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Knipling, Keith Edward. "High-cycle fatigue / low-cycle fatigue interactions in Ti-6Al-4V." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/41290.
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The largest single cause of failure in fan and compressor components in the cold frontal sections of commercial and military gas turbine engines has been attributed to high cycle fatigue (HCF). Additionally, both high-cycle fatigue (HCF) and lowcycle fatigue (LCF) loadings are widely recognized as unavoidable during operation of these components and because the classic Linear Damage Rule (LDR) neglects to account for the synergistic interaction between these damage contributors, dangerous over predictions of lifetime can result.
Combined low-cycle fatigue / high-cycle fatigue (HCF/LCF) loadings were investigated in smooth Ti-6Al-4V. The specimens were subjected to a variable amplitude block loading history comprised of completely-reversed (R = -1) tensioncompression overloads followed by constant-amplitude zero-tension (R = 0) minor cycles. Axial specimens were excised from forgings representative of turbine engine fan blade forgings, and consisted of approximately 60% primary α in a matrix of lamellar α + β.
Data are reported for smooth specimens of Ti-6Al-4V subjected to both constant amplitude and variable amplitude loadings. The axial specimens were prepared according to two distinct specimen conditions: low stress ground and longitudinallypolished (LSG+LP) and stress-relieved and chemically milled (SR+CM) conditions. Significantly longer lives were observed for the LSG+LP specimen condition under both constant and variable amplitude loading, due to the presence of a beneficial compressive surface residual stress. The presence of this residual stress was confirmed by x-ray diffraction, and its magnitude was of the order of 180 MPa (~20% of the yield stress). In either specimen condition, no appreciable effect of periodic overloads on the life of subsequent minor cycles was observed.Master of Science
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Kazymyrovych, Vitaliy. "Very high cycle fatigue of high performance steels." Licentiate thesis, Karlstad University, Faculty of Technology and Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-3066.
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Many engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of enduring an infinite number of cycles provided that the service conditions are unchanged. With the development of modern ultrasonic fatigue testing equipment it became possible to experimentally establish VHCF behaviour of various materials. For most of them the existence of the fatigue limit at 107 load cycles has been proved wrong and their fatigue strength continues to decrease with increasing number of load cycles.
One important group of materials used for the production of high performance components subjected to the VHCF is tool steels. This study explores the VHCF phenomenon using experimental data of ultrasonic fatigue testing of some tool steel grades. The causes and mechanisms of VHCF failures are investigated by means of high resolution scanning electron microscopy, and in relation to the existing theories of fatigue crack initiation and growth. The main type of VHCF origins in steels are slag inclusions.
However, other microstructural defects may also initiate fatigue failure. A particular attention is paid to the fatigue crack initiation, as it has been shown that in the VHCF range crack formation consumes the majority of the total fatigue life. Understanding the driving forces for the fatigue crack initiation is a key to improve properties of components used for very long service lives. Finite element modelling of VHCF testing was added as an additional perspective to the study by enabling calculation of local stresses at the fatigue initiating defects.
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Kazymyrovych, Vitaliy. "Very high cycle fatigue of tool steels." Doctoral thesis, Karlstads universitet, Avdelningen för maskin- och materialteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-5877.
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An increasing number of engineering components are expected to have fatigue life in the range of 107 - 1010 load cycles. Some examples of such components are found in airplanes, automobiles and high speed trains. For many materials fatigue failures have lately been reported to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicts the established concept of a fatigue limit, which postulates that having sustained around 107 load cycles the material is capable of enduring an infinite number of cycles provided that the service conditions are unchanged. With the development of modern ultrasonic fatigue testing equipment it became possible to experimentally establish VHCF behaviour of various materials. For many of them the existence of the fatigue limit at 107 load cycles has been proved wrong and their fatigue strength continues to decrease with increasing number of load cycles. High performance steels is an important group of materials used for the components subjected to VHCF. This study explores the VHCF phenomenon using experimental data generated by ultrasonic fatigue testing of selected tool steels. The overall aim is to gain knowledge of VHCF behaviour of some common tool steel grades, while establishing a fundamental understanding of mechanisms for crack development in the very long life regime. The study demonstrates that VHCF cracks in tested steels initiate from microstructural defects like slag inclusions, large carbides or voids. It is established that VHCF life is almost exclusively spent during crack formation at below threshold stress intensity values which results in a unique for VHCF morphology on the fracture surface. Significant attention is devoted in the thesis to the ultrasonic fatigue testing technique, i.e. the validity and applicability of its results. FEM is employed to give an additional perspective to the study. It was used to calculate local stresses at fatigue initiating defects; examine the effect of material damping on ultrasonic stresses; and to evaluate various specimen geometries with respect to resulting stress gradient and maximum stressed material volume.
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Berchem, Klaus Herbert Hans. "High cycle fatigue and corrosion fatigue performance of two car body steels." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414711.
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Barry, Nathan. "Lead-free solders for high-reliability applications : high-cycle fatigue studies." Thesis, University of Birmingham, 2008. http://etheses.bham.ac.uk//id/eprint/198/.
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The use of lead (Pb) in solders for electronic connections is now extensively restricted in Europe, with its use likely to be phased out completely in the medium term. Although Pb-free solders have been the subject of much research, little investigation has been carried out into their reliability for applications exposed to vibration in service. Aerospace applications, which have service lives measured in decades, are of particular pertinence. The present work shows the development and validation of a method for testing small, model solder joints in high-cycle fatigue. The tests are conducted using common equipment yet provide fast results and objective comparisons between solders without the influence of PCBs or components, which typically obscure the solders’ intrinsic contribution. S-N diagrams are presented which compare the performance of traditional Sn-Pb solder to that of Pb-free alloys at room and high temperatures and with copper and nickel substrates. It is found that in all situations the Pb-free alloys offer lower lifetimes to failure than the traditional Sn-Pb, an unexpected result when considering the inferior mechanical properties of the latter. The large disparity at room temperatures and with copper substrates is significantly reduced by elevated temperatures and by soldering to nickel substrates. In order to investigate these results, a number of techniques are employed. In addition to extensive fractography, the damping capacity of the solders is investigated and a scanning acoustic microscope is used in conjunction with resonant decay tracking of specimens to study the crack propagation paths prior to complete failure. The analysis of results focuses on the possible causes for this performance difference, drawing on existing soldering literature and wider engineering principles. It is concluded that the overall pattern of results presents contradictory evidence for the contribution of various factors, such as yield strength or interfacial adhesion, which are hard to reconcile. It is thought likely that more numerous fatigue initiation sites in the Pb-free alloys are responsible to some degree for their lower cycles to failure, although more research into the effect of substrate and interfacial intermetallics is necessary to determine the mechanism by which these influence the results, in the absence of relevant fractographic evidence.
