shape changes; although the observed fatigue lives were better reproduced using a crackclosure correction factor when compared to crack growth data obtained from standard compact tension specimens. In addition, a series of normalized empiric expressions for both crack front shapes and stress intensity factors are proposed.
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Milonopoulos, Alexis. "Máquina crack". Pontifícia Universidade Católica de São Paulo, 2014. http://tede2.pucsp.br/handle/handle/2487.
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Previous issue date: 2014-09-15Conselho Nacional de Desenvolvimento Científico e Tecnológico
Based on a cartographic writing, Crack Machine shows the games of power and the struggling forces within the cracolandia field, pointing out not only the battles, the gears and specific arrangements placed on networks of strategic places, but also dislocations, sinuosity, transversals, tracks, ruts and thresholds that cross the whole cracolandia issue and question our politics. By showing the profusion of useless actions in that area this dissertation treats this matter reaching beyond the discussions about hygienization process and the real estate speculation, pointing out another dimension of the State and the politics and demonstrating a machine that lives off exclusion, speculation, immolation, safety and potentializing more and more lucrative businesses that go from wars against drugs to humanitarianism. In another movement, it exposes the matter of irrecoverable population management, extrapolating the cracolandia space and the discussion about crack cocaine and the control of the undesirable population through technologies that provide administration and risk management. It also shows how these ungovernable populations have been, also with the formation of a new drug market, the main effect of the austerity politics that have taken the globe, questioning our model of society and our political rationality related to the way power has struggled to manage populations since the appearance of the biopower. Taking a step forward from a strictly biopolitical analysis, rewriting the to make die and to let die in the mark of power technologies, pointing out how death became a normal governmental mechanism, inserted in a military-political project of war on drugs and being a privileged strategy that allows the creation of a tension between to make live, to make die and to let die
A partir de uma escritura cartográfica, Máquina Crack mostra jogos de poder e forças em luta no campo da cracolândia, evidenciando não só batalhas, engrenagens e arranjos específicos situados em redes de lugares estratégicos, mas também deslocamentos, sinuosidades, transversais, rastros, sulcos e limiares que atravessam todo a questão da cracolândia e que colocam a nossa política em questão. Ao mostrar a profusão de ações inócuas na área, trata esta questão indo além das discussões acerca de processos de higienização e do fenômeno da especulação imobiliária, evidenciando uma outra dimensão do Estado e da política e demonstrando toda uma máquina que vive da exclusão, da especulação, da imolação e da segurança e que cada vez mais potencializa lucrativos negócios que vão da guerra às drogas ao humanitarismo. Em um outro movimento, expõe a problemática da gestão de populações irrecuperáveis, extrapolando o espaço da cracolândia e a discussão em torno do crack e problematizando a questão da gestão estratégica de populações, mais precisamente da contenção e do controle de populações indesejáveis por meio de tecnologias que propiciam a administração e a gestão de riscos. Mostra também como estas populações ingovernáveis têm sido, juntamente com a formação de um novo mercado de drogas, o principal efeito das políticas de austeridade que tem tomado o globo, colocando em xeque nosso modelo de sociedade e nossa racionalidade política, relacionada ao modo com que o poder esforçou-se para gerir populações desde o aparecimento do biopoder. Dando um passo para além de uma análise estritamente biopolítica, reinscreve o fazer morrer e o deixar morrer no marco das tecnologias de poder, evidenciando como a morte tornou-se um mecanismo normal de governo, inserido-se em um projeto político-militar de guerra às drogas e sendo uma estratégia privilegiada que permite a criação de uma tensão singular entre fazer viver, fazer morrer e deixar morrer
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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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Lanfranchi, Noe͏̈l. "Toxicologie du crack". Paris 5, 1992. http://www.theses.fr/1992PA05P152.
