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1
Nowicki, Timothy. "Statistical model prediction of fatigue life for diffusion bonded Inconel 600 /". Online version of thesis, 2008. http://hdl.handle.net/1850/7984.
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Fernandes, Paulo Jorge Luso. "Fatigue and fracture of metals in liquid-metal environments". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337963.
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Lunt, William S. "Molecular dynamics simulation of fatigue damage in metals". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FLunt.pdf.
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Erasmus, Daniel Jacobus. "The fatigue life cycle prediction of a light aircraft undercarriage". Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/1527.
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The reliability of systems relies heavily on accurate fatigue life prediction of related components. Fatigue life prediction is a complicated process requiring the correct methodology to determine accurate and reliable predictions. The Palmgren – Miner damage accumulation hypothesis is widely used in determining the fatigue life of components exposed to variable loading conditions. Modifications have been made to this hypothesis trying to achieve a greater degree of accuracy, of these the Liu – Zenner modification has been the most successful. In this report the systematic process of fatigue life prediction using the Liu – Zenner modification to achieve reliable results is calculated. A representative stress time history measured in service on the component forms the basis for defining a flight cycle which is the chosen unit in which to express the fatigue life. Rainflow cycle counting performed on the stress time history allowed the formulation of a load spectrum to which the component is exposed in one cycle. Combining the load spectrum with the developed SN curve of the component and using the Liu – Zenner modification to the Palmgren – Miner rule a reliable fatigue life in cycles is predicted.
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Williams, Zachary. "Krouse Fatigue for Metals with Elevated Mean Stress". Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1597075964521893.
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Repetto, Eduardo A. Ortiz Michael. "On the fatigue behavior of ductile F.C.C. metals /". Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-01242008-133649.
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Zhao, Tianwen. "Fatigue of aluminum alloy 7075-T651 /". abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3342620.
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Thesis (Ph. D.)--University of Nevada, Reno, 2008."December, 2008." Includes bibliographical references (leaves 76-83). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2009]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.
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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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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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Ghodratighalati, Mohamad. "Multiscale Modeling of Fatigue and Fracture in Polycrystalline Metals, 3D Printed Metals, and Bio-inspired Materials". Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104944.
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The goal of this research is developing a computational framework to study mechanical fatigue and fracture at different length scales for a broad range of materials. The developed multiscale framework is utilized to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. The highly-localized stress in a relatively small contact area at the wheel-rail interface promotes micro-crack initiation and propagation near the surface of the rail. 2D and 3D microstructural-based computational frameworks are developed for studying the rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions. The results obtained from studying RCF behavior in different conditions will help better maintenance of the railways and increase the safety of trains.
The developed framework is employed to study the fracture and fatigue behavior in 3D printed metallic alloys fabricated by selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing the manufacturing sector and is being utilized across a diverse array of industries, including biomedical, automotive, aerospace, energy, consumer goods, and many others. Since experiments on 3D printed alloys are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. In this research, a computational framework is developed to study fracture and fatigue in different scales in 3D printed alloys fabricated by the SLM method. Our method for studying the fatigue at the microstructural level of 3D printed alloys is pioneering with no similar work being available in the literature. Our studies can be used as a first step toward establishing comprehensive numerical frameworks to investigate fracture and fatigue behavior of 3D metallic devices with complex geometries, fabricated by 3D printing.
Composite materials are fabricated by combining the attractive mechanical properties of materials into one system. A combination of materials with different mechanical properties, size, geometry, and order of different phases can lead to fabricating a new material with a wide range of properties. A fundamental problem in engineering is how to find the design that exhibits the best combination of these properties. Biological composites like bone, nacre, and teeth attracted much attention among the researchers. These materials are constructed from simple building blocks and show an uncommon combination of high strength and toughness. By inspiring from simple building blocks in bio-inspired materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired composites compared to their building blocks. Furthermore, an optimization methodology is implemented into the designing the bio-inspired composites for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure. This study can be used as an effective reference for creating damage-tolerant structures with improved mechanical behavior.Doctor of Philosophy
The goal of this research is developing a multiscale framework to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. Different computational models are developed for studying rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions and the results will help better maintenance of the railways and increase the safety of trains. The developed model is employed to study the fracture and fatigue behavior in 3D printed metals created by the selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing industries including biomedical, automotive, aerospace, energy, and many others. Since experiments on 3D printed metals are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. Our method for studying the fatigue at the microstructural level of 3D printed alloys can help to create more fatigue and fracture resistant materials. In the last section, we have studied fracture behavior in bio-inspired materials. A fundamental problem in engineering is how to find the design that exhibits the best combination of mechanical properties. Biological materials like bone, nacre, and teeth are constructed from simple building blocks and show a surprising combination of high strength and toughness. By inspiring from these materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired structure compared to its building blocks. Furthermore, an optimization method is implemented into the designing the bio-inspired structures for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure.
