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Tesi sul tema "R-curve"
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1
Dourado, Nuno Miguel Moura Marcelo de Valentin Gérard. "R-Curve behaviour and size effect of a quasibrittle material wood /". S. l. : S. l. : Bordeaux 1 ; Universidade do Porto (Portugal), 2008. http://ori-oai.u-bordeaux1.fr/pdf/2008/DOURADO_NUNO_2008.pdf.
Testo completoAbstract (sommario):
Thèse de doctorat : Sciences physiques et de l'ingénieur. Mécanique : Bordeaux 1 : 2008. Thèse de doctorat : Sciences physiques et de l'ingénieur. Mécanique : Universidade do Porto (Portugal) : 2008.Titre provenant de l'écran-titre.
2
Dourado, Nuno Miguel. "R-Curve behaviour and size effect of a quasibrittle material : wood". Thesis, Bordeaux 1, 2008. http://www.theses.fr/2008BOR13734/document.
Testo completoAbstract (sommario):
Ce travail concerne des expériences mécaniques, des analyses numériques et des modélisations analytiques de la rupture cohésives (Mode I), vis-à-vis de l’étude du comportement mis en évidence par la courbe de Résistance (Courbe-R) et l’effet d’échelle de structures entaillées en bois massif. Des expériences de fissuration sont combinées à des analyses numériques pour déterminer les propriétés de rupture au moyen d’une procédure appelée Théorie de la Mécanique de la Rupture Linéaire Élastique équivalente (TMRLE), basée sur la complaisance de la structure. La courbe-R, obtenue à partir des expériences, selon une méthode de correction du poids propre, montre l’existence d’un domaine endommagé (Zone de Processus de Rupture) de taille non négligeable se développant en fond de fissure. Dans des conditions de fissuration stationnaire, ce domaine atteint une taille critique, et l’énergie nécessaire pour faire propager la fissure avec ce domaine endommagé (par unité de surface de rupture), reste constante. Le taux de libération de l’énergie de fissuration ainsi attendu, joue un rôle important en Mécanique de la Rupture, car il est possible simuler le comportement quasi-fragile du matériau en combinaison avec les autres propriétés de cohésion. La loi d’effet d’échelle de Bažant, utilisée pour prévoir l’influence de la taille sur la contrainte nominale, est estimée à partir de la réunion de deux comportements asymptotiques réalisés sur de petites tailles (Analyse limite ou RdM) et des grandes tailles. Une procédure analytique est présentée pour évaluer le comportement asymptotique additionnel exhibé par la contrainte nominale dans le régime intermédiaire, de façon plus exacte. Une validation numérique est présentée, et l’information expérimentale vient confirmer ce comportement asymptotiqueThis work concerns the mechanical testing, numerical analysis and modelling of cohesive fracture (Mode I) on the purpose to study the Resistance-curve behaviour and the size effect in wooden notched structures. The mechanical testing is combined with the numerical analysis to evaluate fracture properties by means of an equivalent LEFM approach based on the structure compliance. The Resistance-curve being revealed from the experiments, by means of a self-weight compensation method, correction puts into evidence that a non-negligible damaged domain (Fracture Process Zone) is under development in the crack front during the loading process. This being the case, among other fracture parameters issued from the Resistance-curve, the critical (asymptotic) energy release rate is determined, turning possible to use it in combination with other cohesive crack properties in the crack modelling (in Mode I). Thus, for a given geometry it is possible to monitor the critical dimension being revealed by the Fracture Process Zone (FPZ) during the crack propagation. The well known Bažant’s size effect law provides the scaling of the nominal strength through the asymptotic matching performed both on the small (Strength Theory) and on the large (LEFM) structure sizes. An analytical procedure is proposed to determine an additional asymptotic regime in the intermediate size range through a more accurate manner. Numerical validations of the proposed procedure are made and experimental data is presented revealing the scaling of the nominal strength through an envelop of values
3
Bernardini, Chiara. "Un risultato di h-principle per curve a curvatura costante in R^n". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21250/.
Testo completoAbstract (sommario):
Oggetto di questa tesi è mostrare che ogni curva liscia immersa nello spazio euclideo n-dimensionale, può essere deformata in una curva con curvatura costante, mediante una perturbazione arbitrariamente piccola della curva iniziale e delle sue rette tangenti. Tale valore costante della curvatura deve essere maggiore o uguale del massimo della curvatura della curva iniziale, e si dimostra che tale limite inferiore è ottimale. Questo significa che le curve lisce di curvatura costante, soddisfano, secondo la terminologia di Gromov, il `relative C^1-dense h-principle' nello spazio delle curve immerse in R^n.
4
Cheung, C. M. S. "The R-curve approach for the fracture assessment of an aluminium alloy bridge". Thesis, Swansea University, 2001. https://cronfa.swan.ac.uk/Record/cronfa42424.
Testo completoAbstract (sommario):
A result of fatigue testing on a full scale aluminium alloy bridge, which is used by the military for temporary crossings, showed an unexpected increase in fracture resistance, compared with its plane strain K[IC]. This increase was due to a combination of low constraint and large stable crack extension in the bridge components. Previous work had attributed the increase to the loss of constraint alone, but the present work shows stable cracking is equally important. The effect of stable cracking in the bridge alloy was first examined experimentally in large 25mm thick 3PB specimens which were analysed numerically using the finite element method. The numerical 2-D results provided a concave J[R]-curve showing that dJ[R]/da rises increasingly with crack extension. This increase is associated with the transition from flat to slant fracture in the experimental test pieces, due to the loss of plane strain constraint. Fracture assessment using the R-curve approach showed that long cracks, both in large fracture mechanics specimens and the bridge girder, are stable because, although for a given load, G=J[R], dG/dadJ[R]/da when G=J[R]. The J[R]-curve for low constraint geometries should be indexed by the T-stress. The fatigue crack growth rate for the bridge alloy, taken from different sources, was compared. The Paris law index was nearly 4 for large CT and tension specimens, but only about 2 from fatigue tests on a full-scale bridge. For a large tension specimen, the corresponding K[IC] at the change in index was delayed from 35 (the plane strain K[IC] value) to 48MPa√m, because of the effect of low constraint. A simple model based on the J[R]-curve (at initiation) was developed for predicting crack extension under high cyclic load (K[max] > K[IC]), but with limited success.
5
Heinrich, Benedikt [Verfasser], e Heinrich von [Akademischer Betreuer] Weizsäcker. "Curve interactions in R^2: An analytical and stochastical approach / Benedikt Heinrich. Betreuer: Heinrich von Weizsäcker". Kaiserslautern : Technische Universität Kaiserslautern, 2013. http://d-nb.info/1044294183/34.
Testo completo
6
Colafemea, Angelo Antonio. "Modelamento numérico da técnica de normalização linear para determinação de curvas J-R". Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-20092016-115454/.
Testo completoAbstract (sommario):
Neste trabalho os resultados da metodologia de normalização de E. D. Reese e K. H. Schwalbe para a obtenção de curvas J-R, são comparadas com aquelas obtidas pela tradicional Técnica de Variação de Flexibilidade Elástica. Ambos os métodos foram aplicados à um aço de grau nuclear A508-CL3A, quando vários corpos-de-prova miniaturizados 0.394TC[S], foram testados em temperaturas típicas de operação de vasos de pressão nuclear. Corpos-de-prova miniaturizados formam tratados termicamente tentando simular o comportamento exibido pelos aços estruturais quando submetidos à diferentes níveis de exposição de nêutrons, sendo que outros foram ensaiados na condição de como-recebidos. Todos os procedimentos experimentais e analíticos empregados neste estudo foram totalmente computadorizados, incluindo aquisição e refinamento dos dados e o traçado da curva J-R. Esta última foi realizada conforme a mais recente versão das normas ASTM, denominada ASTM-E1820. As variáveis avaliadas influentes do comportamento das curvas de J-R, incluem o incremento de propagação de trinca e o número de pontos de dados de carga versus deslocamento. Também foi analisada a efetividade do método de normalização quando comparada com a técnica de variação de flexibilidade elástica. Os resultados desta pesquisa mostraram que a normalização é uma metodologia confiável e muito simples, tão logo a programação de software seja desenvolvida, para ser aplicada em uma vasta variação de comportamentos mecânicos como amostrados neste estudo.In this research, results from Reese; Schwalbe (1993) linear normalization methodology for deriving J-R curves are compared to those obtained from the traditional unloading elastic compliance technique. Both methodologies were applied to a nuclear grade steel A508-CL3A. Several miniaturized 0.394TC[S] specimens, were tested at typical NPV operating temperatures. Small scale testpieces were heat treated aiming to simulate the embritlemment exhibited by the structural steel when submitted to different levels of neutron exposure, whereas other specimens were tested in the as-received condition. All experimental and analytical procedures employed in this study have been fully computerized, including data acquisition, data refinement and J-R curve plotting, when the guidelines supplied by most recent version of ASTM standard for J-R curves, namely ASTM-E1820, were followed. The assessed variables affecting J-R curves behavior comprised crack propagation increment, number of load-Ioad line displacement data points, and it was also analyzed the agreement of the normalization method when compared to the compliance technique. Research results have shown that linear normalization is a trustworthy and very simple methodology to be applied in a vast range of mechanical behavior as sampled in this study, as long as computer programming is employed.
7
Zúñiga, Munizaga Andrés Jahir. "Entire solutions to the inhomogeneous allen-cahn equation in R^2, with a transition on a noncompact curve". Tesis, Universidad de Chile, 2012. http://www.repositorio.uchile.cl/handle/2250/111186.
Testo completoAbstract (sommario):
Ingeniero Civil MatemáticoEste trabajo de memoria de título presenta un estudio de la ecuación de perturbación singular de Allen-Cahn con inhomogeneidad: \begin{equation}\ep^2\div\left(a(x)\cdot\nabla_{x}u(x)\right)+a(x)f(u(x))=0,\quad\text{ en }\quad\R^2 \label{AllenCahnEq}\end{equation} donde $\varepsilon>0$ es un parámetro pequeño, $a(x)$ es un potencial uniformemente positivo y suave, que induce una forma de medir distancias para puntos en $\R^2$, y $f$ es la nolinealidad dada por $f(u)=u-u^3$. El estudio aborda la construcción de soluciones enteras de~\eqref{AllenCahnEq}, bajo la condición que $u$ se anule cerca de una curva $\Gamma\subset \R^2$. El enfoque propuesto asume que $\Gamma$ es una curva no acotada, geodésica no-degenerada relativa al funcional de longitud de arco $\int_{\Gamma}a(\vec{x})$, con curvatura $k_{\Gamma}$ suave que decae a una tasa polinomial. Es de interés el estudio de la ecuación de Allen-Cahn con presencia de un término de inhomogeneidad $a(x)\not\equiv 1$, ya que esto conlleva el estudio de curvas geodésicas para una métrica no trivial de $\R^2$. Además, es relevante considerar que el conjunto nodal de $u$ yace cerca de una curva no acotada, pues esto se refleja en el estudio de ecuaciones diferenciales en contextos no compactos. El resultado principal asegura la existencia de una solución de~\eqref{AllenCahnEq}, la cual converge exponencialmente a $\pm 1$ cuando $x$ se aleja de $\Gamma$. Un segundo resultado entrega ejemplos de potenciales $a(x)$ y curvas $\Gamma$, para los cuales es posible construir una solución $u$ con el comportamiento antes descrito. La demostración de este resultado está basada en una técnica conocida como reducción infinito dimensional de Lyapunov-Schmidt, la cual motiva a la elección de un candidato a solución del tipo $u = w + \phi$, donde $w$ en coordenadas adecuadas resuelve $w''+f(w)=0$, y determina el perfil de $u$ a orden principal. Además $\phi$ es una función de corrección, con el fin de convertir a $u$ en solución exacta de~\eqref{AllenCahnEq}, lo que obliga a $\phi$ a resolver una ecuación diferencial no lineal. De ahí en más, el problema consiste en estudiar la existencia y unicidad de la última ecuación en un espacio funcional adecuado. Esto se realizó analizando el operador linealizado asociado a la ecuación de Allen-Cahn, y luego el problema no-lineal que es resuelto mediante un esquema de punto fijo. Para el ultimo análisis, fue necesario ajustar $\Gamma$ en un parámetro de perturbación $h$, lo que equivale a una EDO no lineal en $h$ donde participa la segunda variación del funcional de largo $l_{a,\Gamma}$ asociado a $\int_{\Gamma}a(\vec{x})$. Finalmente, el método utilizado no sólo provee la existencia de una solución $u$ de~\eqref{AllenCahnEq}, sino que además entrega una caracterizacón completa de ésta, tanto en tamaño como en comportamiento cualitativo en coordenadas relacionadas a la curva $\Gamma$.
