Dissertations / Theses on the topic 'Small Fatigue Crack Growth'
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1
Li, Xu-Dong. "On kinetics of small fatigue crack growth." Thesis, Open University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296607.
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Zhang, Y. H. "Small fatigue crack growth in high strength aluminium alloys." Thesis, Open University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314821.
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Hennessey, Conor Daniel. "Modeling microstructurally small crack growth in Al 7075-T6." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53947.
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Fatigue of metals is a problem that affects almost all sectors of industry, from energy to transportation, and failures to account for fatigue or incorrect estimations of service life have cost many lives. To mitigate such fatigue failures, engineers must be able to reliably predict the fatigue life of components under service conditions. Great progress has been made in this regard in the past 40 years; however one aspect of fatigue that is still being actively researched is the behavior of microstructurally small cracks (MSCs), which can diverge significantly from that of long cracks. The portion of life spent nucleating and growing a MSC over the first few grains/phases can consume over 90% of the total fatigue life under High Cycle Fatigue (HCF) conditions and is the primary source of the scatter in fatigue lives. Therefore, the development of robust fatigue design methodologies requires that the MSC regime of crack growth can be adequately modeled. The growth of microstructurally small cracks is dominated by influence of the local heterogeneity of the microstructure and is a highly complex process. In order to successfully model the growth of these microstructurally small cracks (MSCs), two computational frameworks are necessary. First, the local behavior of the material must be modeled, necessitating a constitutive relation with resolution on the scale of grain size. Second, a physically based model for the nucleation and growth of microstructurally small fatigue cracks is needed. The overall objective of this thesis is best summarized as the introduction these two computational frameworks, a crystal plasticity constitutive model and fatigue model, specifically for aluminum alloy 7075-T6, a high-strength, low density, precipitation hardened alloy used extensively in aerospace applications. Results are presented from simulations conducted to study the predicted crack growth under a variety of loading conditions and applied strain ratios, including uniaxial tension-compression and simple shear at a range of applied strain amplitudes. Results from the model are compared to experimental results obtained by other researchers under similar loading conditions. A modified fatigue crack growth algorithm that captures the early transition to Stage II growth in this alloy will also be presented.
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Jin, Ohchang. "The characterization of small fatigue crack growth in PH13-8 Mo stainless steel." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19633.
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Gockel, Brian Timothy. "Developing the capability to examine environmental effects on small fatigue crack growth." Dayton, Ohio : University of Dayton, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271184488.
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Thesis (M.S. in Mechanical Engineering) -- University of Dayton.Title from PDF t.p. (viewed 06/22/10). Advisor: Robert Brockman. Includes bibliographical references (p. 42-44). Available online via the OhioLINK ETD Center.
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Goulding, A. "Small fatigue crack growth in a near alpha titanium alloy : crack closure, stress gradient and temperature considerations." Thesis, Swansea University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637082.
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The effect of fatigue crack closure in IMI 829 has been addressed for cracks growing from plain surfaces and under the influence of a stress concentration. Several test-piece configurations were employed, incuding thick and thin section double edge notches and standard corner crack (CC) geometries. All types incorporated an ultra fine corner slit to bias the crack initiation site. A thin double edge notch (DEN) specimen with a through section starter slit was also tested. Crack closure loads were measured using direct current potential drop (PD) and replica techniques. The primary closure mechanism was found to be a plasticity induced closure. The results indicate the dominance of surface effects. They also permit near tip and wake related closure effects to be resolved. At the higher stresses, notch root plasticity in the thick DEN dominates closure. At lower stresses where elastic conditions prevail, the results were comparable to those found in the plain CC specimen. Much work was carried out to characterise closure of part-through and through thickness cracks in the thin section notch. The transition between the two crack types invoked a complex closure response. A secondary closure mechanism was also identified, for all specimen types. This was roughness induced closure. On the basis of the PD measurements, an effective ΔK was derived which improved correlation of data over the range of stress levels and R values tested. At room temperature, crack lengths were measured using the above PD system and an existing photomicroscopic arrangement. A study of crack shape morphology was carried out using optical and SEM techniques. The observed complex stress and crack length dependency of shape development in thick notch specimens at higher stresses, was explained on the basis of enhanced plasticity induced closure in the notch root. Other deviations from expected shape characteristics, could be rationalised in terms of microstructural interactions.
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Steadman, David Lawrence. "Growth-arrest behavior of small fatigue cracks." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/11731.
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Galland, Florent. "An adaptive model reduction approach for 3D fatigue crack growth in small scale yielding conditions." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00596397.
