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Joenoes, Ahmad T. "Quantitative analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of low carbon bainitic steel (SAE 15B13)." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19671.
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Lester, Charles Gilbert IV. "Analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of two high strength steels." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42795.
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Building fuel efficient automobiles is increasingly important due to the rising cost of energy. One way to improve fuel efficiency is to reduce the overall automobile weight. Weight reductions using steel components are desirable because of easy integration into existing manufacturing systems. Designing components with Advanced High Strength Steels (AHSS) has allowed for material reductions, while maintaining strength requirements. Two Advanced High Strength steel microstructures investigated in this research utilize different strengthening mechanisms to obtain a desired tensile strength grade of 590MPa. One steel, HR590, utilizes precipitation strengthening to refine the grain size and harden the steel. The other steel, HR590DP, utilizes a dual phase microstructure consisting of hardened martensite constituents in a ferrite matrix. The steels are processed to have the same tensile strength grade, but exhibit different fatigue behavior. The central objective of this research is to characterize and compare the fatigue behavior of these two steels. The results show the dual phase steel work hardens at a low fatigue life. The precipitation strengthened microstructure shows hardening at low strain amplitudes, softening at intermediate strain amplitudes and little to no effect at high strain amplitudes. These different fatigue responses are characterized and quantified in this research. Additionally, observations showing the fracture surfaces and the bulk microstructure are analyzed.
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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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Hattingh, Daniel Gerhardus. "The fatigue properties of spring steel." Thesis, University of Plymouth, 1998. http://hdl.handle.net/10026.1/2300.
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The nature and scope of this thesis can be divided into three categories, namely stress distribution modelling in coil springs; fatigue and failure analysis, an investigation into measurement of residual stresses and the relation to fatigue life. The operation of springs is directly concerned with the theories of torsion and bending which makes the better understanding of these theories essential. The first part of the thesis is involved with a mathematical evaluation of these theories and a case study of an isolated loop of a coil spring. The mathematical modelling is verified by measuring the strain levels in a coil spring with the aid of strain gauges located at different positions in the coil spring. This evaluation gave a better understanding of the operational stress distribution for input into the two methods currently used by industry for the fatigue testing, namely isolated loop and complete coil spring samples. The remaining part of the thesis revolves around the understanding of the relationship between fatigue life, process effects and residual stresses. The relationship between fatigue failures and process effects was investigated to reveal the mechanism responsible for component fatigue failure in a 55Cr3 automotive suspension spring steel. This was done by subjecting coil springs, withdrawn from different stages of the manufacturing process, to fatigue tests, ensuring that all possible sources of fatigue initiation in this material batch have been identified, including those not dominant in the finished component. Failures prior to shot peen process was mainly surface relate as where those withdrawn after this process were subsurface (inclusions) related. Fractographic analysis, using an XL30 scanning electron microscope, has revealed a number of sources of initiation, which are largely related to mechanical damage and inherent material defects. The results indicate that decreasing defect levels in the material would represent a valid method for enhancing the fatigue response, specifically levels of nonmetallic inclusions and surface mechanical damage, but also that certain manufacturing process stages (cold scragg) are responsible for drop in fatigue life.
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Abdul-Salam, Ezzet Hameed. "Fatigue crack propagation in mild steel." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291749.
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Taylor, H. "Fatigue behaviour in high strength steel." Thesis, University of Salford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372146.
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Cyril, Nisha S. "Anisotropy and Sulfide Inclusion Effects on Tensile Properties and Fatigue Behavior of Steels." Connect to full text in OhioLINK ETD Center, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1198808409.
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Thesis (M.S.)--University of Toledo, 2007.Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 204-209.
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Gaur, Vidit. "Fatigue and corrosion-fatigue in Cr-Mo steel in biaxial tension." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX027/document.
