Дисертації з теми "Brittle and ductile rock"
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1
Ueda, Tadamasa. "Seismogenic deformation structures in the brittle-ductile transition regime: a case study of ultramafic pseudotachylytes and related deformed rocks in the Balmuccia peridotite body, Italy." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/204571.
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2
Mahé, Stéphanie. "Etude de la fracturation et de la déformation d'un massif rocheux aux abords d'une faille d'échelle crustale dans le cadre du tracé du tunnel routier de Saint-Béat." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20254/document.
Повний текст джерелаАнотація:
Le massif de marbres de Saint-Béat se situe dans la Zone Interne Métamorphique des Pyrénées centrales françaises. Il est formé de sédiments mésozoïques métamorphisés lors de l'événement métamorphique extensif Haute température - Basse pression classiquement décrit dans les Pyrénées. L'objet de cette thèse est de caractériser la déformation ductile et la fracturation qui affectent ce massif, et de déterminer dans quelle mesure les processus responsables de la fracturation peuvent être influencés par l'état de déformation. Les caractéristiques de la déformation des marbres et de ses roches encaissantes seront déterminées essentiellement grâce aux orientations préférentielles des axes de la calcite (marbre) et du quartz (socle paléozoïque), déterminées à l'aide de mesures à l'EBSD. L'observation en lame mince des textures de la calcite permet de quantifier les taux de déformation et d'estimer la température de cette déformation. Combinés aux observations de terrain, ces résultats permettent de proposer un modèle structural retraçant l'évolution du bassin depuis l'extension aptio-albienne jusqu'à son état actuel. La fracturation du massif est ensuite regardée à différentes échelles, depuis la photo aérienne jusqu'à l'affleurement. Quatre zones seront étudiées en détail afin de classifier les fractures par familles de mêmes caractéristiques et de reconstituer localement les paléo-régimes de contraintes. On comparera les tenseurs obtenus avec les régimes tectoniques décrits dans la littérature. Trois faciès légèrement différents de marbre servent de base à une étude visant à discuter de l'état d'anisotropie de la roche. Ainsi, des essais en compression simple, en traction indirecte et des mesures de vitesses acoustiques sont pratiqués sur des carottes orientées réalisées dans ces trois faciès ; leurs résultats donnent accès aux caractéristiques internes de la roche. On comparera et discutera les résultats d'un faciès à l'autre, et au sein du même faciès, d'une orientation à l'autre. Les résultats obtenus sur la fracturation servent de guide à la classification des fractures observées sur les fronts de tirs, lors du creusement du tunnel routier de Saint-Béat, recoupant le massif sur plus d'un kilomètre du Nord au SudThe Saint-Béat massif, composed of different marble facies, is part of the Internal Metamorphic Zone of the French Central Pyrenees. It is formed by Mesozoic sediments metamorphosed by the High Temperature – Low Pressure extensional event, classically described in the Pyrenees. The aim of this work is to characterize the deformation and fractured state of the massif, and to understand how the former can constrain the latter. The ductile deformation state is recorded in calcite grains for Mesozoic rocks, or in quartz grains for Paleozoic rocks. Their preferential lattice orientations have been measured with the EBSD method. Calcite texture observations give indications about deformation rates and temperatures. These results, in addition with field observations, allow us to rebuild the structural evolution of the massif, from the Albian extension. Fracturing along the massif is described at different scales. Four outcrops are selected in order to characterize and to classify fractures, and locally reconstruct the paleo stress tensor. The obtained tensors are presented and compared to those already published. Three slightly different marble facies are used to discuss the degree of anisotropy of the rock. Mechanical experiments such as compression tests, tensile tests and velocity measurements of elastic waves are carried out on oriented cores within these three facies. These results provide internal rock characteristics which are discussed and compared for the three facies, and for different orientations of the cores
3
Morgan, Robert Edward. "Ductile-brittle transitions in pipe grade polyethylene." Thesis, Imperial College London, 1994. http://hdl.handle.net/10044/1/7399.
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4
Bannister, Michael Keith. "Toughening of brittle materials by ductile inclusions." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292024.
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5
Samuels, J. "The brittle to ductile transition in silicon." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382682.
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6
Venkatachalam, Sivaramakrishnan. "Predictive Modeling for Ductile Machining of Brittle Materials." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19774.
Повний текст джерелаАнотація:
Brittle materials such as silicon, germanium, glass and ceramics are widely used in semiconductor, optical, micro-electronics and various other fields. Traditionally, grinding, polishing and lapping have been employed to achieve high tolerance in surface texture of silicon wafers in semiconductor applications, lenses for optical instruments etc. The conventional machining processes such as single point turning and milling are not conducive to brittle materials as they produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where the material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a comprehensive predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness required to achieve ductile-regime machining. The input to the model includes tool geometry, workpiece material properties and machining process parameters. The fact that the scale of ductile regime machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions. This research would aid in predicting forces and undeformed chip thickness values for micro-machining brittle materials given their material properties and process conditions. The output could be used to machine brittle materials without fracture and hence preserve their surface texture quality. The need for resorting to experimental trial and error is greatly reduced as the critical parameter, namely undeformed chip thickness, is predicted using this approach. This can in turn pave way for brittle materials to be utilized in a variety of applications.
7
Mohseni, Peyman. "Brittle and Ductile Fracture of X80 Arctic Steel." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19487.
Повний текст джерелаАнотація:
This PhD work has focused on the effect of microstructure and changes in microstructure introduced by welding procedure, on the brittle to ductile transition properties of high strength low alloy steels which have been developed for application at low temperatures (Arctic regions). For this purpose, the experimental work was based on the new pipeline steel API X80 that has a low transition temperature. The relationship between the brittle to ductile transition temperature and the microstructure in the coarse grained heat affected zone, CGHAZ, and the intercritically reheated coarse grained heat affected zone, ICCGHAZ was studied by applying Smitweld TCS1405 weld simulation for producing the HAZ microstructures. During the weld thermal cycles, both single and double cycle, the specimens were resistance heated to 1350°C by a rate of 150°C/s. The cooling rate was adjusted to give a cooling time between 800°C and 500°C (Δt8/5) of 15 seconds. The second heating cycle had a peak temperature, Tp2, of 780°C, and the cooling rate was the same as during the first cycle to simulate the reheated intercritical coarse grained HAZ. Fracture toughness was measured at low temperatures down to -90°C by both tensile and CTOD testing. In order to study the slip system activity of this steel, low cycle three point bending fatigue tests were also performed on polished specimens in the same temperature range. Fracture surfaces and changes in microstructure were analyzed by scanning and transmission electron microscopy and by light optical microscopy. In summary, the present work showed that, at each temperature the ICCGHAZ specimens had lower fracture toughness values than the CGHAZ specimens. Thus, the fracture mechanism is potentially more brittle in the case of ICCGHAZ specimens, and this is probably connected to the microstructure. The microstructure evalutions revealed that the ICCGHAZ contained blocky M-A constituents along prior austenite grain boundaries and stringer M-A constituents between the bainite laths. A more detailed investigation of the fracture surfaces by electron microscopy revealed also the existence of M-A constituents at the initiation points of the cleavage cracks. During deformation, the stress concentration is expected to increase due to the presence of the M-A constituents, and thus the level of stress and strain concentration around the M-A constituents become significantly larger than the nominal stress value and then causes initiation of cleavage fracture. Fracture surface analysis of fractured specimens documented that the cracks initiated either from debonded M-A constituents or from the region between two or more closely separated blocky M-A constituents where the transformation induced stress fields overlapped. In the present work, the initiation of cleavage fracture occurred within the double CTOD distance from the crack tip. This implies that brittle fracture is easily initiated when M-A constituents are located near the fatigue crack tip, and it is also controlled by accumulation of continuum stress fields and local plastic strains. The slip system analysis revealed that several slip systems are activated with a variety of Schmid factors within one grain, and in some cases the first activated slip system is not necessarily that with the highest Schmid factor. Thus, it can be concluded that the Schmid factor is not the only parameter that determines activation of slip. Finally, the crystallographic facet analysis by EBSD illustrated that the {100} planes are the most potent cleavage facet planes in both CGHAZ and ICCGHAZ specimens. It was also shown that the {100} and {110} planes in the case of CGHAZ, and the {100} and {211} planes in the case of ICCGHAZ were the most favourable cleavage facet planes at subzero temperatures.