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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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Suresh, Shyam. "Topology Optimization for Additive Manufacturing Involving High-Cycle Fatigue." Licentiate thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-165503.
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Additive Manufacturing (AM) is gaining popularity in aerospace and automotive industries. This is a versatile manufacturing process, where highly complex structures are fabricated and together with topology optimization, a powerful design tool, it shares the property of providing a very large freedom in geometrical form. The main focus of this work is to introduce new developments of Topology Optimization (TO) for metal AM. The thesis consists of two parts. The first part introduces background and theory, where TO and adjoint sensitivity analysis are described. Furthermore, methodology used to identify surface layer and high-cycle fatigue are introduced. In the second part, three papers are appended, where the first paper presents the treatment of surface layer effects, while the second and third papers provide high-cycle fatigue constraint formulations. In Paper I, a TO method is introduced to account for surface layer effects, where different material properties are assigned to bulk and surface regions. In metal AM, the fabricated components in as-built surface conditions significantly affect mechanical properties, particularly fatigue properties. Furthermore, the components are generally in-homogeneous and have different microstructures in bulk regions compared to surface regions. We implement two density filters to account for surface effects, where the width of the surface layer is controlled by the second filter radius. 2-D and 3-D numerical examples are treated, where the structural stiffness is maximized for a limited mass. For Papers II and III, a high-cycle fatigue constraint is implemented in TO. A continuous-time approach is used to predict fatigue-damage. The model uses a moving endurance surface and the development of damage occurs only if the stress state lies outside the endurance surface. The model is applicable not only for isotropic materials (Paper II) but also for transversely isotropic material properties (Paper III). It is capable of handling arbitrary load histories, including non-proportional loads. The anisotropic model is applicable for additive manufacturing processes, where transverse isotropic properties are manifested not only in constitutive elastic response but also in fatigue properties. Two optimization problems are solved: In the first problem the structural mass is minimized subject to a fatigue constraint while the second problem deals with stiffness maximization subjected to a fatigue constraint and mass constraint. Several numerical examples are tested with arbitrary load histories.
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Morrissey, Ryan J. "Frequency and mean stress effects in high cycle fatigue of Ti-6A1-4V." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17095.
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Pirouznia, Pouyan. "High cycle fatigue properties of stainless martensitic chromium steel springs." Thesis, KTH, Materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103201.
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For many materials and components like in high speed trains and airplanes fatigue failures occur in the range of over 107 load cycles which is called the high cycle fatigue range. A modern version of the springs was invented which are applied in a certain application. Ultrasonic fatigue testing (20 kHz machine) was conducted for evaluating the steel of the springs. This research explores the fundamental understanding of high cycle fatigue testing of strip steel and assesses a stainless martensitic chromium steel at the high cycle fatigue range. Finite element modeling was conducted to gain knowledge about the effect of various parameters. Significant attention was devoted to the fatigue failure initiations by SEM/EDS. The work demonstrated that the method of investigation for high cycle fatigue test is reliable. Fatigue failure at this range was initiated by internal defects which all included non-metallic inclusion. A critical distance was defined Within the strip fatigue specimen where all the fatigue failure initiated. The 3D stress field in the specimen was determined by FEM modeling and the local applied stress at the whole of the flat part of specimen and critical distance was estimated. FEM was also employed to give additional information about the effect of parameters. It was established that damping had the largest influence. The local applied stress of the fatigue test was calculated by means of FEM and SEM analysis. It was used to adjust the S-N curve which resulted in 15% lower values than the nominal applied stress.
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Bantounas, Ioannis. "Microtexture and high cycle fatigue cracking in Ti-6A1-4V." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501436.
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TEIXEIRA, MARIA CLARA CARVALHO. "ULTRA HIGH CYCLE FATIGUE BEHAVIOR OF THE DIN 34CRNIMO6 STEEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=35973@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Estudos recentes têm mostrado que para muitos materiais de Engenharia não existe um limite de fadiga. Numa análise convencional, se admite uma vida infinita em fadiga de alto ciclo quando o material atinge 10(6) - 10(7) ciclos sem a incidência de falhas. Entretanto, em função do desenvolvimento tecnológico atual, a vida-fadiga de inúmeros componentes mecânicos e estruturais pode ultrapassar a fronteira da fadiga de alto ciclo, fazendo com que a avaliação do comportamento em fadiga de altíssimo ciclo (10(7) – 10(12)), tenha se tornado extremamente importante para projetos, por ter estabelecido que uma tensão limite de fadiga não existe em muitos casos. Pesquisas recentes demonstram que a maioria dos materiais, incluindo ligas ferrosas, apresentam falhas em até 10(10) ciclos, com um decréscimo contínuo do limite de fadiga após 10(6) ciclos, o que torna a resistência à fadiga associada com um número de ciclos mais importante do que o próprio limite de fadiga. No regime de altíssimo ciclo de fadiga as trincas se iniciam a partir de defeitos internos do material, como inclusões, gerando mecanismos de iniciação de trincas caraterísticos das superfícies de fratura, tais como olho de peixe (fish-eye), ODA (Optically Dark Area) e FGA (Fine Granular Area). Neste estudo foram usinados corpos de prova do aço DIN 34CrNiMo6, que foram ensaiados entre 10(6) e 10(9) ciclos, sob fadiga ultrassônica do tipo tração-compressão, com frequência de 20 kHz e razão de carregamento -1. Os resultados mostraram que o material tem uma tendência maior a vida-fadiga sob valores baixos de tensão e na superfície de fratura de alguns corpos de prova formação de fish-eye.
Recent studies have shown that for many engineering materials there is no fatigue limit. In a conventional analysis, infinite life in high cycle fatigue is allowed when the material reaches 10(6) - 10(7) cycles without the occurrence of failures. However, due to the current technological development, the fatigue life of several mechanical and structural components can exceed the boundary of high cycle fatigue, making the evaluation of ultra high cyle fatigue behavior (10(7)-10(12)), or fatigue of very high cycle, has become extremely important for projects, because it has established that a stress of fatigue limit does not exist in many cases. Current research has shown that most materials, including ferrous alloys, exhibit failures in up to 10(9) cycles, with a continuous decrease in the fatigue limit after 10(6) cycles, which makes strength fatigue associated with a number of cycles most important than own fatigue limit. In the very high fatigue cycles regime, cracks start from internal defects of the material, such as inclusions, generating a feature mechanisms of crack initiation on the fracture surfaces, such as fish-eye, ODA (Optically Dark Area) and Fine Granular Area (FGA). This study, specimens of DIN 34CrNiMo6 steel were machined and were tested between 10(6) and 10(9) cycles, under ultrasonic fatigue, with a frequency of 20 kHz and a loading ratio of -1. The results showed that the material has a tendency to fatigue life under low stress values and in some fracture sufaces of the specimens the fish-eye formation.