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Les connecteurs clips utilisés pour assembler les tubes de riser pour le forage pétrolier offshore subissent un chargement cyclique dû aux vagues. 90% de la durée de service est passée en mode connecté, avec une contrainte moyenne élevée, alors que 10% est passé en mode déconnecté, avec une faible contrainte moyenne. Des calculs numériques montrent qu’un chargement cyclique de tension biaxiale en phase prévaut dans la zone critique de la structure. Les effets de contrainte moyenne et de biaxialité doivent tous deux être pris en compte pour un design approprié. Les critères de fatigue multiaxiale de la littérature sont basés sur des données de traction-torsion et ne discriminent pas bien l’influence de la tension biaxiale de celle d’une contrainte moyenne. Un des objectif de cette étude est donc de caractériser séparément ces deux effets.Pour étudier les effets de contrainte moyenne, des essais de fatigue uniaxiale ont été menés avec différents rapports R. Les durées de vie diminuent avec l'augmentation de R, et la limite d'endurance suit la parabole de Gerber. À faible contrainte moyenne et amplitude de contrainte élevée, les fissures s’amorcent en surface, tandis que pour des rapports R élevés et des amplitudes faibles, les fissures s’amorcent à partir de défauts internes ou coupant la surface. Cette transition est analysée à partir de calculs élasto-plastiques des champs de contrainte et déformation autour des défauts. Les fissures internes se propagent sous un faible ΔK indépendant de R, ce qui est attribué à la quasi absence d’effets de fermeture.Pour étudier l'effet de biaxialité, des essais cycliques de tension et pression interne combinées en diverses proportions ont été effectuées à rapport R fixe (0,25). Un taux de biaxialité modéré (B = 0,25 et 0,5) a un effet bénéfique, attribué à un retard de l'amorçage des fissures, alors que la tension équibiaxiale a un effet légèrement nuisible, attribué à un "pseudo effet de taille" (probabilité plus grande qu’une microfissure se propage le long de deux plans principaux équivalents, au lieu d’un seul).De facettes intergranulaires révélatrices de fragilisation par l'hydrogène ont été observées sur les surfaces de rupture. L’évolution de leur fraction avec ΔK et la biaxialité suggèrent une réduction de la vitesse de fissuration à B≤0.5, mais l'effet néfaste de la tension équibiaxiale ne peut être attribué à une accélération de la propagation.Plusieurs des critères de fatigue existants échouent à décrire toutes les données de cette étude. Les critères d'endurance avec un terme linéaire de contrainte moyenne ou de tension hydrostatique ne parviennent pas à prédire les variations de la limite d'endurance. Un nouveau critère de fatigue a été proposé sur la base de la parabole de Gerber. Il décrit bien les effets combinés d'une contrainte moyenne et d’un taux de biaxialité positif.Des essais biaxiaux ont également été effectués dans l’eau salée (3.5% NaCl) pour étudier l'influence de ce milieu sur les durées de vie en fatigue, en corrosion libre et avec une protection cathodique qui amplifie le dégagement d’hydrogène.En corrosion libre, l'eau salée réduit fortement les durées de vie et supprime la limite d'endurance. Cela est dû à la formation de piqûres de corrosion qui favorisent l’amorçage précoce et multiples de fissures. La tension équibiaxiale n’accentue pas l’effet nocif de l'eau salée, malgré des mécanismes de fissuration différents: décohésion fragile transgranulaires en tension uniaxiale, mais principalement intergranulaire en tension biaxiale.La protection cathodique annule l'effet néfaste de l'eau salée pour tous les taux de biaxialité, en dépit d'un net accroissement de la fragilisation par l’hydrogène des joints de grains. Les surfaces de rupture deviennent presque entièrement intergranulaire, tandis qu’à l'air, le taux de rupture intergranulaire ne dépasse pas 45%The clip connectors used to join the riser tubes for offshore oil drilling undergo cyclic loading due to sea waves. 90% of the service life is spent in the “connected mode” with a high mean stress and 10% in the “disconnected mode” with a lower mean stress. Finite element computations revealed in-phase biaxial tension in the critical areas of the clip connector along with high mean stresses. Thus, both the mean stress effect and the biaxiality effect need to be addressed for proper design of these structures. However, most of the multiaxial fatigue criteria are based on tension-torsion fatigue data and do not discriminate the influence of biaxial tension from that of a mean stress. This study investigates separately these two effects.For investigating the mean stress effect, uniaxial fatigue tests were run on Cr-Mo steel with various R ratios (σmin/σmax). The fatigue lives, as well as the slope of the S-N curves were found to decrease with increasing R, and the endurance limit to follow Gerber’s parabola. At low R ratios and thus relatively high stress ranges, fatigue cracks initiated from the surface, while for high R ratios, and thus low stress ranges, cracks initiated from internal or surface-cutting defects. This transition was analyzed based on elastic-plastic computations of stress-strain fields around the defects. The threshold for internal fatigue crack growth from defects was found to be quite low and independent from the R ratio. This was attributed to a nearly closure-free propagation.To investigate the effect of positive stress biaxiality, combined cyclic tension and internal pressure tests with various proportions of each loading were run on tubular specimens, at fixed R ratio (0.25). Moderate stress biaxialities (B= 0.25 and 0.5) had a beneficial effect on fatigue lives, attributed mainly to a retardation of crack initiation, while equibiaxial tension had a slightly detrimental effect, attributed to a “pseudo size effect” (higher probability for an incipient crack to grow along two possible planes, compared to a single one).Intergranular facets associated with temper and H2 embrittlement were observed on the fracture surfaces. The evolutions of their surface fraction with ΔK and load biaxiality suggested a possible reduction in crack growth rate at moderate biaxialities, but the detrimental effect of equibiaxial tension could not be explained in terms of crack growth rate.Several popular fatigue criteria failed to describe all fatigue data. Endurance criteria that include a linear mean stress term or contain a hydrostatic tension term fail to predict the variations of the endurance limit of this material with the R ratio and biaxiality ratio. Thus, a new fatigue criterion based on Gerber’s parabola was proposed. It captured the evolution of the endurance limit under the combined effects of positive mean stress and biaxiality.Similar tests were run to investigate the influence of salt water (3.5% NaCl) on fatigue lives under two types of test conditions: 1) free corrosion and 2) cathodic protection.In free corrosion, salt water strongly reduced the fatigue lives and suppressed the endurance limit. This was due to the formation of corrosion pits that favor early, multiple crack initiations. The detrimental effect of salt water was not enhanced by equibiaxial tension, which did not modify the size and density of corrosion pits. Fatigue lives in uniaxial and biaxial tension were nearly the same, although the crack growth mechanism was different: transgranular brittle decohesion in uniaxial loading and mostly intergranular in biaxial tension.Cathodic protection cancelled the detrimental effect of salt water for all biaxialities, in spite of a clear enhancement of H-induced embrittlement of the grain boundaries. The fracture surfaces were nearly fully intergranular, irrespective of load biaxialities, while in air the proportion of intergranular fracture was less than 45%
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Mukherjee, Sunit. "Quantitative characterization of void nucleation and growth in HY-100 steels." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/19574.