8
Serbena, F. C. "The brittle-ductile transition of NiAl single crystals." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294341.
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9
Ellis, M. "The ductile to brittle transition in BCC metals." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306220.
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10
Jeng, Fu Shu. "Deep penetration into frictional ductile and brittle materials." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13096.
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11
Zhao, Yue. "How Plasticizer Makes a Ductile Polymer Glass Brittle?" University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460160287.
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12
Lu, Yue. "Polystyrene Glasses Under Compression: Ductile and Brittle Responses." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1523271245493476.
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13
Do, Xuan Nam. "Localized failure in dynamics for brittle and ductile materials." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2356.
Повний текст джерелаАнотація:
La défaillance des matériaux et structures d'ingénierie peut être considéré comme le résultat d'une interaction complexe entre différents phénomènes physiques tels que la nucléation des cavités, les microfissures, les microvides et d'autres processus irréversibles. Ces micro-défauts se fondent éventuellement en une ou plusieurs macro-fissures conduisant à une diminution de la capacité portante et finalement à une défaillance de la structure considérée. La prévention des défaillances des structures et des composants structurels a toujours été un sujet important et une préoccupation majeure en ingénierie. Cette thèse vise à représenter une défaillance localisée dans des matériaux non linéaires sans dépendance de maillage. Un intérêt particulier sera le cas de l’adoucissement dynamique des déformations. Les phénomènes localisés sont pris en compte en utilisant l'approche des discontinuités embarquées fortes dans laquelle le champ de déplacement est amélioré pour capturer la discontinuité. Sur la base de cette approche, on a d'abord développé un modèle unidimensionnel de barres élasto-plastique capable de représenter une défaillance pour des matériaux ductiles avec un durcissement combiné dans une zone de processus de fracture FPZ et un adoucissement avec des discontinuités fortes encastrées. Les résultats comparant le modèle unidimensionnel proposé aux travaux (semi-) analytiques sont présentés. Il a été démontré que la stratégie proposée offre des solutions indépendantes de maillage. La déformation augmente dans le domaine de l’adoucissement avec une diminution simultanée de la contrainte. Le problème se décharge élastiquement à l'extérieur de la zone d’adoucissement de déformation. L'énergie dissipée se trouve à disparaître. Le modèle a également été comparé à un modèle de dommage unidimensionnel capable de représenter la fracture dynamique de la barre d'endommagementélasto-endommagée dans la zone de traitement de fracture - FPZ et de adoucissement avec de discontinuités fortes encastrées pour trouver un bon accord entre deux modèles. Un modèle d'éléments finis bidimensionnel a été développé, capable de décrire à la fois le mécanisme de dommage diffus accompagné d'un durcissement initial et d'une réponse d’adoucissement ultérieure de la structure. On a analysé les résultats de plusieurs simulations numériques effectuées sur des essais mécaniques classiques sous des charges progressivement croissantes telles que le test Brésilien ou le test de flexion en trois points. Le cadre de dynamique proposé est montré pour augmenter la robustesse de calcul. On a constaté que la direction finale des macro-fissures est assez bien prédite et que l'influence des effets d'inertie sur les solutions obtenues est assez modeste notamment en comparaison entre différentes mailles. Ce modèle bidimensionnel a été étendu plus loin dans le modèle bidimensionnel de discontinuité intégrée en viscodamage pour aider à explorer brièvement la mise en œuvre du schéma de point intermédiaire de second ordre qui peut fournir des résultats améliorés sous limitation de la régularisation visqueuse du modèle de dégâts localisésFailure of engineering materials and structures can be considered as a result of a complex interplay between different physical phenomena such as nucleation of cavities, microcracks,microvoids and other irreversible processes. These micro-defects eventually coalesce into one or more macro-cracks leading to a decrease in the load-bearing capability and finally, to failure of the structure under consideration. Prevention of failure of structures and structural parts has always been a critical subject and a major concern in engineering. This thesis aims to represent localized failure in non linear materials without mesh dependency. Of special interest will be the case of dynamic strain-softening. Localized phenomena are taken into account by using the embedded strong discontinuities approach in which the displacement field is enhanced to capture the discontinuity. Based upon this approach, a one-dimensional model for elasto-plastic bar capable of representing failure for ductile materials with combined hardening in FPZ-fracture process zone and softening with embedded strong discontinuities was first developed. Results comparing the proposed one-dimensional model to (semi-) analytical works are presented. It was shown that the proposed strategy provides mesh independent solutions. Strain increases in the softening domain with a simultaneous decrease of stress. The problem unloads elastically outside the strain softening region. The strain energy is found to vanish. The model was also compared with a one dimensional damage model capable of representing the dynamic fracture for elasto-damage bar with combined hardening in fracture process zone - FPZ and softening with strong embedded discontinuities to find a good agreement between two models. A two-dimensional finite element model was developed, capable of describing both the diffuse damage mechanism accompanied by initial strain hardening and subsequent softening response of the structure. The results of several numerical simulations, performed on classical mechanical tests under slowly increasing loads such as Brazilian test or three-point bending test were analyzed. The proposed dynamics framework is shown to increase computational robustness. It was found that the final direction of macro-cracks is predicted quite well and that influence of inertia effects on the obtained solutions is fairly modest especially in comparison among different meshes. This two-dimensional model was expanded further into the two dimensional continuum viscodamage-embedded discontinuity model to help briefly explore the implementation of the second order mid-point scheme that can provide improved results under limitation of viscous regularization of localized failure damage model
14
Bezenšek, Boštjan. "Elastic-plastic crack problems in the ductile-brittle transition." Thesis, University of Glasgow, 2003. http://theses.gla.ac.uk/6946/.
Повний текст джерелаАнотація:
Margins in defect assessment procedures such as BS 7910 and R6/4 have been examined for cleavage and ductile tearing from complex and re-characterised defects. A range of crack profiles with re-entrant sectors developed from two co-planar surface breaking defects by fatigue has been examined experimentally and numerically. Both studies show enhanced crack driving forces in the re-entrant sector combined with a loss of crack tip constraint. Cleavage failures from complex and re-characterised defects demonstrated that the re-characterisation procedure is not conservative when cleavage occurs at small fractions of the limit load. Failures close to the limit load benefit from constraint loss which counteract the amplified crack driving forces in re-entrant sectors and cause re-characterised defects to be more detrimental than the original complex defects. Benefit may be taken from statistical size effects, which are strongly dependent on the crack geometry. Experimental fatigue and ductile tearing studies show similar development of complex cracks towards the re-characterised shape and re-characterisation procedures, such as those given in BS 7910 and R6/4, are conservative for fatigue and ductile tearing. A procedure has been developed to quantify enhanced temperature margins due to constraint loss by comparing the self similar stress fields at a critical local fracture stress (the Ritchie-Knott-Rice approach) and through the Weibull stress. Agreement with the experimental data has been demonstrated and the temperature dependence of the material parameters has been discussed. Following Li (1997) and Karstensen (1996), a toughness mapping technique was discussed that allows mode I toughness to be translated into mixed-mode I+II toughness for stress controlled fracture. In support of the arguments, toughness of Mode I and mixed-mode I+II configurations was measured on a mild steel. The experimental data clearly show increased cleavage toughness for unconstrained mode I and mixed-mode fields and the correlation with the predictions from the numerical models was demonstrated.