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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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Karlsson, Daniel. "Life and fracture in very high cycle fatigue of a high strength steel." Thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik (from 2013), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-86135.
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Classical fatigue models teach that there is an intrinsic fatigue limit for steels, representing a level of stress that is too low for regular crack growth where every cyclic load propagates a fatigue crack through the material. Modern application with extreme lifetimes has shown that fatigue will still take place in steels with stress levels well below the expected fatigue limit. This relatively new area of study has been named Very High Cycle Fatigue, or VHCF, and describes fatigue failures with a number of load cycles exceeding 107. Fractography of steels that has suffered VHCF tends to reveal an especially rough crack surface adjacent to where the fatigue crack originates, which is typically some form of defect in the bulk of the steel. This area is believed to be critical for VHCF and has been referred to in a number of ways by different studies, but will herein be called Fine Granular Area, or FGA. The aim of this study is to try and get a better understanding of VHCF. This was done by fractography analysis of test specimens of high strength tool steel that suffered fatigue failure at lifetimes ranging from about 106 cycles to 1,9x109 cycles. The lower lifetimes were achieved using hydraulic testing equipment, while the specimens in the VHCF range suffered fatigue failure in ultrasonic testing equipment allowing the application of a cyclic stress at a rate of 20 000 Hz. The resulting fracture surfaces were then investigated using a scanning electron microscope, or SEM, taking special note of the fatigue initiating defects and, in the case of VHCF, the rough area found adjacent to it. In combination with the SEM an elemental analysis of the fatigue initiating defects as well as the bulk of the material was done using energy-dispersive X-ray spectroscopy, or EDS. This was done to find out what the defects consisted of; confirming that they were slags and checking that the composition of the material of the bulk of the specimen matches what was expected. Using light optical microscopy in combination with acid etching of the surface of samples cut out of the test specimens the structure of the steel was investigated. Calculating the local stresses at the location of the fatigue initiating defect was done using FEM in combination with displacement amplitude gathered from the ultrasonic testing equipment. The data gathered was then measured and compared to that of previous studies, using models of prediction and seeing how they match the experimental results. The results suggest that the stress intensity factor at the internal slags is critical for VHCF and that with lower stress intensity factors one can expect longer lifetimes. Another observation is a relatively consistent stress intensity factor at the edge of the FGA combined with the original defect, likely signifying the transition from the creation of FGA to traditional crack propagation. There also seems to be a connection between the size of the FGA and the number of cycles to failure, with larger FGA with increasing lifetimes. The most glaring shortcoming of this study is the amount satisfactory tests conducted, and thus amount of data points, is very low due to the majority of specimens suffered failure at the threading used to connect them to the ultrasonic testing equipment at lifetimes far too low to be relevant.Klassiska utmattningsmodeller lär ut att det finns en utmattningsgräns för stål, vilket representerar en spänningsnivå som är för låg för regelbunden sprickväxt där varje cyklisk belastning sprider en utmattningsspricka genom materialet. Moderna applikation med extrema livstider har visat att utmattning fortfarande äger rum i stål med spänningsnivåer långt under den förväntade utmattningsgränsen. Detta relativt nya studieområde har fått namnet Very High Cycle Fatigue, eller VHCF, och beskriver utmattningsfall med ett antal belastningscykler som överstiger 107. Fraktografi av stål som har drabbats av VHCF tenderar att ha en särskilt gropig sprickyta som ligger intill där utmattningssprickan har sitt ursprung, vilket typiskt är någon form av defekt i stålets bulk. Detta område tros vara kritiskt för VHCF och har hänvisats till på ett antal sätt av olika studier, men kommer här att kallas Fine Granular Area eller FGA. Syftet med denna studie är att försöka få en bättre förståelse för VHCF. Detta gjordes genom fraktografianalys av testprover av verktygsstål med hög hållfasthet som drabbades av utmattningsbrott vid livstider från cirka 106 cykler till 1,9x109 cykler. De lägre livslängderna uppnåddes med hjälp av hydraulisk testutrustning, medan proverna i VHCF-området drabbades av utmattningsbrott i ultraljudstestutrustning som klarar att applicera en cyklisk stress med en frekvens på 20 kHz. De resulterande sprickytorna undersöktes sedan med hjälp av ett svepelektronmikroskop, eller SEM, med särskild fokus på utmattningsinitierande defekter och, i fallet med VHCF, det grova området som hittades intill det, FGA. I kombination med SEM utfördes en elementanalys av utmattningsinitierande defekter liksom huvuddelen av materialet med energidispersiv röntgenspektroskopi, eller EDS. Detta gjordes för att ta reda på vad inneslutningarna bestod av för att bekräfta att de var slagg samt kontrollera att sammansättningen av materialet i huvuddelen av provet matchar det som förväntades. Med användning av optisk ljusmikroskopi i kombination med syraetsning av ytan på prover som skars ut ur testproverna undersöktes stålets struktur. Beräkning av de lokala spänningarna på platsen för den utmattningsinitierande defekten gjordes med hjälp av FEM i kombination med förskjutningsamplituden som samlats från ultraljudsutrustningen. De insamlade uppgifterna mättes sedan och jämfördes med tidigare studier genom att använda diverse modeller och se hur de matchar de experimentella resultaten. Resultaten antyder att stressintensitetsfaktorn vid inneslutningarna är kritisk för VHCF och att man med lägre stressintensitetsfaktorer kan förvänta sig längre livstid. En annan observation är en relativt konsekvent stressintensitetsfaktor vid kanten av FGA, vilket sannolikt markerar övergången från skapandet eller utbredning av FGA till traditionell sprickutbredning. Det verkar också finnas en koppling mellan storleken på FGA och antalet cykler till fel, med större FGA med ökande livslängd. Den mest uppenbara bristen i denna studie är mängden tillfredsställande tester som genomförts. Därmed är mängden datapunkter mycket låg, detta på grund av att majoriteten av proverna misslyckades vid gängningen som användes för att ansluta dem till ultraljudstestutrustningen vid livstider alltför låga för att vara relevanta.
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Berchem, Klaus [Verfasser]. "The High-Cycle Fatigue and Corrosion Fatigue Performance of two Car Body Steels / Klaus Berchem." Aachen : Shaker, 2005. http://d-nb.info/1181607590/34.
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Radonovich, David Charles. "Methods of Extrapolating Low Cycle Fatigue Data to High Stress Amplitudes." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3460.