8
Pásztor, Bálint. "Analýza přežití v R". Master's thesis, Vysoká škola ekonomická v Praze, 2015. http://www.nusl.cz/ntk/nusl-202126.
Testo completoAbstract (sommario):
Survival analysis is a statistical discipline that analyzes the time to occurrence of certain events. The aim of this thesis is to describe the possibilities of survival analysis in the environment of statistical software R. Theoretical knowledge is applied to real data, parametric and nonparametric estimates of survival functions are evaluated by different methods and compared with each other. In the section focusing on nonparametric models Kaplan-Meier and Nelson-Aalen functions are described. Among the parametric estimates there were included well-known probability distributions, survival functions and risk functions derived from these distributions are presented and there is discussed their usefulness in survival analysis. Another aim is to show the possibility of deriving transition probabilities from estimates and building a Markov chain model to capture the changes of studied cohort over time. The second part of the work contains a description of the applications of the theory of survival analysis. In this section there are shown possibilities of statistical modeling in the field of survival analysis using the software R. Outputs from R were used to create Markov model. There are presented possibilities of pharmacoeconomic models and description of the basic concepts of HTA. Cost-effectiveness calculations using ICER were conducted in accordance with the methodology of SUKL. It was shown that the statistical modelling of survival plays an important role in the evaluation of the cost-effectiveness of medicines.
9
Dzugan, Jan. "Crack lengths calculation by unloading compliance technique for Charpy size specimens". Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29077.
Testo completoAbstract (sommario):
The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that measured compliance should be corrected for various factors, but satisfying results were not attained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for the specimens of different than Charpy size.
10
Tilbrook, Matthew Thomas Materials Science & Engineering Faculty of Science UNSW. "Fatigue crack propagation in functionally graded materials". Awarded by:University of New South Wales. Materials Science & Engineering, 2005. http://handle.unsw.edu.au/1959.4/21885.
Testo completoAbstract (sommario):
Propagation of cracks in functionally graded materials (FGMs) under cyclic loading was investigated via experiments and finite element (FE) analysis. Alumina-epoxy composites with an interpenetrating-network structure and tailored spatial variation in composition were produced via a multi-step infiltration technique. Compressed polyurethane foam was infiltrated with alumina slip. After foam burn-out and sintering, epoxy was infiltrated into the porous alumina body. Non-graded specimens with a range of compositions were produced, and elastic properties and fatigue behaviour were characterised. An increase in crack propagation resistance under cyclic loading was quantified via a novel analytical approach. A simulation platform was developed with the commercial FE package ANSYS. Material gradient was applied via nodal temperature definitions. Stress intensity factors were calculated from nodal displacements near the crack-tip. Deflection criteria were compared and the local symmetry criterion provided the most accurate and efficient predictions. An automated mesh-redefinition algorithm enabled incremental simulation of crack propagation. Effects of gradient and crack-geometry parameters on crack-tip stresses were investigated, along with influences of crack-shape, crack-bridging, residual stresses and plasticity. The model provided predictions and data analysis for experimental specimens. Fatigue cracks in graded specimens deflected due to elastic property mismatch, concordant with FE predictions. In other FGMs, thermal or plastic properties may dominate deflection behaviour. Weaker step-interfaces influenced crack paths in some specimens; otherwise effects of toughness variation and gradient steps on crack path were negligible. Crack shape has an influence, but this is secondary to that of elastic gradient. Cracks in FGM specimens initially experienced increase in fatigue resistance with crack-extension followed by sudden decreases at step-interfaces. Bridging had a notable effect on crack propagation resistance but not on crack path. Similarly, crack paths did not differ between monotonic and cyclic loading, although crack-extension effects did. Recommendations for analysis and optimisation strategies for other FGM systems are given. Experimental characterization of FGMs is important, rather than relying on theoretical models. Opportunities for optimization of graded structures are limited by the properties of the constituent materials and resultant general crack deflection behaviour.
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Dzugan, Jan. "Crack lengths calculation by unloading compliance technique for Charpy size specimens". Forschungszentrum Rossendorf, 2003. https://hzdr.qucosa.de/id/qucosa%3A21733.
Testo completoAbstract (sommario):
The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that measured compliance should be corrected for various factors, but satisfying results were not attained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for the specimens of different than Charpy size.
12
Sorin, Edouard. "Fissuration en modes mixtes dans le bois : diagnostic et évaluation des méthodes de renforcement local". Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0264/document.
Testo completoAbstract (sommario):
Cette thèse s’effectue au sein de l’université de Bordeaux. Ce projet concerne la construction en bois et en particulier la compréhension des phénomènes à l’origine des fissures dans les structures bois. L’un des objectifs étant de concevoir des méthodes efficaces de renforcement local pour les éléments de structure. Pour cela, l’étude se décompose en plusieurs étapes, la compréhension des phénomènes mis en jeu dans la création des fissures sur des bois de construction. Ce travail s’orientera sur la modélisation de fissure en mode mixte, la recherche de solution de renforcement avec compréhension fine de l’impact de types de renforts sur la propagation de la fissure. Cette étude sera accompagnée d’une campagne d’essais, afin de vérifier l’efficacité des renforcements choisis et d’identifier l’impact de l’effet d’échelle sur les modèle de prédiction. Des essais de grandes dimensions seront donc réalisés pour mieux appréhender les effets de groupes et les effets d’échelle sur du matériau d’emploi. On vise ensuite à définir des outils prédictifs de la résistance des systèmes renforcés et de moyens de contrôles pour les Plan d’Assurance QualitéThe purpose of reinforcing assemblies and structural elements inwood is to overcome the resistance limits of the material, by transferring greaterefforts in areas which can lead to premature cracking in structures. The reinforcementsused can be made of steel, composite materials or wood. Their hook can bemechanical (screwed bodies) or by adhesion (structural bonding like glued-in rodsfor example). In both cases, the transfer of solicitations remains poorly known, andthe effect of the beginning and the deflection of crack are not well apprehended. Inengineering techniques, the wood resistance in the reinforced area is neglected, whichis in line with the precautionary principle. Currently, the scientific investigations areinterested in the resistance of those kind of techniques without considering the interactionsbetween the quasi-brittle behavior of the wood and the reinforcementswhich govern the gain in mechanical performance. However, these solutions can leadto a failure caused by the progressive splitting of the wood and the anchor loss ofthe reinforcement. So it seems accurate to propose predictions of the short-termstrength for splitting of reinforced and unreinforced beams, which can be used tofurther exploration of the long-term failure mechanism. That is why, in this study, aglobal prediction model of the ultimate strength of structural components subjectedto splitting, reinforced and unreinforced ones, was developed. It considers the quasibrittlebehavior of the wood and crack propagation in mixed mode, using a mixinglaw established on the R-curves. The relevance of this modeling was then comparedto the current dimensioning methods of the Eurocodes 5, for notched beams, withexperimental campaigns conducted at different scales
13
Stratil, Luděk. "Určování lomově-mechanických charakteristik z podrozměrných zkušebních těles". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-234223.
Testo completoAbstract (sommario):
The standards of fracture toughness determination prescribe size requirements for size of test specimens. In cases of limited amount of test material miniature test specimens offer one from the possibilities of fracture toughness evaluation. Because of small loaded volumes in these specimens at the crack tip the loss of constraint occur affecting measured values of fracture toughness. In such cases the size requirements for valid fracture toughness characteristics determination are not fulfilled. These specimens can be even on limits of load range of test devices and handle manipulation by their small dimensions. The important task related to these specimens is, apart from methodology of their preparation and measurement of deformations, the interpretation of measured values of fracture toughness and their possible correction to standard test specimens. Moreover, in the upper shelf region of fracture toughness quantification and interpretation of size effects is still not resolved sufficiently. This thesis is by its aims experimentally computational study focused on evaluation of size effect on fracture toughness in the upper shelf region. The size effect was quantified by testing of miniature and large specimens’ sizes in order to determine J R curves. Two geometries of miniature test specimens, there point bend specimen and CT specimen, were used. The experimental materials were advanced steels developed for applications in nuclear and power industry, Eurofer97 steel and ODS steel MA956. Finite elements analyses of realized tests together with application of micromechanical model of ductile fracture were carried out in order to evaluate stress strain fields at the crack tip in tested specimens from Eurofer97 steel. By comparison of experimental results and numerical simulations of J R curves the mutual dependencies between geometry of specimens and element sizes at the crack tip were derived. On the basis of acquired relationships, the methodology of J R curve prediction for standard specimen size from limited amount of test material was proposed. Main contribution of thesis is description of effect of material’s fracture toughness level on resistance against ductile crack propagation in miniature specimens. For material where significant crack growth occurs after exceeding the limit values of J integral (Eurofer97), the loss of constraint is considerable and highly decreases resistance against tearing. Miniature specimens then show significantly lower J R curves in comparison with standard size specimens. This effect is the opposite to the behaviour of miniature specimens in transition region. In case of material with low toughness, in which significant crack growth occurs in the region of J integral validity (ODS MA956), the effect of constraint loss is small without large impact on resistance against tearing. In such case miniature specimens demonstrate comparable J R curves as specimens of larger sizes. Next important contribution is proposed methodology for prediction of J R curve from small amount of test material using micromechanical modeling.
14
Adamiec, Grzegorz. "Aspects of pre-dose and other luminescence phenomena in quartz absorbed dose estimation". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325679.
Testo completo
15
Holas, Jiří. "Testování lomové houževnatosti za vysokých teplot s využitím miniaturních CT těles". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231783.
Testo completoAbstract (sommario):
This master´s thesis deals with the evaluation of fracture behavior of ODS steel MA956 at high temperature range. This behavior was tested by using miniaturized CT specimens, on which were performed experiments to measure of ductile crack growth resistance curves (J-R curves). The value of the fracture toughness was determined from these J-R curves. Fracture properties were consequently evaluated by using fractographic analysis of the fracture surfaces. Structural properties of material was identified by hardness measurement and analyzed by metallographic methods. Results of the measurements show drop of the fracture toughness with respect to the increasing temperature.