15
Komoroczi, Andrea [Verfasser]. "Numerical simulation of combined brittle-ductile deformation processes / Andrea Komoroczi." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2015. http://d-nb.info/1076096107/34.
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16
Joseph, T. D. "Materials for Fusion Reactors - The Brittle-Ductile Transition in Vanadium." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491624.
Повний текст джерелаАнотація:
This thesis describes experiments investigating the brittle-ductile transition in single and polycrystalline vanadium using four-point bend specimens. Pre-cracks were created in the beams by machining a notch into the tensile surface using EDM, which produced a network of sharp cracks in the base ofthe notch. Single crystal material was vacuum annealed at 1000°C and 400°C. The material annealed at 1000°C was had a low concentrations of dislocations and interstitial hydrogen. It produced a sharp BOT typical of dislocation free material, with an activation energy of 0.26 eV ± 0.07 eV. Material annealed at 400°C had a low concentration of interstitial hydrogen and a normal dislocation density and produced a soft transition, typical of metallic materials with active dislocations, with an activation energy of 0.22 eV ± 0.02 eV. Unannealed single crystal material had a high concentration of interstitial hydrogen and a normal dislocation density and produced a soft transition with an activation energy of 0.14 eV ± 0.04 eV. Its behaviour was thought to be dominated by the effects of interstitial hydrogen. Annealed polycrystalline vanadium was found to be ductile at temperatures of 77 K and above. Unannealed polycrystalline vanadium was ductile at 77 K and at high temperatures but exhibited a region of brittle failure between approximately 100 K and 300 K. A number of unusual phenomena were observed in this material and were attributed to competing effects of interstitial hydrogen. A number of attempts to measure the velocity of dislocations in vanadium were unsuccessful but direct imaging of the plastic zones of a number of samples using EBSD was used to investigate dislocation activity at different points in the transition curves.
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Eberhardt, Erik Brian. "Brittle rock fracture and progressive damage in uniaxial compression." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/NQ27403.pdf.
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18
Narström, Torbjörn. "Microstructural aspects of the ductile-to-brittle transition in pressure vessel steels." Doctoral thesis, KTH, Materials Science and Engineering, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3007.
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Hütter, Geralf. "Multi-scale simulation of crack propagation in the ductile-brittle transition region." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-121281.
Повний текст джерелаАнотація:
In the present thesis the crack propagation in the ductile-brittle transition region is studied on two scales with deterministic models. In the macroscopic model the ductile failure is described by a non-local Gurson-model whereas the discrete void microstructure is resolved around the crack tip in the microscopic model. The failure by cleavage is not evaluated by means of a post-processing criterion but is modeled equivalently using a cohesive zone model on both scales. Thus, cleavage is not a priori identified with unstable crack propagation but the transition between stable and unstable mode of propagation is a result of the simulation. The problem of handling completely failed material within the framework of non-local damage models is pointed out. A method to overcome this problem is proposed and successfully applied. The case of contained plastic yielding at the crack tip is addressed with a modified-boundary layer model. The macroscopic simulations reproduce many features which are known from experiments like the formation of stretch zones, cleavage after initial ductile tearing, pop-ins with crack arrest, among others. The microscopic simulations substantiate the understanding of the macroscopically observed behavior. Systematic parameter studies are performed. Starting with considerations on the limit cases like pure ductile failure or the lower-ductile brittle transition region allows to separate the effects of the different constitutive parameters. Based on these results, a methodology is proposed to extract the macroscopic material parameters from experiments. This scheme is successfully applied to experimental data from literature. The results show that the behavior of a low-constraint specimen can be reliably predicted with the parameters extracted from a high-constraint specimenIn der vorliegenden Arbeit wird die Rissausbreitung im spröd-duktilen Übergangsbereich auf zwei Skalen mittels deterministischer Modelle untersucht. Das duktile Versagen wird im makroskopischen Modell durch ein nichtlokales Gurson-Modell beschrieben, während im mikroskopischen Modell die Porenmikrostruktur im Bereich um die Rissspitze diskret aufgelöst wird. Das mögliche Versagen durch Spaltbruch wird nicht, wie üblich, nachträglich durch ein spannungsbasiertes Kriterium bewertet. Stattdessen wird der Spaltbruch auf beiden Skalen durch ein Kohäsivzonenmodell abgebildet. Somit wird die Spaltbruchinitiierung nicht a priori mit instabiler Rissausbreitung gleichgesetzt. Vielmehr ist die Stabilität der Rissausbreitung ein Ergebnis der Simulationen. Außerdem wird das Problem der der Handhabung vollständig ausgefallenen Materials im Rahmen nichtlokaler Schädigungsmodelle herausgestellt. Es wird eine Methode vorgestellt, dieses Problem zu behandeln und erfolgreich angewendet. In den Simulationen wird der Fall vollständig eingebetteten, plastischen Fließens untersucht. Die Simulationen mit dem makroskopischen Modell geben viele Effekte wieder, die aus Experimenten bekannt sind. Dazu zählen die Ausbildung von Stretchzonen, die Spaltbruchinitiierung nach anfänglichem, duktilem Reißen oder lokale Instabilitäten mit Rissarrest. Die mikroskopischen Simulationen tragen zum Verständnis des makroskopisch beobachteten Verhaltens bei. In der vorliegenden Arbeit werden systematische Parameterstudien durchgeführt. Zunächst werden Grenzfälle wie das rein duktile Versagens oder der Spaltbruch in Abwesenheit der Mikroporen untersucht, um die Einflüsse der einzelnen Materialparameter abzugrenzen. Ausgehend von diesen Ergebnissen wird eine Prozedur vorgeschlagen, die Materialparameter des makroskopischen Modells Schritt für Schritt aus Experimenten zu bestimmen. Diese Prozedur wird erfolgreich auf experimentelle Daten aus der Literatur angewendet. Die Ergebnisse zeigen, dass es das entwickelte Modell erlaubt, das Verhalten einer Bruchmechanikprobe mit geringer Dehnungsbehinderung an der Rissspitze mit denjenigen Materialparametern vorherzusagen, die an Proben mit einer hohen Dehnungsbehinderung ermittelt wurden
20
Kamel, Simon. "The effects of constraint and residual stress on ductile and brittle fracture." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11425.
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Tanne, Erwan. "Variational phase-field models from brittle to ductile fracture : nucleation and propagation." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX088/document.