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Modern gas turbine component design applies much effort into prediction and avoidance of fatigue. Advances in the prediction of low-cycle fatigue (LCF) cracks will reduce repair and replacement costs of turbine components. These cracks have the potential to cause component failure. Regression modeling of low-cycle fatigue (LCF)test data is typically restricted for use over the range of the test data. It is often difficult to characterize the plastic strain curve fit constants when the plastic strain is a small fraction of the total strain acquired. This is often the case with high strength, moderate ductility Ni-base superalloys. The intent of this project is to identify the optimal technique for extrapolating LCF test results into stress amplitudes approaching the ultimate strength. The proposed method to accomplish this is by finding an appropriate upper and lower bounds for the cyclic stress-strain and strain-life equations. Techniques investigated include: monotonic test data anchor points, strain-compatibility, and temperature independence of the Coffin-Manson relation. A Ni-base superalloy (IN738 LC) data set with fully reversed fatigue tests at several elevated temperatures with minimal plastic strain relative to the total strain range was used to model several options to represent the upper and lower bounds of material behavior. Several high strain LCF tests were performed with stress amplitudes approaching the ultimate strength. An augmented data set was developed by combining the high strain data with the original data set. The effectiveness of the bounding equations is judged by comparing the bounding equation results with the base data set to a linear regression model using the augmented data set.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
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Courty, Diana [Verfasser]. "Ultra high cycle fatigue of thin Al-based films / Diana Courty." Aachen : Shaker, 2010. http://d-nb.info/1104047705/34.
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Seidt, Jeremy Daniel. "Development of a novel vibration based high cycle fatigue test method." Connect to resource, 2001. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1209585565.
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MONTAGNOLI, FRANCESCO. "Very-High Cycle Fatigue: Size Effects and Applications in Civil Engineering." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2945177.
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Ge, Yindong. "HIGH CYCLE FATIGUE STUDIES OF CARBURIZED NICKEL-BASE SUPERALLOYS AND STAINLESS STEELS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1244230393.
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Roy, Alexander M. "Prediction of low and high cycle multiaxial fatigue of superelastic nitinol stents via uniaxial fatigue based equations." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527412.
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Bobyliov, Konstantin. "Casting voids influence on spheroid graphite cast iron high-cycle fatigue strength." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2008. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20081128_120950-42235.
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The influence of casting voids on spheroid cast iron cracking threshold is investigated. The experimental results and their analytical and numerical analysis basing on linear fracture mechanics is presented.Nagrinėjamas liejimo tuštumų poveikis stipriojo ketaus pleišėjimo slenksčiui. Pateikiami eksperimentiniai rezultatai ir jų analitinė bei skaitinė analizė, remiantis tiesine irimo mechanika.
Исследуется влияние литейных пустот на порог трещиностойкости чугуна с шаровидным графитом. Представлены результаты экспериментального исследования и их аналитический и численный анализ, опираясь на линейную механику разрушения.
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Hastings, Abel Z. 1973. "An investigation of the high cycle fatigue behavior of bovine trabecular bone." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/30123.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2004.Includes bibliographical references (p. 64-70).
Fractures can be caused by fatigue loading due to prolonged exercise and age-related fragility. Fatigue loading causes microdamage in bone that leads to both a loss of stiffness and strength. Some engineering materials, such as steels, have a fatigue limit, which is represented by a stress plateau in the stress-life (S-N) curve. When loaded to levels below the stress plateau, these materials have an infinite fatigue life. Other materials, such as aluminum, do not exhibit a fatigue limit. For these materials, the endurance limit is defined as the stress amplitude corresponding to a somewhat arbitrary large number of cycles of fatigue (e.g. various texts suggest 10⁶ to 10⁸ cycles ). In previous work on compressive fatigue of bovine trabecular bone, it was hypothesized that there was a fatigue limit at a normalized stress, [Delta] [rho]/E₀, of approximately 0.0035. This study tested this hypothesis by fatigue testing bovine trabecular bone loaded to one of four normalized stresses ranging from 0.0015 to 0.0035. Failure was defined as a 10% loss in the secant modulus of the specimen. The data show that the rate of decrease of modulus reduction per cycle increased with increasing normalized stress. A fatigue limit in bovine trabecular bone was not found. While a threshold below which the fatigue life is infinite was not found, an endurance limit corresponding to 10⁶ cycles to failure was found at a normalized stress of about 0.00137. The study also showed that normalized secant modulus decreased with normalized number of cycles in the same manner for all normalized stresses.
by Abel Z. Hastings.
S.M.
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Cheng, Deborah Wen-hsin. "Compressive high cycle at low strain fatigue behavior of bovine trabecular bone." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38042.
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Tofique, Muhammad Waqas. "Very high cycle fatigue of duplex stainless steels and stress intensity calculations." Licentiate thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-34591.
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Very high cycle fatigue (VHCF) is generally considered as the domain of fatigue lifetime beyond 10 million (107) load cycles. Few examples of structural components which are subjected to 107-109 load cycles during their service life are engine parts, turbine disks, railway axles and load-carrying parts of automobiles. Therefore, the safe and reliable operation of these components depends on the knowledge of their fatigue strength and the prevalent damage/failure mechanisms. Moreover, the fatigue life of materials in the VHCF regime is controlled by the fatigue crack initiation and early growth stage of short cracks. This study was focussed on the evaluation of fatigue properties of duplex stainless steels in the VHCF regime using the ultrasonic fatigue testing equipment. The ultrasonic fatigue tests were conducted on the cold rolled duplex stainless strip steel and hot rolled duplex stainless steel grades. Two different geometries of ultrasonic fatigue test specimens were tested. Considerable attention was devoted to the evaluation of fatigue crack initiation and growth mechanisms using the high resolution scanning electron microscopy. The fatigue crack initiation was found to be surface initiated phenomena in all the tested grades, albeit different in each case. The second part of this thesis work was the development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane. Cracks with dimensions much smaller than the overall size of the domain were considered. The main goal of the development of this technique was the evaluation of stress intensity factor at each crack tip. The comparison of results from the stress intensity factor evaluation by the developed procedure and the well-established Finite Element Method software ABAQUS showed difference of less than 1% for Jacobi polynomial expansion of sixth order in the dipole density representation.Article III was still in manuscript form at the time of the defense.
Very high cycle fatigue of stainless steels
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Torabiandehkordi, Noushin. "High and very high cycle fatigue behavior of DP600 dual-phase steel : correlation between temperature, strain rate, and deformation mechanisms." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0020/document.