16
Mrňa, Tomáš. "Vliv velikosti tělesa na R-křivku a na otupení čela trhliny". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-242858.
Testo completoAbstract (sommario):
The thesis deals with the determination of fracture toughness using compact tension (CT) test specimens at elevated and high temperatures. The experimental material steel P91 designated for application at temperatures 550650°C was used. The fracture toughness in the ductile fracture region of the steel was characterized by the R curve, which characterises the resistance against crack propagation depending on the crack length. The effect of temperature on the R curve at range 23600°C was evaluated. Next the specimen size effect using three sizes of CT specimens at 23°C and the effect of loading rate (2, 0,2 a 0,02 mm/min) at 600°C was examined. The results showed that the temperature has distinct effect on the R-curve, which yields minimal values at 400°C. Only the smallest test specimen size with thickness 6.25mm showed the specimen size effect giving about 10% lower values of toughness comparing to larger specimens. The effect of loading rate was clearly distinguishable. The values of toughness varied about 20% of the toughness value comparing individual loading rate.
17
Lokvenc, Martin. "Testování lomové houževnatosti za vysokých teplot s využitím miniaturních CT těles". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231784.
Testo completoAbstract (sommario):
This thesis deals with a high temperature testing of fracture toughness and studies the size effect on measured values using miniature size CT specimen. Two types of specimen geometry were manufactured from P91 steel, the standard size and the quarter size specimen. J-R curves were obtained in the temperature range from 23°C to 600°C. No specimen size effect was observed at room temperature tests. The realized experiments together with fractography analysis demonstrated the drop of toughness at 400°C caused by the effect of dynamic strain aging.
18
坂井田, 喜久, Yoshihisa SAKAIDA, 啓介 田中 e Keisuke TANAKA. "多孔質セラミックスの破壊靭性評価". 日本機械学会, 2001. http://hdl.handle.net/2237/9161.
Testo completo
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SAKAIDA, Yoshihisa, e Keisuke TANAKA. "Evaluation of Fracture Toughness of Porous Ceramics". The Japan Society of Mechanical Engineers, 2003. http://hdl.handle.net/2237/9181.
Testo completo
20
Eu, David. "Polygonal curve approximation". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56992.
Testo completoAbstract (sommario):
Given a polygonal curve $P = lbrack p sb1,p sb2 ... p sb{n} rbrack$, the polygonal approximation problem considered in this thesis calls for determining a new curve $P sp prime = lbrack p sbsp{1}{ prime}, p sbsp{2}{ prime}, ..., p sbsp{m}{ prime} rbrack$ such that (i) m is significantly smaller than n, (ii) the vertices of $P sp prime$ are a subset of the vertices of P and (iii) any line segment $ lbrack p sbsp{A}{ prime}, p sbsp{A+1}{ prime} rbrack$ of $P sp prime$ that substitutes a chain $ lbrack p sb B, ...,p sb C rbrack$ in P is such that for all i where $B le i le C$, the approximation error of $p sb{i}$ with respect to $ lbrack p sbsp{A}{ prime}, p sbsp{A+1}{ prime} rbrack$, according to some specified criterion and metric, is less than a predetermined error tolerance. Using a popular error criterion, we study the following problems for a curve P in $R sp{d}$, where $d ge 2$: (i) minimize m for a given error tolerance and (ii) given m, find the curve $P sp prime$ that has the minmum approximation error over all curves that have at most m vertices. These problems are called the min-# and min-$ varepsilon$ problems, respectively. For R$ sp2$ and with any one of the L$ sb1$, L$ sb2$ or L$ sb{ infty}$ distance metrics, we give algorithms to solve the min-# problem in $O(n sp2)$ time and the min-$ varepsilon$ problem in $O(n sp2 log n)$ time. When P is a polygonal curve in $R sp3$ that is strictly monotone with respect to one of the three axes, we show that if the $L sb1$ and $L sb infty$ metrics are used then the min-# problem can be solved in $O(n sp2)$ time and the min-$ varepsilon$ problem can be solved in $O(n sp3)$ time. If distances are computed using the $L sb2$ metric then the min-# and min-$ varepsilon$ problems can be solved in $O(n sp3)$ and $O(n sp3 log n)$ time respectively. All of our algorithms exhibit $O(n sp2)$ space complexity.
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Kramoliš, Ondřej. "Extrakce a modifikace vlastností číslicových zvukových signálů v dynamické rovině". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218782.
Testo completoAbstract (sommario):
This thesis deals with basic methods of root mean square and peak value measurement of a digital acoustic signal, algotithms to measure audio programme loudness and true-peak audio level according to recommendation ITU-R BS.1770-1 and digital systems for control of signal dynamic range. It shows achieved results of root mean square and peak value measurement and results of implementation of dynamic processor with general piecewise linear non-decreasing static curve and algorithms according to recommendation ITU-R BS.1770-1.
22
Nkgau, Tallman Zacharia. "Elliptic curve cryptosystems : a survey". Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21614.
Testo completoAbstract (sommario):
Elliptic curves have been a subject of much mathematical study since early in the past century. Recently, through the work of Koblitz and Miller, they have found application in the area of publickey cryptography. The basic reason is that, elliptic curves over finite fields provide an abundance of finite abelian groups which could be used as a basis for public-key cryptosystems. The objective of this thesis is to survey the field of elliptic curve public-key cryptography as it exists now, with an attempt to identify key ideas and contributions. We are particularly interested in elliptic curve cryptosystems defined over Zp (p > 3 and prime) and the ring Zn (n is a product of two large distinct primes).
23
Rempel, William. "Curve evolution and integrable systems". Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95240.
Testo completoAbstract (sommario):
In this thesis, we explain the connection between completely integrable systems of evolution equations and the evolution of the differential invariants of group actions in the particular case of a curve in Rⁿ acted on by an affine group defined as the semidirect product of G and Rⁿ, where G is semisimple, as it is presented in the work of Marì-Beffa. This connection involves Fels and Olver's work on the theory of moving frames, infinite-dimensional Hamiltonian systems and Poisson brackets, and centrally extended loop groups and algebras. We also summarize the relevant theory both of Lie groups and Lie algebras and of differential invariants and symmetries of differential equations. groups and algebras. We also summarize the relevant theory both of Lie groups and Lie algebras and of differential invariants and symmetries of differential equations.Dans cette thèse, on explique le lien entre les systèmes d'équations d'évolution complètement intégrables et l'évolution des invariants différentiels de l'action d'un groupe dans le cas particulier d'une courbe dans Rⁿ , sous l'action du produit semidirect d'un groupe G avec Rⁿ, où G est semisimple, tel que présenté par Marì-Beffa. Cette connection fait intervenir la théorie de repères mobiles de Fels et Olver, les systèmes hamiltoniens de dimension infinie et les crochets de Poisson, ainsi que les groupes et algèbres de lacets à extension centrale. On présente aussi un ré́sumé de la théorie pertinente des groupes et algèbres Lie et des invariants différentiels ainsi que les symmétries d'équations différentielles.
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Hemzalová, Zuzana. "Evoluční algoritmy pro ultrazvukovou perfúzní analýzu". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442504.
Testo completoAbstract (sommario):
This thesis deals with the principles of ultrasonic perfusion analysis and methods for determining perfusion parameters. It examines Evolutionary algorithms and their ability to optimize the approximation of dilution curves from ultrasond tissue scannig. It compares the optimization performance of three evolutionary algorithms. Continuous genetic algorithm GA, algorithm SOMA and PSO. Methods are evaluated on simulated and clinical data.
25
Parent, Pierre 1953. "Trace inference, curvature consistency, and curve detection". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66100.
Testo completo
26
Tarragó, Cifre Jose María. "Damage tolerance of cemented carbides under service-like conditions". Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/403888.
Testo completoAbstract (sommario):
Hardmetal industry is continuously seeking for high-performance products at reduced costs. In addition, it is strongly struggled by the high and volatile prices of raw materials. At this juncture, producers and end-users are deeply concerned in increasing the performance and enhancing service-life and reliability of engineering products, and replacing current constituents by alternative and less critical materials. Premature and unexpected fracture, together with wear, is the main damage phenomenon limiting the life in most cemented carbide applications. In the vast majority of cases such ruptures stem from the combination of high monotonic and cyclic stresses, together with different damage-related features associated with harsh service conditions, such as corrosion, and thermal shock. Therefore, relevant consideration of fracture toughness and fatigue resistance is required if reliability and lifetime of hardmetals applications is to be increased. Following the above ideas, the purpose of this thesis is to improve the performance and increase the reliability of cemented carbides in rupture-limited applications on the basis of enhanced damage tolerance and reduced fatigue sensitivity through an optimal microstructural design. Within this framework, this investigation is composed of three main subjects covering different aspects related to the performance of hardmetals under service-like conditions. The first two sections are devoted to conduct a comprehensive study on the influence of the microstructure on fracture and fatigue behaviour of hardmetals. The aim of the third section is to evaluate microstructural effects on the tolerance of cemented carbides to service-like damage, induced either by localised corrosion or thermal shock.
Main contribution to toughness in cemented carbides derives from plastic stretching of crack-bridging ductile enclaves at the crack wake, referred to as the multiligament zone. Hence, the development of a multiligament zone implies the existence of a rising crack growth resistance (R-curve) behaviour in cemented carbides. This effectiveness of this toughening mechanism is intimately related to the microstructural characteristics. Within this context, the first section of this thesis is dedicated to carry out a detailed investigation of fracture mechanics and mechanisms in cemented carbides, and to propose a relation to capture microstructural effects on the R-curve characteristics of these materials.
Strength reduction of hardmetals under the application of cyclic stresses is related to the inhibition of the crack-tip bridging mechanism. For WC¿Co cemented carbides, the degradation of bridging ligaments is mainly associated with an accumulation of the fcc to hcp phase transformation. However, this mechanism does not apply for Ni binders; therefore, it remains unclear if effective fatigue susceptibility of Co-base hardmetals is comparable to that of cemented carbides consisting of alternative binders. Moreover, hardmetals exhibit crack-deflection as an additional toughening mechanism, but contrary to the case of crack-bridging, it is immune to fatigue loads. The effective action of this toughening mechanism is speculated to increase with rising carbide mean grain size. Hence, the second part of this thesis is devoted to study and understand the fatigue sensitivity of cemented carbides consisting of binders with deformation mechanisms beyond phase transformation as well as medium/coarse microstructures.