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It has been known for decades that fatigue crack propagation in elastic-plastic media is very sensitive to load history since the nonlinear behavior of the material can have a great influence on propagation rates. However, the raw computation of millions of fatigue cycles with nonlinear material behavior on tridimensional structures would lead to prohibitive calculation times. In this respect, we propose a global model reduction strategy, mixing both the a posteriori and a priori approaches in order to drastically decrease the computational cost of these types of problems. First, the small scale yielding hypothesis is assumed, and an a posteriori model reduction of the plastic behavior of the cracked structure is performed. This reduced model provides incrementally the plastic state in the vicinity of the crack front, from which the instantaneous crack growth rate is inferred. Then an additional a priori model reduction technique is used to accelerate even more the time to solution of the whole problem. This a priori approach consists in building incrementally and without any previous calculations a reduced basis specific to the considered test-case, by extracting information from the evolving displacement field of the structure. Then the displacement solutions of the updated crack geometries are sought as linear combinations of those few basis vectors. The numerical method chosen for this work is the finite element method. Hence, during the propagation the spatial discretization of the model has to be updated to be consistent with the evolving crack front. For this purpose, a specific mesh morphing technique is used, that enables to discretize the evolving model geometry with meshes of the same topology. This morphing method appears to be a key component of the model reduction strategy. Finally, the whole strategy introduced above is embedded inside an adaptive approach, in order to ensure the quality of the results with respect to a given accuracy. The accuracy and the efficiency of this global strategy have been shown through several examples; either in bidimensional and tridimensional cases for model crack propagation, including the industrial example of a helicopter structure.
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Ward, D'Anthony Allen. "The Effect of Dwell Loading on the Small Fatigue Crack Growth at Notches in IN100." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1355235018.
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Johnston, Stephen R. "FINITE ELEMENT SIMULATIONS OF THREE-DIMENSIONAL MICROSTRUCTURALLY SMALL FATIGUE CRACK GROWTH IN 7075 ALUMINUM ALLOY USING CRYSTAL PLASTICITY THEORY." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-10242005-133331/.
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This thesis discusses plasticity-induced crack closure based finite element simulations of small fatigue cracks in three dimensions utilizing crystal plasticity theory. Previously, modeling has been performed in two dimensions using a double-slip crystal plasticity material model. The goal of this work is to extend that research using a full three-dimensional FCC crystal plasticity material model implementation that accounts for all twelve FCC slip systems. Discussions of Python scripts that were written to perform analyses with the commercial finite element code ABAQUS are given. A detailed description of the modeling methodology is presented along with results for single crystals and bicrystals. The results are compared with finite element and experimental results from the literature. A discussion of preliminary work for the analysis of crack growth around an intermetallic particle is also presented.
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Patel, Akshay Mahesh. "Growth of small fatigue cracks in PH 13-8 Mo stainless steel." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/18185.
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Locke, W. R. "The growth of small fatigue cracks under conditions of confined notch plasticity." Thesis, University of Portsmouth, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303183.
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Salgado, Goncalves Flora. "Caractérisation expérimentale et modélisation des interactions entre fissures et perçages multiples à haute température en élastoplasticité généralisée ou confinée." Thesis, Paris, ENMP, 2013. http://www.theses.fr/2013ENMP0094/document.
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Cette étude s'intéresse à la fissuration des structures multi-perforées, soumises à des sollicitations pouvant aller de la plasticité confinée à la plasticité généralisée. Le cas d'étude considéré est celui des chambres de combustion des turbomachines aéronautiques. Le matériau utilisé est le Haynes 188, un superalliage à base de Cobalt, spécialement conçu pour ce type d'applications. La fissuration des structures multi-percées a été souvent étudiée dans des conditions de plasticité confinée. Ces études doivent être étendues au domaine de la plasticité généralisée.Afin d'étudier les interactions entre fissures et perçages, une éprouvette originale a été conçue. Dans le but de reproduire un motif de base simplifié correspondant aux trous de refroidissement des chambres de combustion, l'éprouvette est percée en son centre par trois trous. Des essais de fissuration isotherme à 900°C sous des chargements de fatigue ont été réalisés avec des niveaux de chargement allant de la plasticité confinée à la plasticité généralisée. Ces essais ont permis d'étudier la durée de vie du motif de base. A partir des résultats expérimentaux de contrainte et de déformation, les essais ont été modélisés à une échelle dite macroscopique avec un modèle de fissuration en énergie. Dans le but d'améliorer la description des essais, la modélisation a été ensuite réalisée à une échelle intermédiaire, dite mésoscopique, à partir de calculs par éléments finisThe purpose of this study is to investigate crack growth of multi-perforated structures when loading can vary from small scale yielding to large scale yielding conditions. In this study we focus on combustion chambers of aerospace engines. The material used in crack growth tests is the Haynes 188, a cobalt based superalloy, specially developed for this type of applications. Studies on crack growth of multi-perforated structures are often made in small scale yielding conditions. These studies have to be extended to large scale yielding conditions.In order to study interactions between cracks and perforations, an original specimen has been developed. The specimen is perforated in the center by three holes inspired by cooling holes of combustion chambers. Fatigue crack growth tests at 900°C have been conducted with loads from small scale to large scale yielding conditions. These tests were used to study life of a base pattern. Using experimental stresses and strains, tests were modeled at a macroscopic scale with an energy based crack growth model. In order to improve experimental results description, tests were modeled at an intermediate mesoscopic scale using finite element calculations
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Kuběna, Ivo. "Early Stages of Fatigue Damage of Steels for Fusion Energetics." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234021.