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Ce travail vise à améliorer notre compréhension du comportement en fatigue à grand et très grand nombre de cycles d’un acier ferrito-martensitique dual phase, notamment les effets de la température et de la vitesse de déformation résultant de chargements cycliques à haute fréquence. L'effet de la fréquence sur la réponse en fatigue de l'acier DP600 a été étudié en effectuant des essais de fatigue sur une machine ultrasonique travaillant à 20 kHz et sur une machine conventionnelle travaillant à des fréquences inférieures à 100 Hz. Des études de fractographie et des observations microscopiques à la surface des échantillons ont été effectuées pour étudier les mécanismes de déformation et de rupture. De plus, la thermographie infrarouge in situ a été utilisée pour étudier la réponse thermique et les mécanismes dissipatifs du matériau lors des essais de fatigue. Les courbes S-N ont été déterminées à partir de chargements de fatigue ultrasoniques à 20 kHz et d’essais conventionnels à 30 Hz. La durée de vie pour une amplitude de contrainte donnée est plus élevée dans le cas de la fatigue ultrasonique bien que la limite de fatigue soit identique dans les deux cas. L’augmentation inévitable de la température en fatigue ultrasonique à fortes amplitudes de contraintes, ainsi que le comportement dépendant de la vitesse de déformation de la ferrite, en tant que structure CC, ont été trouvés comme les paramètres clés expliquant le comportement observé en fatigue, et la réponse thermique sous les fréquences faibles et ultrasoniques. Les écarts observés entre l’essai de fatigue conventionnel et celui ultrasonique ont été évalués à travers les mécanismes de mobilité des dislocations vis dans la phase ferritique de structure cubique centrée (CC). La durée de vie plus élevée et l’amorçage de la fissure principale sur une inclusion observés en fatigue ultrasonique ont été attribués au vieillissement dynamique résultant du fort auto-échauffement du matériau aux fortes amplitudes de contraintes. L'existence d'une transition du régime thermiquement activé au régime athermique avec l’augmentation de l'amplitude de contrainte a été mise en évidence. Au-dessous de la limite de fatigue, la déformation a lieu dans un régime thermiquement activé alors qu'elle est dans un régime athermique au-dessus de la limite de fatigue. En fatigue conventionnelle, la déformation est athermique pour toutes les amplitudes de contrainte. Une carte de transition a été produite en utilisant les résultats expérimentaux pour l'acier DP600 ainsi que les données disponibles dans la littérature pour d'autres aciers à base de ferrite, montrant ainsi la corrélation entre le mouvement des dislocations vis thermiquement activé et l'absence de rupture en fatigue à très grand nombre de cycleThis work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue
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Pacheco, Roman Oscar. "Evaluation of Finite Element simulation methods for High Cycle Fatigue on engine components." Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-148779.
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This document reflects the results of evaluating three computational methods to analyse the fatigue life of components mounted on the cylinder block; two currently in use at Scania and one that has been further developed from its previous state. Due to the cost of testing and the exponential increase in computational power throughout the years, the cheaper computational analyses have gained in popularity. When a component is mounted in a fairly complex assembly such as an engine, simplifications need to be made in order to make the analysis as less expensive as possible while keeping a high degree of accuracy. The methods of Virtual Vibrations, VROM and VFEM have been evaluated and compared in terms of accuracy, computational cost, user friendliness and general capacities. Additionally, the method VFEM has been further developed and improved from its previous state. A in-depth investigation regarding the differences of the methods has been conducted and improvements to make them more efficient are suggested herein. The reader can also find a decision matrix and recommendations regarding which method to use depending on the general characteristics of the component of interest and other factors. Two components, which differ in complexity and mounting nature, have been used to do the research.
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Ozdes, Huseyin. "The Relationship Between High-Cycle Fatigue and Tensile Properties in Cast Aluminum Alloys." UNF Digital Commons, 2016. http://digitalcommons.unf.edu/etd/716.
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Cast aluminum alloys are common in automotive and aerospace applications due to their high strength-to-density ratio. Fracture data for cast aluminum alloys, such as fatigue life, tensile strength and elongation, are heavily affected by the structural defects, such as pores and bifilms. There have been numerous studies in which either fatigue performance or tensile deformation were characterized and linked to casting defects. However, a comprehensive study that correlates tensile and fatigue properties has not been reported. The present study is motivated to fill this gap. The main objective of the investigation is to analyze the link between tensile and fatigue performance of commonly used cast aluminum alloys, and determine whether fatigue performance of cast aluminum alloys can be predicted. To accomplish this task, four research questions were developed: (i) how well do equations developed to account for mean stress effects perform in cast aluminum alloys, especially in datasets with various levels of structural quality, (ii) is the strong correlation between fatigue life and structural quality index obtained from tensile data reported for A206 alloy castings applicable to other aerospace and automotive casting alloys, (iii) how do methods to estimate high cycle fatigue from tensile data perform with aluminum castings, and (iv) can the axial fatigue performance of an A356-T6 casting be predicted from rotating beam fatigue data. Among the three mean stress correction models analyzed by using seven datasets from the literature, the one developed by Walker with an adjustable exponent has provided the best fit. It has been hypothesized that the adjustable Walker parameter is related to the structural quality index, QT, estimated from tensile data. Results have shown that there is indeed a strong correlation between QT and the Walker parameter. Moreover the parameters of the xvi Weibull distribution estimated from corrected data have been found to be strongly influenced by the mean stress correction method used. Tensile and fatigue life data for 319, D357 and B201 aluminum alloy castings reported in the literature have been reanalyzed by using a maximum likelihood method to estimate Basquin parameters in datasets with run-outs, Weibull statistics for censored data and mean stress correction. After converting tensile data to QT, a distinct relationship has been observed between the expected fatigue life and mean quality index for all alloys. Moreover, probability of survival in fatigue life has been found to be directly linked to the proportions of the quality index distributions in two different regions, providing further evidence about the strong relationship between elongation, i.e., structural quality, and fatigue performance [1]. Specimen geometry has been found to make the largest difference whereas the two aerospace alloys, B201 and D357, with distinctly different microstructures, have followed the same relationship, reinforcing the findings in the literature that fatigue life in aluminum castings is mainly determined by the size distribution and number density of structural defects. Six methods to predict fatigue life from tensile data have been compared by using data from the literature as well as the experimental A356 data developed in this study. Results have shown that none of the six methods provide reliable results. The consistently poor performance of the methods developed for steels and wrought alloys can be attributed to the major structural defects, namely bifilms, in aluminum castings. A new method to estimate the S-N curve from tensile data have been developed by using data for seventy-one S-N curves have been collected and Basquin parameters have been determined. Analysis showed that there is a strong relationship between QT and the Basquin exponent. xvii The Basquin parameters estimated by using the empirical relationships developed in the present study have provided better fits to the same datasets tested for the six methods. Hence the model developed in this study is proposed as the most reliable method to estimate high cycle fatigue properties. Finally, three methods to convert rotating bending fatigue test results to uniaxial fatigue data have been investigated by using the data developed in this study. Results have indicated that the method developed by Esin, in which both the fatigue life and alternating stress are corrected, provide the best estimate. Analyses of fracture surfaces of broken specimens via scanning electron microscopy have shown that tensile, axial fatigue and rotating beam fatigue properties are all strongly influenced by the same structural defects, confirming the validity of the approach taken in this study.