Finally, the third section of this thesis consists of a systematic study on the influence of the microstructure on damage-related features induced by either thermal shock or corrosion, in order to set out guidelines for optimal microstructural design. In doing so, the structural integrity of damaged cemented carbides is assessed on the basis of residual strength, and microstructural effects on damage tolerance are captured by means of considering induced damage level as a critical parameter.Por un lado, la industria del metal duro está sumergida en una búsqueda constante de materiales de altas prestaciones a un coste reducido. Por el otro lado, las materias primas tienen precios altos y volátiles, que comprometen la estabilidad del mercado. En esta coyuntura, los productores y los usuarios finales están muy interesados, tanto en aumentar el rendimiento, incrementar la vida útil y mejorar la fiabilidad de estos productos, como en su sustitución por materiales alternativos y considerados menos críticos. En este contexto, el desgaste y la ruptura prematura son los dos principales mecanismos que limitan la vida útil de las aplicaciones de metal duro. En la gran mayoría de los casos las rupturas prematuras derivan de la combinación de altas tensiones, tanto monótonas como cíclicas, con el daño inducido durante la vida en servicio, como la corrosión, y el choque térmico. Por lo tanto, con el fin de aumentar fiabilidad en estas aplicaciones, es necesario entender los mecanismos de daño y fallo en estos materiales. Así, el propósito de esta tesis es mejorar el rendimiento y aumentar la fiabilidad de los carburos cementados a partir del desarrollo de materiales con una mayor tolerancia al daño y una menor sensibilidad a fatiga, a través de un óptimo diseño microestructural. La presente investigación se compone de tres partes que abarcan diferentes aspectos relacionados con el desempeño de los metales duros en condiciones de servicio. Las dos primeras secciones están dedicadas a realizar un estudio general sobre la influencia de la microestructura en el comportamiento a fractura y fatiga del metal duro. El objetivo de la tercera sección es evaluar los efectos microestructurales en la tolerancia al daño de los carburos cementados, ya sea inducido por corrosión o por choque térmico. El principal mecanismo de tenacidad en los carburos cementados reside en el estiramiento plástico de ligamentos metálicos de puenteo que se forman detrás de la punta de la grieta, llamada la zona de multiligamentos. El desarrollo del mecanismo de puenteo implica un incremento de la resistencia a fractura a medida que aumenta la longitud de la grieta. Este mecanismo es conocido como curva-R y su eficacia está íntimamente relacionada con las características microestructurales del material. Así, la primera parte de esta tesis doctoral está dedicada a llevar a cabo una investigación detallada de los mecanismos de fractura en los carburos cementados, y a proponer una relación que permita captar los efectos microestructurales en las características de curva-R de estos materiales. Por otro lado, la segunda parte de la tesis está dedicada a estudiar la influencia de la microestructura, incluyendo tanto el tamaño de grano de la fase carburo como el contenido de la fase ligante y su naturaleza química, en la sensibilidad a fatiga de los carburos cementados. Así, se ha prestado una atención particular en estudiar el comportamiento a fatiga de los carburos cementados con base níquel y en su comparación con los de base cobalto. Por otro lado, también se ha estudiado la influencia del tamaño de grano en la deflexión de grieta como un mecanismo adicional de aumento de tenacidad, inmune a las solicitaciones cíclicas. Por último, la tercera sección de esta tesis consiste en un estudio sistemático de la influencia de la microestructura de los carburos cementados en su tolerancia al daño, inducido tanto por corrosión como por choque térmico, con el fin de establecer las directrices para un diseño microestructural óptimo. De este modo, la integridad estructural de carburos cementados se evalúa sobre la base de su resistencia residual a flexión después de la inducción de daño
27
Torchiani, Carolin [Verfasser]. "Enumerative geometry of rational and elliptic tropical curves in R m / Carolin Torchiani". München : Verlag Dr. Hut, 2014. http://d-nb.info/1055863834/34.
Testo completo
28
Karastamatis, Thomas. "Measuring the R-curves of lead zirconate titanate (PZT) from a surface crack in flexure (SCF)". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16713.
Testo completo
29
Li, Zhe 1974. "The environmental Kuznets curve reexamined for CO₂ emissions in Canadian manufacturing industries /". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80319.
Testo completoAbstract (sommario):
Recent studies of the environmental Kuznets curve raise questions regarding the relationship between environmental indicators and GDP and the fundamental reasons that explain this relationship. In response, this thesis presents one-sector and two-sector models to analyze the alternative causal relationships between an environmental indicator and GDP at different stages of economic development. These models analyze how economic scale, technology, preferences, and economic structure influence the causality and shape of the relationship. These theoretical studies are followed by two empirical studies. The first tests the causal relationship between CO2 emissions and GDP in Canadian manufacturing industries. The second explores several factors as the fundamental causes that influence the CO2 emissions in the same industries. Factors, such as economic scale, preferences, technological progress, structural change, and energy input, are found to be crucial in the determination of CO2 emissions. The empirical results are positive, but there are data limitations. The empirical studies can be re-evaluated as more data becomes available.
30
Matoušek, Petr. "Vyhodnocení účinnosti komplexních ochranných opatření k.ú. Jerlochovice v povodí Husího potoka". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227551.
Testo completoAbstract (sommario):
A subject of this Thesis is the design of the complex system of measures of soil conservation in given catchment area, which will serve as a concept of complex land consolidation in cadaster Jerlochovice. Based on the analysis and the land survey, a feasible solution was designed using the hydrological and erosive tools of ArcGIS. For the identification of areas endangered by erosion and for the identification of runoff conditions, the Universal Soil Loss Equation of Wischmeier-Smith was used (in grid modification). Based on the calculated values, the suitable technical and agrotechnical measures of soil erosion control were designed. Each component was designed for the values of Qn from the model DesQ. Subsequently the efectivity of the designed measures was evaluated by the comparison of results of erosive and runoff conditions before and after the aplication of the soil and water conservation measures.
31
田中, 啓介, Keisuke TANAKA, 義明 秋庭, Yoshiaki AKINIWA, 泰樹 北, Yasuki KITA, 永次 佐藤 e Eiji SATO. "多孔質セラミックスの切欠き破壊強度のR曲線法による評価". 日本機械学会, 2003. http://hdl.handle.net/2237/9143.
Testo completo
32
Ramsay, Craig R. "Assessing the learning curves of health technologies". Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602014.
Testo completoAbstract (sommario):
Many health technologies exhibit some form of learning effect, and this represents a barrier to rigorous assessment by randomised controlled trials. There is reluctance to evaluate while the technique is being learnt, yet unwillingness to admit uncertainty once it has been learnt. In principle, statistical description of a learning curve and subsequent adjustment of an evaluation to take account of learning effects should solve this problem. Exactly how the analyses should be performed has been unclear. This thesis has three components: Systematic review of health technology assessment literature: a systematic description of studies that directly assessed the learning curve effect of health technologies. Systematic search of non-health technology assessment literature: a systematic identification of 'novel' statistical techniques applied to learning curve data in other fields, such as psychology and manufacturing. Testing of statistical methods: testing of these statistical techniques in sets of data describing a variety of health technologies where learning curve effects are known to exist.
33
Lexen, Ernst R. [Verfasser], e Peter H. [Akademischer Betreuer] Hauschildt. "Parameter sensitivity of synthetic spectra and light curves of Type Ia supernovae / Ernst R. Lexen. Betreuer: Peter H. Hauschildt". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1048626199/34.
Testo completo
34
SOARES, P. A. "Determinação da Tenacidade à Fratura do Aço API-X65 Utilizado em Tubos na Indústria de Petróleo e Gás". Universidade Federal do Espírito Santo, 2011. http://repositorio.ufes.br/handle/10/4160.
Testo completoAbstract (sommario):
Made available in DSpace on 2016-08-29T15:32:55Z (GMT). No. of bitstreams: 1
tese_5382_Dissertação de Mestrado (Polliana Alexandre Soares).pdf: 5558925 bytes, checksum: f527e57bc2fba9b5e555b52004855328 (MD5)
Previous issue date: 2011-12-27Este trabalho foi desenvolvido com o intuito de determinar a tenacidade à fratura em estruturas contendo trincas em suas juntas soldadas. O material ensaiado foi o aço API X65 que é usado em tubos na indústria de produção de petróleo e gás, por exemplo. O tubo tem diâmetro de 20 polegadas com espessura de 6,8 mm. Foram estudadas duas condições diferentes: materiais metal base e metal soldado e, para cada condição, foram ensaiados nove e oito corpos de prova, respectivamente. O processo de soldagem utilizado foi a soldagem por resistência elétrica (Electric Resistence Welding - ERW). Os corpos de prova foram confeccionados segundo a norma ASTM E 1820 01 e o critério da mecânica da fratura empregado foi o da Curva de Resistência (Curva R), que fornece o tamanho e a abertura máxima da trinca sem que ocorra a ruptura do material. A tenacidade à fratura foi verificada e o metal base e metal soldado apresentaram os mesmos valores desta propriedade. Através de microscopia eletrônica de varredura (MEV), pode-se notar que a fratura é dúctil e apresenta microcavidades (dimples) e inclusões. Na microscopia óptica, vê-se que o aço API X65 no metal base possui uma estrutura perlítica-ferrítica com grãos refinados e no metal soldado aumenta-se o tamanho dos grãos.
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Botros, Lucy L. "Windowed direct exponential curve resolution quantification of nuclear magnetic resonance spectroscopy with applications to amniotic fluid metabonomics". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100769.
Testo completoAbstract (sommario):
This thesis presents a quantitative protocol of proton nuclear magnetic resonance (1H NMR) that allows the determination of human amniotic fluid metabolite concentrations, which are then used in a metabonomic study to establish patient health during gestation. 1H NMR free inductive decays (FIDs) of 258 human amniotic fluid samples from a 500MHz spectrometer are acquired. Quantitative analyses methods in both the frequency- and time-domain are carried out and compared. Frequency-domain analysis is accomplished by integration of the metabolite peaks before and after the inclusion of a known standard addition of alanine. Time-domain analysis is accomplished by the direct exponential curve resolution algorithm (DECRA). Both techniques are assessed by applications to calibration biological solutions and a simulated data set. The DECRA method proves to be a more accurate and precise route for quantitative analysis, and is included in the developed protocol. Well-defined peaks of various components are visible in the frequency-domain 1H NMR spectra, including lactate, alanine, acetate, citrate, choline, glycine, and glucose. All are quantified with the proposed protocol. Statistical t-test and notched box and whisker plots are used to compare means of metabolite concentrations for diabetic and normal patients. Glucose, glycine, and choline are all found to correlate with gestational diabetes mellitus early in gestation. With further development, time-domain quantitative 1H NMR has potential to become a robust diagnostic tool for gestational health.
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Khor, WeeLiam. "Crack tip opening displacement (CTOD) in single edge notched bend (SEN(B))". Thesis, Brunel University, 2018. http://bura.brunel.ac.uk/handle/2438/16198.
Testo completoAbstract (sommario):
This thesis investigates the quantity Crack Tip Opening Displacement (CTOD) as a means to assess fracture toughness when measured in the Single Edge Notched Bend (SENB) specimen setup. A particular objective is to assess the effectiveness of the test when used for high strain-hardening materials (e.g. stainless steels). This has been an increasing concern as the current available methods were generally designed for lower strain hardening structural steel. Experimental work on CTOD tests included silicone casting of the crack, and constant displacement tests were also performed. The silicone castings enable physical measurement of the crack under an optical microscope. Results from a series of Finite Element (FE) models were validated from the experiments. δ5 surface measurements were obtained using Digital Image Correlation (DIC) as a courtesy of TWI, which were compared to surface CTOD measurements from the silicone castings. In addition to the experiments and Finite Element modelling, archived test data from TWI was processed, showing analytical differences between current Standard CTOD equations. CTOD calculations from BS 7448, ISO 12135, ASTM E1820 and WES 1108 were compared to the experimental and FE modelling results. For high strain hardening material, CTOD predicted by Standard equations (apart from those in BS 7448 and single point CTOD from ISO 12135) were lower than the values determined from silicone measurements and modelling. This potentially leads to over conservative values to be used in Engineering Critical Assessments (ECA) or material approval. Based on a series of different strain hardening property models, a relationship between strain hardening and the specimen rotational factor, rp was established. An improved equation for the calculation of CTOD is proposed, which gave good estimation of the experimental and Finite Element modelling results. The improved equation will be proposed for future amendments of the ISO 12135 standard. The results of this research enable the accurate fracture characterisation of a range of engineering alloys, with both low and high strain hardening behaviour in both the brittle and ductile fracture regime.