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Glass, Bradley Smyth. "Continuum mechanics approaches to the study of fracture and fatigue in metals". Faculty of Engineering, 2004. http://ro.uow.edu.au/theses/264.
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This thesis investigates continuum mechanics based means of metal failure assessment. A basic science approach was employed throughout the study to examine the fundamental relationships responsible for metal failure. The extension of previously existing continuum mechanics based theories to encompass a wider range of application was considered in this thesis. Research was conducted as two separate studies which examine specific aspects of the metal failure spectrum, namely failure due to monotonic loading, and fatigue failure due to cyclic loading. The failure due to monotonic loading research was conducted to examine the influence of hydrostatic stress on metal ductility. A fundamental relationship in the form of a monotonic failure criterion was proposed based on a relationship between equivalent plastic fracture strain and hydrostatic stress. An experimental program incorporating uniaxial tensile testing of notched specimens was conducted to examine the proposed relationship for the hydrostatic tensile stress range. Finite element analyses were produced to confirm the mechanical properties and obtain the stress-strain state present at specimen failure. A good correlation was established between the load-displacement results obtained from experiment and finite element analysis, providing confirmation of the stress-strain data. The stress-strain results confirmed the existence of a relationship between hydrostatic stress and ductility in the form of a monotonically decreasing value of equivalent plastic fracture strain with increasing hydrostatic tensile stress. The relationship determined was in accordance with the trend indicated by various researchers for the hydrostatic compressive stress range. The potential application of such a criterion to finite element methods was amply demonstrated from this research. The fatigue failure due to cyclic loading research examined the application of energy based methods to fatigue life characterisation. Based on the hypothesis that irreversible damage may be attributed entirely to plastic deformation, the application of the plastic strain energy approach to the entire fatigue life spectrum was pursued. For application to high cycle fatigue, a thermodynamic approach was developed to allow plastic strain energy determination beyond the range of application of conventional mechanical measurement. Thermodynamic models consisting of varying degrees of free surface contribution to heat dissipation were developed as possible representations of the high cycle fatigue damage process. An experimental program was conducted incorporating mechanical and thermodynamic means of measurement. Thermodynamic measurement was achieved via an experimental apparatus incorporating precision temperature measurement and thermal isolation at the specimen surface. Assuming an appropriate thermodynamic model, a finite difference analysis allowed a quantitative determination of plastic strain energy. Close agreement was indicated from comparison of the low cycle fatigue plastic strain energy results obtained from mechanical and thermodynamic measurement. A qualitative determination of plastic strain energy for high cycle fatigue was achieved, subject to confirmation of the thermodynamic model. The qualitative assessment verified the existence of measurable plastic strain energy during high cycle fatigue.
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Hansen, Robert C. "Thermal and mechanical fatigue of 6061 Al - P100 Gr metal matrix composite". Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA238795.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 1990.Thesis Advisor(s): Dutta, Indranath ; Mitra, Shantanu. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Fatigue (mechanics), thermal fatigue, metal matrix composites, laminates, bending, ultimate strength, fiber reinforced composites, theses. Author(s) subject terms: Aluminum-graphite composite, bend fatigue, thermal fatigue. Includes bibliographical references (p. 64-65). Also available in print.
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Ralph, William Carter. "Assessment of hole drilling procedures on resulting fatigue lives". Thesis, Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04072004-180146/unrestricted/ralph%5Fwilliam%5Fc%5F200312%5Fms.pdf.
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Heffern, Thomas V. "Probabilistic modeling and simulation of metal fatigue life prediction". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FHeffern.pdf.
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Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 2002.Thesis advisor(s): Ramesh Kolar, E. Roberts Wood. Includes bibliographical references (p. 113). Also available online.
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Fan, Zhengxuan. "Atomistic simulation of fatigue in face centred cubic metals". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX076/document.