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HASANI, NAJAFABADI SEYED HUSEIN. "Numerical-Experimental Assessment of Stress Intensity Factors in Ultrasonic Very-High-Cycle Fatigue." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2712549.
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The continuous enhancement of reliability and durability requirements for many machinery components is significantly pushing the experimental research on the Very-High-Cycle Fatigue (VHCF) response of metallic materials. In order to significantly reduce testing time, ultrasonic testing machines are widely adopted when carrying out VHCF tests.
In the VHCF literature, the critical Stress Intensity Factor (SIF) is estimated by applying analytical SIF formulations to the typical semi-circular surface crack geometry revealed by fracture surfaces at final failure. However, when subjected to ultrasonic VHCF tests, analytical SIF formulations valid for static loading conditions could eventually lead to significant estimation errors.
The correct computation of the SIF in ultrasonic VHCF loading conditions is a key issue when investigating the crack growth rate curve with pre-cracked specimens or when evaluating critical SIF values from fracture surfaces of failed specimens. Dynamic conditions related to the resonance of the vibrating specimen, contact nonlinearity between crack faces and stress singularity at the crack tip make the SIF computation difficult and cumbersome. Numerical computation through Finite Element Models under non-linear dynamic conditions makes use of direct integration methods (implicit or explicit). However, in the high-frequency regime of ultrasonic VHCF tests, the procedure may lead to unacceptable computational time.
The present thesis aims at finding a robust, accurate, and simple method to calculate the critical SIF at final failure fracture of VHCF samples. In order to cope with the inefficiency of the time domain direct integration method, frequency domain analysis, and Multi Harmonic Balance Method were employed in this thesis. Even though the frequency domain analysis significantly reduced the computational time the overall reduction was still considered insufficient. Hence, reduction techniques via Reduce Order Modeling were also applied to decrease the total number of degrees of freedom for the system.
The solution obtained with the ABAQUS implicit solver was employed to verify the proposed hybrid technique. Results showed that the present method can accurately predict the displacement field and the SIF together with a drastic decrease of the computational time.
The proposed method was then applied to two models based on real sample geometries (Hourglass and Gaussian samples failed under ultrasonic VHCF) in order to evaluate the effect of the geometry on the critical SIF value. Results calculated by classical solutions valid for static conditions were also compared with the results obtained with the proposed hybrid method.
The comparison showed that conventional static solutions for SIFs could not be used to compute SIF values in ultrasonic conditions since computational errors are significant.
Another important finding was that, for the Gaussian sample, the SIF in both loading conditions (static and dynamic) is smaller than that for the Hourglass sample. The difference in static conditions is considerable and larger than that in dynamic conditions.
Besides the efficient and accurate computation of the critical SIF values from samples failed under ultrasonic VHCF tests, the proposed method can also be used: i) to design fatigue crack growth samples for investigating the near-threshold region with ultrasonic testing machines; ii) to accurately evaluate the SIF at the border of the relevant crack growth zones in ultrasonic VHCF (e.g., at the border of the fisheye and of the Fine Granular Area).
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Schäfer, Hans Joachim. "Auswertealgorithmus auf der Basis einer Modifikation des goniometrischen Modells zur stetigen Beschreibung der Wöhlerkurve vom Low-Cycle-Fatigue- bis in den Ultra-High-Cycle-Fatigue-Bereich." Aachen Mainz, 2008. http://d-nb.info/99179804X/04.
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Burger, Sofie [Verfasser]. "High Cycle Fatigue of Al and Cu Thin Films by a Novel High-Throughput Method / Sofie Burger." Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.
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Moreno, Oscar Ray. "Investigation and development of oil-injection nozzles for high-cycle fatigue rotor spin test." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Mar%5FMoreno.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, March 2005.Thesis Advisor(s): Raymond Shreeve, Garth Hobson. Includes bibliographical references (p. 91-93). Also available online.
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Li, Jinxia. "THE EFFECT OF MICROSTRUCTURE AND TEXTURE ON HIGH CYCLE FATIGUE PROPERTIES OF AL ALLOYS." UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/522.
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High cycle fatigue tests were carried out on a medium strength continuous casting AA 5754 Al alloy, and new generation high strength AA 2026 and AA 2099 Al alloys. The effect of texture on fatigue properties and short crack behavior were studied. The strengthening mechanisms were also thoroughly investigated for the two high strength alloys.Texture played an important role in the anisotropy of fatigue strength for the AA 5754 Al alloy. Being a solution strengthened alloy, it had a fatigue strength of 120% σy. High strength Al alloys had a strong tendency for planar slip due to the high density of coherent and shearable precipitates in the alloys. Texture was a key factor controlling the crack initiation and propagation. The crack path and the possible minimum twist angles were measured using EBSD and calculated theoretically by a crystallographic model. Based on the micro-texture measured by EBSD, the crack paths were predicted for the AA 2099 alloy and confirmed by the observed values.The excellent balance of superior fatigue properties and high tensile strength of AA 2026 and AA 2099 was attributed to the reduced population of Fe-containing particles, homogeneously distributed precipitates and dislocations. The addition of Zr coupled with the optimized thermo-mechanical treatment strongly restrained the recrystallization, refined the grain structure and promoted the homogenization of the precipitates. Moreover, the retainment of the deformation texture developed during the hot extrusion provided significant orientation strengthening in the high strength Al alloys.Fatigue cracks tended to initiate at coarse second phase particles on sample surfaces and the crack population varied markedly with the applied stresses in the high strength Al alloys. The relationship between of the crack population and the applied stress level was studied and quantified by a Weibull distribution function. Since the measured cracknumbers were associated with the crack initiate sites (i.e., the weakest links) in an alloy, the fatigue weakest-link density, which is defined as the crack population per unit area when stress close to the ultimate tensile stress, and the weakest-link strength distribution can all be calculated and regarded as a property of the studied materials.
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Kiefer, Konstanze. "Simulation of high-cycle fatigue-driven delamination in composites using a cohesive zone model." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25155.
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In this PhD thesis several published strategies for the simulation of high-cycle fatigue-driven delamination using cohesive elements are investigated in mode I using an efficient analytical model which eliminates the numerical errors involved in a finite element simulation. A detailed sensitivity study of all the models is performed with respect to the element size and the cycle-jump. The models are then compared and their advantages and disadvantages highlighted. For two of the models improvements are proposed and investigated using the analytical model. Necessary conditions for a successful fatigue model are then highlighted and a new model is proposed. A sensitivity study demonstrates a very good performance of this model. The new fatigue degradation strategy is implemented into a user defined element (UEL) within the commercial finite element software ABAQUS. Two simulations are then performed for pure mode I and mode II fatigue-driven delamination. The new strategy is shown to achieve good agreement with the input Paris law and is also shown to perform well in comparison with FE implementations of some of the published cohesive element strategies for fatigue-driven growth of delamination.