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Hlavním cílem této práce bylo vysvětlit únavové chování ocelí ODS Eurofer, 14Cr ODS feritické oceli vyráběné v CEA (Commissariat a l’énergie atomique, Saclay, France) a 14Cr ODS feritické oceli vyráběné v EPFL (École Polytechnique Fédérale de Laussane, Switzerland). Pokud to bylo možné byly získané výsledky porovnány s ocelí Eurofer 97. Tato práce je součástí široké spolupráce, která je zaměřena na vývoj konstrukčních materiálů pro fuzní reaktory. V průběhu práce byly provedeny následující experimenty: • Standardní únavové zkoušky za pokojové teploty, při 650 a při 750 , byly získány křivky cyklického zpevnění/změkčení, cyklické deformační křivky, Coffinovy–Mansonovy a Wöhlerovi křivky. Hysterezní smyčky byly detailně analyzovány. • Pozorování mikrostruktury výchozího stavu pomocí TEM a porovnání s mikrostrukturou po cyklickém zatížení. • Pozorování povrchového reliéfu, který vznik díky lokalizaci cyklické plastické deformace - byla odhalena místa iniciace únavových trhlin a byl analyzován mechanismus jejich vzniku. • Měření kinetiky únavových trhlin. Oxidická disperse značně zpevňuje materiály, redukuje cyklické změkčení a stabilizuje mikrostrukturu v celém rozsahu teplot. Byly nalezeny velké rozdíly v životnosti jednotlivých ocelí. Ty byly vysvětleny pomocí rozdílných mechanismů iniciace trhlin a jejich různou rychlostí.
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Junet, Arnaud. "Étude tridimensionnelle de la propagation en fatigue de fissures internes dans les matériaux métalliques." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI006.
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La fatigue est le principal phénomène causant la rupture de structures mécaniques. Pour les très grandes durées de vie, l’amorçage des fissures menant à la rupture des pièces en service passe de la surface au volume. Du fait des difficultés expérimentales, la propagation des fissures internes n’a que très peu été étudiée in situ et en 3D. Il est cependant crucial du point de vue du dimensionnement de connaître le comportement de telles fissures. Dans ces travaux, le suivi in situ de l’amorçage et de la propagation de fissures internes a été réalisé par tomographie aux rayons X (source synchrotron). Premièrement, une méthode de fabrication d’éprouvettes a été élaborée pour permettre de visualiser de manière systématique, non destructive et en 3D la propagation à 20 Hz de fissures internes dans un alliage de titane (Ti-6Al-4V). Un défaut artificiel a pour cela été usiné à la surface d’une tôle laminée de ce matériau. Une seconde tôle, placée sur la première, a été soudée par diffusion au frittage flash, permettant ainsi de rendre le défaut volumique. Des essais de fatigue in situ ont permis de montrer le rôle crucial de l’environnement (vide) ainsi que, dans une moindre mesure, celui de la texture cristallographique sur les vitesses de propagation des fissures internes. Deuxièmement, une machine de fatigue ultrasonique (fréquence de cyclage de 20 kHz) permettant de réaliser des essais in situ au synchrotron a été utilisée pour étudier la propagation 3D de fissures internes dans des éprouvettes d’alliage d’aluminium A357-T6 contenant un défaut interne artificiel. L’obtention préalable de la distribution 3D des grains par tomographie en contraste de diffraction (DCT) a permis d’étudier les mécanismes d’interaction entre la microstructure et le chemin de fissuration en 3DFatigue is the main phenomenon causing the failure of mechanical structures. For very long service lives the initiation of cracks leading to the failure of in service mechanical parts changes from surface to volume. Due to experimental difficulties the propagation of internal cracks has only been studied to a limited extent in situ and in 3D. However, it is crucial from a dimensional point of view to know the behaviour of such cracks. In this work, in situ monitoring of the initiation and propagation of internal cracks was carried out by X-ray tomography (synchrotron source). Firstly, a method for manufacturing specimens was developed to enable systematic, non-destructive, and 3D visualization of the propagation of internal cracks in a titanium alloy (Ti-6Al-4V) at 20 Hz. For this purpose, an artificial defect was drilled on the surface of a rolled sheet of this material. A second sheet, placed on top of the first one, was diffusion bonded by spark plasma sintering, making it possible to make the defect volumetric. In situ fatigue tests showed the crucial role of the environment (vacuum) and, to a lesser extent, that of the crystallographic texture on the internal crack propagation rates. Secondly, an ultrasonic fatigue machine (cycling frequency of 20 kHz) allowing in situ testing at the synchrotron was used to study the 3D propagation of internal cracks in A357-T6 aluminium alloy specimens containing an artificial internal defect. The 3D grain distribution obtained by Diffraction Contrast Tomography (DCT) was used to study the interaction mechanisms between the microstructure and the 3D crack path
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Ahmad, Haider Yousif. "Fatigue crack growth at notches." Thesis, University of Sheffield, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360410.
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Vethe, Stine. "NUMERICAL SIMULATION OF FATIGUE CRACK GROWTH." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18721.
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The purpose of this study was to explore the posibilities and challenges with simulating fatigue crack growth (FCG) by the extended finite element method (XFEM). Another aim was to develope a procedure for XFEM FCG simulations in Abaqus by means of scripting. Finally was the procedure used to simulate FCG in an API standard, cone shaped threaded connection. Different FCG models were reviewed by a limited litterature search and a procedure 2D FCG simulations was carried out by a python script. The procedure succeeded with the simulation of FCG when applied to a model with refined mesh around the crack tip. In the suggested partial tasks of the thesis description were a procedure 3D FCG simulation also suggested, but as this required more computer capacity than available in the study this was not carried out.