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La fatigue induite par chargement cyclique est un mode d'endommagement majeur des métaux. Elle se caractérise par des effets environnementaux et de grandes dispersions de la durée de vie qui doivent être mieux comprises. Les matériaux analysés sont de type cfc : aluminium, cuivre, nickel et argent. Le comportement de marches naturellement créées en surface par le glissement cyclique de dislocations est examiné par simulations en dynamique moléculaire sous vide et sous environnement oxygène pour le cuivre et le nickel. Un phénomène de reconstruction est observé sur les marches en surface, qui peut induire une forte irréversibilité. Trois mécanismes de reconstruction des marches apparues en surface sont observés et décrits. L’irréversibilité de ces marches est ensuite analysé. Elles sont irréversibles pour des chargements expérimentaux, sauf arrivée de dislocations de signe opposé sur un plan de glissement directement voisin.Avec arrivée de dislocations sur des plans non voisins, l'irréversibilité s’accumule cycle par cycle et il est possible de reproduire l’apparition de fissures en surface dont la profondeur augmente graduellement.Un environnement oxygène modifie la surface (début d’oxydation) mais pas l’irréversibilité parce que l’oxygène n’a pas d'influence majeure sur les différents mécanismes liés à l’évolution du relief.Une estimation grossière de l'irréversibilité est faite pour des dislocations coin pures dans une bande de glissement persistante pour les matériaux dits ondulés. On obtient un facteur d’irréversibilité entre 0,5 et 0,75 pour le cuivre, sous vide et sous l’environnement oxygène, en accord avec des mesures récentes en microscopie à force atomique.La propagation de fissures est simulée en environnement inerte. Les fissures peuvent se propager à cause de l'irréversibilité des dislocations générées, liée à leurs interactions allant jusqu’à la création de jonctionsFatigue is one of the major damage mechanisms of metals. It is characterized by strong environmental effects and wide lifetime dispersions which must be better understood. Different face centred cubic metals, Al, Cu, Ni, and Ag are analyzed. The mechanical behaviour of surface steps naturally created by the glide of dislocations subjected to cyclic loading is examined using molecular dynamics simulations in vacuum and in air for Cu and Ni. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. Three different mechanisms of reconstruction are defined. Surface slip irreversibility under cyclic loading is analyzed. All surface steps are intrinsically irreversible under usual fatigue laboratory loading amplitude without the arrival of opposite sign dislocations on direct neighbor plane.With opposite sign dislocations on non direct neighbour planes, irreversibility cumulates cycle by cycle and a micro-notch is produced whose depth gradually increases.Oxygen environment affects the surface (first stage of oxidation) but does not lead to higher irreversibility as it has no major influence on the different mechanisms linked to surface relief evolution.A rough estimation of surface irreversibility is carried out for pure edge dislocations in persistent slip bands in so-called wavy materials. It gives an irreversibility fraction between 0.5 and 0.75 in copper in vacuum and in air, in agreement with recent atomic force microscopy measurements.Crack propagation mechanisms are simulated in inert environment. Cracks can propagate owing to the irreversibility of generated dislocations because of their mutual interactions up to the formation of dislocation junctions
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Yoon, Kee Bong. "Characterization of creep fatigue crack growth behavior using C[superscript](t[superscript]) parameter". Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17523.
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Kirmani, Ghulam Ashraf-Ul-Harmain. "Single overload fatigue crack growth retardation : an implementation of plasticity induced closure". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32752.pdf.
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Bian, Lichun, e 卞立春. "Fatigue crack growth analysis of metallic plates with an inclinedsemi-elliptical crack". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31242844.
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Cretegny, Laurent. "Use of atomic force microscopy for characterizing damage evolution during fatigue". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/20141.
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Dallmeier, Johannes. "Experimental analysis and numerical fatigue modeling for magnesium sheet metals". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-209124.
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The desire for energy and resource savings brings magnesium alloys as lightweight materials with high specific strength more and more into the focus. Most structural components are subjected to cyclic loading. In the course of computer aided product development, a numerical prediction of the fatigue life under these conditions must be provided. For this reason, the mechanical properties of the considered material must be examined in detail. Wrought magnesium semifinished products, e.g. magnesium sheet metals, typically reveal strong basal textures and thus, the mechanical behavior considerably differs from that of the well-established magnesium die castings. Magnesium sheet metals reveal a distinct difference in the tensile and compressive yield stress, leading to non-symmetric sigmoidal hysteresis loops within the elasto-plastic load range. These unusual hysteresis shapes are caused by cyclic twinning and detwinning. Furthermore, wrought magnesium alloys reveal pseudoelastic behavior, leading to nonlinear unloading curves. Another interesting effect is the formation of local twin bands during compressive loading. Nevertheless, only little information can be found on the numerical fatigue analysis of wrought magnesium alloys up to now.