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Polasik, Alison K. "The Role of Microstructure on High Cycle Fatigue Lifetime Variability in Ti-6Al-4V." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1412676768.
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Holycross, Casey M. "A multiscale analysis and extension of an energy based fatigue life prediction method for high, low, and combined cycle fatigue." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462572899.
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Li, Rui. "NUMERICAL INVESTIGATION OF THE INFLUENCE OF FRONT CAMBER ON THE STABILITY OF A COMPRESSOR AIRFOIL." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_theses/345.
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With the advent of smart materials it is becoming possible to alter the structural characteristics of turbomachine airfoils. This change in structural characteristics can include, but is not limited to, changes in the shape (morphing) of the airfoil. Through changes in the airfoil shape, aerodynamic performance can be improved. Moreover, this technique has the potential to act as a flutter suppressant. In this investigation changes in the airfoil front camber while maintaining the airfoil thickness distribution are made to increase airfoil stability. The airfoil section is representative of current low aspect ratio fan blade tip sections. To assess the influence of the change in airfoil shape on stability the work-per-cycle was evaluated for torsion mode oscillations around the mid-chord at an inlet Mach number of 0.5 with an interblade phase angle of 180 degree Cchordal incidence angles of both 0 degree and 10 degree, and a reduced frequency of 0.4.
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Anguo, Wang. "The effect of grain size on the low-cycle fatigue behaviours of a CrMnFeCoNi high entropy alloy." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/21129.
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High-entropy alloys (HEAs) alloys are alloys formed by at 5 or more elements, which have high strength, excellent ductility, and wear, corrosion and creep resistance. While the above-mentioned properties are very important and widely studied, fatigue properties are a more critical issue in most industrial applications. Fatigue causes over 90% of failure. Yet, the fatigue properties of HEAs have been less investigated. So, it worth to study the fatigue properties. It has been well-known that grain size plays a critical role in determining the mechanical properties of HEAs. However, the grain size effects on fatigue properties of HEAs has not been clear. This project aims to study the effect of grain size on the low-cycle fatigue (LCF) properties of a CrMnFeCoNi HEA. Results show that the fatigue life increased with decreasing grain size and/or decreasing strain amplitude. Fatigue-induced structural evolution of the HEA was complicated. Deformation of samples with fine and coarse grain sizes occurred mainly via planar slip at low strain levels, while wavy slip dominated the deformation of samples with the intermediate grain size. Planar slip was suppressed at a high strain regime. Dislocation cell structures, which are classic wavy slip microstructures, were commonly seen in intermediate grains at the high strain regime. The fatigue cracking behaviour at twin boundaries (TBs) in the HEA was also explored. Irrespective of grain size, the change from slip band cracking to TB cracking occurred with increasing the difference in the Schmid factors between matrix and twin. However, the required critical difference of Schmid factors for the transition of the dominant cracking mode decreases with decreasing grain size due to the reduced slip band spacing that increases the impingement sites on the TBs and facilitates the coalescence of defects and voids to initiate TBs cracks
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Ekström, Madeleine. "Oxidation and corrosion fatigue aspects of cast exhaust manifolds." Doctoral thesis, KTH, Mekanisk metallografi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166274.
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Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis. The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated. The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life. These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field.QC 20150507
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Kern, Paul Calvin. "Improvements to the computational pipeline in crystal plasticity estimates of high cycle fatigue of microstructures." Thesis, Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55070.
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The objective of this work is to provide various improvements to the modeling and uncertainty quantification of fatigue lives of materials as understood via simulation of crystal plasticity models applied to synthetically reconstructed microstructures.
A computational framework has been developed to automate standardized analysis of crystal plasticity models in the high cycle fatigue regime. This framework incorporates synthetic microstructure generation, simulation preparation, execution and post-processing to analysis statistical distributions related to fatigue properties. Additionally, an improved crack nucleation and propagation approach has been applied to Al 7075-T6 to improve predictive capabilities of the crystal plasticity model for fatigue in various loading regimes. Finally, sensitivities of fatigue response to simulation and synthetic microstructure properties have been explored to provide future guidance for the study of fatigue quantification based on crystal plasticity models.
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Wang, Bowen Wang. "Surface Drying and Rehydration Does Not Affect the High Cycle Fatigue Behavior of Human Bone Tissue." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1527784382697425.
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Visagie, Willem Johannes. "Blade tip timing to determine turbine blade fatigue in high backpressure conditions." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/75831.
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This dissertation presents an approach to use blade tip timing measurements with finite element analysis to predict the fatigue life of a low pressure steam turbine last stage blade under high backpressure and low flow conditions. Material fatigue properties were determined through the extended universal material law for FV566 material, along with different temper scenarios. A finite element model of a blade with damping pins was developed, using the principle of cyclic symmetry for a perfectly tuned model. Pre-stress modal analysis was conducted, incorporating damping via friction and plasticity for initial 20% overspeed test. The finite element model was verified by two experimental tests: the first being a blade impact test and the second a telemetry strain gauge test in a balance pit. Fatigue life analysis was conducted under the assumption that non-synchronous vibration is experienced by the blade and that only one mode is dominant in the vibration. The results from the fatigue analysis corresponded to the location of the cracks experienced on the blades. The results show twelve orders of magnitude lower life at low load, high backpressure conditions, compared to high load high pressure conditions. The research was further extended to check the same vibratory response on the first three modes, up to their tenth nodal diameters. This was done to analyse fatigue life in a case that a different mode was excited.Dissertation (MEng)--University of Pretoria, 2020.
Eskom Rotek Industries
Mechanical and Aeronautical Engineering
MEng
Unrestricted
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Zhao, Mengxiong. "Ultrasonic fatigue study of Inconel 718." Thesis, Paris 10, 2018. http://www.theses.fr/2018PA100063/document.