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Zanotto, Daniele Farina. "Usuários de crack". reponame:Repositório Institucional da UFSC, 2016. https://repositorio.ufsc.br/xmlui/handle/123456789/172180.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde, Programa de Pós-Graduação em Saúde Coletiva, Florianópolis, 2016.Made available in DSpace on 2017-01-03T03:15:53Z (GMT). No. of bitstreams: 1 343122.pdf: 1296653 bytes, checksum: fb56bd92cf8165b2e622c174b163e35a (MD5) Previous issue date: 2016
O consumo e os conceitos do uso de drogas passaram por modificações em seu significado no desenrolar da história. Hoje é o crack que detém a atenção e é veiculado constantemente pelos meios de comunicação. Seus primeiros registros no Brasil datam do final dos anos 1980, mas somente a partir de 2010 sua visibilidade ganhou mais espaço nas pesquisas, na atenção e assistência a saúde, no Plano de Enfrentamento do Governo Federal, mas principalmente na mídia, escrita, falada e televisionada. Diante desse cenário esta tese parte do pressuposto que o conhecimento transmitido por reportagens forma opiniões sobre o tema, e essa forma de apresentar o usuário de crack vem na contramão da Reforma Psiquiátrica Brasileira. A Lei nº 10.216/2001, que dispõe sobre a proteção e os direitos das pessoas portadoras de transtornos mentais e redireciona o modelo assistencial em saúde mental, não foi suficiente para atingir estas lacunas e são reproduzidas, por esta via de informação, formas biomédicas e medicalizadas do cuidado a estes indivíduos. Dessa forma desenvolvemos uma pesquisa documental com abordagem qualitativa, que buscou compreender como os usuários desta droga são descritos nas reportagens de um jornal e duas revistas de circulação nacional nos últimos 5 anos. O material encontrado foi submetido à análise textual discursiva. A base teórica para acessar o objeto de estudo contou com os autores Michel Foucault, Erwin Goffman, Howard Becker e John Thompson. Buscamos, por meio do percurso metodológico e marco teórico, desnaturalizar as maneiras como os discursos sobre os usuários de crack são veiculados pela mídia. Nosso corpus de pesquisa mostrou que as propostas de cuidado, presentes na maioria das reportagens, continuam mantendo seu caráter disciplinar e normalizador, muito mais do que terapêutico em relação aos usuários de crack. Bem como na história da loucura na Idade Clássica de Foucault, estas pessoas continuam sendo excluídas com o intuito de deixar a população livre dos perigos de seu convívio. Os textos analisados também permitiram afirmar que o discurso veiculado pela mídia constrói no senso comum um perfil negativo sobre o usuário de crack, permeado por preconceito e estigma. É transmitido de forma sensacionalista e em alguns casos higienista, dando ênfase ao enfrentamento aos usuários e não somente à droga em si. Por fim, a forma como os usuários de crack são apresentados pela mídia é capaz de materializar as representações da classe dominante e de refletir na forma em que a sociedade convive com eles. Entende-se como classe dominante aquela representada pelo modelo biomédico de cuidado em saúde mental.
Abstract : The consume and the ideas of drugs use have been changed in the course of time. Nowadays, the crack cocaine got so visibility in the media. Althought your history on Brazil began in the eights end, the studies, the healthcares, the Federal Combat Plan and the media (writennpress, oralpress, tvpress) have been show it from the penultimate year of first decade of 21 century. In view of this, this thesis pressuppose that the reports make ideias about the crack cocaine users. This description, however, affront the brasilian Psychiatric Reform. The reports reveal that the Law 10.216/2001 doesn´t implanted inside de the brasilian society. The biomedics healthcares are still strongs, same more than ten years after that. This law intend protect and guarantee the citizens mental disorders rights as well as reorganize the mental heath politics. The reseach is a documental qualitative study. The aim is comprehend the descriptions about the crack cocaine users in a national newspaper and in two national magazines between january 2009 and july 2015. The reports was submitted to discourse textual analysis. Michel Foucault, Erwin Goffman, Howard Becker and John Thompson compose the theoretical base. We seek denaturalize the media discourses about the crack cocaine users. According with our reseach corpus, the heathcares still keep a normalizing and disciplining line much more than a real therapy. As in Foucault´s madness history, the crack cocaine users currently are censure to exclusion. The idea is repel them to avoid your problems. The reports created a negative portrait of crack cocaine users. This portraits are prejudice and full of stigmas. The discourse is sensacionalist and sometimes hygienist, emphasizing the confront with the crack cocaine users. At last, the crack cocaine users portraits are still controled by the biomedic model of mental health.
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Yandow, Chantelle. "Crack mothers, crack babies, and black male dope dealers productions of deviance during america's crack cocaine panic in the 1980s". Honors in the Major Thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/529.
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A moral panic erupted during the 1980s among the American public when stories about crack cocaine saturated the media. In this thesis I analyze how discursive productions of deviancy operated in the CBS news documentary: 48 Hours on Crack Street (1986) and other print news sources at that time. Three salient characters that appear in news media discourse during the panic are "crack mothers," "crack babies," and "Black male dope dealers." The news media frightened the public with such representations (among others) and the public urged politicians to get tough on drug crime to control the so-called crack cocaine plague. Politicians responded with omnibus drug reforms that established mandatory minimum sentences and the controversial 100:1 sentencing disparity between crack and powder cocaine. The enforcement of the draconian drug laws that were passed in response to the crack cocaine panic continues to be a contributing factor to America's current prison crisis. Moreover, the laws are enforced in ways that disproportionately punish the poor and African-Americans. I conclude that the criminal disenfranchisement of millions of people since the 1980s relates to the media's representation of the crack cocaine "epidemic" and the legislation that was passed to control illicit drugs such as crack cocaine.B.A.