Повний текст джерелаАнотація:
Les simulations numériques des fissures fragiles par les modèles d’endommagement à gradient deviennent main- tenant très répandues. Les résultats théoriques et numériques montrent que dans le cadre de l’existence d’une pre-fissure la propagation suit le critère de Griffith. Alors que pour le problème à une dimension la nucléation de la fissure se fait à la contrainte critique, cette dernière propriété dimensionne le paramètre de longueur interne.Dans ce travail, on s’attarde sur le phénomène de nucléation de fissures pour les géométries communément rencontrées et qui ne présentent pas de solutions analytiques. On montre que pour une entaille en U- et V- l’initiation de la fissure varie continument entre la solution prédite par la contrainte critique et celle par la ténacité du matériau. Une série de vérifications et de validations sur diffèrent matériaux est réalisée pour les deux géométries considérées. On s’intéresse ensuite à un défaut elliptique dans un domaine infini ou très élancé pour illustrer la capacité du modèle à prendre en compte les effets d’échelles des matériaux et des structures.Dans un deuxième temps, ce modèle est étendu à la fracturation hydraulique. Une première phase de vérification du modèle est effectuée en stimulant une pré-fissure seule par l’injection d’une quantité donnée de fluide. Ensuite on étudie la simulation d’un réseau parallèle de fissures. Les résultats obtenus montrent qu’il a qu’une seule fissure qui se propage et que ce type de configuration minimise mieux l’énergie la propagation d’un réseau de fractures. Le dernier exemple se concentre sur la stabilité des fissures dans le cadre d’une expérience d’éclatement à pression imposée pour l’industrie pétrolière. Cette expérience d’éclatement de la roche est réalisée en laboratoire afin de simuler les conditions de confinement retrouvées lors des forages.La dernière partie de ce travail se concentre sur la rupture ductile en couplant le modèle à champ de phase avec les modèles de plasticité parfaite. Grâce à l’approche variationnelle du problème on décrit l’implantation numérique retenue pour le calcul parallèle. Les simulations réalisées montrent que pour une géométrie légèrement entaillée la phénoménologie des fissures ductiles comme par exemple la nucléation et la propagation sont en concordances avec ceux reportées dans la littératurePhase-field models, sometimes referred to as gradient damage, are widely used methods for the numerical simulation of crack propagation in brittle materials. Theoretical results and numerical evidences show that they can predict the propagation of a pre-existing crack according to Griffith’s criterion. For a one- dimensional problem, it has been shown that they can predict nucleation upon a critical stress, provided that the regularization parameter is identified with the material’s internal characteristic length.In this work, we draw on numerical simulations to study crack nucleation in commonly encountered geometries for which closed-form solutions are not available. We use U- and V-notches to show that the nucleation load varies smoothly from the one predicted by a strength criterion to the one of a toughness criterion when the strength of the stress concentration or singularity varies. We present validation and verification of numerical simulations for both types of geometries. We consider the problem of an elliptic cavity in an infinite or elongated domain to show that variational phase field models properly account for structural and material size effects.In a second movement, this model is extended to hydraulic fracturing. We present a validation of the model by simulating a single fracture in a large domain subject to a control amount of fluid. Then we study an infinite network of pressurized parallel cracks. Results show that the stimulation of a single fracture is the best energy minimizer compared to multi-fracking case. The last example focuses on fracturing stability regimes using linear elastic fracture mechanics for pressure driven fractures in an experimental geometry used in petroleum industry which replicates a situation encountered downhole with a borehole called burst experiment.The last part of this work focuses on ductile fracture by coupling phase-field models with perfect plasticity. Based on the variational structure of the problem we give a numerical implementation of the coupled model for parallel computing. Simulation results of a mild notch specimens are in agreement with the phenomenology of ductile fracture such that nucleation and propagation commonly reported in the literature
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Li, Song. "Modeling fracture and deformation of brittle rock under compressive loading." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0014/NQ41619.pdf.
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Johnsson, Helena. "Plug shear failure in nailed timber connections : avoiding brittle and promoting ductile failures /." Luleå : Univ, 2004. http://epubl.luth.se/1402-1544/2004/03.
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Cullers, Cheryl Lynne. "Deformation mechanisms of NiA1 cyclicly deformed near the brittle-to-ductile transition temperature." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20050.
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Cheng, Shiwang. "Tensile Deformation of Polymer Glasses: Crazing, the Brittle-Ductile Transition and Elastic Yielding." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1382525654.
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Yin, Binghong. "Characterisation of Brittle and Ductile Fracture of 3D-Printed Single-Layer Polymer Films." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/24954.
Повний текст джерелаАнотація:
Fused filament fabrication (FFF) is an additive manufacturing technology in which a fused filament is deposited in a controlled manner over or adjoining previous deposited filaments, leading to the construction of a structural part. Although many studies have been conducted to characterise polymer components fabricated by the FFF process, most have relied on the mechanical testing of printed bulk specimens comprising multiple layers, showing overall performance. However, it is also interesting to characterise the extent of fusion bonding between individual filaments using printed single-layer films, which is critical to understand the process–structure–property relationship and optimise processing parameters involved in the FFF process.
In the first part of the study, polylactic acid (PLA), a brittle semi-crystalline polymeric material, was investigated to gain an insight into the fracture behaviour of thin single- layer PLA sheets printed by the FFF process. A double-edge notched tensile (DENT) specimen with sharp cracks parallel to the deposition direction was fabricated using different extrusion temperatures (from 200 C to 260 °C ) and deposition speeds (from 30 mm/s to 90 mm/s). The DENT PLA specimens were then quantitatively characterised to determine fracture toughness (Kc), defined as the critical stress intensity
factor at the critical load for the brittle fracture of DENT specimens produced at different printing temperatures and velocities.
The second part of the study was aimed at characterising the influence of printing parameters on fusion bonding between filaments of a ductile polymer, polypropylene (PP), printed by the FFF process. The specific essential work of fracture (we), which is considered an indicator of the fracture toughness of ductile polymers, was characterised using single-layer DENT PP sheets, fabricated within a range of extrusion temperatures (from 200 °C to 260 °C ) and deposition speeds (from 20 mm/s to 60 mm/s).
The individual and combined effects of the two processing parameters (i.e. extrusion temperature and deposition speed) on we of printed thin PP films were examined. The we value increased with an increase in printing speed at high extrusion temperatures, while an adverse trend was observed at low extrusion temperatures. An analysis of variance regression model was adopted to quantify the contribution of deposition speed and extrusion temperature to the extent of fusion bonding characterised by we. To obtain more insights into the process–structure–property relationship, rheology and differential scanning calorimetry tests were also performed to characterise the effects of the two process parameters on the viscosity and crystallinity of PP in relation to the extent of fusion bonding.
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Tempest, Simon Aaron. "Fluid-rock interaction in ductile shear zones, central-eastern Pyrenees." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303629.
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Gally, Brian James 1970. "Experimental investigation of the brittle to ductile transition in fracture of single crystal silicon." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85252.
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Bianculli, Steven. "Fracture of a Brittle-Particle Ductile Matrix Composite with Applications to a Coating System." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/805.
Повний текст джерелаАнотація:
In material systems consisting of hard second phase particles in a ductile matrix, failure initiating from cracking of the second phase particles is an important failure mechanism. This dissertation applies the principles of fracture mechanics to consider this problem, first from the standpoint of fracture of the particles, and then the onset of crack propagation from fractured particles. This research was inspired by the observation of the failure mechanism of a commercial zinc-based anti-corrosion coating and the analysis was initially approached as coatings problem. As the work progressed it became evident that failure mechanism was relevant to a broad range of composite material systems and research approach was generalized to consider failure of a system consisting of ellipsoidal second phase particles in a ductile matrix. The starting point for the analysis is the classical Eshelby Problem, which considered stress transfer from the matrix to an ellipsoidal inclusion. The particle fracture problem is approached by considering cracks within particles and how they are affected by the particle/matrix interface, the difference in properties between the particle and matrix, and by particle shape. These effects are mapped out for a wide range of material combinations. The trends developed show that, although the particle fracture problem is very complex, the potential for fracture among a range of particle shapes can, for certain ranges in particle shape, be considered easily on the basis of the Eshelby Stress alone. Additionally, the evaluation of cracks near the curved particle/matrix interface adds to the existing body of work of cracks approaching bi-material interfaces in layered material systems. The onset of crack propagation from fractured particles is then considered as a function of particle shape and mismatch in material properties between the particle and matrix. This behavior is mapped out for a wide range of material combinations. The final section of this dissertation qualitatively considers an approach to determine critical particle sizes, below which crack propagation will not occur for a coating system that exhibited stable cracks in an interfacial layer between the coating and substrate.
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Xu, Wenting. "Molecular Dynamics Simulations of the Size-dependent Brittle-to-ductile Transition of Silicon Nanowires." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613751523441622.