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L’Inconel 718 est utilisé dans les disques de turbine des moteurs d’avion, de par sa haute résistance à la corrosion, à l’oxydation, au fluage et sa haute résistance mécanique à très haute température. Le nombre total de cycles de ces composants mécaniques s’élève à 109~1010 durant sa vie. Ils subissent des chargements de grande amplitude à faible fréquence, comme les forces centrifuges ou les contraintes thermiques mais aussi des chargements de faibles amplitudes à très haute fréquence, du aux vibrations des pales. Dans ce travail, on se propose d’étudier la fatigue à très grand nombre de cycles (VHCF) de l’Inconel 718 en utilisant des machines de fatigue ultrasonique, fonctionnant à 20KHz. Le système d’acquisition utilise des cartes NI et le logiciel LabView pour superviser la fréquence, la température, les déplacements durant toute la durée des tests. Des capteurs laser Keyence utilisant deux sondes pour les faces supérieure et inférieure de l’éprouvette permettent de capturer la fréquence et les modes de vibration. La différence entre les valeurs moyennes mesurées permet d’accéder à l’allongement de l’éprouvette, dû à l’auto-échauffement.3 types de matériaux avec différents traitements thermiques, AR, DA et DAHQ de l’ONERA et SAFRAN sont comparés. La différence au niveau de la taille de grain, de la phase, des précipités, … est analysée par micrographie métallographique en utilisant un microscope optique (MO) et un microscope électronique à balayage (MEB). Le comportement en traction quasi-statique et sous chargement cyclique contrainte-déformation est aussi proposé. La transition entre durcissement et adoucissement cyclique apparait à l’issue du traitement thermique. Finalement, les surfaces de ruptures sont observées en utilisant des caméras optiques et un MEB afin d’identifier les mécanismes de ruptures de l’Inconel 718 dans le domaine de la fatigue à très grand nombre de cyclesInconel 718 is widely used in turbine disk of aeronautic engines, due to its high resistance to corrosion, oxidation, thermal creep deformation and high mechanical strength at elevated temperature. The total cycle of these mechanical components is up to 109~1010 during its whole lifetime. It endures high-amplitude low-frequency loading including centrifugal force or thermal stress, and also low-amplitude high-frequency loading came from vibration of blade.In this work, the very high cycle fatigue (VHCF) behaviour of Inconel 718 with self-heating phenomenon without any cooling is studied using ultrasonic fatigue system at 20KHz. Acquisition system is improved using NI capture card with LabView for monitoring the frequency, temperature, displacement and so on during all the tests. Keyence laser sensor with two probes at the top and bottom surfaces of the specimens is used to reveal the frequency and vibration mode. The difference of mean values between these two probes is the elongation of the specimen caused by self-heating phenomenon.Three sets of materials with different heat treatment, As-Received (AR), Directly Aged (DA) and Directly Aged High Quality (DAHQ) from ONERA and SAFRAN are compared. The difference of grain size, phase, precipitate particle, etc. is investigated by metallographic micrograph using optical microscope (OM) and scanning electron microscope (SEM). Quasi-static uniaxial tensile property and cyclic stress-strain response is also proposed. The transition from cyclic hardening to cyclic softening appears after aged heat treatment. Finally, fracture surfaces are observed using optical camera and scanning electron microscope in order to identify the mechanism of fracture of Inconel 718 in the VHCF domain
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Xiang, Shengmei. "High-Temperature Corrosion-Fatigue of Cast Alloys for Exhaust Manifolds." Licentiate thesis, KTH, Materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-235170.
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The introduction of gas-driven Otto engine and the corresponding usage of bio-fuels in heavy-duty engines will render the exhaust atmosphere more corrosive and bring a higher working temperature to exhaust manifolds. The current service material, a ferritic ductile cast iron called SiMo51, will soon meet its upper temperature limit set by the ferrite-austenite transformation at 860ºC. Three alternative materials, as well as SiMo51 serving as reference, are investigated in the present thesis emphasizing on high-temperature corrosion fatigue. The first aim of this study is to obtain material data and give a quantitative ranking of the materials’ performance. Low-cycle fatigue (LCF) tests at 800ºC in a synthetic exhaust gas (5%O2-10%CO2-5%H2O-1ppmSO2-N2 bal.) are conducted to evaluate the materials’ performance in simulated real working scenarios, where high-temperature, corrosive atmosphere and fatigue conditions during testings are similar to the conditions experienced by the exhaust manifolds. To evaluate the individual effect from high-temperature fatigue and isolate the impact from corrosion, the materials are tested under the same settings but in an argon atmosphere. To evaluate the individual effect from high-temperature corrosion and isolate the impact from mechanical deformation, oxidation tests are carried out at 800ºC in the same synthetic exhaust gas. The second aim is to identify and understand different oxidation behavior and failure mechanisms in the materials, realized by considerable characterizations of the tested specimens. From the fatigue tests, it is found that the austenitic stainless steel HK30 has the highest fatigue resistance, followed by the austenitic cast iron Ni-resist D5S, and the ferritic ductile cast irons SiMo1000 and SiMo51, a ranking valid in both atmospheres. In the exhaust atmosphere, for instance, the improvement in fatigue strength at 15,000 cycles relative to SiMo51 are 260%, 194% and 26%, respectively. Different crack initiation and propagation mechanisms are found for the various combinations of materials and atmospheres. In the exhaust atmosphere, for instance, crack initiation is assisted by oxide intrusion in SiMo51 and crack propagation is affected by crack branching in HK30, mechanisms not observed in argon. By comparing the S-N fatigue curves in the two atmospheres, the influence of oxidation on fatigue life is evaluated. The fatigue life of the cast irons are surprisingly found to be higher in the exhaust atmosphere. Several explanations are suggested for this, considering their very different oxidation behaviors. This study provides accurate test data that can be used to help industry avoid over-dimensioned design. The investigation of the failure mechanisms promotes better understanding of the correlation between microstructure and mechanical properties. Moreover, the combination of fatigue tests in argon, fatigue tests in exhaust and oxidation tests in exhaust, shows how corrosion and fatigue individually and synergistically affect the materials’ performance at high temperature.QC 20180917
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Oakley, Sharon Yvonne. "On the high- and low-cycle fatigue of aero-engine compressor blades following foreign object damage." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403979.
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DuoÌ, Pierangelo. "A predictive study of foreign object damage in gas turbine compressor blades under high cycle fatigue." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418633.
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Rohm, Thomas [Verfasser]. "Der Einfluss oberflächennaher Spannungsgradienten auf das Very High Cycle Fatigue Verhalten des Vergütungsstahls 42CrMo4 / Thomas Rohm." Düren : Shaker, 2019. http://d-nb.info/120080838X/34.
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Bhamare, Sagar D. "High Cycle Fatigue Simulation using Extended Space-Time Finite Element Method Coupled with Continuum Damage Mechanics." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352490187.
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Holycross, Casey M. "A Critical Assessment of the High Cycle Bending Fatigue Behavior of Boron-modified Ti-6Al-4V." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1283881630.
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Saiedi, Mohammad Reza. "Behaviour of CFRP-Prestressed Concrete Beams under Sustained Loading and High-Cycle Fatigue at Low Temperature." Thesis, Kingston, Ont. : [s.n.], 2009. http://hdl.handle.net/1974/5365.
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Stille, Sebastian [Verfasser], Lorenz [Akademischer Betreuer] Singheiser, and Tilmann [Akademischer Betreuer] Beck. "Very high cycle fatigue behavior of riblet structured high strength aluminum alloy thin sheets / Sebastian Stille ; Lorenz Singheiser, Tilmann Beck." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1127531611/34.
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