The aim of this thesis is the investigation of the mechanical properties of wrought magnesium alloys and the development of an appropriate fatigue model. For this purpose, twin roll cast AM50 as well as AZ31B sheet metals and extruded ME21 sheet metals were used. Mechanical tests were carried out to present a comprehensive overview of the quasi-static and cyclic material behavior. The microstructure was captured on sheet metals before and after loading to evaluate the correlation between the microstructure, the texture, and the mechanical properties. Stress- and strain-controlled loading ratios and strain-controlled experiments with variable amplitudes were performed. Tests were carried out along and transverse to the manufacturing direction to consider the influence of the anisotropy. Special focus was given to sigmoidal hysteresis loops and their influence on the fatigue life. A detailed numerical description of hysteresis loops is necessary for numerical fatigue analyses. For this, a one-dimensional phenomenological model was developed for elasto-plastic strain-controlled constant and variable amplitude loading. This model consists of a three-component equation, which considers elastic, plastic, and pseudoelastic strain components. Considering different magnesium alloys, good correlation is reached between numerically and experimentally determined hysteresis loops by means of different constant and variable amplitude load-time functions.
For a numerical fatigue life analysis, an energy based fatigue parameter has been developed. It is denoted by “combined strain energy density per cycle” and consists of a summation of the plastic strain energy density per cycle and the 25 % weighted tensile elastic strain energy density per cycle. The weighting represents the material specific mean stress sensitivity. Applying the energy based fatigue parameter on modeled hysteresis loops, the fatigue life is predicted adequately for constant and variable amplitude loading including mean strain and mean stress effects. The combined strain energy density per cycle achieves significantly better results in comparison to conventional fatigue models such as the Smith-Watson-Topper model. The developed phenomenological model in combination with the combined strain energy density per cycle is able to carry out numerical fatigue life analyses on magnesium sheet metals.
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Kucz, Daniel Allen. "Analysis of distortion-induced fatigue cracking in a steel trapezoidal box girder bridge". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 177 p, 2009. http://proquest.umi.com/pqdweb?did=1885755701&sid=9&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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KJERENGTROEN, LIDVIN. "RELIABILITY ANALYSIS OF SERIES STRUCTURAL SYSTEMS (PROBABILITY, DESIGN, FATIGUE)". Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187909.
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Reliability analysis of series structural systems with emphasis on problems typical for metal fatigue is addressed. Specific goals include the following: (1) Given the distribution of strength of the components and the distribution of external loads on the system what is the probability of failure of the system? (2) Given the target safety index for the system, what would be the target safety index for the components? Exact solutions in the analysis of series structural systems only exists for some special problems. Some of these special problems are investigated. In particular some special cases of the problem of unequal element reliabilities are considered and some interesting observations are made. Numerical integration is in general required even when an exact solution exists. A correction or adjustment factor is developed for an important class of problems. This factor makes it possible to relate element and system probabilities of failure without numerical integration. However in most cases no exact solution to the structural series system problem exists. Approximations by for instance bounds on the probability of failure or Monte Carlo simulation has been the only way of approximating solutions. These two methods are generally not good approximation schemes since they are either too crude or too expensive. In this dissertation an approximation scheme for analysis of series systems where no exact solution exists is developed. The method only requires a simple numerical integration if the component safety index and the correlation coefficient between failure modes is known. Numerous examples are used to verify the method against known exact results and excellent estimates are obtained. Applications by practical examples is also given. In the appendix the problem of convergence of fatigue life distribution is also summarized.
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Peters, Donald Michael Dirk. "The effects of shot peening on low cycle fatigue life of 7075-T6 aluminium alloy round bar". Thesis, Nelson Mandela Metropolitan University, 2014. http://hdl.handle.net/10948/2929.
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The aim in this dissertation was to improve our understanding of the effectiveness of shot peening in prolonging fatigue life, of 7075-T6 Aluminium Alloy round bar, taking into consideration surface residual stress, microstructural and micro-hardness parameters. Three point bending, high stress, moderately low cycle, fatigue tests were conducted to study the effects of shot peening and associated surface residual compressive stresses on fatigue life. The influence of shot peening on the microstructure was explored, including the application of mechanical small plastic straining and surface skimming, to vary the surface residual compressive stresses and induce strain hardening. Tests were performed to measure residual stress-depth distribution, plastic straining, micro-hardness, and the microstructure analysed on scanning electron microscopy (SEM) fractographs. The Juvinall and Marshek life prediction model was used in conjunction with the Gerber equation for non-zero mean stress applications to generate a proposed life prediction model for this material which is user-friendly. The proposed life prediction model has a linear equation format with the flexibility to conservatively accommodate most of the various types, and combinations, of treatments applied in this research by the use of customised constants. The results show that there was good correlation between actual and predicted fatigue life as well as useful insights into the role of the microstructure in explaining fatigue life behaviour.
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Pape, John Andrew. "Design and implementation of an apparatus to investigate the fretting fatigue of PH 13-8 Mo stainless steel". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/18394.
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Dunn, DeRome Osmond. "Modeling cycle and time dependent creep/relaxation effects on fatigue lives of notched members". Diss., Virginia Polytechnic Institute and State University, 1991. http://hdl.handle.net/10919/54823.