Bachelors
Arts and Humanities
Religious Studies
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Perng, Jia-Der. "Analysis of crack propagation in asphalt concrete using a cohesive crack model". Connect to this title online, 1989. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1094737677.
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Bian, Lichun, i 卞立春. "Fatigue crack growth analysis of metallic plates with an inclinedsemi-elliptical crack". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31242844.
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Fuleki, Daniel M. Carleton University Dissertation Engineering Mechanical and Aerospace. "Crack initiation and short crack growth characteristics of notched merl 76 specimens". Ottawa, 1995.
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GIULIETTI, NICOLA. "Crack Analyser: a novel image-based NDT approach for measuring crack severity ". Doctoral thesis, Università Politecnica delle Marche, 2022. http://hdl.handle.net/11566/295503.
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In Europa, le infrastrutture civili e di trasporto necessitano di una manutenzione efficace e proattiva per garantire il continuo funzionamento in sicurezza durante l'intero loro ciclo di vita. I paesi europei devono ogni anno stanziare enormi risorse per mantenere il loro livello di funzionalità. Ciò fa sorgere la necessità urgente di adottare approcci di ispezione di monitoraggio più rapidi e affidabili per aiutare ad affrontare questi problemi. Il deterioramento delle strutture è più spesso anticipato dalla formazione di fessure sulla superficie del calcestruzzo. La presenza di fessurazioni può essere sintomo di diverse problematiche quali dilatazioni e ritiri dovuti a sbalzi di temperatura, assestamenti della struttura, copertura impropria fornita in fase di getto, corrosione delle armature in acciaio, carichi pesanti applicati, vibrazioni insufficienti al momento della posa del calcestruzzo o perdite d'acqua per ritiro superficiale del calcestruzzo. Diventa quindi di primaria importanza l'identificazione, la misurazione e il monitoraggio delle fessurazioni sulla superficie del calcestruzzo. I principali metodi di ispezione attualmente adottati si basano su strumenti manuali e righelli: un’attività lunga e ingombrante, soggetta a errori e scarsamente oggettiva sull'analisi quantitativa perché fortemente dipendente dall'esperienza dell'operatore. Secondo la norma UNI EN 1992-1-1:2005, la larghezza massima delle fessure del calcestruzzo ammessa per una generica classe di rischio è di 0,3 mm. Per questo motivo, per misurare in modo accurato e affidabile la dimensione della fessura, è necessario l’impiego di strumenti di misura con caratteristiche metrologiche adeguate (es. precisione e accuratezza almeno un ordine inferiore al valore da misurare). In caso contrario, la severità della fessura potrebbe essere classificata erroneamente. Questo lavoro di tesi propone un nuovo approccio automatico, basato su immagini, in grado di localizzare e misurare fessure su superfici in calcestruzzo rispettando il vincolo metrologico imposto dalla norma UNI EN 1992-1-1:2005. Utilizzando una sola immagine, il metodo sviluppato è in grado di localizzare e misurare automaticamente e rapidamente la larghezza e la lunghezza di una fessura su una superficie. Il sistema di misura sviluppato sfrutta una singola telecamera operante nel campo del visibile per acquisire un'immagine digitalizzata della superficie da ispezionare. Il componente software del sistema riceve in input la singola immagine che inquadra la crepa e fornisce in output un'immagine aumentata dove viene evidenziata la crepa e la sua larghezza e lunghezza media/max. La misura della larghezza della fessura viene eseguita perpendicolarmente alla linea centrale della fessura con una precisione sub-pixel. Il sistema di misurazione è stato implementato su uno smartphone per eseguire ispezioni manuali da parte dell'operatore e su sistemi integrati per l'ispezione remota con robot o velivoli senza pilota (UAV)). Le strategie sviluppate possono essere facilmente estese a qualsiasi altro contesto in cui sia richiesto un controllo di qualità superficiale mirato all'identificazione e misura di eventuali danni o difettosità. Europe’s ageing transport infrastructure needs effective and proactive maintenance in order to continue its safe operation during the entire life cycle; European countries have to allocate huge resources for maintaining their service-ability level. This give rise to the necessity of an urgent need to adopt faster and more reliable monitoring inspection approaches to help tackling these issues. The deterioration of structures is most often foreseen by the formation of cracks on concrete surface. The presence of cracks can be a symptom of various problems like expansion and shrinks due to temperature differences, settlement of the structure, improper cover provided during concreting, corrosion of reinforcement steel, heavy load applied, insufficient vibration at the time of laying the concrete or loss of water from concrete surface shrinkage, therefore the identification, measurement and monitoring of cracks on the concrete surface becomes of primary importance. The main currently adopted inspection methods rely on visual marking and rulers, long and cumbersome activity, prone to errors and poorly objective on quantitative analysis because it strongly