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Appleton, Richard Joseph. "Corrosion fatigue of a C-Mn steel." Thesis, University of Glasgow, 1985. http://theses.gla.ac.uk/2176/.
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Martinsson, Johan. "Fatigue assessment of complex welded steel structures." Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166.
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selvaraj, nadar vighneish. "Fatigue testing of scratched flapper valve steel." Thesis, Karlstads universitet, Avdelningen för maskin- och materialteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-31704.
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A flapper valve is made from a hardened and tempered high strength strip steel which opens and shuts as it is subjected to very high cyclic loads. Steel strip of which flapper valves are made from can encounter a surface defect which are anticipated to influence fatigue life negatively. In this study, the influence of surface scratches on fatigue life of flapper valve strip was investigated. The analysis was carried out by using thirty samples that were blanked out of eight different steel strips in the transverse direction. Of these samples, fifteen of them had scratches on the surface and fifteen did not, all these samples were fatigue tested by constant amplitude method. An S-N curve was plotted based upon the values and results from the fatigue test, considering the curve as the nerve center in relation with fractrographic studies using the Scanning electron microscope. Therefore this master thesis work aims to explain the influence of scratches on fatigue life of flapper valve strip and suggest future improvements based on the findings.
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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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Shohel, Muhammad Shah Newaz. "Panting Fatigue of Welded Steel Tee Details." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428328220.
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Prasannavenkatesan, Rajesh. "Microstructure-sensitive fatigue modeling of heat treated and shot peened martensitic gear steels." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31713.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: David L. McDowell; Committee Member: G. B. Olson; Committee Member: K. A. Gall; Committee Member: Min Zhou; Committee Member: R. W. Neu. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Connaughton, M. D. "A study of cumulative fatigue and creep-fatigue damage in Type 316 steel." Thesis, Open University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234153.
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Guirgis, Sameh. "Fatigue crack propagation in steel components at resonance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62216.pdf.
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Marrow, Thomas James. "Fatigue mechanisms in an embrittled duplex stainless steel." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386998.
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Lang, Christopher Leslie. "Composite patching of fatigue cracks in steel structures." Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2041.
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Aggelopoulos, Eleftherios S. "Composite patch repair of fatigue-damaged steel members." Thesis, University of Surrey, 2007. http://epubs.surrey.ac.uk/840/.
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The use of adhesively bonded composite reinforcements for strengthening metallic structures is a relatively new technique that has been introduced in the past few years. The technique was first applied for crack patching of aircraft components, with the first civil engineering applications on steel bridge members, which have been damaged due to corrosion or fatigue, being more recent. The finite element (FE) method was employed in order to analyse a steel plate containing a crack and reinforced with an adhesively bonded composite patch. The role of parameters such as the crack size and the properties (modulus and thickness) of the patch and the adhesive was examined. Results in tenns of the stress magnification factor at the crack tip and the shear and peel stress distributions at the steel/adhesive interface were obtained. Following this, the FE results were used in order to develop an analytical model for estimating the stress magnification factor (YJ for patched cracks. The effects of patch pre-stressing and thennal loading due to mismatch in thennal expansion coefficients of the materials involved were also examined. Patch debonding was also investigated. Two different cases were considered, namely a patched plate without a crack and a patched plate containing a crack. For the latter, apart from debonding being initiated from the patch extremities (patch end debonding), crack mouth debonding was also considered. The effect of debonding on Yp was determined. Following this, debonding was modelled as a crack located at the steel/adhesive interface and a fracture parameter, namely the energy release rate G, was obtained at the interface crack tip. An analytical model for G pertaining to patch end debonding was also developed. An experimental study was carried out in order to validate the model proposed for Yp' Fatigue tests of patched cracked specimens were performed and crack growth data was obtained and compared with predictions using the analytical model for Yp inside the well known Paris crack growth law. Prior to this, the tensile properties for steel and composite and the fatigue properties of steel were determined from tests. The results indicate that the models obtained can be used for the design of composite patch repairs of steel members. Therefore, they were included in a design methodology, which is also presented. The latter could form the basis of a more ,comprehensive future design guide, or even complete existing guides, such as the CIRIA . guide (Cadei et a1. 2004).