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VanDeVelde, Sharon Ann. "Distribution and Transport of Water in Natural Quartz Arenites Near Brittle-Ductile Transition Conditions." Bowling Green State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1237586551.
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DI, BATTISTA EMANUELA. "Interpretation of fracture mechanisms in ductile and brittle materials by the Acoustic Emission Technique." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2607555.
Повний текст джерелаАнотація:
Nowadays, the measure of the damage phenomena inside a structure is a complex problem that requires the use of innovative Structural Health Monitoring (SHM) and non-destructive investigation methodologies. The non-destructive method based on the Acoustic Emission (AE) technique has proved highly effective, especially to predict fracture behavior that take place inside a material subjected to mechanical loading.
Objective of the research is to use the Acoustic Emission monitoring to evaluate the fracture propagation process during tensile tests, three-point bending (TPB) tests and compression tests. The most representative AE parameters have been measured by sensors in order to obtain detailed information on the wave propagation velocity, signals localization as well as on the dominant fracture mode. As a matter of fact, the waves frequency and the Rise Angle are used to discriminate the prevailing cracking mode from pure opening or sliding. Moreover, the cumulated number of AE events and their amplitude are used to compute the signal energy. For the three-point bending tests on concrete beams, the energy dissipated to create the fracture surfaces and the energy emitted and detected by the AE sensors have been compared on the basis of their cumulative value at the end of the test and their rate during the process loading, in order to investigate on their correlation.
A numerical simulation of the mechanical response of the TPB tests has been also performed on the basis of the cohesive crack model. This approach has permitted to obtain a step-by-step evaluation of the crack propagation and a more detailed analysis of the mechanical energy dissipation rate during the loading test.
In addition, a dedicated in-situ monitoring at the San Pietro - PratoNuovo gypsum quarry located in Murisengo (AL) - Italy, is started and it is still in progress, developing the application aspects of the AE technique, which has been widely studied from a theoretical and experimental point of view by some Authors in the safeguard of civil and historical buildings.
Preliminary laboratory compression tests on gypsum specimens with different slenderness (λ=0.5, λ=1, λ=2) were conducted to assess the validity and efficiency of the system in view to a permanent installation for in-situ monitoring.
Currently the quarry is subjected to a multiparameter monitoring, by the AE technique and the detection of the environmental neutron field fluctuations, in order to assess the structural stability and, at the same time, to evaluate the seismic risk of the surrounding area.
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Passa, Eleni. "Study of the microstructure of Nb3Al based alloys." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/843837/.
Повний текст джерелаАнотація:
Nb3Al base alloys were produced in ingot or ribbon form using cold hearth non-consumable tungsten arc melting and chill block casting by melt overflow on a Mo wheel. The following alloys were studied: Nb-25Al, Nb-18Al, Nb-18Al-xMo (x=20,30,40) and Nb-18Al-9Cr-5Ti (at%). Low levels of interstitials (< 200 wppm O2, < 10 wppm H2) were achieved in all alloys. The effects of alloy chemistry and method of solidification processing on phase selection, solidification microstructures and solid state phase transformations were studied. Room temperature microhardness and hardness of the alloys were evaluated. The A2 structure (disordered beta Nbss) transformed to the B2 structure (ordered beta Nbss) by solid state transformation in the Nb-18Al and Nb-18Al-xMo (x=20,30,40) alloys. The experimental results showed that Al promoted A2→B2 ordering in Nb rich binary Nb-Al alloys and confirmed the predictions of thermodynamic modelling of A2→B2 ordering in the Nb-Al system. Mo addition inhibited the A2→B2 ordering whereas Cr+Ti additions favoured ordering. Formation of an o-phase was observed for the first time in the binary Nb-Al system after prolonged annealing of the Nb-18Al ribbons (973 K / 500 h). It is suggested that the o-phase forms as a transition phase in the transformation B2→o→Al5. While o-phase formation has been reported in alloys of the Nb-Al-Ti system, it is shown that Mo addition does not favour the o-phase in Nb-18Al-xMo alloys (x=20,30,40). Formation of o diffuse in the beta phase supports a previous hypothesis that addition of Al to transition metal elements such as Nb,Mo,V can enhance formation of the o phase in the beta phase. Mo addition in the Nb-Al solid solution increases the electron density of A2 or B2 phases and consequently the deviation | Delta | of the o diffuse from crystalline o. A new ternary o type phase, o*, was formed as a transition phase in the B2?Al5 transformation in heat treated Nb-18Al-xMo (x=20,30,40) alloys (973 K / 500 h). The orientation relationship of o* is [111]B2//[0001]o* and (110)B2//(0110)o* and the lattice parameters are ao* = 61/2aB2 and = c o* = 31/2aB2. Rapid solidification refined the alloy microstructures by two orders of magnitude. The room temperature solid solubility of Al in Nb was extended from 6 at% to 25 at% Al. In Nb-18Al-9Cr-5Ti up to 5at%Ti+8.4at%Cr were retained in solid solution. Suppression of Nb3Al and Nb2Al formation was achieved in the ribbons of Nb-25Al. Nb3Al formation was suppressed in the ribbons of Nb-18Al, Nb-18Al- xMo (x=20,30,40) and Nb-18Al-9Cr-5Ti. The A2-*B2 ordering was suppressed in the ribbons of all Nb-18Al-xMo alloys and in the as cast ingots of Nb-18Al-40Mo. Aluminium additions in Nbss increased its microhardness by 16.6 kgmm-2/at%Al and Mo addition hardened the Nbss (16.1at%Al) by 4.2 kgmm-2/at%Mo. Regarding the oxidation behaviour, the Nb-18Al-20Mo and Nb-18Al-9Cr-5Ti alloys exhibited lower weight gain rates as compared to Nb3Al. No protective scale was formed on any of the alloys studied in this work.
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Swankie, Troy Dennis. "The role of shear and constraint in mixed mode fracture." Thesis, University of Bristol, 1999. http://hdl.handle.net/1983/5021402d-5ea5-435e-a286-6d4e1c6673ce.
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Tarleton, Edmund. "Dislocation-dynamics modelling of crack-tip plastic zones and brittle-ductile transitions in BCC metals." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526123.
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Chao, C. L. "Investigations of the machining of glasses and other normally brittle materials in the ductile regime." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302733.
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Novovic, Milorad. "Effects of microstructure and prestraining on ductile to brittle transition in carbon-manganese weld metals." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246758.