depends on operator experience. According to UNI EN 1992-1-1:2005 standard , the maximum admitted concrete crack width is 0.3 mm. For this reason, to accurately and reliably measure the target dimension, it is necessary to employ measurement instruments with suitable metrological characteristics (e.g. precision and accuracy at least one order lower than the value to be measured). Otherwise, the crack severity could be misclassified. This thesis work proposes a novel automatic image-based approach able to locate and measure cracks on concrete surfaces respecting the metrological constraint imposed by UNI EN 1992-1-1:2005 standard. Using only one image, the developed method is able to automatically and rapidly locate and measure the average width and length of a crack in an existing concrete structure. The measurement system developed exploits a single camera working in the visible range to acquire a digitized image of the structure being inspected. The software component of the system receives as input the single image framing the crack and gives as output an augmented image where the crack is highlighted as well as its average/max width and length. The measure of the crack width is performed perpendicularly to the crack central line with sub-pixel accuracy. The measurement system has been deployed on a smartphone for operator-based manual inspections as well on embedded systems for remote inspection with robots or Unmanned Aerial Vehicles (UAVs). The strategies developed can be easily extended from concrete inspection applications to any other context where a surface quality control targeted to the identification of eventual damages/defects is required. The activity was triggered by an explicit need within the EnDurCrete project.
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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.
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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.
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Kapanadze, David, i Bert-Wolfgang Schulze. "Pseudo-differential crack theory". Universität Potsdam, 2000. http://opus.kobv.de/ubp/volltexte/2008/2575/.
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Crack problems are regarded as elements in a pseudo-differential algbra, where the two sdes int S± of the crack S are treated as interior boundaries and the boundary Y of the crack as an edge singularity. We employ the pseudo-differential calculus of boundary value problems with the transmission property near int S± and the edge pseudo-differential calculus (in a variant with Douglis-Nirenberg orders) to construct parametrices od elliptic crack problems (with extra trace and potential conditions along Y) and to characterise asymptotics of solutions near Y (expressed in the framework of continuous asymptotics). Our operator algebra with boundary and edge symbols contains new weight and order conventions that are necessary also for the more general calculus on manifolds with boundary and edges.
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Hoffman, Jeffrey. "A Crack in Everything". Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5305.
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Contained herein is a close examination of self-awareness and self-portraiture as it applies to the works of artist Jeffrey Hoffman. Water, frozen into various forms and combined with natural elements of wood, slowly melt over an indeterminable amount of time, each droplet documented as the process transforms the elements. Through this process, we see change. We see time. We see truth. This documentation of change and time through natural elements is where the artwork comes full circle. Working with new media to explore man's interconnectivity to life, energy, and the cosmos, he produces time based installations, photographs, videos, and sculptures that serve as both existential metaphors and Tantric symbols. With the use of digital cameras and video, a record is created by which the disintegration which occurs from the unseen forces of gravity, heat and time upon sculptures made from natural elements and ice is examined. In its sculptural form, his work can be categorized as Installation art and Performance art due to its evolving nature. Each piece is intended to either change over time or to have that change halted by another temporal force like that of flowing electricity. The possibility of allowing varying levels of self-awareness to emerge through self portraiture is also examined. The existential, as well as the metaphysical, can be present in a physical form when the form is imbued with evidence of an evolutionary process. In many ways, the work serves as a self portrait. It is a means for Hoffman to examine his own existentialism as a student of the modern western world and life.ID: 031001330; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Title from PDF title page (viewed April 8, 2013).; Thesis (M.F.A.)--University of Central Florida, 2012.; Includes bibliographical references (p. 31).
M.F.A.
Masters
Visual Arts and Design
Arts and Humanities
Emerging Media; Studio Art and the Computer
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Miller, James Thomas Ph D. Massachusetts Institute of Technology. "Crack coalescence in granite". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/47771.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references.