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Clark, Anita. "Fatigue mechanisms in FV520B, a turbine blade steel." Thesis, Sheffield Hallam University, 1999. http://shura.shu.ac.uk/3127/.
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An investigation has been undertaken to examine the effect of microstructure on the mechanical properties of FV520B, a precipitation hardenable martensitic stainless steel. This high performance grade of stainless steel was heat treated to three commercially available material specifications, namely the peak hardened, standard and softened overaged conditions. These three precipitation hardened conditions were found to exhibit a range of tensile properties. In order to determine the role of the microstructure, a full materials characterisation programme was performed. The investigative techniques used to characterize the microstructures, were Transmission Electron Microscopy (TEM); Analytical Scanning Electron Microscopy (ASEM); optical microscopy; dilatometry and X-Ray Diffraction (XRD). The microstructural phases and features identified were measured and quantified wherever possible. The effect of the material microstructure and environment on the fatigue properties of FV520B have been investigated. Fatigue tests were performed under uniaxial loading conditions at a stress ratio R (omin/omax) of -1. The tests were undertaken using highly polished specimens to determine the fatigue strength of the three precipitation hardened conditions. The test conditions employed were air and a corrosive 3.5% sodium chloride environment, at pH2 and ambient temperature. The role of the microstructure and the effectiveness of the tensile strengthening mechanisms on the fatigue and corrosion fatigue strength have been discussed. Using SEM, the fatigue crack nucleation mechanisms prevalent within the three microstructures in air and the chloride environment have also been identified. For the peak hardened material, nonmetallic inclusions dominated the fatigue crack nucleation process in air and chloride environments. For the softened overaged condition, multiple site nucleation due to slip band cracking was the prevalent mechanism especially at higher nominal stress amplitudes. The tolerance of this high strength material to small defects at higher stress levels and the actual size of the critical microstructural defects initiating failure have also been highlighted. The microstructure has been shown to strongly influence the processes of fatigue crack nucleation, Stages I and II crack propagation and the concept of the microstructure acting as barriers and providing resistance to crack growth have been discussed. The effectiveness and the size of these microstructural barriers to crack growth have been considered. This discussion has led to the proposal of a model that facilitates flow stress and fatigue lifetime predictions as a function of the quantity of a key microstructural phase. The key microstructural phase, namely reverted austenite affected both the tensile and fatigue properties of FV520B as a function of the heat treatment. The standard overaged material was found to exhibit the greatest resistance to fatigue crack propagation.
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Smallwood, Russell. "Fretting fatigue of steel roping wire in seawater." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328387.
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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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CORREA, LUIZ DINIZ. "FATIGUE LIFE IMPROVEMENT OF THE R4 STUCTURAL STEEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8207@1.
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PETRÓLEO BRASILEIRO S. A.Esta pesquisa teve como objetivo avaliar o efeito do jateamento de partículas (shot-peening) sobre a vida-fadiga do aço estrutural R4, largamente adotado na fabricação de componentes estruturais para sistemas de ancoragem de unidades flutuantes. Inicialmente, amostras cilíndricas do material foram retiradas das seções retas de elos tipo Kenter. Em seqüência, algumas amostras foram temperadas e revenidas em diferentes tempos de tratamento, com o objetivo de se promover uma homogeneidade microestrutural, bem como propriedades mecânicas similares àquelas dos elos tratados industrialmente. As amostras foram submetidas a ensaios de dureza e tração e, com base nos resultados, providenciou-se o tratamento térmico de todas as amostras. Dando continuidade a etapa experimental, corpos de prova para ensaios de fadiga foram usinados das amostras tratadas e submetidos a jateamento com microesferas de aço temperado sob pressões de 20 psi, 30 psi e 40 psi. Finalmente, corpos de prova nas condições sem jateamento e após jateamento foram submetidos a ensaios de fadiga por flexão rotativa, com o objetivo de se levantar a curva tensão versus número de ciclos para a falha (curva S-N) do aço estrutural R4 nas diferentes condições de superfície. A extensão da vida em fadiga do aço estrutural R4 foi relacionada com o jateamento de microesferas. De acordo com os resultados, houve uma influência benéfica do tratamento de superfície sobre a vida-fadiga do material. Tal influência foi caracterizada por um maior número de ciclos para a falha e aumento do limite de resistência à fadiga. Os resultados mostraram que a extensão da vida útil esteve diretamente relacionada com a intensidade do jateamento, significando que uma maior intensidade de jateamento provocou uma maior extensão da vida-fadiga do material.