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Rosa, Vinicius. "Efeito da troca iônica nos parâmetros de Weibull, de crescimento subcrítico de trincas e no comportamento de curva R de uma porcelana odontológica". Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/23/23140/tde-03012008-102313/.
Testo completoAbstract (sommario):
O objetivo deste estudo foi avaliar o efeito da temperatura de troca iônica (TI) nas propriedades mecânicas da porcelana Ultrapaline ST e o efeito da TI nos parâmetros de crescimento subcrítico de trincas (SCG) (coeficiente de SCG - n, parâmetro escalar - ?f0), de Weibull (resistência característica - ?0, módulo de Weibull - m) e no comportamento de curva R desta porcelana. 250 discos (12 mm diâmetro x 1 mm espessura) foram fabricados de acordo com as instruções do fabricante, usinados em retificadora plana e polidos até 1 ?m. Para determinar o efeito da temperatura de TI na resistência à flexão biaxial (?), dureza (H) e tenacidade à fratura (KIc), 40 discos foram divididos em 4 grupos (n=10): GI (controle) - sem TI; e GII, GIII e GIV submetidos a TI com KNO3 por 15 min a 450°C; 470°C e 490°C, respectivamente. A ? foi determinada por \"pistão sobre três esferas\" em saliva artificial a 37°C a 10 MPa/s. Para dureza e tenacidade à fratura, foram feitas 3 indentações Vickers em cada espécime (2kg, 30s) e as diagonais e trincas radiais foram medidas e os valores de H e KIc calculados. As médias e desvios-padrão para ? (MPa), H (GPa) e KIc (MPa.m1/2) foram: GI: 57,95 ± 8.97, 7,24 ± 0,79 e 1,14 ± 0,14; GII: 125,04 ± 23,58, 5,80 ± 0,14, 2,62 ± 0,14; GIII: 133,00 ± 11,00, 5,88 ± 0,45, 2,54 ± 0,22; GIV: 137,67 ± 12,05, 5,88 ± 0,17, 2,57 ± 0,10, respectivamente. Para determinação dos parâmetros de SCG e de Weibull, 140 espécimes foram divididos em 2 grupos: GC (controle) e GT (submetidos à TI por 15 min a 470°C). Para determinação de n e de ?f0, 50 espécimes de cada grupo foram testados em saliva artificial a 37°C em flexão biaxial em uma das seguintes taxas de tensão: 10-2, 10-1, 100, 101 e 102 MPa/s. Para determinação dos parâmetros de Weibull, mais 20 espécimes de cada grupo foram ensaiados na taxa de 100 MPa/s. Os valores de n, ?f0, m e ?0 foram, respectivamente (valores entre parênteses representam intervalos de confiança de 95%): 24,1 ± 2,5; 58,1 ± 0,01; 13,8 (10,0 a 18,8) e 60,4 (62,2 a 58,5) para GC e 36,7 ± 7,3; 127,9 ± 0,01; 7,4 (5,3 a 10,1) e 136,8 (129,1 a 144,7) para GT. Para determinação do efeito da TI no curva R, 7 espécimes de cada grupo receberam uma indentação Vickers em uma das seguintes cargas de indentação (kg): 0,18; 0,32; 0,56; 1,0; 3,2. Após armazenados ao ar por 24 h os espécimes foram ensaiados a 10 MPa/s em saliva artificial a 37°C. Os parâmetros ?, ?, q foram, respectivamente: 62,57; 0,12 e 0,2857 para GC e 161,50; 0,34 e -0,0074 para GT. Os valores de k variaram de 0,371 a 0,515 para GC e de 1,240 a 0,804 para GT. Não houve diferença nas propriedades mecânicas entre as três temperaturas de TI testadas. A TI promoveu aumento significativo do valor de n, ?f0 e ?0, entretanto resultou em diminuição do valor de m e também suprimiu o comportamento de curva R, presente no material antes da realização da TI.The objectives of this study were to determine the influence of different ion exchange (IE) temperatures on mechanical properties of a dental porcelain Ultrapaline ST and the effect of IE on slow crack growth (SCG) (coefficient of SCG - n, scale parameter - ?f0) and Weibull parameters (characteristic strength - ?0; Weibull modulus - m) and R-curve behavior of this porcelain. 250 specimens (12 mm diameter x 1 mm height) were fabricated according to the manufacturer\'s instructions, grounded with a surface-grinding device and polished up to 1?m. To determine the effect of IE temperature on biaxial flexural strength (?), hardness (H) and fracture toughness (KIc), 40 specimens were divided in four groups (n=10) as follow: GI - control (no ion exchange); GII, GIII and GIV submitted to IE with KNO3 for 15 min at 450°C; 470°C e 490°C, respectively. The ? was determined using a piston-on-three-balls device, in artificial saliva at 37°C and constant loading rate of 10 MPa/s. For hardness and fracture toughness, 3 Vickers indentations (2kg, 30s) were made on each specimen. The diagonals and radial cracks were measured in order to calculate H and KIc. Mean and standard deviations values of ? (MPa), H (GPa) and KIc (MPa.m1/2) were: I: 57.95 ± 8.97; 7.24 ± 0.79; 1.14 ± 0.14; II: 125.04 ± 23.58; 5.80 ± 0.14; 2.62 ± 0.14; III: 133.00 ± 11.00; 5.88 ± 0.45; 2.54 ± 0.22; IV: 137.67 ± 12.05; 5.88 ± 0.17; 2.57 ± 0.10, respectively. To determine the effect of IE on SCG and Weibull parameters, 140 specimens were divided in 2 groups: GC (control) and GIE (submitted to IE at 470°C for 15 min). To determine the SCG parameters, 10 specimens of each group were tested in biaxial flexural strength in each one of five constant stress rates: 10-2, 10-1, 100, 101 e 102 MPa/s. To determine the Weibull parameters, 20 specimens of each group were tested in the stress rate of 100 MPa/s. The n, ?f0, m and ?0 (values in parenthesis represent the confidence interval) were: 24.1 ± 2.5; 58.1 ± 0.01; 13.8 (10.0 to 18.8) and 60.4 (62.2 to 58.5) for GC and: 36.7 ± 7.3; 127.9 ± 0.01; 7.4 (5.3 to 10.1) and 136.8 (129.1 to 144.7) for GIE, respectively. To determine the effect of IE on R-curve behavior, 7 specimens of each group received a Vickers indentation in one of the following indentation loads (kg): 0.18; 0.32; 0.56; 1.0; 3.2. After stored on air for 24 h, the specimens were tested biaxial flexure strength in artificial saliva at 37°C in a stress rate of 10 MPa/s. The ?, ?, q parameters were, respectively: 62.57; 0.12 and 0.2857 for GC and 161.50; 0.34 and -0.0074 for GIE. The values of k varied from 0.371 to 0.515 for GC and from 0.34 to 0.0074 for GIE. There are no differences on mechanical properties among the three IE temperatures tested. The IE promoted significantly increase of n, ?f0 and ?0 however, decreased the m value and suppressed the R-curve behavior originally present on material before the IE.
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Varadarajan, Ravikumar. "On the Nature of Static and Cyclic Fracture Resistance of Ultra High Molecular Weight Polyethylenes Used in Total Joint Replacements". Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1164903681.
Testo completo
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Dotta, Fernando. "Previsão da pressão de colapso em dutos para transporte de gás e petróleo contendo defeitos planares incorporando curvas de resistência J-R: uma abordagem micromecânica utilizando critérios locais". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-27112006-172735/.
Testo completoAbstract (sommario):
Este estudo estende a abordagem micromecânica baseada em células computacionais e a abordagem baseada em deformação utilizando o critério de CTOA para descrever extensão dúctil de trincas longitudinais em dutos de aços de elevada tenacidade sob alta pressão. Ensaios laboratoriais realizados em aços API 5L X60 e X70 utilizando corpos-de-prova padronizados de fratura com trinca profunda, produzem os resultados necessários para medir as curvas de resistência à propagação de trincas e calibrar os parâmetros dos modelos de Gurson e CTOA para estes materiais. O foco central deste trabalho é a aplicação da metodologia de células computacionais e o critério de CTOA para prever as pressões de colapso medidas experimentalmente em dutos de paredes finas contendo trincas longitudinais. O programa experimental inclui espécimes pré-trincados com 508 mm (20") e 219 mm (8 5/8") com diferentes profundidades de trincas. Foram conduzidas análises de elementos finitos, sob estado plano de deformações e no contexto 3D pleno utilizando modelos detalhados dos dutos para descrever a extensão de trinca com o incremento de pressão. As simulações numéricas demonstram a eficiência e limitações de ambas as abordagens para descrever a resposta de crescimento de dúctil e prever a pressão de colapso para os dutos testados. Enquanto o critério de CTOA ainda parece ter limitada aplicabilidade para prever o comportamento dúctil dos dutos, a previsão da resposta dúctil do dutos pré-trincados utilizando o modelo de células computacionais mostrou boa concordância com as pressões de colapso medidas experimentalmente.This study extends a micromechanics approach based upon the computational cell methodology incorporating the Gurson model and a deformation-based approach using the CTOA criterion to describe ductile crack extension of longitudinal crack-like defects in high pressure pipeline steels. Laboratory testing of API 5L X60 and X70 steels at room temperature using standard, deeply cracked fracture specimens provides the data needed to measure the crack growth resistance curve and to calibrate the Gurson and the CTOA parameters for these materials. A central focus of the paper is the application of the cell methodology and the CTOA criterion to predict experimentally measured burst pressures for thin-walled gas pipeline containing longitudinal cracks. The experimental program includes precracked pipe specimens with 508 mm (20 inches) O.D. and 219 mm (8 5/8 inches) O.D. with varying crack depth to thickness ratios (at). Plane-strain and full 3D computations are conducted on detailed finite element models for the pipe specimens to describe crack extension with increased pressure. The numerical simulations demonstrate the effectiveness and limitations of both approaches to describe crack growth response and to predict the burst pressure for the tested pipes. While the CTOA criterion still appears to have limited applicability to predict ductile cracking behavior for the pipe specimens, the cell model predictions of the ductile response for the precracked pipes show good agreement with experimentally measured burst pressures.
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Bonazzi, Luís Henrique Camargo. "Comportamento em fadiga da liga Al-Li AA 2050". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-17112017-172453/.