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Chambers, A. C. "Mixed mode creep/fatigue crack growth." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328464.
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Ratsimba, Christian H. H. "Fatigue crack growth of filled elastomers." Thesis, Queen Mary, University of London, 2000. http://qmro.qmul.ac.uk/xmlui/handle/123456789/26243.
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In the past, the use of a fracture mechanics approach to describe crack growth in elastomers has been shown to work well for specimens of simple test geometry, simply loaded. This has been the case because elastic strain energy density (e.s.e.d.) functions could reliably be used to calculate both the magnitude of elastic stored energy available to drive a crack and the magnitude of the rate of release of such energy as the crack grows. The aim of this thesis was to investigate the applicability of such a methodology to situations of more complex loading. To this end two novel test-piece geometries were developed. The first consisted of a pure shear geometry with the sample having been pre-strained in the longitudinal direction to varying extents, hence introducing a type of bi-axial deformation. The second consisted of a pure shear geometry test-piece inclined at 30° to the horizontal and loaded in the vertical direction, hence inducing simultaneously pure shear and simple shear loading. Both types of test-piece were used to study the validity of the particular e.s.e.d. functions, the energetics and mechanics of crack growth and crack growth geometries on a macro and micro scale. The constants in particular e.s.e.d. functions were determined by uniaxially deforming in pure shear each of the carbon black reinforced materials used in this study. The resulting functions became progressively less good at predicting the elastic strain energy in the novel geometry test-pieces as the deformation modes became more complex. Anisotropy induced by deforming specimens in one direction was not easily removed even by an imposed large deformation in another direction. Nevertheless, the functions were successfully used to predict crack growth directions in the 30° inclined test-piece. However in the pre-strain pure shear test-pieces the functions significantly underestimated the elastic strain energy. Hence the real energies had to be determined from the forces and extensions measured during cyclic crack growth tests. In these tests crack growth rates for a given tearing energy (elastic energy release rate) increased as the magnitude of the pre-strain increased. This significant weakening was associated with the development of a strain induced molecular and carbon black anisotropy.
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Lin, Xiaobin. "Numerical simulation of fatigue crack growth." Thesis, University of Sheffield, 1995. http://etheses.whiterose.ac.uk/14437/.
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This thesis describes the advances made by the author on the direct modelling of the fatigue growth of planar cracks A versatile step-by-step 3D finite element technique has been developed, which calculates the stress intensity factors at a set of points on the crack front according to linear elastic fracture mechanics principles and then applies a fatigue crack growth la\v to this set of points to obtain a new crack profile The software DUCK developed has a good capability of automatic remeshing so that the fatigue propagation of arbitrary shaped cracks can be conveniently followed The stress intensity factor calculation using the 3D finite element method has been improved and widely verified to be of good accuracy generally, which provides an important guarantee for the fatigue growth prediction. Several major problems associated with the stress intensity factor calculation, such as crack front definition, free surface layer and mesh abutting the crack front, as well as J-integral path independence, have been discussed A variety of cracked geometries of either theoretical or practical significance have been modelled by the numerical technique, including internal defects in infinite solids, surface cracks in finite thickness plates, round bars and pressure vessels, and initially multiple surface small cracks. Many results useful for the fatigue assessment of each kind of crack, such as stress intensity factor variations, fatigue shape changes and fatigue lives, have been obtained. By comparing with existing numerical methods and some limited experimental data found in the literature, it is shown that the numerical simulation technique is reliable and can predict the fatigue propagation of complex crack configurations, which is seldom possible for methods with assuming crack front configurations Meanwhile, due to the highly automated procedure or the technique, it has become straightforward to model the fatigue growth of practical cracked components, as demonstrated by the computations in this thesis. It is believed that such a numerical simulation technique has a great potential and will play an useful role in the area of fatigue study and assessment.
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Verma, Dhirendra. "Stochastic modeling of fatigue crack growth." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1054565393.
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Zhang, Hong Carleton University Dissertation Engineering Mechanical. "Fatigue crack growth and coalescence study." Ottawa, 1993.
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Nosair, S. I. M. "Fatigue crack growth in aluminium alloy structures." Thesis, University of Salford, 1986. http://usir.salford.ac.uk/26840/.
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Fatigue cracks have been reported in the super structure of the surface ships in the navy. Repair techniques have been proposed and applied on compact tension specimens. Such techniques were; either by creating compressive residual stresses using welding anisotropy, local plastic deformation and spot heating. Or, constraining the crack tip using tightened bolt or steel/carbon fibre patches. Complete F.C.G. data were obtained for the metal in the as-rolled and welded conditions. A metallurgical study has also been made. Fractography, the influence of residual stresses and second phases have been studied. The study showed that superior crack resistance was obtained from spot heated specimens, which were very simple to prepare. Considerable retardation was also obtained using welding anisotropy, local plastic deformation and tightened bolts. Patching seems to provide limited improvement. The influence of compressive residual stress was found to improve the crack resistance. The influence of the inclusions was found to depend on their morphology. Medium sized and homogeneously distributed inclusions provided a retarding effect on the crack speed. More inclusion interaction was reported in the presence of residual stresses.
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Ljustell, Pär. "On predictions of fatigue crack growth rates /." Stockholm : Royal Institute of Technology, Department of Solid Mechanics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-281.