The objective of the present work was to evaluate the effect of shot peening on the fatigue life of a grade R4 structural steel, largely adopted for fabricating offshore mooring chains. Initially, cylindrical samples of the material were cut of from the straight sections of Kenter links. In the sequence, a number of specimens were austenitized ed and tempered making use of different treatment times, in order to promote a microstructural homogeneity as well as mechanical properties similar to those associated with industrial heat treatments. The specimens were subjected to hardness and tensile tests and on the basis of the results, all samples were heat treated. After that, fatigue specimens were machined from the treated samples and shot peened with quenched steel shots under pressures of 20 psi, 30 psi and 40 psi. Finally, rotating bend fatigue tests were performed with unpeened and shot peened specimens aiming to establish the stress-life curves of the grade R4 structural steel. The fatigue life extension of the grade R4 structural steel was related to the shot peening. Regarding the results, the surface treatments affected the fatigue life of the material beneficially. This influence was characterized by a longer fatigue cycles and a fatigue life improvement. The results showed that the fatigue life extension was directly related to the shot peening intensity, i.e., the fatigue life extension has increased when increasing the shot peening intensity.
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Grundy, David C. (David Christopher). "Fatigue and fracture of a railway wheel steel." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28114.
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Rahgozar, Reza. "Fatigue endurance of steel structures subjected to corrosion." Thesis, University of Bristol, 1998. http://hdl.handle.net/1983/ea197da9-80da-4385-a7ed-eabd7acdedec.
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Wang, Ruoqi. "Reliability-based fatigue assessment of existing steel bridges." Licentiate thesis, KTH, Bro- och stålbyggnad, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-281997.
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Fatigue is among the most critical forms of deterioration damage that occurs tosteel bridges. It causes a decline of the safety level of bridges over time. Therefore,the performance of steel bridges, which may be seriously affected by fatigue, shouldbe assessed and predicted. There are several levels of uncertainty involved in thecrack initiation and propagation process; therefore the probabilistic methods canprovide a better estimation of fatigue lives than deterministic methods. Whenthere are recurring similar details which may have correlation with each other andbe regarded as a system, there are distinct advantages to analyze them from asystem reliability perspective. It allows the engineer to identify the importance ofan individual detail or the interaction between details with respect to the overallperformance of the system. The main aim of this licentiate thesis is to evaluate probabilistic methods for reliabilityassessment of steel bridges, from both a single detail level and a systemlevel. For single details, an efficient simulation technique is desired. The widelyapplied Monte Carlo simulation method provides accurate estimation, however, isvery time-consuming. The Subset simulation method is investigated as an alternativeand it shows great feasibility in dealing with a multi-dimensional limit statefunction and nonlinear crack propagation. For larger systems, the spatial correlationis considered between details. An equicorrelation-based modelling approachhas been proposed as supplement to common simulation techniques to estimate thesystem reliability analytically and significantly reduce the simulation time. Withcorrelation considered, the information of one accessible detail could be used topredict the status of the system. While reliability analysis aims for a specific safety level, risk analysis aims to findthe most optimal solution. With consequences considered, a risk-based decisionsupport framework is formulated for the selected system, which is presented asa decision tree. It reveals that the decisions based on reliability assessment canbe different from those based on risk analysis, since they have different objectivecriteria.Utmattning är en av de mest allvarliga nedbrytningsmekanismer som stålbroarutsätts för. Den orsakar en försämrad säkerhet för broar över tid. Därav måstestålbroars tillförlitlighet, som kan påverkas allvarligt på grund av utmattning, bedömasoch förutsägas. Flera olika nivåer av osäkerheter är involverade i initieringoch propagering av utmattningssprickor, varför sannolikhetsbaserade metoder kange en bättre uppskattning av utmattningslivslängden än deterministiska metoder.När liknande detaljer återkommer i en konstruktion och med korrelation mellanvarandra kan dessa betraktas som ett system, för vilket tillförlitlighetsmetoder påsystemnivå kan utnyttjas. Det gör det möjligt för ingenjören att identifiera betydelsenav en individuell detalj eller interaktionen mellan detaljer med avseende påsystemets totala tillförlitlighet. Det huvudsakliga syftet med denna licentiatuppsats är att utvärdera sannolikhetsbaserademetoder för uppskattning av stålbroars tillförlitlighet, både med avseendepå enskilda detaljer och på systemnivå. För enskilda detaljer eftersträvas en tidseffektivsimuleringsteknik. Den allmänt tillämpade Monte Carlo-simuleringsmetodenger en robust uppskattning, men är mycket tidskrävande. Subset-simuleringsmetodenundersöks som ett alternativ och den visar stor potential när det gäller att hanteraen flerdimensionell gränsfunktion och en olinjär sprickpropageringsmodell. På systemnivåbeaktas den rumsliga korrelationen mellan detaljer. En modelleringsmetodbaserad på konstant korrelation mellan detaljer har föreslagits som komplement tillvanliga simuleringstekniker för att uppskatta tillförlitligheten analytiskt och avsevärtminska simuleringstiden. Genom att utnyttja korrelationen kan informationom en tillgänglig detalj användas för att förutsäga systemets status. Medan en tillförlitlighetsanalys bedöms mot en specifik säkerhetsnivå används riskanalysenför att hitta den mest optimala åtgärden. Genom att beakta konsekvenserhar ett riskbaserat verktyg för beslutsstöd föreslagits och presenterats i form av ettbeslutsträd. Resultaten visar att besluten baserade på tillförlitlighet kan skilja sigfrån de som baseras på en uppskattad risk, eftersom metoderna har olika målfunktioner.