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Mechanical cyclic variations in mean stress and strain amplitude is a well-known occurrence for metals even at room temperature. Many fatigue analysis procedures ignore these variations. Fatigue analysis which included both time and cycle dependent mechanical material behavior for metals at room temperature had not been previously studied except for the case of creep. An investigation studying transient mechanical effects on Ti-6Al-4V titanium and 7475-T651 Al alloys was done to determine how great an effect transients at room temperature would have on fatigue life under cyclic conditions. The mechanical material response was modeled using viscoplasticity constitutive laws and Neuber’s rule eliminating the need for finite element modeling of uniaxially loaded notched members. However, the Nenber’s modeling may be used with any material constitutive law. The procedures for fatigue damage used cycle counting to compute strain amplitude and mean stress. Since a large amount of fatigue data is reported as strain-life curves, the fatigue analysis was developed using this fatigue data although it did not include transients. If favorable results are obtained, development of modeling and testing to include transients in strain-life fatigue data could be avoided, and the existing fatigue data base utilized.
Experimental work was undertaken and nonlinear optimization techniques used to compute model constants for the two alloys. However, small amounts of rate dependence was found for cyclic strain control testing. The viscoplasticity models became stiff when rate dependence was low causing numerical problems, and model constants for the viscoplastic constitutive law could not be determined since convergence was not achieved. Also, only small amounts of transient static stress relaxation was observed for extended hold periods.
Finally, experimental verification was done for the local surface stresses in a notched member under load using advanced x-ray stress equipment. Measurements during brief pauses were made over a cycle. From the x-ray results, an anomalous surface behavior was observed. The surface yielded before the bulk material with the lower surface yielding seeming to be time dependent in nature. Since rolled plates of the alloys were used, texture was measured and studied in the form of pole figures, and extreme texture was found for both alloys. However. successful x-ray measurements were made for the alloys studied even though assuming linear d-spacing versus sin²ψ. Finally. x-ray measurements for a cycled notched member, exhibited relaxation of mean stress and not relaxation of residual stress.Ph. D.
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Bennett, Valerie P. "A microscale study of small crack propagation in multiaxial fatigue". Diss., Atlanta, Ga. : Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/23957.
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Wannenburg, Johann. "A study of fatigue loading on automotive and transport structures". Thesis, University of Pretoria, 2007. http://upetd.up.ac.za/thesis/available/etd-04032008-100638/.
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Li, Zongbao. "Crack detection in annular components by ultrasonic guided waves". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15920.
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Kienle, Ulrich F. B. "A laboratory simulation of adhesive wear of high speed reciprocating components in water powered mining equipment". Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/22575.
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Bibliography: pages 117-120.A high-speed reciprocating sliding wear test rig was used to examine the metal on metal surface interactions of materials under consideration for application in water powered stoping equipment. The suitability of this test rig was investigated by implementing a test programme covering self-mated stainless steel and stainless steel-on-bronze couples. These couples were examined under water lubricated conditions in a broad test matrix, covering sinusoidal peak velocities of 1, 5 and 10 m/s; loads of 5, 10 and 20N and surface roughness values ranging from 0.2 to 0.4 μm, CLA. Due to poor reproducibility and inconclusive wear behaviours, no inferences could. be made as to the relative performance of the couples tested and no ranking tables could be compiled, In response to these findings, the emphasis changed to the design of a better test facility which could more accurately simulate the tribological interactions of interest. A new laboratory test rig, capable of investigating the performance of material surfaces, rubbing against one another under conditions of high speed reciprocating sliding in specific environments, was designed, built and commissioned. Subsequent tests conducted on this new facility showed average reproducibility for a 122 stainless steel rubbing against a CZ114 manganese bronze to have improved by a factor of two to approximately ± 20%. Initial results confirmed that adhesive wear is the dominant wear mode for the materials under consideration. This is manifested by homogeneous transfer layers and subsequent grooving of these layers.
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Queiroz, Syme Regina Souza. "Propriedades mecânicas e micromecanismos de fratura de corpos-de-prova usinados de rodas ferroviárias fundidas e forjadas". [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265223.