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Chahardehi, Amir Ebrahim. "Fatigue Crack Growth in Complex Stress Fields." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3481.
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Fatigue crack growth has been traditionally modelled using LEFM through the use of
the Paris law. This requires an accurate method for stress intensity factor (K)
calculation. Weight functions have been developed for one-dimensional cracks (e.g.
edge and through cracks); these are functions that enable separation of the loading and
geometry and considering the effect of each one of these two factors on the stress
intensity factor (SIF) separately. They have been proven to be useful for arbitrary stress
distributions where an accurate empirical formula for the stress intensity factor does not
exist. Such cases include residual stress fields due to surface treatments or welds.
However, in the case of surface cracks, or part-through cracks, the problem of
modelling the growth of these cracks poses two main questions, namely, how should the
Paris law be generalised to suit the two-dimensional scenario, and under arbitrary
loadings, how can the SIFs be calculated for these cracks. Current solutions involve
tedious mathematical calculations and are complicated functions.
In this thesis, the concept of root mean square (RMS) SIF is examined and by drawing
mathematical analogy with the one-dimensional case, a novel weight function is derived
which enables calculation of RMS SIF values for a range of semi-elliptical surface
cracks under arbitrary loadings. The accuracy of the weight function is verified through
comparisons with finite elements results for a variety of loadings/geometries. The
simplicity of the weight function construction method makes it a useful tool for fatigue
life predictions where incremental recalculations of SIF is required as the crack grows.
Surface treatments such as shot peening and laser peening are used for crack growth
retardation. It is generally believed that it is through the introduction of what is termed
‘beneficiary compressive residual stresses’ that crack retardation occurs. The
compressive residual stresses are superimposed on the ‘detrimental tensile stresses’ due
to loading and hence lead to a lower SIF level. By having such a strong tool as weight
functions, this general belief can be put to test. To this end, a set of experiments were
carried out to study the behaviour of cracks in residual stress fields arising from laser
peening. Edge cracks were grown in partially-peened specimens. Neutron diffraction
stress measurements were taken and stress profiles were obtained for these specimens.
Measurements of strain fields near the crack show the interaction between the crack and
the stress field induced by the peening process. The effect of laser peening on crack
growth is discussed and recommendations for future work are proposed.
Overall the thesis proposes a weight function for surface cracks the uniqueness of which
is in its simplicity, and develops an understanding of the nature of induced and transient
stresses in laser-peened components. The concept of ‘effective fatigue stress’ is
introduced and its calculation is described, and conclusions are drawn from the nature of
this stress distribution.
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Henderson, M. B. "Fatigue crack growth in single crystal superalloys." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314993.
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Monahan, Craig C. "Early fatigue crack growth in offshore structures." Thesis, University College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271908.
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Isogai, Takeshi. "Creep-fatigue crack growth in engineering materials." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627408.
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Bold, P. E. "Multiaxial fatigue crack growth in rail steel." Thesis, University of Sheffield, 1990. http://etheses.whiterose.ac.uk/14807/.
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In the introduction to a recent symposium on rolling contact fatigue, R.A.Smith stated that it was difficult to apply our greatly increased understanding of metal fatigue, to rolling contact fatigue, because of "the apparent lack of alternating tensile stresses to drive the cracks." He went on to say "alternating shear stresses are easily found, but the reproduction of continuous crack growth controlled by shear (Mode II in fracture mechanics terms), has proved to be near impossible." This project has demonstrated that under specific conditions this mode of growth does occur. The project began by studying rolling contact fatigue defects, in particular the 'squat' defect in railway lines, and the stress analyses that have been performed on them. It was concluded that the largest stress cycle experienced by the cracks must be a shear stress. It. series of tests were then performed that loaded a crack in pure shear, or a mixture of tension and shear, looking at the effects of using fully reversed shear loading, and the effects of applying tensile mean stresses to reduce the friction on the crack flanks. However these tests all produced less than one millimetre of mode II growth, before the cracks arrested or branched. The final series of tests however applied a tensile load cycle before each shear load cycle. This time coplanar growth was produced, that is the crack grew in the direction of the maximum shear stress. This type of load cycle is a simplification of the load cycle calculated by Bower and Johnson of Cambridge University, where the tensile load is produced by fluid trapped in the crack. Two crack growth rate formulae were produced that fitted the data, indicating that the growth rate was dependent on both the tensile and the shear parts of the cycle.
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Geary, W. "Fatigue crack growth in iron silicon alloys." Thesis, Sheffield Hallam University, 1985. http://shura.shu.ac.uk/20609/.
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A technique for accurately monitoring fatigue crack growth at near threshold growth rates has been established. The characteristics of near threshold fatigue crack growth of a number of iron-silicon alloys has been quantitatively and qualitatively investigated. Relationships have been established relating the stress intensity factor, AK, and the fatigue crack growth rate da/dN. At fatigue crack growth rates approaching threshold the material has shown some microstructural sensitivity and this has been related to the stress intensity factor and the yield stress. A relationship has been shown to exist between the value of the threshold stress intensity factor and the inverse root of the grain size, d~2, for each of the alloys investigated. A model for near threshold fatigue crack growth has been proposed and includes the contributions made by grain size and crack tip plasticity. This work has also shown that fatigue crack closure plays an important role in the micromechanisms of fatigue crack growth near the threshold at low R ratio s. A number of mechanisms have been identified: crack closure due tothe presence of oxidation products on fracture surfaces in tests conducted in air, and closure due to the presence of fatigue fretting, facet contact and a contribution of mixed mode opening.