This thesis experimentally investigates crack coalescence in prismatic Barre Granite specimens with two pre-cut, open flaws under uniaxial compression. Using a high-speed video system, crack initiation, propagation, and coalescence are observed. Flaw geometries are chosen to allow one to compare the results with those of studies in other materials as well as to better understand fracturing and coalescence processes. Specifically, the effect of ligament length (L), flaw inclination angle (p3), and bridging angle (a) on coalescence is investigated. The same crack types as in other materials are observed. Coalescence patterns observed fit into a previously developed framework (for molded gypsum and Carrara marble) with the exception of one new coalescence pattern. Crack processes and coalescence patterns suggest a more tensile behavior as grain size increases from gypsum to marble to granite. Similar to previous work in marble and granite, white patches are observed during compression tests. These white patches can be categorized as either diffuse or linear, with linear white patches further subdivided into two more types, namely boundary-following and through-going. The white patches are essentially process zones. The effect of water pressure on coalescence pattern is also investigated. Flaw water pressure is seen to affect coalescence in granite, although further work is needed.
by James Thomas Miller.
S.M.
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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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Piyasena, Ratnamudigedara, i n/a. "Crack Spacing, Crack Width and Tension Stiffening Effect in Reinforced Concrete Beams and One-Way Slabs". Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20030606.165418.
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An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.
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Piyasena, Ratnamudigedara. "Crack Spacing, Crack Width and Tension Stiffening Effect in Reinforced Concrete Beams and One-Way Slabs". Thesis, Griffith University, 2003. http://hdl.handle.net/10072/366060.
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An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
Full Text
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Santos, e. Lucato Sergio Luis dos. "Constraint induced crack initiation and crack growth at electrode edges in piezoelectric ceramics". Phd thesis, [S.l.] : [s.n.], 2002. http://elib.tu-darmstadt.de/diss/000191.
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Alencar, Rodrigo. "Porque a guerra às drogas? do crack na política ao crack do sujeito". Pontifícia Universidade Católica de São Paulo, 2012. https://tede2.pucsp.br/handle/handle/16964.
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Previous issue date: 2012-03-28Conselho Nacional de Desenvolvimento Científico e Tecnológico
Drugs, albeit under other symbolic coordinates, have always been in the most varied places, societies and human groups. However, since the turn of the 19th century, drug use and trade has been object of international treaties. These agreements urge the signatory countries to take measures to control and combat drugs, through the mobilization of the military in their drug policies. As a result of this strategy, the fields of health and public safety intertwine, causing some blurring between who should be treated and who should be fought. Therefore, this work is dedicated to the task of identifying the unconscious operations at stake in the game of prohibition. We establish as object delimitation the highlight given to crack in the drug policies, since it is the most recent episode about the topic in Brazil. Based on this understanding of the theme, we draw on both the contribution of the psychoanalytical theory and its interpretations of group interaction, as well as the political resources that act to camouflage the subject s division. Thus our analysis concludes that the policies to combat crack deny the discontent in the cultural life, insofar as they present this substance as a threat to the social bond
As drogas, ainda que sob outras coordenadas simbólicas, ocuparam diversos lugares nas mais variadas sociedades e agrupamentos humanos. No entanto, desde a passagem do século XIX para o século XX, seu uso e circulação tem sido objeto de acordos internacionais. Tais acordos estabelecem aos países participantes medidas de combate e controle, aplicadas por meio da mobilização de aparatos militares em suas políticas sobre drogas. Esta mobilização opera por estratégias que entrelaçam os campos da saúde e da segurança pública, provocando certo obscurecimento entre quem deve ser tratado e quem deve ser combatido. Portanto, neste trabalho, nos lançamos à tarefa de identificar as operações inconscientes em jogo no discurso da proibição. Estabelecemos enquanto recorte de objeto o destaque dado ao crack nas políticas de atenção às drogas por o considerarmos o episódio mais recente sobre o tema no Brasil. Pautados nesta compreensão do problema, recorremos aos aportes da teoria psicanalítica e às suas interpretações sobre o funcionamento grupal, bem como aos recursos políticos que operam no escamoteamento da divisão do sujeito. Deste modo, analisamos que as políticas de combate ao crack negam o mal-estar inerente à vida cultural, recorrendo à apresentação desta substância como uma ameaça para o laço social
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Stierle, Claudia. "Entscheidung zu Crack? : Eine handlungstheoretische Erklärung des Crackkonsums /". Hamburg : Kovač, 2006. http://www.verlagdrkovac.de/3-8300-2250-6.htm.
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Rehman, Atiq-Ur. "An investigation of methods of reducing fatigue crack growth by artificial crack-closure effects". Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315379.
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Wan, Victor. "Fundamental modelling studies of fatigue crack nucleation & microstructurally short crack growth in superalloy". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/61023.