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Lorenzon, Alberto. "Wind-induced fatigue simulation approach for steel megastructures." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3423179.
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Wind-induced fatigue is the phenomenon of progressive degradation and, eventually, rupture in structural elements due to continuous cyclic action of wind. The assessment of wind-induced fatigue is in general an extremely demanding and multidisciplinary activity. In fact, it requires multiple blocks which range from the simulation of wind action, simulation of structural dynamic response, climatic statistics analysis, local stress analysis and detailed fatigue calculations. For some structural cases, i.e. simple cantilever structures, light poles, traffic signals, closed formulations for assessing this loading have been proposed in recent years in literature and standards.
The proposed research focuses, on the contrary, on large, complex steel structures, often called megastructures, which can be very sensitive to wind action and for which the calculation of wind-induced fatigue is not feasible using closed formulations and which is an underdeveloped subject in literature. Since megastructures are unique, simulations are necessary all along the design process, including both wind simulation and structural analysis. Up to now, wind tunnels have been the standard tool for simulating wind loading, but recent advances in High-Performance Computing (HPC), have also permitted to use numerical approaches of Computational Wind Engineering (CWE), which adopt Computational Fluid Dynamics (CFD) models.
This thesis proposes a complete approach for the calculation of wind-induced fatigue in megastructures where CFD is introduced in the fatigue design process, making the process entirely numerical. Since CFD must responds to strict requirements related to accuracy, robustness and computational cost, an original development is proposed in the context of the recent and promising class of Partially Averaged Navier Stokes (PANS) models. New PANS models are developed in view of the application on transient analyses on large steel structures. These models are validated using standard benchmark cases showing improvements compared to reference models. Finally, a complete calculation of wind-induced fatigue is shown relative to the real-world application of a stadium roof thus proving the feasibility and the results of the procedure, where PANS models are envisioned as the missing link to perform an entirely numerical calculation at reasonable computational cost.
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Harty, Brian Dudley. "Corrosion fatigue of engineering alloys in aqueous environments." Doctoral thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/18215.
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A comparative study of the fatigue crack growth rate (FCGR) behaviour of five alloys in air and in aqueous environments has been performed. The alloys tested include: mild steel as a reference material, a corrosion resistant dual phase steel, 3CR12, a proprietary martensitic stainless steel, AISI 431, a newly developed 8% Cr martensitic steel, Alloy 825, and a newly developed corrosion-abrasion resistant metastable austenitic alloy, 1210. Tests were conducted in laboratory air, distilled water at rest potential, 500 ppm chloride solution at rest potential, 1000 ppm chloride solution at rest potential, and 1000 ppm chloride solution at -1200 m V see; solution temperatures were maintained at 25⁰ C. Crack growth rate tests were performed using sinusoidal loading at a load ratio R = 0.1, a frequency of 3Hz in the laboratory air, and a frequency of 1 Hz in the aqueous environments. At the completion of testing, fracture surfaces were studied using a scanning electron microscope. In air, the mild steel and 3CR12 display comparable rates of cracking and exhibit a greater resistance to fatigue crack propagation than the martensitic AISI 431 and Alloy 825; Alloy 825 shows the least resistance to fatigue crack propagation. The deformation induced transformation in 1210 gives this alloy the greatest resistance to fatigue crack propagation in air. Fatigue crack growth rates were all enhanced in the aqueous environments. The greatest overall rate of environmentally assisted cracking was shown by alloy 825 while the lowest was shown by the mild steel. Although the rate of cracking of 1210 in the aqueous environments was less than that of Alloy 825, 1210 was influenced the most by the aqueous environments. An environmentally assisted cracking index shows that the rate of fatigue crack propagation in 1210 is increased by 32 times in the 500 ppm chloride solution at low stress intensities. The fatigue crack growth rates of mild steel and AISI 431 were significantly influenced by the cathodically polarised conditions in the 1000 ppm chloride solution, compared to the rest potential conditions. In these cases hydrogen was seen to be evolved from the specimen surfaces. Changes in the fatigue crack growth rate behaviour were accompanied by changes in the fracture surface morphologies. The observed changes varied for each alloy and for each environment, and were manifest by the degree of intergranular cracking, cleavage, quasi cleavage, and increased coarseness of the transgranular cracking. The fracture surface morphologies are reported and discussed in detail. In general, the fracture surface morphologies could be directly related to the relative degrees of environmental influence on the rate of cracking; results are explained in terms of existing hypotheses. It is suggested that the environmentally assisted cracking of mild steel and AISI 431 at cathodic potentials in the 1000 ppm chloride solution could only be attributed to hydrogen assisted cracking. Similarly, it is suggested that the large crack growth rate acceleration of 1210 in the aqueous environments could also be attributed to hydrogen. The similar fracture surface morphologies observed on the other specimens after tests in the aqueous environments suggests-that hydrogen could be responsible for the environmentally assisted cracking of all the steels in aqueous environments.