Testo completoAbstract (sommario):
As novas ligas de alumínio que contém lítio são atraentes devido à sua baixa densidade, alto módulo elástico, elevada resistência mecânica e por terem boa resistência à corrosão em comparação com ligas similares que não contém lítio. A degradação do material devido à fadiga e corrosão são os dois principais fatores que contribuem para o envelhecimento de uma aeronave. O objetivo deste trabalho é estudar a resistência à fadiga de uma nova liga de Al-Li, denominada de AA 2050-T84, considerando os estágios de nucleação e de propagação. No primeiro caso são avaliados o efeito da variação do concentrador de tensão (kt) e o efeito da razão de tensões (R), enquanto que no segundo caso são estudados os efeitos da direção de laminação e da razão de tensões (R) na taxa de propagação da trinca por fadiga. Para o estágio de iniciação é possível observar que quanto maior o valor de R, menor é a vida em fadiga. Para um R constante, o concentrador de tensão reduz significantemente a vida em fadiga. Considerando a vida de propagação de trinca por fadiga, observa-se que, independente da direção de laminação, quanto maior o valor de R, para um mesmo ΔK, maior foi a taxa de propagação de trinca. Para um mesmo R, o expoente m da equação de Paris é maior na direção TL indicando maior velocidade de crescimento de trinca. Independentemente da direção tomada, quanto maior o valor de R maior o valor de m. O modelo matemático utilizado previu muito bem o efeito de R na taxa de propagação de trinca. A liga AA 2050 apresenta resistência à fadiga similar ligas das famílias 2XXX e 7XXX e similar a da liga Al-Li AA 2198 T8.The new Al-Li alloys are very attractive due to its low density, high elastic modulus, increased mechanical strength, as well as good corrosion resistance in comparison with similar alloys that don\'t contain lithium. The material\'s degradation due to fatigue and corrosion are the main factors of aircrafts aging, and it is quite important to take them in account to guarantee the aircraft structural integrity. The aim of this work is to study the fatigue strength of a new Al-Li alloy, denominated as AA 2050 T84, considering both nucleation and propagation fatigue lives. In the first case were evaluated the effect of the variation of the stress concentrator (kt) and the effect of the stress ratio (R), while in the propagation life were considered the effect of the rolling direction and the stress ratio (R). From the initiation life results, it is possible to observe that as higher was R, lower is fatigue life and that the intensity of the stress concentrator reduces fatigue life significantly, independent of the R value. The results from the propagation life shows that in both LT e TL directions and for a constant ΔK, higher R induces larger fatigue crack propagation rates. Considering a constant R, the TL direction presents a larger exponent m of Paris equation, which is an indicative of higher larger crack propagation rate. Also, larger R causes larger m, independently of the rolling direction. The mathematical model used was able to take in account the R effect on the crack propagation rate. Considering the more traditional Al alloys from 2XXX and 7XXX families, and the Ali-Li alloys AA 2198 T8, the AA 2050 presented a quite similar fatigue behavior.
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Costa, Aratã Oliveira Cortez. "Estudo in vitro e in silico da atividade antifúngica dos isômeros r-(+) e s-(-)citronelal sobre fungos do gênero cryptococcus". Universidade Federal da Paraíba, 2017. http://tede.biblioteca.ufpb.br:8080/handle/tede/9471.
Testo completoAbstract (sommario):
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COSTA, A.O.C. In vitro and in silico evaluation of the antifungal activity of the R- (+) and S-(-) citronelal isomers, aginst fungi of the genus Cryptococcus. 2017. 52f. Dissertação (Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Farmacologia). UFPB/CCS – João Pessoa – PB. Cryptococcus neoformans is an opportunistic pathogenic yeast with a wide geographical distribution, capable to infect the most varied types of animals. In humans, cryptococcosis mainly affects the central nervous system and lungs, less frequently the skin, presenting in general a serious and fatal evolution. Individuals with deficient immune systems are more likely to develop cryptococcosis, especially those afflicted with the human immunodeficiency virus. The conventional treatment of cryptococcosis uses potentially toxic antifungals for long periods and they have been target of resistance of these microorganisms, besides the high costs with the treatment. Given this panorama, the search for natural products with antifungal properties has been a promising alternative, with great attention of the students regarding the analysis of the essential oils and their constituents. Thus, the present research aimed to evaluate the biological effect of the R and S isomers of the citronellal phytoconstituent on fungi of the genus Cryptococcus, which could lead to the discovery of a molecule to the development of a new antifungal, besides contributing to obtain more information on the pharmacological potential of this phytoconstituent. MIC and MFC were determined, of the compounds, being 64 and 64 the values for R - (+) citronellal respectively, and 256 and 512, respectively, for citronellal S - (-), on fungi of the genus Cryptococcus; The antifungigram of the strains of Cryptococcus sp. was carried out with the antifungal agents amphotericin B, fluconazole and fluorocytosine where a resistance of fluconazole and flucytosine was observed; This study investigated the possible interference of monoterpenes in the study associated with the activity of these antifungal agents, noting that citronellal R did not present an apparent synergic effect, whereas S showed a much more synergistic effect, even capable of inhibiting the resistance caused by fluconazole; The microbial death curve of the R - (+) and S - (-) isomers of the citronellal phytoconstituent was determined on a previously chosen strain (FGF-3) and the fungicidal effects of the citronellal S isomer and concentration dependent fungicidal effect Of R citronelal; Its in silico variables were of good prospecting. In conclusion, the substances exhibited a good biological activity and correlation with other antifungal agents, showing synergistic effects in the association study and their in silico variables were well prospective, thus characterizing these fully viable substances to be continued their studies.
Cryptococcus neoformans é uma levedura patogênica oportunista, com ampla distribuição geográfica, capaz de infectar os mais variados tipos de animais. No homem, a criptococose acomete principalmente o sistema nervoso central e pulmões, com menor frequência a pele, apresentando-se de uma forma geral com evolução grave e fatal. Indivíduos com o sistema imunológico comprometido são mais susceptíveis de desenvolver a criptococose, principalmente os acometidos pelo vírus da imunodeficiência humana. O tratamento convencional da criptococose utiliza antifúngicos potencialmente tóxicos por longos períodos e que vêm sendo alvo de resistência desses micro-organismos, além dos elevados custos com o tratamento. Diante desse panorama, a busca por produtos naturais com propriedades antifúngicas têm sido uma alternativa promissora, com grande atenção dos estudiosos quanto à análise dos óleos essenciais e seus constituintes. Dessa forma, a atual pesquisa, teve por finalidade avaliar o efeito biológico dos isômeros R e S do fitoconstituinte citronelal, sobre fungos do gênero Cryptococcus, o que poderá conduzir à descoberta de uma molécula ao desenvolvimento de um novo antifúngico, além disso, contribuir para a obtenção de maiores informações sobre o potencial farmacológico desse fitoconstituinte. Foi determinada CIM e a CFM, dos compostos sendo 64 e 64 os valores para o R-(+) citronelal respectivamente, e 256 e 512, respectivamente, para o S-(-) citronelal, sobre fungos do gênero Cryptococcus; Foi realizado o antifungigrama das cepas de Cryptococcus Sp. com os antifúngicos anfotericina B, fluconazol e fluorcitosina onde observou-se uma resistência por parete do fluconazol e da flucitosina; Com isso foi investigado a possível interferência dos monoterpenos em estudo associados à atividade desses antifúngicos, observando que o R citronelal não apresentou efeito sinérgico aparente, enquanto o S apresentou um efeito bem mais sinérgico, capaz ate de inibir as resistências causadas com o fluconazol; Foi determinada a curva de morte microbiana dos isômeros R-(+) e S-(-) do fitoconstituinte citronelal, sobre uma cepa previamente escolhida (FGF-3) e foram observados os efeitos fungicidas do isômero S citronelal e efeito fungicida dependente de concentração do R citronelal; suas variáveis In silico foram de boa prospecção. Concluindo que as substancias exibiram uma boa atividade biológica e correlação com outros antifúngicos, apresentando efeitos sinérgicos no estudo de associação e suas variáveis In silico foram de boa prospecção, caracterizando assim essas substancias totalmente viáveis para que sejam continuados seus estudos.
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Rádsetoulal, Milan. "Hodnocení lomového chování svarových spojů používaných v energetickém průmyslu". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442748.
Testo completoAbstract (sommario):
This thesis is focused on assessment of fracture behaviour of heterogeneous welded joint. The goal is to determine fracture behaviour at the interface of ferritic base metal and austenitic weld metal at temperature of 255°C. This kind of weld is widely used at energy industry. Fracture toughness was evaluated using CT specimens with size 0,5T in order to determine the initiation values of stable crack propagation. Fracture behaviour of the weld is correlated with results of metallography and fractography analysis. Both light and scanning electron microscopy is used for fractography analysis. An assessment of fracture behaviour of the interface of the weld joint is first of all connected with a need of suitable location of cycled crack to the interface of metals. In the case of well-prepared crack the lowest values of J-integral are observed. In other cases of slight crack deviation from the notch plane fracture values increase. Due to a large scatter of mechanical properties of heterogeneous weld joints an increased number of test specimens is needed to obtain relevant and conservative fracture toughness values. Correlation of fracture toughness with the results of fractography analysis leads to clarification of the crack trajectory and to description of fracture mechanism.
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Francisco, Julio Cesar de Souza. "Resistência à propagação dúctil de trincas em aço API 5L X70 com teor de nióbio modificado". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18150/tde-30032016-110448/.
Testo completoAbstract (sommario):
Aplicações de alto desempenho, como as de dutos utilizados no transporte de derivados de petróleo, exigem materiais com uma combinação excepcional de propriedades mecânicas, dentre as quais, elevada resistência mecânica, tenacidade e resistência à fadiga. O aço API 5L X70 com adição de nióbio apresenta-se, quando comparado com o API 5L X70 padrão, como sendo uma opção para a melhora em seu processo de fabricação, sendo sua composição química diferenciada, devido a um maior teor de nióbio. A Arcelor Mittal Tubarão tem mostrado interesse em fabricar aços API X70/X80, sem a adição de V e com adições de Nb acima do recomendado pela Petrobras. O objetivo principal deste trabalho é o estudo da resistência mecânica e de tenacidade à fratura de dois aços API 5L X70, com teores de Nb de 0,06% e Nb de 0,09% em peso, processados conforme processo HSM Arcelor Mittal Tubarão. Para o atendimento deste objetivo, serão executadas a caracterização microestrutural conforme norma ASTM E3, ensaios de tração conforme ASTM E8M e ensaios de tenacidade à fratura conforme a norma ASTM E1820 com obtenção das curvas J-R\'s. Foram retirados corpos de prova da região de material base, região da solda e zona termicamente afetada. A partir dos resultados obtidos observa-se que o processo de laminação controlada a quente da Arcelor Mittal, produziu microestruturas bastante similares para ambas as composições, produzindo parâmetros de resistência mecânica similares e que atenderam o especificado pela Norma API 5L X70, nível PSL2. As soldas se apresentaram, a partir de valores de dureza, ligeiramente superiores ao do metal base (overmatch), sendo o resultado de microestruturas bastante similares. Os ensaios para obtenção das curvas J-R foram capazes de apresentar resultados representativos da resistência à propagação dúctil de trinca, para as espessuras de tubos estudadas. Estes resultados indicaram elevada resistência a propagação dúctil de trinca em ambos os aços, sendo que, o MB do aço NNb apresentou resistência superior ao ANb. O MS apresentou curvas J-R bem inferiores às do MB e ZTA. Estas diferenças foram atribuídas a composição microestrutural de cada região.High performance applications such as pipelines used to transport oil products require materials with an exceptional combination of mechanical properties, such as high mechanical strength, toughness and fatigue resistance. The API 5L X70 steel with enhanced niobium as an option to the production of this type of HSLA steel. Arcelor Mittal, Tubarão/Brazil has great interest in producing API 5L X70/X80 steels, without V and with Nb content above the recommended by Petrobras. Thus, the main objective of this thesis is the study of the mechanical strength and fracture toughness of API 5L X70 steel with Nb content of 0.06% Nb and 0.09% by weight processed as HSM Arcelor Mittal Tubarão process. To meet this goal, microstructural characterization following the ASTM E3, tensile tests following the ASTM E8M and Elastic Plastic Fracture toughness testing, according to ASTM E1820, were carried out. Specimens were taken from the base material region, weld bead and heat affected zone. From the results obtained it was observed that the controlled hot rolling process from ArcelorMittal, produced very similar microstructures for both compositions, as a consequence similar mechanical resistance and both met the criteria specified by the API Standard 5L X70, PSL2 level. The produced girth welds presented hardness values slightly higher than those from the base metal (overmatch), and resulted in very similar microstructures. The fracture toughness tests were able to provide valid JR curves that are representative results of resistance to ductile crack propagation for this pipe thickness. Both steels presented resistance to ductile crack propagation, and that the MB of the NNB steel showed superior resistance to the ANb steel. MS showed the lowest J-R curves, while MB and ZTA presented similar behavior. These differences were attributed to microstructural composition of each region.