Повний текст джерелаАнотація:
The effects of microstructure and prestraining on toughness of a multipass carbon-manganese (C-Mn) weld metal have been investigated. The toughness has been assessed in terms of both Charpy impact energy and Crack Tip Opening Displacement values. An extensive Charpy impact test experimental programme has been carried out on the C-Mn pressure vessel steel weld metal resulting in comprehensive databases for the weld metal in as-received and prestrained conditions. Charpy specimens were machined from multipass submerged arc weld metals with various notch tip locations and orientations relative to the weld metal. The impact energy was evaluated over a range of temperatures from -196 to 150°C. Mechanical prestraining levels of 2,9, and 12% have been applied to impact specimens to provide the trends in impact toughness that approximate some effects of irradiation embrittlement in service. Statistical interpretation of the results, in conjunction with the measurements from the fracture surfaces of Charpy specimens and fractography, has been carried out to provide a quantitative assessment of transition temperature shifts from the full and sub-populations of impact energy data pertaining to a particular notch root location relative to the weld microstructure. Impact energy values of a multipass submerged-arc C-Mn weld metal in both as-received and prestrained conditions are found to be subject to substantial scatter in the transition and upper shelf regions. Lower shelf impact energy values are found to be insensitive to microstructure and prestraining. The microstructure is found to have a significant influence on the ductile to brittle transition curve. Impact toughness for specimens with notch root locations in the reheated microstructure is greater than the impact toughness of specimens with notches located in the as-deposited microstructure. This trend is observed in both transition and upper shelf regions and is valid for both as-received and prestrained material conditions. The OT40Js hift between the transition curves corresponding to the as-received specimens with notch root locations on the centreline of the last deposited bead and in reheated microstructure has been estimated to be approximately 50°C. Prestraining (cold deformation) is found to provide the same trends in Charpy impact energy transition curve as irradiation embrittlement. Prestraining thus reduces the as-received upper shelf energy level and shifts the as-received transition curve towards higher temperatures. The magnitude of these effects depends on the amount of prestraining. The as-received and 2% prestrained datasets are found to be very similar, as are the datasets obtained after 9 and 12% prestraining.The transition curve for specimens with the notch root located in the reheated microstructure in the as-received material condition and transition curve for the specimens with notch root located on the centreline of the last deposited bead in the 9% prestrained material condition form the boundaries of the region of all possible locations for the transition curves along the temperature axis. The width of this "window" at the 40 J energy level, i. e. the OT4o4 temperature shift between the "best" (upper bound) dataset in as-received condition and the "worst" (lower bound) impact energy dataset in 9% prestrained material is estimated to be 102°C. The microstructure is also found to have a marked influence on the CTOD values of the as-received material with reheated microstructure showing better CTOD toughness across the whole temperature range examined. Prestraining at the 9% level shifts the onset of plastic collapse to lower values of the opening displacement resulting in the reduction in upper shelf CTOD values of more than 50% relative to the as-received upper shelf CTOD values. The transition region is also shifted along the temperature axis.
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Attfield, Peter Richard. "Mechanisms of shear zone deformation." Thesis, Keele University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253688.
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Voskoboinikov, Roman E. "Analytical Description of Brittle-to-Ductile Transition in bcc Metals. Nucleation of dislocation loop at the crack tip." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29522.
Повний текст джерелаАнотація:
Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Depencence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc.) in the crack tip vicinity.
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Pallaspuro, S. (Sakari). "On the factors affecting the ductile-brittle transition in as-quenched fully and partially martensitic low-carbon steels." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526218977.
Повний текст джерелаАнотація:
Abstract From the largest discontinuities to the smallest of the elements, various factors can threaten structural integrity. Susceptibility to these factors elevates with higher yield strengths. As-quenched low-carbon steels with a martensitic or martensitic-bainitic microstructure are modern ultra-high-strength structural steels. They can possess sufficient toughness, formability, and weldability, and are typically used in weight-critical and high-performance structures. Common problems with as-quenched steels with a yield strength of 900 MPa or more are that they do not obey the conventional correlation between the fracture toughness reference temperature T₀ and the impact toughness transition temperature T₂₈ᴊ used in many standards and structural integrity assessment procedures, and a lack of design rules in general. This thesis studies the relationship between the T₀ and T₂₈ᴊ to provide additional knowledge for future standardisation, the microstructural features governing the toughness at these temperatures on both global and local scale, and whether hydrogen embrittlement is present at subzero temperatures. It uses steels produced via laboratory rolling and quenching as well as from pilot-scale and full-scale industrial production, studying them with standardised toughness tests, microstructural characterisation, fractography, and cohesive zone modelling. As-quenched steels have a distinct correlation between T₀ and T₂₈ᴊ. An improved general T₀ – T₂₈ᴊ correlation applies to a wide range of steels. T₂₈ᴊ correlates closely with a dynamic reference toughness, which can be used together with the fraction of detrimental {100} cleavage planes near the main fracture plain to effectively estimate the transition temperatures. On a local scale, centreline segregation decreases the effective coarse grain size, which more than compensates for the harmful effects associated with the higher hardness and inclusion content of the centreline, resulting in increased fracture toughness. Hydrogen embrittlement causes a decrease in fracture toughness and local deformability, thereby increasing T₀ while leaving T₂₈ᴊ unaffected. Overall, the results show that high toughness demands good control of effective coarse grain size and hydrogen contentTiivistelmä Tekijät suurimmista epäjatkuvuuskohdista aina pienimpään alkuaineeseen voivat uhata rakenteellista eheyttä, minkä lisäksi alttius näille kasvaa materiaalin myötölujuuden kasvaessa. Modernit karkaistun tilan ultralujat matalahiiliset rakenneteräkset voivat silti omata riittävän sitkeyden, muovattavuuden ja hitsattavuuden. Tyypillisiä käyttökohteita näille ovat painon suhteen kriittiset ja korkean suorituskyvyn rakenteet. Yleinen ongelma myötölujuudeltaan noin ja yli 900 MPa karkaistun tilan teräksillä on se, että ne eivät noudata perinteistä murtumissitkeyden referenssilämpötilan T₀ ja iskusitkeyden transitiolämpötilan T₂₈ᴊ välistä korrelaatiota, jota käytetään useissa standardeissa ja suunnitteluohjeissa, jotka eivät myöskään vielä salli näin lujien terästen käyttöä. Tämä väitöstyö tutkii transitiolämpötilojen T₀ ja T₂₈ᴊ välistä suhdetta edistääkseen näiden terästen sisällyttämistä standardeihin, haurasmurtuma-sitkeyteen vaikuttavia mikrorakenteellisia tekijöitä sekä yleisellä että paikallisella tasolla, ja vetyhaurautta matalissa lämpötiloissa. Koeteräkset ovat laboratoriovalmisteisia, tuotantokokeita ja tuotantolaatuja. Niitä tutkitaan standardisoiduilla sitkeyskokeilla, mikrorakenteen karakterisoinnilla, fraktografialla ja koheesiovyöhykettä hyödyntävällä mallinnuksella. Tulokset osoittavat karkaistun tilan terästen omaavan erityisen korrelaation T₀ ja T₂₈ᴊ välillä. Muokattu, ultralujat teräkset huomioiva yleinen T₀ – T₂₈ᴊ -korrelaatio soveltuu laajalti eri terästyypeille. T₂₈ᴊ korreloi läheisesti dynaamisen referenssisitkeyden kanssa, jonka avulla yhdessä haitallisten {100} lohkomurtumatasojen osuuden kanssa voidaan estimoida joukko transitiolämpötiloja. Paikallisella tasolla keskilinjasuotauma pienentää efektiivistä karkeiden rakeiden kokoa, mikä suotauman suurista sulkeumista ja kovuudesta huolimatta parantaa murtumissitkeyttä. Vetyhauraus taas huonontaa sitkeyttä ja paikallista muodonmuutoskykyä myös matalissa lämpötiloissa nostaen T₀ lämpötiloja. Kokonaisuutena erinomainen transitiolämpötilasitkeys vaatii efektiivisen karkearaekoon ja vetypitoisuuden minimointia
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Hennecke, Thomas [Verfasser], and Thomas [Akademischer Betreuer] Sonar. "Mathematical modeling of the ductile-brittle-transition and an application to ferritic steel / Thomas Hennecke ; Betreuer: Thomas Sonar." Braunschweig : Technische Universität Braunschweig, 2013. http://d-nb.info/1175822906/34.
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Voskoboinikov, Roman E. "Analytical Description of Brittle-to-Ductile Transition in bcc Metals. Nucleation of dislocation loop at the crack tip." Forschungszentrum Rossendorf, 2002. https://hzdr.qucosa.de/id/qucosa%3A21779.
Повний текст джерелаАнотація:
Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Depencence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc.) in the crack tip vicinity.
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Golchinfar, Nader. "Numerical modeling of brittle rock failure around underground openings under statis and dynamic stress loadings." Thesis, Laurentian University of Sudbury, 2013. https://zone.biblio.laurentian.ca/dspace/handle/10219/2103.