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Shademan, Sassan Steven. "Mechanism-based models of fatigue crack growth /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488203857249745.
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Doré, Matthew James. "An investigation of fatigue crack growth acceleration." Thesis, Open University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.700486.
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The problem of fatigue crack growth acceleration was investigated in crack propagation studies and endurance testing. The study was driven by the needs of designers and researchers alike, to provide a better understanding of the mechanisms associated with accelerated growth, and recommendations on the use of Miner's rule to calculate fatigue life under variable amplitude loading. The study was conducted on S355 structural steel and 6082 T6 aluminium alloy using centre-crack tension (CCT) specimens, with and without additional welding, and longitudinal fillet welded specimens. Crack growth rates under simple sequence loading and more complex variable amplitude CV A) loading, all cycling down from fixed tensile stress levels, were determined using optical or direct current potential' drop methods and scanning electron microscope examination of fracture surface striations. Under simple loading sequences, comprising two magnitudes of stress range, the presence of tensile underloads resulted in accelerated growth rates compared with those based on constant amplitude (CA) loading. Various possible mechanisms to explain crack growth acceleration and factors that might influence it, notably crack closure and welding residual stress, were evaluated. The most promising outcome came from finite element analysis (FEA) of the crack tip stress and strain. This showed that whereas under CA loading the material near the crack tip cycled about zero mean stress, the mean stress was tensile after the application of a tensile underload, thus resulting in a higher crack growth rate. Fatigue endurance testing of welded joints performed under the same types of loading confirmed that Miner's rule overestimated the actual lives, consistent with the occurrence of acceleration. Thus, it was concluded that modification of the principle and application of Miner's rule is required to allow for stress interactions that cause crack growth acceleration. Preliminary design recommendations were made.
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Hu, Haiyun. "Fatigue and corrosion fatigue crack growth resistance of RQT501 steel." Thesis, University of Sheffield, 1997. http://etheses.whiterose.ac.uk/5999/.
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This project is concerned with the fatigue response of roller quenched and tempered (RQT50I) steels. Three closely related aspects are considered: (i) the relationship between the microstructure and fatigue properties, (ii) the influence of the environment on fatigue properties, (iii) theoretical modelling of fatigue crack growth. The material used is an RQT501 grade steel. Two steels have been chosen: (A) without Mo and V additions, (B) with Mo and V additions. The second condition is chosen to evaluate the role of these elements, as hydrogen traps, on the resistance to corrosion fatigue crack growth. In order to evaluate these effects, tests have been carried out under freely corroding conditions and applied cathodic polarisation (-9 . SO mV/SCE). Metallographic examination has been carried out to evaluate grain size and inclusion distribution, size and morphology. To enable a comparison between short and long fatigue crack growth, smooth shallow hour-glass specimens have been used to study initiation and growth of short fatigue cracks, and compact tension specimens were used to monitor propagation of long fatigue cracks. The fatigue response (S - Nf curve) and fatigue crack growth rate behaviour has been studied in air (5 - 10 biz) and in 3.5%NaCI solution (0.2 Hz) or artificial seawater (0.2 Hz) with an applied stress ratio of 0. I and sinusoidal waveform. The generation and growth behaviour of cracks from smooth hour-glass specimens has been investigated through successive observation using the plastic replication method. Long fatigue crack lengths were measured using a Direct Current Potential Drop (DCPD) technique and monitored via a chart recorder. Based upon the results of these tests a fatigue crack growth model was developed based on non-equilibrium statistical theory incorporating a consideration of the influence of microstructure, e. g. grain boundaries and hydrogen embrittlement. A stochastic theory of corrosion has also been developed for the use with corrosion fatigue test data.
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Mohin, Ma. "Fatigue crack growth assessment and fatigue resistance enhancement of aluminium alloys." Thesis, University of Hertfordshire, 2018. http://hdl.handle.net/2299/20824.
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Fatigue damage of aluminium alloys is one of the key concerns in transport industries, particularly in the aerospace industry. The purpose of the project is to develop new knowledge and techniques against fatigue failure for these industries through a systematic investigation of fatigue resistance and crack growth behaviours of aluminium alloys. Fatigue and fracture mechanics have been investigated analytically, numerically and experimentally in this project. Overload transient effect on fatigue crack growth has been examined by considering various parameters including crack closure, overload ratio (OLR), load ratio (R ratio), baseline stress intensity factor range, (∆K)_BL and geometry. It was found that crack closure can be correlated qualitatively and quantitatively to all other parameters associated with overload transient behaviour. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve can be separated to obtain reliable crack closure measurement. In this project, different methods are used to better understand the transient retardation process so that the damage tolerance design (DTD) of the components made of aluminium alloys can be enhanced. Another important parameter for fatigue and damage tolerance design (DTD) of engineering components is the threshold stress intensity factor range for fatigue crack growth, ∆K_th. A small variation in identification of ∆K_th can lead to a big change in overall estimation of fatigue life. In this project, an analytical model has been developed for aluminium alloys by fitting an analytical curve with raw crack growth data in order to identify the ∆K_th. This model has the capacity to identify ∆K_th for different aluminium alloys at various R ratios. There is a great demand for enhanced fatigue life of aluminium alloys in the transport industry. This project has carried out a detailed investigation of electromagnetic treatment (ET) in the form of electropulsing treatment to develop an efficient technique for fatigue resistance enhancement. ET parameters including the treatment intensity, treatment time and the number of applications have been optimised. It is suggested that the duration of ET treatment can be used as the main parameter among all these to control the fatigue resistance of the aluminium alloy. The improvement in fatigue resistance has been explained by the change in microhardness and conductivity of aluminium alloy due to ET. Additionally, the fracture morphology was analysed using scanning electron microscopy (SEM). The precipitates and dislocation characteristics were also studied using transmission electron microscopy (TEM). The outcomes of this investigation will help improve structural integrity by enhancing fatigue resistance of aluminium alloys.