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Current lifing techniques for metal superalloys have largely remained empirical, particularly those addressing the nucleation or initiation of fatigue cracks. However, there is growing interest within both the academic literature and industrial users to move away from the approaches which are dependent on empirical models. Instead, there has been greater focus on the advancement of developing fundamental mechanistically-based models to predict alloy behaviour in order to help better understand and predict defect nucleation processes. Early lifing methods in face centred cubic (fcc) and body centred cubic (bcc) polycrystalline alloys are of interest due to the relevance of cubic alloys in industrial applications, where microstructural fatigue behaviour to crack nucleation and short crack growth are studied. A stored energy criterion for fatigue crack nucleation is introduced which is validated with ferritic steel polycrystal specimens to reveal new evidence and address the scattered cycles to crack nucleation. The criterion is extended into a 3D crystal plasticity finite element model (CPFEM) representation of RS5 Nickel superalloy where the method provided a new perspective to quantify microstructurally sensitive cycles to fatigue crack nucleation in RS5 alloys. Comparisons of experimental and CPFEM investigation of microstructural stress distributions is presented across a polycrystalline copper where fatigue hotspots identified provided new insight of common nucleation hotspots, and is typically associated on/near grain boundaries. The work is extended using FEM to address Microstructural Sensitive Short Crack Growth (MSCG) in microstructurally different ferritic notched specimens. Our assessments and methodology introduced based on Extended Finite Element Method (XFEM) revealed information on the role of anisotropy to better capture the MSCG paths. In addition, user-defined materials and grain boundary properties were introduced to address the difficulties in capturing intergranular cracks where grain boundary properties were introduced to promote the grain boundary cracks as witnessed in experiments.
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Alvaredo, Alejandra Mónica. "Drying shrinkage and crack formation /". Zürich, 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10754.
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Yasaee, Mehdi. "Interlaminar crack arrest in composites". Thesis, University of Bristol, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566834.
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The formation of damage in a fibre reinforced polymer composite is, in the absence of plastic deformation, an inevitable feature of the various mechanisms by which energy is absorbed. To develop a damage tolerant composite material it is essential to understand and characterise the expected damage morphologies and subsequently design to mitigate their manifestation. Methods to achieve this have typically been attempted via optimised laminate stacking sequences or development of increasingly stronger and tougher constituents. However, an alternative approach towards damage tolerance could be to manipulate and control the formation and location of damage patterns using techniques that are generic in their application and non-detrimental to the global properties of the composite. The overarching aim of this research project was to identify a technique and demonstrate its ability to suppress interlaminar crack growth in a composite laminate under compressive loading. Initial literature review on the subject of interlaminar crack arrest determined six different techniques as potential candidates for the purpose of suppression and manipulation of delamination propagation within a composite material. These methods where subsequently explored experimentally which helped highlight discrete interleaved materials as the most promising technique. Further investigation of interleaving materials aided in characterisation of various interleaved material types with thermoplastic films exhibiting the most desirable properties. Discretely spaced thermoplastic films were then implemented in a composite panel and successfully shown to suppress delaminations induced through low velocity impact tests. Simulations studies confirmed that influence of delaniination interface location on the compressive strength of composite dominates over the overall damage footprint area. Further experimental tests successfully demonstrated the control of delamination damage propagation in a panel under cyclic compressive loading using discrete interleaved films. Although current practice for composites design in safety critical applications is to employ a 'no growth' damage tolerance design philosophy, the hypothesis of this study was to promote a re-evaluation of this mind set. There are many potential application of the proposed technique which raises stimulating suggestions for future work.
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Sjoberg, Brian David. "Crack widths in reinforced concrete". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ38642.pdf.
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Hodgkins, Andrew D. "Crack propagation in nuclear graphite". Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488486.
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Li, Junhong. "Elastic - plastic interfacial crack problems". Thesis, University of Glasgow, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297517.
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Ahmad, Haider Yousif. "Fatigue crack growth at notches". Thesis, University of Sheffield, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360410.
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Dumpleton, P. "Fatigue crack propagation in polyethylene". Thesis, Cranfield University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373987.
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Shin, C. S. "Crack growth at stress concentrations". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355680.
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Nakamura, Takatoshi. "Fatigue crack initiation in weldments". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/38349.
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Thesis (Ocean. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1994, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994.Includes bibliographical references (leaves 160-162).
by Takatoshi Nakamura.
M.S.
Ocean.E.
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Zanganeh, Mohammad. "Experimental investigation of crack paths". Thesis, University of Sheffield, 2009. http://etheses.whiterose.ac.uk/14645/.