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Francisco, Julio Cesar de Souza. "Avaliação da tenacidade à fratura de aço API 5L X70 utilizado na fabricação de dutos transportadores de gás e petróleo". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18150/tde-19012011-111506/.
Testo completoAbstract (sommario):
A avaliação da integridade estrutural de dutos pelo uso de corpos-de-prova laboratoriais depende da escolha de corpos-de-prova de geometrias que representem condições de restrições plásticas na frente da trinca, similares às encontradas nas condições operacionais dos dutos. O Núcleo de Ensaios de Materiais e Análise de Falhas, NEMAF do SMM, EESC-USP vem realizando pesquisas para o desenvolvimento de corpos-de-prova e metodologias experimentais que melhor represente esta situação. Entretanto, no caso de dutos existem situações onde a geometria e o tamanho do corpo-de-prova são limitados pelas dimensões do duto. Este trabalho apresenta o desenvolvimento e aplicação de espécimes SE(T) em aço API 5L X70, avaliando a influência da geometria e dimensões do corpo-de-prova na tenacidade à fratura do citado aço, sendo este utilizado na fabricação de dutos para transporte de gás e petróleo. Para isto, foram obtidas curvas de resistência à propagação dúctil de trincas, curvas J-R\'s, utilizando a metodologia do espécime único (single specimen) em conjunto com a técnica da variação da flexibilidade elástica (unloading elastic compliance), medida na boca da trinca (CMOD) que fornece ao mesmo tempo a área plástica abaixo da curva de carregamento versus deslocamento e o tamanho da trinca, segundo a norma de ensaios ASTM E1820-05. Foram ensaiados corpos-de-prova SE(T) com trincas rasa (a/W=0,2) e profunda (a/W=0,5) e razão W/B de 2,5 e 1,0, com a finalidade de garantir que o ensaio seja realizado em dominância de um estado plano de deformação como recomendado pela referida norma, para outros tipos de corpos-de-prova. Dos resultados observou-se que, independente do tamanho de trinca inicial adotado, não foram observadas diferenças significativas nas curvas J-R. Este fato pode ser comprovado nos casos de W/B = 2,5 e 1,0, sendo obtidas curvas J-R similares para cada caso, independente do valor de a/W. Entretanto, na grande maioria dos CDP\'s, foi obtida uma propagação dúctil de trinca anômala, ou seja, trincas que apresentam um tunelamento acentuado, decorrente de um elevado estado de tensão plana próximo das laterais, mesmo com o entalhe lateral de 20% da espessura. Os corpos-de-prova com W/B = 1,0 foram capazes de produzir curvas J-R, sem que as trincas apresentassem tunelamento e que os valores médios de trinca (ai e af) medidos conforme a norma (ASTM, 2005), são bastante próximos dos valores obtidos pelo método da variação de flexibilidade elástica. As razões para este fato são discutidas em detalhes. De um modo geral as delaminações, quando existente, não permitem uma correta medição do tamanho de trinca. Ainda, contrário à observação de outros pesquisadores, neste trabalho, foi observado que em vários casos as delaminações induziram fratura instável.The evaluation of pipes´ structural integrity from laboratories specimens depends on choosing the right specimen geometry that is able to present the conditions of plastic constrain at the crack tip, similar to the one found in the pipes´ operational conditions. The NEMAF Group from SMM, EESC-USP has been performing studies in this area, trying to develop specimen´s geometry that is able to represent this situation, as well as the necessary experimental methodologies to evaluate the fracture toughness of pipes. However, in some cases, the pipe size is a limiting factor in determining the specimen size and geometry. In this work is presented the development and application of specimens SE(T), evaluating the influence of the geometry and dimensions of the specimens on the fracture toughness of API 5L X70 steel, regularly used in the pipes for gas and petroleum transportation. Therefore, the resistance curves to ductile crack propagation, J-R`s curves, using the single specimen methodology, together with the variation of the elastic compliance technique (multiple unloading), measure at the crack mouth (CMOD) that provides both the plastic area under the load x displacement curve and crack size, according to the ASTM E1820-05 standard. The SE(T) specimens with shallow (a/W=0.2) and deep (a/W=0.5) cracks and W/B ratio of 2.5 and 1.0 trying to reduce the amount of plastic deformation and a straight crack front, as well as a dominance of a plane strain state at the crack tip, as recommended by the ASTM E1820-05 standard for other specimens type. From the results it was observed that, independent of the initial a/W, no significant differences were observed in the J-R curves. This fact is verified in both cases, this is, W/B = 2.5 and 1.0. However, in the great majority of CDP\'s with W/B = 2.5, it was obtained an anomalous crack propagation during testing, in other words, they presented an accentuated tunneling due to a high plane tension state near the CDP´s lateral faces, even with the side groove of 20% thickness. The specimens with W/B = 1.0 were capable to produce J-R curves with straight crack fronts, this is, without tunneling, allowing the measurement of medium values of the crack (ai e af) according to the ASTM E1820-05 standard. The reasons for this fact are discussed in details in this work. In general, the split, when present, did not allow a correct crack size measurement. Still, contrary to the other researchers\' observation, in this work, it was observed that in several cases the splits were able to induced unstable fracture.
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Lima, Toni Roger Schifelbain de. "Desenvolvimento de metodologia para determinação de curvas de resistência à fratura de materiais elasto-plásticos pela análise do campo deformacional à frente da ponta da trinca". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/36011.
Testo completoAbstract (sommario):
Os conceitos de mecânica da fratura têm sido cada vez mais utilizados em projetos de engenharia, permitindo a determinação de tamanhos críticos de defeito ou limites de solicitação em função da presença de trincas. No entanto, para aplicar com sucesso esses conceitos em uma avaliação de integridade estrutural é de suma importância a determinação exata do comportamento a fratura do material. Materiais com comportamento elasto-plástico têm ocupado cada vez mais lugar de destaque em estruturas e componentes críticos de engenharia e a maneira mais utilizada para caracterização da tenacidade à fratura desse tipo de material é a curva J-R. Embora existam métodos normatizados para determinação dessas curvas, esses possuem muitas vezes inconvenientes e limitações que tem justificado o desenvolvimento de vários estudos com vista à determinação de métodos alternativos. Nesse trabalho foi investigada a hipótese de que, a partir do estudo do campo deformacional nas proximidades da ponta de uma trinca, é possível desenvolver uma metodologia para determinação da curva de resistência à fratura de um material com comportamento elasto-plástico. Para tanto, um sistema óptico de medição de deformação baseado na técnica de correlação de imagem digital foi empregado para monitorar a deformação na superfície de corpos de prova do tipo SE(B) durante o ensaio de tenacidade à fratura. O objeto de estudo foi uma junta do aço API X65 soldada por processo de soldagem a laser. Os resultados obtidos demonstram o sucesso da técnica utilizada para obtenção da evolução do campo deformacional durante o ensaio. Além disso, a metodologia empregada possibilitou a determinação de expressões matemáticas que permitem associar valores de deformação com valores de integral J e Δa. Essas expressões são válidas para qualquer uma das três distintas regiões da junta soldada e permitem determinar com sucesso a curva J-R a partir da evolução da deformação durante o ensaio de um único corpo de prova.The use of fracture mechanics has become increasingly popular in damage tolerance analysis or during determination of load limits in engineering components and structures. Nevertheless, the success of applying the concepts of fracture mechanics to investigate structural integrity assessment is highly dependent upon the correct determination of fracture mechanics material properties. The accurate prediction of ductile fracture behavior plays an important role in structural integrity assessment of critical engineering structures, including nuclear reactors, petrochemical vessels and tanks, pipelines in oil and gas industries and aircraft structures. J-R curve has become the most popular material parameters in elastic-plastic fracture mechanics and has been applied widely in practical engineering. There are procedures to determine J-R curves and they are widely presented in books and international standards. However, these procedures sometimes present some practical limitations or restrictions which have prompted research effort to develop alternative methods. In this work the hypothesis that is possible to develop a methodology to determinate J-R curve to materials with elastic-plastic behavior from analysis of near crack tip strain field was verified. For this purpose, an optical strain measurement system (OSMS) was used in order to monitor strains on surface of SE(B) specimens during fracture toughness testing. The methodology was applied to a laser welded joint of API X65 steel. The measurements successfully evaluate the strain field during testing. Besides of this, the methodology proposed allowed the determination of mathematical expressions to associate strain values with values of J-integral and crack extension (Δa). These expressions are valid to characterize these fracture toughness parameters to any one of the three distinct regions of the weld joint and made possible to determine J-R curve by monitoring the surface strain field evolution during a testing of a single specimen.
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Pauletti, Ederson. "ESTUDO DA INFLUÊNCIA DO FENÔMENO DA DELAMINAÇÃO NA TENACIDADE À FRATURA DE AÇOS API 5L X60 E X70 EM ESPÉCIMES SE(T)". UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2013. http://tede2.uepg.br/jspui/handle/prefix/1424.
Testo completoAbstract (sommario):
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In this work the ductile crack growth resistance curves (J-R curves) was evaluated for the steels used in the oil and gas pipelines from the X60 and X70 API 5L grades using the unloading compliance technique. The non standardized SE (T) specimens were used due to the same has low constraint, it is feature of pipelines. The plastic area for the obtaining the J integral was performed by measuring from the crack mouth open displacement, (CMOD). The central emphasis this research was evaluated the delamination phenomenon influence from the fracture toughness and along the J-R curve. As also the microtexture in close to delamination and ductile fracture regions, by using the Electron Backscatter Diffraction (EBSD) technique. The results have shown that value average of 355kJ/m2 was similar for both the shallow and deep crack specimens. The J-R curve values average from the shallow crack specimens have displayed most steep J-R curves, namely, it obtained higher energy values along the ductile crack propagation. Specimens that showed delaminations, during fracture process, obtained higher energy values along the ductile crack propagation. The occurrence of delaminations was more common in deep crack specimens. The microtexture results have shown a random grain sizes distribution. The components with higher intensity in the delamination region were α-fiber textures: {113} <110>, {112} <110>, {223} <110> the same cause anisotropy of mechanical properties and can be influenced out-of-plane constraint during the test. Moreover, there was the occurrence of the {100} <110> recrystallization texture component, which have deleterious effect in occurrence of delamination in microalloyed steels. Whereas in the ductile fracture region occurred the {111} <231>, {111} <132> and {111} <123> γ-fiber, which it can be influenced the ductile crack propagation process.