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Nagaralu, Ramesh. "Fatigue Crack Growth Under Residual Stresses Around Holes." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11112005-143754/.
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Compressive residual stresses induced by tensile overloads, compressive under loads, or by a cold-expansion process in specimens containing a circular hole and their influence on subsequent fatigue crack growth in aluminum alloys are studied. The finite element method is used to calculate residual stresses. The superposition method, which uses crack-tip stress intensity factors for cases involving remote loading and residual stresses, is used to calculate crack growth life for three kinds of tests from the literature: (1) fatigue of a circular hole specimen after an overload or under load, (2) single crack growing from a circular hole after a severe tensile overload, and (3) single crack growing from a circular hole after cold-working, reaming and notching. All specimens were subjected to subsequent constant amplitude loading. The superposition method worked fairly well for most cases, but tended to over predict fatigue life for small cracks and for cracks growing under residual stresses, which produce compressive (maximum and minimum) stress intensity factors.
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Damri, Daniel. "Transient fatigue crack growth in a structural steel." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386012.
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Ferreira, João Guilherme Gaspar Cordeiro. "Numerical modelling of fatigue crack growth using XFEM." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14344.
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Mestrado em Engenharia MecânicaThe Finite Element Method (FEM) is one of the most efficient tools used, in computational solid mechanics, for the numerical solution of Partial Differential Equations (PDE). This numerical technique has been extensively used in the past decades for finding approximate solutions to PDE in both engineering and science fields. A main feature of the FEM is the subdivision of a continuum into a discrete set of elements, being these elements connected by a topological map, usually referred to as the finite element mesh. The FEM can generally be used to model and predict the behaviour of continuous structures. However, problems arise when FEM is used on a domain with a discontinuity (like a crack). In this case, it is usual to use adaptive mesh refinement around the discontinuity. This process works ne, but has a very high computational cost. Alternatively, the eXtended Finite Element Method (XFEM) is a numerical method for modelling strong and weak discontinuities using local enrichment. It is a FEM generalization that enables the incorporation of local enrichment of approximation spaces. This enrichment is done through the partition of unity concept by adding special functions to the finite element approximation. For crack modelling in isotropic linear elasticity, the Heaviside function is used to enrich the completely cut elements and an asymptotic function is used to enrich the crack tip elements. This enrichment creates new degrees of freedom that must be integrated into the analysis during a post-processing step. This enables the domain to be modelled without explicitly meshing the crack surfaces and without a remeshing process for the crack propagation. In this context, this work addresses the main concepts of FEM and XFEM, the creation of a pedagogical XFEM software (with its numerical implementation process and software manual) and the differences between a standard FEM implementation and a XFEM program. Finally, some numerical results of the XFEM application are presented.
O Método dos Elementos Finitos (Finite Element Method - FEM) é uma das ferramentas mais eficientes para a obtenção de soluções numéricas de Equações Diferenciais Parciais (EDP) em mecânica dos sólidos computacional. Esta técnica numérica tem vindo a ser utilizada extensivamente durante as últimas décadas para a obtenção de soluções aproximadas de EDP, tanto a nível de engenharia como a nível científico. Uma das principais características do FEM é a subdivisão de um meio contínuo numa série de elementos discretos, estando esses elementos ligados por um mapa topológico, normalmente referido como malha dos elementos finitos. O FEM é utilizado geralmente para modelar e prever o comportamento de estruturas contínuas. Contudo, surgem problemas quando o FEM é utilizado em domínios que contenham descontinuidades (tais como fendas). Neste caso, é normalmente utilizado um refinamento de malha adaptativo em torno da descontinuidade. Este processo funciona perfeitamente, mas acarreta um enorme custo computacional. Alternativamente, o Método dos Elementos Finitos Estendidos (eXtended Finite Element Method - XFEM) é um método numérico utilizado para modelar descontinuidades fortes e fracas, utilizando enriquecimento local. É uma generalização do FEM que permite a incorporação de enriquecimento local de aproximação de espaços. Este enriquecimento é feito através do conceito de partição de unidade, ao adicionar funções especiais à aproximação por elementos finitos. Para a modelação de uma fenda em regime linear elástico isotrópico, é utilizada a função de Heaviside para enriquecer os elementos que são completamente cortados pela fenda, e a função assimptótica para enriquecer os elementos que contenham a ponta de fenda. Este processo de enriquecimento cria novos graus de liberdade que têm de ser incorporados no sistema, através de uma etapa de pós-processamento. Isto permite que o domínio possa ser modelado, sem que exista a preocupação de fazer coincidir a malha com a localização da fenda, e que seja preciso recorrer a um processo de remalhamento caso exista propagação da fenda. Neste contexto, o presente trabalho aborda os principais conceitos de FEM e XFEM, a criação de um software pedagógico de XFEM (com o seu processo de implementação numérica e manual do software) e as principais diferenças entre a implementação padrão do FEM e um programa de XFEM. Finalmente, são apresentados alguns resultados numéricos da aplicação do XFEM.