Повний текст джерелаАнотація:
Stability of underground excavations is a prerequisite for the proper functioning of all other systems in a mining environment. From a safety point of view, the lives of people working underground rely on how well the support systems installed underground are performing. The ground control engineer cannot design an effective support system unless the area of the rock mass around the opening, prone to failure, is well identified in advance, even before the excavation of the tunnel.
Under high stress conditions, usually experienced at deep mining levels, stress-induced rock failure is the most common type of instability around the underground openings. This thesis focuses firstly on the use of the finite difference numerical tool FLAC to simulate brittle rock failure under static in-situ stresses. Brittle failure of the rock mass around underground openings is a particular type of stress-induced failure, which can result in notch-shaped breakouts around the boundary of the tunnel. Generation of these breakout zones is a discontinuum process and approximating this process using FLAC, which is a continuum tool, requires careful consideration of the stress conditions and the stress related behavior of rock material. Based on plasticity theory, this thesis makes an effort to estimate the breakout formation using an elastic – brittle - plastic material model.
Due to seismic challenges that deep mining operations are currently experiencing, rockbursting is a major hazard to the stability of underground structures. Therefore in this research, brittle failure of rock in the vicinity of the underground excavations is approximated also under dynamic loading conditions. The numerically modeled results of two different material models
iv
are compared with each other along with a previously developed empirical graph. This assessment, when further validated by field observations, may provide a different perspective for underground support design under burst-prone conditions.
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Brauer, Nancy A. "Fluid inclusions as a monitor of progressive grain-scale deformation during cooling of the Papoose Flat pluton, eastern California." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36556.
Повний текст джерелаАнотація:
Analyses of fluid inclusions and microstructures within the Papoose Flat pluton were used to investigate the chemistry and temperatures of fluids circulating with the pluton during cooling. Based on previous microstructural analyses, the interior of this late Cretaceous granitic to granodioritic pluton has been divided into three domains: i) a central core characterized by magmatic microstructures, ii) a middle domain of high temperature (>500°C) solid-state deformation, and iii) an outermost domain characterized by relatively low temperature (<5000°C) solid-state deformation. According to previously published anisotropy of magnetic susceptibility analyses and pluton cooling models, plastic flow occurred in both the outer part of the pluton and within its aureole rocks while the core of the pluton was still molten. Solid-state deformation is proposed to have stopped when the pluton interior cooled through its solidus less than 100,000 years after magma emplacement.
Microstructural analysis of samples from all three domains confirmed the transition from magmatic flow in the core of the pluton to solid-state deformation at the pluton margin. However, weakly developed solid-state microstructures overprint the dominant magmatic microstructures in samples from the core domain. The existence of solid-state microstructures in all three domains indicates that deformation continued during and after crystallization of the interior of the pluton.
Two phase, low salinity (< 26 wt% NaCl equivalent), liquid-rich aqueous fluid inclusions predominate within both quartz and feldspar grains in all samples. Throughout the pluton, the majority of fluid inclusions are hosted by deformed grains. Feldspar-hosted primary inclusions are associated with sericitic alteration. Inclusions were also observed in feldspar as secondary or pseudosecondary inclusions along fractures. Inclusions in quartz are frequently found near lobate grain boundaries or near triple junctions; linear pseudosecondary inclusion assemblages are commonly truncated against lobate boundaries between adjacent quartz grains, indicating that discrete microcracking events occurred during plastic deformation.
Homogenization temperatures overlap for all three microstructural domains. Coexisting andalusite and cordierite in the contact aureole, and the intersection of the Mus + Qtz dehydration reaction with the granite solidus, indicate trapping pressures between 3.8 and 4.2 kb. Ninety-eight percent of the calculated fluid inclusion trapping temperatures at 3.8 - 4.2 kb are below the granite solidus of 650°C. Seventy-six percent of the trapping temperature data fall within the more restricted range of 350-500°C; i.e. at temperatures which are lower than the commonly cited brittle-ductile transition temperatures for feldspar at natural strain rates, but above those for quartz. No correlation could be established between trapping temperatures and either host mineral or microstructural domain within the pluton.
The similar, relatively low trapping temperatures indicate that the majority of inclusions preserved in all three domains were trapped during the late low strain magnitude stages of solid-state deformation. The most common fluid inclusion trapping temperatures (400-500°C) in all three microstructural domains are similar to the deformation temperatures indicated by microstructures and crystal fabrics in the outer part of the pluton; these trapping temperatures are obviously lower than temperatures associated with contemporaneous solid state and magmatic flow in the pluton interior. The similar trapping temperatures within the pluton core and margin must indicate that the inclusion-trapping event migrated from the margin to the core of the pluton as it cooled, because fluid inclusions would rapidly equilibrate to a density appropriate for the PT conditions of their host minerals.
Master of Science
45
Chan, Hing Chuen Mark. "Automatic two-dimensional multi-fracture propagation modelling of brittle solids with particular application to rock." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/14977.
Повний текст джерелаАнотація:
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Vita.
Bibliography: leaves 557-564.
by Hing Chuen Mark Chan.
Sc.D.
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Day, Erik. "Characterization of Structures and Deformation in the Brittle-Ductile Transition, Western Termination of the Chugach Metamorphic Complex, Southern Alaska." ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/529.
Повний текст джерелаАнотація:
Field mapping along the western termination of the Chugach Metamorphic Complex (CMC) revealed a new D2 structure, the Bremner foliation fan. This structure has a high strain, vertically foliated core, with moderate-shallow dipping cleavages to the north and south which rollover into the core. The fan appears to have propagated from below by a shear-zone at depth (O'Driscoll, 2006). Description of the Bremner foliation fan revealed that the Bremner shear zone of Pavlis and Sisson (2003) is a D3 structure, and that the Stuart Creek fault is a younger brittle fault with 90km of dextral offset. Electron Back Scatter Diffraction (EBSD) and microstructural observations revealed deformation mechanisms were primarily compositionally controlled, whereas P-T-t conditions played a secondary role. Other factors, deemed to be of lesser influence included increased pressure solution caused by high fluid mobility, a lack of pore space, high levels of free aluminum, and a load-bearing framework of phyllosilicates.
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Sánchez, Alfaro Pablo. "Interplay between brittle deformation, fluid-rock interaction and mineralization in hydrothermal systems from the Southern Andes." Tesis, Universidad de Chile, 2015. http://repositorio.uchile.cl/handle/2250/135071.
Повний текст джерелаАнотація:
Doctor en Ciencias, Mención GeologíaThe interactions between seismic activity, fluid flow and mineral precipitation exerts a first-order control on the strength and permeability of the crust and plays a critical role in promoting the development of hydrothermal systems and the formation of giant ore deposits. However the role of such interactions on the evolution of hydrothermal systems and its transient effects on mineralization is poorly constrained. This thesis contributes to establish the nature of the dynamic interplay between brittle deformation, heat-fluid-rock interaction and mineralization of hydrothermal systems in volcanic arcs. An ideal natural laboratory used to study such interplay is the Andean Cordillera of Central-Southern Chile, where hydrothermal systems occur in close spatial relationship with active volcanism as well as major seismically-active fault systems. The combination of regional-scale structural analysis of active geothermal areas with geochemical modeling of hot springs in the Villarrica Chihuio area in southern Chile unravel the role of crustal deformation in facilitating and inhibiting the development of geothermal systems. Results reveal the presence of two magmatic-tectonic-geothermal domains and indicate that the chemical evolution of hydrothermal fluids in the area is strongly dependent on structurally controlled mechanisms of heat transfer. This contribution provides new insights towards efficient exploration strategies of geothermal resources in Southern Andes. The high enthalpy, metal-rich active Tolhuaca geothermal system north of Villarica was studied in detail in order to (1) address how the interplay between seismic activity, heat-fluid rock interaction, fluid flow and mineral precipitation controls the physicochemical evolution of hydrothermal systems in the studied region and (2) analyze the transient effects of earthquake-triggered pressure perturbations on metal solubility and mineralization. To achieve this, a comprehensive structural and mineralogical analysis at field and drillhole scales was combined with geochemical and thermometric data of borehole fluids and fluid inclusions, and numerical simulations of fluid evolution and rock failure conditions. Results obtained from this study reveal that hydrothermal alteration modifies the response of rock to deformation at Tolhuaca, produces a vertical compartmentalization of the system and promotes the development of a clay-rich low permeability zone. Moreover, they indicate that the life span and thermal structure of this system were highly affected by the low-permeability zone developed on top. Furthermore, thermodynamic modeling of metal (gold) and mineral (silica) solubility at Tolhuaca reveals that the optimum physical and chemical conditions for metal precipitation are reached at liquid-saturated conditions with a saturated liquid temperature less than 310°C, under which small pressure changes triggered by transient fault-rupture can drop solubility several orders of magnitude. The observations resulting from the thesis not only provide new insights about how hydrothermal reservoirs develop through a combination of sustained heat and high permeability conditions that are strongly conditioned by active tectonics, but also unveil how hydrothermal systems evolve to maximize the efficiency earthquake-induced mineral precipitation.