Neste trabalho foram investigadas as curvas de resistência ao crescimento de trinca dúctil para aços utilizados em tubulações de petróleo e gás, das classes API 5L X60 e X70, utilizando-se da técnica de variação da flexibilidade elástica. Espécimes SE(T) não padronizados foram utilizados, pois o mesmo possui baixa restrição ao fluxo plástico, característica de tubulações. A área plástica para obtenção da integral J foi obtida através da medida de deslocamento de abertura de trinca (crack mouth open displacement, CMOD). A ênfase central desta pesquisa foi avaliar a influência do fenômeno da delaminação na tenacidade à fratura (JIC) e na curva J-R em geral. Como também a obtenção da microtextura em regiões próximas à delaminação e fratura dúctil, que ocorrem durante o processo de fratura no ensaio de tenacidade à fratura, pelo uso da técnica de difração de elétrons retroespalhados (EBSD). Os resultados mostraram que o valor médio de tenacidade à fratura, de 355 kJ/m2 foi equivalente para espécimes com tamanho de trinca rasa e profunda. A média dos valores de curva J-R para espécimes com tamanho de trinca rasa mostrou curvas J-R mais íngremes, ou seja, obtiveram maiores valores energia ao longo da propagação dúctil de trinca. Os espécimes que apresentaram delaminações, durante o processo de fratura, obtiveram maior valor de energia ao longo do crescimento de trinca dúctil. A ocorrência das delaminações foi mais comum em espécimes com tamanho de trinca profunda. Os resultados de microtextura mostraram uma distribuição aleatória de tamanhos de grão. As componentes com maior intensidade na região próxima à delaminação foram as texturas de fibras α: {113}<110>, {112}<110>, {223}<110> que causam anisotropia das propriedades mecânicas e podem ter influenciado no estado triaxial de tensões durante o ensaio. Além disso, houve ocorrência da componente de textura de recristalização {100}<110>, a qual tem efeito deletério na ocorrência de delaminações em aços microligados. As componentes de fibra mais intensas na região próxima à fratura dúctil foram as texturas de fibra γ: {111}<231>, {111}<132> e {111}<123>, as quais podem influenciar no processo de propagação de trinca dúctil.
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Silva, Maurício de Carvalho. "Caracterização das propriedades mecânicas e metalúrgicas do aço API 5L X 80 e determinação experimental de curvas J-R para avaliação da tenacidade a fratura". Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-11022005-162828/.
Testo completoAbstract (sommario):
Caracterizar propriedades de resistência à propagação de trinca em materiais dúcteis é um elemento central em métodos de avaliação de integridade estrutural de dutos destinados ao transporte de gás, petróleo e seus derivados que utilizam os aços ARBL. Sendo assim, o objetivo deste trabalho foi estudar as propriedades de fratura dúctil do aço API 5L X80, através da obtenção da curva de resistência à propagação estável de defeitos (curvas J-R) do material. O ensaio de tenacidade à fratura para obtenção da curva J-R foi conduzido utilizando a técnica do corpo-de-prova único (single specimen) empregando o método da flexibilidade no descarregamento (unloading compliance), segundo a norma de ensaios ASTM E1820-96. Os corpos-de-prova compactos C(T) apresentaram espessura B=15mm, largura W=2B e uma relação aproximada entre o tamanho de trinca (a) e a largura, a/W=0,6. O ensaio foi conduzido numa máquina universal de ensaios (MTS) servo-controlada e capacidade máxima de 250kN. Adicionalmente, foram conduzidos ensaios convencionais de tração (limite de escoamento 550MPa, limite de resistência 676MPa e alongamento total em 50mm 27%), ensaios de impacto Charpy (energia absorvida de 220J à 0ºC sentido longitudinal) e análises metalográficas (microestrutura refinada composta por ferrita, colônias de perlita e presença do constituinte MA). Tais caracterizações permitirão uma maior precisão na comparação da curva J-R do aço API 5L X80 em estudo com estudos futuros de tenacidade à fratura.Assessments of crack growth resistance in ductile materials play a key role in structural integrity procedures for high strength, low alloy (HSLA) pipeline steels commonly employed in gas and petroleum trasmission systems. This work presents an investigation of the ductile tearing properties for an API 5L X80 pipeline steel using experimentally measured crack growth resistance curves (J-R curves) for the material. Testing of the X80 pipeline steel employed compact tension (C(T)) fracture specimens to determine the J-R curves based upon the unloading compliance method using a single specimen technique in accordance with the ASTM E1820 standard procedure. The C(T) specimens have thickness B=15mm, width W=2B and a ratio between crack size (a) and width, a/W=0,6. The experimental tests utilized a 250 kN MTS universal machine. Conventional tensile tests were also performed to determine the tensile properties for the tested material: yield strength of 550MPa, tensile strength of 676MPa and elongation of 27% (gage length of 50 mm). The Charpy V-notch impact tests also provided and absorbed energy of 220J at 0ºC. The metallographic analysis showed colonies of perlite and MA constituent islands in a ferrite matrix. This experimental characterization provides additional toughness and mechanical data against which the general behavior of X80 class pipeline steel can be compared.
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Canterle, Joseane Ortiz Breitenbach. "Avaliação da tenacidade à fratura do aço API 5L X70 em diferentes meios de etanol". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/114982.
Testo completoAbstract (sommario):
Com a implementação do Programa Nacional do Álcool (Proálcool), Protocolo de Quioto e substituição do MBTE (metil-terci-butil eter) em alguns países nos últimos anos, houve um aumento significativo da produção de etanol. Os dois maiores produtores mundiais de etanol são os Estados Unidos e o Brasil, sendo o etanol oriundo do Milho e da Cana-de-açucar, respectivamente. Transporte por dutos é a forma mais econômica para grandes quantidades, porém, há evidências de que esses dutos de transporte, e também fundo de tanques de armazenamento, possam ser susceptíveis ao fenômeno de corrosão sob tensão quando operam com etanol. Este fenômeno pode ser avaliado, por exemplo, por ensaios de baixa taxa de deformação (BTD) e de tenacidade à fratura, com corpos de prova definidos em normas já conhecidas internacionalmente. Este trabalho tem por objetivo avaliar a susceptibilidade do aço API X70 em diferentes meios de etanol (Etanol combustível simulado (SFGE), Milho e Cana) através de ensaios de mecânica da fratura. Foram preparados corpos de prova pré-trincados do tipo C(T) (Compact Tension), de acordo com a norma ASTM E647-08. A análise dos resultados foi realizada através das equações da mecânica da fratura linear elástica. Nos ensaios de curvas K-R, apesar de somente o etanol de Milho apresentar uma queda de tenacidade, o K de iniciação aparente e as análises fractográficas, confirmam a fragilização do material nos meios etanol SFGE e Milho. Ensaios de baixa taxa de deformação (BTD) interrompidos e os de step loading com carga flutuante também confirmam estes resultados.In recent years, there have been significant increases in ethanol production due to Brazilian Alcohol Program (Proálcool) implementation, Kyoto Protocol and replacement MBTE in some countries. The world’s largest producers of ethanol are United States and Brazil, being produced from Corn and Sugar Cane, correspondingly. Pipeline transportation is the most cost effective in large volumes, although, there are evidences that these pipelines and the bottom of ethanol storage tanks might be susceptible to the stress corrosion cracking phenomenon. This phenomenon can be assessed, for example, by slow strain rate tests (SSRT) and fracture toughness tests, with specimens well defined by international standards. This study aims to evaluate the susceptibility of steel API X70 in different ethanol environment (Simulated fuel-grade ethanol (SFGE), Corn and Sugar Cane) through fracture mechanics specimens. The tests were carried out on pre-cracked C(T) (Compact Tension) specimens, according to ASTM E647-08. The analysis of results was performed using linear elastic fracture mechanics equations. The analysis of K-R curves initially presented a decrease in toughness only in Corn environment, however the K for crack initiation apparent and fractography investigation confirm the material embrittlement in both SFGE and Corn ethanol environments. Tests of the slow strain rate test (SSRT) interrupted and loading step with fluctuating load also confirm these results.
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"Lagrangian angles of foliation in R² under curve shortening flow". 2011. http://library.cuhk.edu.hk/record=b5894787.
Testo completoAbstract (sommario):
Ma, Man Shun.Thesis (M.Phil.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 75-76).
Abstracts in English and Chinese.
Chapter 1 --- Introduction --- p.6
Chapter 2 --- Basic notions in Riemannian geometry --- p.10
Chapter 2.1 --- Basic manifold theory --- p.11
Chapter 2.2 --- "Connection, curvature" --- p.19
Chapter 2.3 --- Submanifold theory --- p.29
Chapter 3 --- Basic facts in symplectic and complex geometry --- p.33
Chapter 3.1 --- "Symplectic manifolds, Lagrangian submanifolds" --- p.34
Chapter 3.2 --- Kahler and Calabi-Yau manifolds --- p.39
Chapter 3.3 --- Calibration --- p.49
Chapter 4 --- Mean curvature flow --- p.52
Chapter 4.1 --- Basic equations in Lagrangian immersions --- p.53
Chapter 4.2 --- Evolution equation for --- p.57
Chapter 4.3 --- Evolution equations for H and θ --- p.62
Chapter 5 --- Lagrangian angle of a foliation --- p.67
Chapter 5.1 --- "Proof of equation (5.1), (5.2)" --- p.68
Chapter 5.2 --- Main theorem --- p.70
Chapter 5.3 --- Examples of invariant solution --- p.73
Bibliography --- p.75
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Webb, James Ernest. "Elevated temperature effects on R-curve behavior in alumina ceramics". 1995. https://scholarworks.umass.edu/dissertations/AAI9541165.
Testo completoAbstract (sommario):
I. Crack wake bridges were studied in glassy alumina s-DCB specimens at elevated temperatures. Direct observation of fracture surfaces in unmodified s-DCB specimens revealed the sizes and shapes of the high temperature bridges in the crack wake relative to the position of the crack front. Similar fracture surface observations made on s-DCB specimens modified to include a rear notch wedge, allowing the measurement of the high temperature bridging forces, were used to analyze bridge behavior in terms of viscous and power law creep models. The sizes and positions of the bridges were found to be highly stochastic but there was a clear trend toward decreased area bridged with increasing COD. Simple uniaxial viscous or creeping columns were inadequate to explain the load supported by the bridges. II. R-curve behavior and slow crack growth were studied in 99.5% alumina chevron notched short bar specimens at temperatures up to $1200\sp\circ\rm C.$ Constant loading rate tests measured toughness as a function of crack length at various loading rates. Constant load tests measured subcritical crack growth as a function of time. The intrinsic toughness decreased with increasing temperature while the bridging contribution to the R-curve remained independent of temperature. The effect of loading rate on R-curve tests was masked by experimental scatter at all temperatures except $1200\sp\circ\rm C.$ Subcritical crack growth tests showed high n-values at 700 and $1000\sp\circ\rm C,$ indicative of region III type behavior and an n-value indicative of region I at $1200\sp\circ\rm C.$ Predictions using the obtained subcritical crack growth parameters showed a small decrease in the level of the R-curve with decreasing loading rate at 700 and $1000\sp\circ\rm C$ that was within the range of the experimental scatter. A discrepancy between the R-curve predictions and the data at $1200\sp\circ\rm C$ was attributed to a rate dependence of the bridging behavior that was not considered in the analysis.