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McFadyen, Neil B. (Neil Barry) Carleton University Dissertation Engineering Mechanical. "Fatigue crack growth in semi-elliptical surface cracks." Ottawa, 1987.
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Bian, Lichun, and 卞立春. "Fatigue crack growth analysis of metallic plates with an inclinedsemi-elliptical crack." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31242844.
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Sabuncuoglu, Baris. "Fatigue Crack Growth Analysis Models For Functionally Graded Materials." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607024/index.pdf.
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The objective of this study is to develop crack growth analysis methods for functionally graded materials under mode I cyclic loading by using finite element technique. The study starts with the analysis of test specimens which are given in
ASTM standard E399. The material properties of specimens are assumed to be changing along the thickness direction according to a presumed variation function used for the modeling of functionally graded materials. The results of the study reveal the influence of different material variation functions on the crack growth
behavior.
In the second part, the growth of an elliptical crack which is a common case in engineering applications is analyzed. First, mode I cycling loading is applied perpendicular to the crack plane and crack growth profiles for a certain number of cycles are obtained for homogeneous materials. Then, the code is extended for the analysis functionally graded materials. The material properties are assumed to vary as an exponential function along the major or minor axis direction of the crack. The results can be used to examine the crack profile and material constants&rsquoinfluence for a certain number of cyclic loading.
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De, Noronha Motta Carlos Henrique. "A fatigue crack growth model with mean stress effects." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq21163.pdf.
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LaRue, James Edward. "The Influence of Residual Stress on Fatigue Crack Growth." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04072005-095303/.
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This thesis discusses the analysis of fatigue crack growth in the presence of residual stresses to determine a suitable method for fatigue life predictions. In the research discussed herein, the prediction methodologies are compared to determine the most accurate prediction technique. Finite element analysis results are presented as well as laboratory test data. The validity of each methodology is addressed and future work is proposed.
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Adair, Benjamin Scott. "Thermo-mechanical fatigue crack growth of a polycrystalline superalloy." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/46027.
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A study was done to determine the temperature and load interaction effects on the fatigue crack growth rate of polycrystalline superalloy IN100. Temperature interaction testing was performed by cycling between 316°C and 649°C in blocks of 1, 10 and 100 cycles. Load interaction testing in the form of single overloads was performed at 316°C and 649°C. After compiling a database of constant temperature, constant amplitude FCGR data for IN100, fatigue crack growth predictions assuming no load or temperature interactions were made. Experimental fatigue crack propagation data was then compared and contrasted with these predictions. Through the aid of scanning electron microscopy the fracture mechanisms observed during interaction testing were compared with the mechanisms present during constant temperature, constant amplitude testing. One block alternating temperature interaction testing grew significantly faster than the non-interaction prediction, while ten block alternating temperature interaction testing also grew faster but not to the same extent. One hundred block alternating testing grew slower than non-interaction predictions. It was found that as the number of alternating temperature cycles increased, changes in the gamma prime morphology (and hence deformation mode) caused changes in the environmental interactions thus demonstrating the sensitivity of the environmental interaction on the details of the deformation mode. SEM fractography was used to show that at low alternating cycles, 316°C crack growth was accelerated due to crack tip embrittlement caused by 649°C cycling. At higher alternating cycles the 316°C cycling quickly grew through the embrittled crack tip but then grew slower than expected due to the possible formation of Kear-Wilsdorf locks at 649°C. Overload interaction testing led to full crack retardation at 2.0x overloads for both 316°C and 649°C testing. 1.6x overloading at both temperatures led to retarded crack growth whereas 1.3x overloads at 649°C created accelerated crack growth and at 316°C the crack growth was retarded.
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Woollin, Paul. "Aspects of fatigue crack growth in nickel-based superalloys." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316765.
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Yang, Rong. "Creep-fatigue crack growth in a nickel base superalloy." Thesis, Imperial College London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320941.
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Hall, Rodney H. F. "Crack growth under combined high and low cycle fatigue." Thesis, University of Portsmouth, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290404.
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Hawkyard, Miles. "The fatigue crack growth resistance of Ti-6Al-4V." Thesis, University of Portsmouth, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339512.
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Dodd, A. "Fatigue crack growth in an aluminium-lithium (8090) alloy." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381174.
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Stacey, A. "Prediction of fatigue crack growth in thick-walled tubing." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37864.
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Hughes, Rachelle J. (Rachelle Jane) 1974. "Fatigue crack growth of Incoloy 908 at high temperature." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85272.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999.Includes bibliographical references (leaves 155-159).
by Rachelle J. Hughes.
S.M.