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Orientador: Itamar FerreiraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: A tendência mundial das estradas de ferro é utilizar carga elevada por vagão no transporte de produtos e alta velocidade no setor de passageiros. Em ambas as situações, as rodas ferroviárias são muito solicitadas mecanicamente e, em função disso, as propriedades mecânicas dessas rodas devem ser rigorosamente controladas, tendo em vista que as principais causas de acidentes envolvendo trincas nas rodas, ou a retirada da roda antes do final de sua vida, estão direta ou indiretamente associadas a baixos níveis de resistência mecânica, resistência à fadiga e tenacidade à fratura. O conhecimento do comportamento mecânico das rodas ferroviárias com base nas suas propriedades mecânicas é imprescindível para o projeto de rodas ferroviárias e para o aprimoramento de seu processo de fabricação. Este trabalho tem como objetivo caracterizar e analisar a microestrutura, as propriedades mecânicas e os micromecanismos de fratura de cinco rodas ferroviárias, duas fundidas e três forjadas, a partir de corpos-de-prova usinados dos aros e discos dessas rodas. As propriedades mecânicas analisadas são as básicas (limite de escoamento, limite de resistência à tração, alongamento específico até à fratura, redução de área, dureza e energia de impacto Charpy), a resistência à fadiga e a tenacidade à fratura, de corpos-de-prova usinados das rodas ferroviárias. Além das microestruturas e das propriedades mecânicas, foram também caracterizados e analisados os micromecanismos de fratura dos corpos-de-prova dos ensaios de fadiga e impacto, por meio de microscopia eletrônica de varredura. Os resultados dos ensaios indicam, em relação aos limites de escoamento e de resistência à tração, que não houve diferenças significativas entre as rodas fundidas e forjadas analisadas. Quanto à dureza (HRC), ductilidade (alongamento específico e redução de área) e tenacidade à fratura, as rodas forjadas apresentaram valores superiores. Em relação à resistência à fadiga, uma propriedade importante no caso de rodas ferroviárias, os corpos-de-prova usinados das rodas forjadas apresentaram melhores resultados em relação às rodas fundidas. Pode-se também concluir que, tanto para as propriedades mecânicas básicas e nobres como também para os micromecanismos de fratura, os resultados obtidos são compatíveis aos encontrados na literatura especializada, validando e comprovando que a metodologia de análise pode ser utilizada para melhorar os projetos e os processos de fabricação de rodas ferroviárias de aço fundidas e forjadas
Abstract: The word wide tendency of railroads is to use high load per wagon in cargo transport and high-speed in passenger sector. In both situations, the railway wheels are very mechanically requered, and as a result, the mechanical properties of these wheels should be controlled strictly in order that the main causes of accidents involving wheels cracks, or withdrawal of the wheel before end of its life, are directly or indirectly associated with low levels of strength, fatigue resistance and fracture toughness. Knowledge of the mechanical behavior of railway wheels based on their mechanical properties is essential for the design of railway wheels and the improvement of its manufacturing process. This work aims to characterize and analyze the microstructure, mechanical properties and fracture micromechanisms of five railway wheels, two cast and three forged, from the machined specimens of the rim and web of these wheels. The analyzed mechanical properties are the basics (yield strength, tensile strength, elongation, reduction in area, hardness and Charpy impact energy) the fatigue resistance and the fracture toughness, from the specimens machined of railway wheels. In addition to the microstructures and mechanical properties were characterized and analyzed the micromechanisms of fracture of the specimens of fatigue and impact tests, using scanning electron microscopy. The test results indicate, with respect to the yield strength and tensile strength, there were no significant differences between cast and forged wheels analyzed. The hardness (HRC), ductility (elongation and reduction in area) and fracture toughness of the forged wheels showed higher values. Regarding resistance to fatigue, an important property in the case of railway wheels, the forged wheels machined specimens shown better results compared to cast wheels. One can also conclude that, for both the basic and noble mechanical properties as well as for the micromechanisms of fracture, the results are compatible with those found in the literature, validating and verifying that the method of analysis can be used to improve the castings and forgings steel railway wheels and manufacturing processes and projects
Doutorado
Materiais e Processos de Fabricação
Doutora em Engenharia Mecânica
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Bansal, Shubhra. "Characterization of Nanostructured Metals and Metal Nanowires for Ultra-High Density Chip-to-Package Interconnections". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14041.