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Hayes, Alethea M. "Compression behavior of linear cellular steel." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/32857.
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Wärner, Hugo. "High-Temperature Fatigue Behaviour of Austenitic Stainless Steel : Influence of Ageing on Thermomechanical Fatigue and Creep-Fatigue Interaction." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-153100.
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The global energy consumption is increasing and together with global warming from greenhouse gas emission, create the need for more environmental friendly energy production processes. Higher efficiency of biomass power plants can be achieved by increasing temperature and pressure in the boiler section and this would increase the generation of electricity along with the reduction in emission of greenhouse gases e.g. CO2. The power generation must also be flexible to be able to follow the demands of the energy market, this results in a need for cyclic operating conditions with alternating output and multiple start-ups and shut-downs. Because of the demands of flexibility, higher temperature and higher pressure in the boiler section of future biomass power plants, the demands on improved mechanical properties of the materials of these components are also increased. Properties like creep strength, thermomechanical fatigue resistance and high temperature corrosion resistance are critical for materials used in the next generation biomass power plants. Austenitic stainless steels are known to possess such good high temperature properties and are relatively cheap compared to the nickel-base alloys, which are already operating at high temperature cyclic conditions in other applications. The behaviour of austenitic stainless steels during these widened operating conditions are not yet fully understood. The aim of this licentiate thesis is to increase the knowledge of the mechanical behaviour at high temperature cyclic conditions for austenitic stainless steels. This is done by the use of thermomechanical fatigue- and creepfatigue testing at elevated temperatures. For safety reasons, the effect of prolonged service degradation is investigated by pre-ageing before mechanical testing. Microscopy is used to investigate the microstructural development and resulting damage behaviour of the austenitic stainless steels after testing. The results show that creep-fatigue interaction damage, creep damage and oxidation assisted cracking are present at high temperature cyclic conditions. In addition, simulated service degradation resulted in a detrimental embrittling effect due to the deterioration by the microstructural evolution.
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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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Pape, John Andrew. "Fretting fatigue damage accumulation and crack nucleation in high strength steels." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/18382.
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Hong, Hyun-Soo. "A metallurgical study of the oxidational theory of mild wear in stainless steel and surface modified stainless steel." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/19597.
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Chang, Chung-Shing. "Fracture processes in simulated HAZ microstructures of stainless steel." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367606.
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Leander, John. "Refining the fatigue assessment procedure of existing steel bridges." Doctoral thesis, KTH, Bro- och stålbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127707.
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This thesis treats the fatigue assessment process of steel bridges. The purpose is to identify areas with potential of enhancement with an overall aim of attaining a longer service life. The aging bridge stock in Sweden and in many other developed countries is an impending economical burden. Many bridges have reached their expected service life and increased axle loads, speeds, and traffic intensity further accelerate the deterioration. An immediate replacement of all our bridges approaching their expected service life will not be possible. For economical and environmental reasons, effort should be put on extending the theoretically safe service life as far as possible. Fatigue is one of the major reasons limiting the service life of steel bridges .A specific example is the Söderström Bridge in Stockholm, Sweden. Fatigue cracks have been found in the webs of the main beams and theoretical assessments have shown an exhausted service life. As a mean to reduce the uncertainties in the theoretical assessments a monitoring campaign was started in 2008 and continued in periods until 2011. The first continuous period of 43 days of measurements in 2008 forms the experimental foundation for this thesis. A fatigue life prediction involves (i) an estimation of the load effect, (ii) an estimation of the resistance, and (iii) the selection of a prediction model. This thesis treats in some sense all three of them. Considering part (i), the load effect, a theoretical study on the influence of dynamics has been performed. The quasi static approach suggested in the standards does not necessarily reflect the true dynamic behavior of the structure. Performing a dynamic moving load analysis gives for all cases studied a more favorable fatigue life. A further enhancement of the assessment is to perform in situ measurements. The uncertainties related to dynamics, loads, and structural behavior are thereby captured in the response. Routines for processing the measured response and performing life predictions are treated, moreover the quality of the measured response. The resistance, part (ii), in form of the fatigue endurance has a funda- mental influence on the fatigue life. As an attempt to reach a more adequate fatigue endurance a refined assessment of a typical joint is performed using linear elastic fracture mechanics (LEFM). A descriptive detail category is suggested which renders a somewhat more favorable resistance. Part (iii), the prediction model, is treated considering the safety format. A reliability-based model is suggested which enables a consideration of the uncertainties in each stochastic variable. Thereby, all aforementioned parts and uncertainties can be combined within the same prediction. The reliability-based model is used for a code calibration of partial safety factors to be used in semi-probabilistic assessments according to the standards. The implementation of the suggested procedures is shown with a numerical example. The outcome should not be generalized but the example clearly shows an increase in fatigue life with the proposed enhancements of the assessment procedure.QC 20130917
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Bérard, Jean-Yves Adrien. "Low cycle fatigue behavior of a low carbon steel." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/20130.