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Wang, Hongjian. "Evaluation of Orthogonal Cutting as a Method for Determining Mechanical Properties of Polymers." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/16136.
Повний текст джерелаАнотація:
The purpose of this thesis is to study and evaluate orthogonal cutting as a novel testing method for simultaneously determining the yield stress and fracture toughness of polymeric materials. The work is of particular importance to the fracture toughness characterisation of the tough and ductile thermoplastic polymers as the toughness of such materials is difficult to measure via conventional fracture mechanics testing techniques. In addition, the new cutting theory is applied to the study of machining characteristics of the thermosetting epoxies and epoxy composites. The main focus is to understand the mechanism of brittle- to- ductile transition in the cutting-induced material separation process. An energy based analysis of the orthogonal cutting process was adopted for the determination of the yield stress and fracture toughness, i.e. σY and Gc of a polymeric workpiece material. It is found that varying tool rake angle from 0° to 30° does not exert significant influence on the determination of Gc. However, Gc shows a decreased tendency with decreasing depth of cut as the crack-tip plastic zone ahead of the tool cutting edge is constrained by the limited depths of cut. It is also observed that simultaneous bending and shearing take place on the shear plane during the orthogonal cutting chip formation process. The inclusion of the bending energy in the cutting analysis can correct the previously derived high values of yield stress. In addition, the brittle- to- ductile chip formation behaviour in machining of the brittle epoxies is clarified. The transition is ascribed to ductile-regime cutting as the depth of cut is reduced to be comparable with the size of plane strain crack-tip plastic zone. Furthermore, not only the depth of cut, but also the ratio of Gc/σY of a material controls the characteristics of the cutting-induced material separation process.
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Arsène, Sylvie. "Effet de la microstructure et de la température sur la transition ductile-fragile des zircaloy hydrures." Châtenay-Malabry, Ecole centrale de Paris, 1997. http://www.theses.fr/1997ECAP0550.
Повний текст джерелаАнотація:
Le zircaloy est largement utilisé dans les centrales nucléaires, notamment pour les tubes de gainage. Ces tubes sont susceptibles de subir une pression interne lors de leur séjour en réacteur. Notre but est de déterminer l'influence de la microstructure, de la température, de l'hydruration et finalement de l'irradiation sur la transition ductile-fragile et les propriétés mécaniques des tubes sollicites en traction dans la direction circonférentielle. Pour les besoins de l'étude, nous avons propose une amélioration de l'essai de traction sur anneau classique. Les modélisations de cet essai avec la méthode des éléments finis ont permis de vérifier que les contraintes et les déformations sont bien homogènes dans la partie entaillée de l'anneau et de proposer une méthode pour dépouiller les résultats expérimentaux et de la valider sur les alliages connus. Des essais sur anneau effectues sur deux alliages de zirconium (détendu et recristallisé), pour différentes concentrations en hydrogène, à 20°C et à 300°C ont permis de déterminer l'influence de la température et l'hydruration sur le comportement et la rupture de ces alliages. L’observation des surfaces et des profils de rupture a mis en évidence les paramètres physiques et mécaniques gouvernant la transition ductile-fragile dans les différents cas. La distance interhydrures est le paramètre primordial dans le cas du matériau détendu alors que la longueur d'hydrures radiaux contigus est le facteur déterminant dans le cas du matériau recristallisé. La ductilité importante du zircaloy détendu de notre étude et les résultats des observations au MEB nous ont incité à étudier plus en détail les hydrures, leur rupture et leur comportement. Les observations, faites lors d'essais a 20°C dans l'enceinte du MEB, ont montre que les hydrures se déforment de 20 a 80% avant de rompre dans les alliages hydrures a 1000 ppm. Nous avons pu évaluer la loi de comportement des hydrures puis la contrainte a rupture des hydrures par méthode inverse grâce à une modélisation micro-macro. Nous proposons une hypothèse expliquant la plasticité importante observée.
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Lessmann, Moritz. "Non-ductile design of demo divertor armour : towards the probabilistic reliability assessment of brittle tungsten components in their irradiated state." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/nonductile-design-of-demo-divertor-armour-towards-the-probabilistic-reliability-assessment-of-brittle-tungsten-components-in-their-irradiated-state(2be9bcee-5d9f-41cc-82fb-4f7b662b0a6a).html.
Повний текст джерелаАнотація:
In-vessel tungsten components of a future demonstration fusion reactor are likely to be operated in the material's non-ductile regime. Assessment of the components' reliability is not possible with current ductile design codes or through experimental qualification. There is therefore an urgent need for non-ductile assessment procedures. One such approach currently considered is Weibull's weakest link theory, which is based on linear-elastic fracture mechanics and has its origins in ceramics. A full assessment of its validity has been performed, and the challenge of obtaining irradiated material data addressed. Bend tests at the macroscopic scale confirm previous findings that the scatter in strength of pure tungsten follows a two-parameter Weibull distribution, provided the material fractures within its elastic regime. However, tests conducted over a range of specimen sizes reveal the technique's shortcomings in accurately predicting the material's size effect in fracture, questioning its applicability to pure tungsten and also other brittle metallic materials. Fracture strength tests conducted at the micrometre scale through cantilever bending have addressed the challenge of obtaining irradiated material data. An ultra-fine grained self-passivating tungsten alloy, considered as an alternative contender to tungsten for in-vessel components, is shown to fracture within its linear-elastic regime at the microscopic scale. A reliable and repeatable measurement of its strength of approximately 5.9 GPa is obtained. The scatter in measurements is shown to be greater than random errors, and to be described well by a two-parameter Weibull distribution. Cantilever tests conducted over a range of specimen sizes reveal a strong size effect (4.3 - 9.0 GPa), which is accurately predicted by Weibull's weakest link theory. Ion implantations, conducted in the tungsten alloy to mimic neutron induced elastic collision damage, result in a statistically confirmed drop (6 %) in cantilever measured fracture strength at low doses (0.7 dpa), and an increase (9-16 %) at higher doses (7 dpa).The cantilever test technique is therefore suitable for the measurement of ion and neutron irradiation effects on the material's fracture strength. Provided a full validation of Weibull's weakest link theory strength extrapolation from the micro- to macroscopic scale is realised on a future heterogeneity free material batch, irradiated material data obtained from cantilever tests could be used to assess the reliability of in-vessel components fabricated from a self-passivating tungsten alloy, and fill the current gap in non-ductile design assessment procedures.