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Nanocrystalline materials are being explored as potential off-chip interconnects materials for next generation microelectronics packaging. Mechanical behavior and deformation mechanisms in nanocrystalline copper and nickel have been explored. Nanostructured copper interconnections exhibit better fatigue life as compared to microcrystalline copper interconnects at a pitch of 100 and #956;m and lower. Nanocrystalline copper is quite stable upto 100 oC whereas nickel is stable even up to 400 oC. Grain boundary (GB) diffusion along with grain rotation and coalescence has been identified as the grain growth mechanism. Ultimate tensile and yield strength of nanocrystalline (nc) Cu and Ni are atleast 5 times higher than microcrystalline counterparts. Considerable amount of plastic deformation has been observed and the fracture is ductile in nature. Fracture surfaces show dimples much larger than grain size and stretching between dimples indicates localized plastic deformation. Activation energies for creep are close to GB diffusion activation energies indicating GB diffusion creep. Creep rupture at 45o to the loading axis and fracture surface shows lot of voiding and ductile kind of fracture. Grain rotation and coalescence along direction of maximum resolved shear stress plays an important role during creep. Grain refinement enhances the endurance limit and hence high cycle fatigue life. However, a deteriorating effect of grain refinement has been observed on low cycle fatigue life. This is because of the ease of crack initiation in nanomaterials. Persistent slip bands (PSBs) at an angle of 45o to loading axis are observed at higher strain ranges (> 1% for nc- Cu) with a width of about 50 nm. No relationship has been observed between PSBs and crack initiation. A non-recrystallization annealing treatment, 100 oC/ 2 hrs for nc- Cu and 250 oC/ 2 hrs for nc- Ni has been shown to improve the LCF life without lowering the strength much. Fatigue crack growth resistance is higher in nc- Cu and Ni compared to their microcrystalline counterparts. This is due to crack deflection at GBs leading to a tortuous crack path. Nanomaterials exhibit higher threshold stress intensity factors and effective threshold stress intensity is proportional to the elastic modulus of the material.
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Grover, Parmeet Singh. "An accelerated test procedure for creep-fatigue crack growth testing". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20188.
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Cook, Daniel Adam. "Monitoring small fatigue cracks using ultrasonic surface waves". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17381.
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Peiffer, John P. "Fatigue testing of stiffened traffic signal structures". Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1888253611&sid=11&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Stobbe, David M. "Acoustoelasticity in 7075-T651 aluminum and dependence of third order elastic constants on fatigue damage". Thesis, Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-07172005-140635/.
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Bartlett, Martin L. "The use of a laser extensometer to study the behavior of small fatigue cracks". Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11879.
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Aguado, Clodoaldo Garcia. "Estudo da análise de fadiga pelo MEF considerando os efeitos da estampagem". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263060.
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Orientador: Alfredo Rocha de FariaDissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: As simulações dentro do ambiente de projeto devem prever a utilização de novas variáveis, especialmente de processos, de forma a aumentar a proximidade entre os modelos virtual e real e, com isso, aumentar a precisão das simulações. O objetivo deste trabalho foi o de estudar um modelo pelo Método dos Elementos Finitos que incluísse os efeitos da variação de espessura provenientes do processo de estampagem para a análise de vida em fadiga de um componente do sistema de exaustão automotivo. Primeiramente foi realizada a simulação do processo de estampagem, onde foi possível identificar as mudanças de espessura na geometria do componente estudado. O resultado dessa simulação foi transportado para a malha de elementos finitos, de forma que as análises posteriores, estrutural e de fadiga, considerassem os efeitos da redução e aumento da espessura local. Como base de comparação, as mesmas análises foram realizadas para a condição de espessura constante, tradicionalmente adotada durante a fase de projeto. Utilizando o modelo de Wöhler-Goodman-Miner para o cálculo do Dano acumulado e comparando com dados experimentais aquisitados em simulador veicular, os resultados cálculo de fadiga demonstraram que ambas as condições de espessura atingem vida infinita. Entretanto, após a seleção e análise de algumas regiões consideradas críticas nas simulações precedentes (estampagem e estrutural), pôde-se notar que na maior parte das regiões os valores de dano acumulado eram inferiores para a condição de espessura constante. Já a condição de espessura variável se aproximou mais ao resultado medido. Pôde-se concluir com os resultados que a variação de espessura, como efeito do processo de estampagem, desempenha um papel importante na vida do componente estudado, indicando que a utilização dos dados de processo auxilia na aproximação entre os resultados do cálculo de vida e a condição real
Abstract: The simulations within the Product Development environment must give the chance to use new variables, particularly from processes, in order to improve the correlation between the virtual and real models, and thus enhance the accuracy of the simulations. The objective of this work was to study a model by the finite element method (FEM) that includes the effects of thickness variation from stamping process for the fatigue life prediction in an automotive exhaust system component. Firstly it was carried out a simulation of the stamping process, where it was possible to identify the thickness distribution all along the geometry of selected component. Then, the result of this simulation was transported to the finite element mesh, so that further analyses, structural and fatigue, could consider the effects of reduction and increasing in local thickness. As a basis for comparison, the same analyses were performed for the homogeneous geometry (uniform thickness), which are typically taken during the design phase. Using the model proposed by Wöhler-Goodman-Miner to calculate the accumulated damage and comparing with real data acquisited from a vehicle, the calculation results of fatigue showed that both conditions (equal and unequal thickness) reached infinite life. However, after the selection and analysis of some critical regions in the previous simulations (stamping and structural), it might be noted that, in most regions, the values of accumulated damage were lower for the uniform thickness condition. Besides, for the unequal thickness condition, the results got closer to those measured in vehicle. With these results, it could be demonstrated that the unequal thickness, as a process variable, plays an important role in the component life, indicating that the use of process data helps in bringing together the results from fatigue calculation and real condition
Mestrado
Manufatura
Mestre em Engenharia Automobilistica
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Langøy, Morten A. "Fatigue crack growth of Ti-6A1-4V-01Ru (ELI GRADE) in ocean environments". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19642.