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The knowledge of crack path mechanism could improve the safety issues, design and finally reduce the cost of the maintenance or production of structures in aerospace and energy industries. However, the physical mechanism behind the crack path development is not still completely understood although many criteria have been developed to predict the crack path. It is even more challenging to predict the crack trajectory in areas such as multi site damage zones where there are interactions between cracks. A study has been undertaken on sets of cracks with different interaction properties, both numerically, using a finite element (FE) method, and experimentally, using Thermoelastic Stress Analysis (TSA) where the effectiveness of three of the most common criteria was assessed. It was shown that the crack paths are not always repeatable as expected by FE models. It was found that the crack path criteria are capable of an acceptable prediction only in the early stages of the crack growth. Furthermore, the Stress Intensity Factors (SIF) only partially control the crack path and it has been recognised that the T -stress is one the influential parameters of the crack trajectory. Despite the vital role of T-stress, not only in directional stability problems but also in crack growth rate and the shape and size of the plastic zone ahead of the crack tip, little attention has been paid to experimentally determine the T-stress. Therefore, based on both Muskhelishvili's and Williams' approaches, methodologies were developed to determine the SIF and the T -stress from both stress field and displacement data generated artificially and using a finite element method. These methodologies were successfully employed to experimentally determine the SIF and the T -stress for different types of notched and fatigue cracked specimens manufactured from Al 7010 T765 I using TSA and Digital Image Correlation (DIC) technique. It was shown that the Muskhelishvili's approach is equivalent to the Williams' 2 terms stress solution for SIF determination. However, the 2 terms solution is not sufficient to determine the T -stress and, three or more terms are needed both from the stress and displacement fields. Results obtained from the stress field are numerically unstable if more than four terms are used. However, results obtained from the displacement field show more robustness with an increased number of terms.
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Butrym, Brad A. "Crack Detection in Aluminum Structures". Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/32276.
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Structural health monitoring (SHM) is the process of using measurements of a structureâ s response to known excitations and trying to determine if damage has occurred to the structure. This also fits the description of non-destructive evaluation (NDE). The main difference is that NDE takes place while the structure is out of service and SHM is intended to take place while the structure is in service. As such, SHM provides the opportunity to provide early warning against structural failure. This thesis intends to advance the state of the art in SHM by examining two approaches to SHM: vibration based and impedance based, and to associate these with the NDE method of stress intensity factors. By examining these methods the goal is to try and answer some of the important questions in SHM process. The first is to experimentally validate a crack model and to see how small of a crack can be detected by vibration methods. The second is to use the concept of stress intensity factor to perform an SHM type of measurement to determine the remaining life of a structure once the impedance method has determined that damage has occurred.
The measurement system considered consists of using several different piezoceramic materials as self-sensing actuators and sensors. The structures are a simple beam and a more complex lug element used in aircraft applications. The approach suggested here is to use the impedance and vibration methods to detect crack initiation and then to use the proposed stress intensity method to measure the stress intensity factor of the structure under consideration.Master of Science
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Sheu, Yih-Chyun. "Dynamic elastic-viscoplastic crack growth /". The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487587604133479.
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Abrahams, Ayesha. "The Crack in the Mountain". Master's thesis, Faculty of Humanities, 2020. http://hdl.handle.net/11427/32437.
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Mohammed, Ilyas. "Crack nucleation from bimaterial corners /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Xu, Linlin 1963. "Stress singularities at crack corners". Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/291540.
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In this thesis the stress and displacement fields near an embedded crack corner in a linear elastic medium are analytically computed. The conical-spherical coordinate system is introduced to solve this problem. It is observed that the strength of the stress singularity is dependent on the angle of the crack corner. The singularity becomes weaker, varying from r⁻¹ to r⁰, as the angle of the crack corner varies from 360° to 0°. Both symmetric and skew-symmetric loadings give the same variation of the behavior of the stress singularity. It is also observed that the order of the singularity is independent of Poisson's ratio, unlike the corner cracks at a free surface where Poisson's ratio sects the results.
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Gualandi, Gabriele. "Crack modeling and crack propagation in structures using damage model and extended finite element techniques". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/3931/.
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Le, Page Brian Hamilton. "The assessment and behaviour of crack bridging and crack accommodating protective coatings on reinforced concrete". Thesis, University of Surrey, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244776.