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Kim, Tae Hyun. "Fatigue of surface engineered steel in rolling-sliding contact." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325019.
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Karl, Justin. "Thermomechanical Fatigue Life Prediction of Notched 304 Stainless Steel." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5796.
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The behavior of materials as they are subjected to combined thermal and mechanical fatigue loads is an area of research that carries great significance in a number of engineering applications. Power generation, petrochemical, and aerospace industries operate machinery with expensive components that undergo repeated applications of force while simultaneously being exposed to variable temperature working fluids. A case of considerable importance is found in steam turbines, which subject blades to cyclic loads from rotation as well as the passing of heated gases. The complex strain and temperature histories from this type of operation, combined with the geometric profile of the blades, make accurate prediction of service life for such components challenging. Development of a deterministic life prediction model backed by physical data would allow design and operation of turbines with higher efficiency and greater regard for reliability. The majority of thermomechanical fatigue (TMF) life prediction modeling research attempts to correlate basic material property data with simplistic strain and thermal histories. With the exception of very limited cases, these types of efforts have been insufficient and imprecise in their capabilities. Early researchers did not account for the multiple damage mechanisms that operate and interact within a material during TMF loads, and did not adequately address the extent of the relationship between smooth and notched parts. More recent research that adequately recognizes the multivariate nature of TMF develops models that handle life reduction through summation of constitutive damage terms. It is feasible that a modification to the damage-based approach can sufficiently include cases that involve complex geometry. The focus of this research is to construct an experimentally-backed extension of the damage-based approach that improves handling of geometric discontinuities. Smooth and notched specimens of Type 304 stainless steel were subjected to several types of idealized fatigue conditions to assemble a clear picture of the types of damage occurring in a steam turbine and similarly-loaded mechanical systems. These results were compared with a number of idealized TMF experiments, and supplemented by numerical simulation and microscopic observation. A non-uniform damage-summation constitutive model was developed primarily based on physical observations. An additional simplistic model was developed based on phenomenological effect. Findings from this study will be applicable to life prediction efforts in other similar material and load cases.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
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Takeuchi, M. "Fretting and fatigue of a roping steel in seawater." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384690.
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Donohoe, C. J. "Corrosion fatigue of a high strength low alloy steel." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322985.
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Murrell, Pamela. "Fatigue and fracture of a high strength cast steel." Thesis, Cranfield University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359549.
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Foroughi, Reza. "Fatigue resistance of a structural steel under random loading." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37695.
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Romo, Arango Sebastian A. "Low-Cycle Fatigue of Low-Alloy Steel Welded Joints." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1573054310351145.
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Mashiri, Fidelis Rutendo 1968. "Thin-walled tubular connections under fatigue loading." Monash University, Dept. of Civil Engineering, 2001. http://arrow.monash.edu.au/hdl/1959.1/8784.
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Qiu, Xiaonong. "Rolling contact fatigue behavior of three eutectoid rail steels /." Full text open access at:, 1987. http://content.ohsu.edu/u?/etd,153.
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Mathieson, P. A. R. "Acoustic emissions from fatigue cracks in steels." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379486.
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Zheng, Hang. "Tempcore reinforcing steel : microstructure and mechanical properties." Phd thesis, Department of Civil Engineering, 1998. http://hdl.handle.net/2123/8671.
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Jamwal, Ranbir Singh. "Microstructural origins of variability in the tensile ductility of dual phase steels." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39477.
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Quantitative relationships among processing parameters, microstructure, and material properties are of considerable interest in the context of development of robust processing routes that optimize the required material properties. As a result, the scientific literature contains a large number of experimental and theoretical studies on microstructure-properties relationships. Fracture sensitive mechanical properties such as ductility, ultimate tensile strength, fatigue life, and fracture toughness depend on the average microstructural parameters as well as the distributions of microstructural parameters and their extrema.Development of quantitative relationships between such material properties and microstructural distributions and extrema has received considerably less attention, particularly in the wrought metals and alloys. Accordingly, an important objective of this research is to perform a systematic investigation in this direction.
The dependence of the fracture-sensitive mechanical properties on the microstructural distributions and extrema often leads to substantial variability in these properties: a set of specimens having the same average chemistry, the same average processing history, and the same average microstructural parameters such as volume fractions of different constituents can exhibit substantially different material properties. The present research (i) is concerned with high strength (~ 1000 MPa) high martensite (>50%) dual phase steel where the martensite is a topologically continuous phase (matrix) containing a dispersion of islands of ferrite, and (ii) focuses on understanding the microstructural origins of the variability in fracture sensitive mechanical properties, in particular variability in the room temperature uniaxial tensile ductility. The research involves quantitative microstructure characterization using stereology and digital image processing and quantitative fractography using scanning electron microscopy (SEM) and fracture profilometry. The analysis of the quantitative fractographic and microstructural data obtained in this research leads to useful guidelines for reducing the variability in the tensile ductility of the dual phase steel under investigation.
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Mesmari, H. R. A. "Strength and fatigue behaviour of dual phase steels." Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382450.
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