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The ingress of carbon dioxide and chloride ions into reinforced concrete can cause corrosion of the steel reinforcement. Cracks and poor quality cover can accelerate this process. Coating the surface of the concrete can increase the life of the structure. A coating must have the ability to bridge cracks that form in the substrate concrete and to accommodate any subsequent movement of that crack without failure. If the coating itself is damaged by substrate cracking then the coating becomes less effective as it no longer provides a barrier to the deleterious agents. There are currently few methods to assess the performance of a coating on a reinforced concrete surface subject to crack formation and subsequent movement. In this thesis a test specimen, machine and methodology are developed to evaluate the crack bridging and crack accommodation performance of these coatings. The specimen is 40mm x 40mm x 160mm mortar prism, coated on one face and axially reinforced with an 8mm steel bar. A crack in the specimen is opened by the application of a tensile load to the ends of the reinforcing bar by a pneumatically powered testing machine. Initial investigations confirmed that the testing machine was reliable and gave reproducible results. A testing program was then carried out to investigate the effects of temperature, coating thickness, artificial weathering and crack width on the crack bridging and crack accommodation behaviour of the coatings. It was found that increasing the thickness of a coating allowed wider cracks to be bridged. Crack accommodating behaviour was found to fall into three regions dependent upon the test temperature. At the lowest temperatures both crack bridging and crack accommodation did not occur. As the temperature was increased crack bridging and crack accommodation occurred but the crack accommodation behaviour was highly variable. As the temperature was increased further a region is encountered where reliable crack bridging and crack accommodation occurred and the variability in crack accommodation behaviour was reduced. Artificial weathering was found to have a detrimental effect on both crack bridging and accommodation performance
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McMaster, Fraser J. "The effects of load interaction on fatigue crack growth and crack closure in aluminium alloys". Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297844.
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Powell, Dawn Louise. "Maternal attitude towards unborn child in crack cocaine using and non-crack cocaine using mothers". DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 1994. http://digitalcommons.auctr.edu/dissertations/2578.
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The overall objective of this descriptive research was to show that there was no significant difference between the maternal attitude towards the unborn child in crack cocaine using and non-crack cocaine using mothers. The population was comprised of a total of 30 subjects, 15 crack cocaine users and 15 non-crack cocaine users, who were patients at Maternity and Infant Health in the Metropolitan Cleveland, Ohio area. The results revealed that there is statistical significance between the attitudes of crack cocaine using and non-crack cocaine using mothers. This statistical significance revealed that pregnant women that abuse crack cocaine during pregnancy have the same attitude towards their unborn child as pregnant women who do not abuse crack cocaine during pregnancy.
This study was an attempt to provide a clear understanding about crack cocaine addiction, the effects the addiction has on an unborn child and school age children and how pregnant women feel towards themselves and their unborn baby.
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Loureiro-Homs, Jordi. "Modelling of TMF Crack Growth in Polycrystalline Gas Turbine Alloys : Accounting for Crack Closure Effects". Licentiate thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-170275.
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The main objective of the work presented in this Licentiate of Engineering thesis is to investigate and model the fatigue crack propagation behaviour of the nickel-based superalloy Inconel 792, with special attention to the industrial lifing of high-temperature components. In-phase (IP) crack propagation tests have been performed at different temperatures and loading regimes, including extended hold times. The observations from these tests have been the basis for establishing several hypotheses to describe the crack growth behaviour, which progressively have been verified experimentally and numerically. Most prominently, it has been observed that crack closure has a substantial impact on crack growth and can explain, to a large degree, the crack growth behaviour for this material under the conditions studied. This phenomenon has been observed experimentally and modelled numerically to extend further the precision of the methodology.Huvudsyftet med arbetet som presenteras i denna licentiat avhandling är att undersöka och modellera utmattnings sprickväxtbeteendet hos den nickelbaserade superlegeringen Inconel 792, med särskild uppmärksamhet riktad mot liuslängsdmodellering av högtemperaturkomponenter i en industriell kontext. I-fas (IP) sprickväxtprov har utförts vid olika temperaturer och belastningsregimer, inklusive hålltider. Observationerna från dessa tester har legat till grund för hypoteser för att förklara spricktillväxtbeteende, vilka successivt har verifierats experimentellt och numeriskt. Mest framträdande har det observerats att sprickslutning har en väsentlig inverkan på sprickväxten, och kan i stor utsträckning förklara sprickväxten för detta material under studerade förhållanden. Detta fenomen har observerats experimentellt och modellerats numeriskt för att förbättra metodens precision.
Ytterligare forskningsfinansiär: Siemens Energy through "Turbines for Future Energy Systems" (Turbiner forframtidens energisystem), Grant No.44100-1
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WATANABE, Katsuhiko, Hideyuki AZEGAMI i Yasuo HIRANO. "An Evaluation of the Fracture Resistance of a Stably Growing Crack by Crack Energy Density (2nd Report, Application to a Ductile Crack in Thin Plate)". 日本機械学会, 1986. http://hdl.handle.net/2237/12160.
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Deogekar, Sai Sharad. "A Computational Study of Dynamic Brittle Fracture Using the Phase-Field Method". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439455086.
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Kim, Dong Sub. "Analysis of fatigue crack propagation behavior of a surface crack at fillet toe of tubular joints /". The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487668215808373.
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