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Nelaturu, Phalgun. "Fatigue Behavior of A356 Aluminum Alloy". Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849720/.
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Metal fatigue is a recurring problem for metallurgists and materials engineers, especially in structural applications. It has been responsible for many disastrous accidents and tragedies in history. Understanding the micro-mechanisms during cyclic deformation and combating fatigue failure has remained a grand challenge. Environmental effects, like temperature or a corrosive medium, further worsen and complicate the problem. Ultimate design against fatigue must come from a materials perspective with a fundamental understanding of the interaction of microstructural features with dislocations, under the influence of stress, temperature, and other factors. This research endeavors to contribute to the current understanding of the fatigue failure mechanisms. Cast aluminum alloys are susceptible to fatigue failure due to the presence of defects in the microstructure like casting porosities, non-metallic inclusions, non-uniform distribution of secondary phases, etc. Friction stir processing (FSP), an emerging solid state processing technique, is an effective tool to refine and homogenize the cast microstructure of an alloy. In this work, the effect of FSP on the microstructure of an A356 cast aluminum alloy, and the resulting effect on its tensile and fatigue behavior have been studied. The main focus is on crack initiation and propagation mechanisms, and how stage I and stage II cracks interact with the different microstructural features. Three unique microstructural conditions have been tested for fatigue performance at room temperature, 150 °C and 200 °C. Detailed fractography has been performed using optical microscopy, scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). These tools have also been utilized to characterize microstructural aspects like grain size, eutectic silicon particle size and distribution. Cyclic deformation at low temperatures is very sensitive to the microstructural distribution in this alloy. The findings from the room temperature fatigue tests highlight the important role played by persistent slip bands (PSBs) in fatigue crack initiation. At room temperature, cracks initiate along PSBs in the absence of other defects/stress risers, and grow transgranularly. Their propagation is retarded when they encounter grain boundaries. Another major finding is the complete transition of the mode of fatigue cracking from transgranular to intergranular, at 200 °C. This occurs when PSBs form in adjacent grains and impinge on grain boundaries, raising the stress concentration at these locations. This initiates cracks along the grain boundaries. At these temperatures, cyclic deformation is no longer microstructure- dependent. Grain boundaries don’t impede the progress of cracks, instead aid in their propagation. This work has extended the current understanding of fatigue cracking mechanisms in A356 Al alloys to elevated temperatures.
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Ketabchi, Amirhossein. "Influence of Nanoscale Surface Modifications on the Fatigue Resistance of Medically Relevant Metals". Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24116.
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With an increasingly aging population, a significant challenge in implantology is the creation of biomaterials that actively promote and accelerate tissue integration while offering excellent mechanical properties. Engineered surfaces with superimposed micro and nanoscale topographies showed great potential to control and direct biomaterial-host tissue interactions. However, these modified surfaces require a careful assessment to prevent potential adverse effects on the fatigue resistance, a factor which may ultimately cause premature failure of biomedical implants.
In this context, the surfaces of two widely used biocompatible metals, namely CP Ti and Ti-6Al-4V, were engineered through simple yet efficient chemical treatments which demonstrated the ability to confer exciting new bioactive capacities. The qualitative and quantitative assessments of the fatigue resistance of polished and treated metals were carried out. Results from this study highlight the importance of mechanical considerations in the development and evaluation of nanoscale surface treatments for metallic biomedical implants.
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Müller, Ruan. "Characterising the stress-life response of mechanical formed AISI-1008 steel plate components". Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1008102.
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The main purpose of this research project was to determine the fatigue-life behaviour of AISI 1008 sheet steel which has been mechanically formed to a radius of curvature of 120mm and then to correlate the fatigue-life behaviour to that of the parent or “as manufactured” material. During the forming process it was felt important to induce plastic strain through stretch-bending by clamping the sides of a plate sample’s (width) edges in the bending fixture before being bent by a single acting mechanical press. It was determined through actual testing that there was a decrease in fatigue-life when the mechanical formed data was compared to fatigue data of the parent material. Standard fatigue mathematical models were used to relate the actual fatigue data. Due to the material being cold formed to a radius of curvature of 120mm, residual stresses induced during the forming process played an essential role during the fatigue-life prediction calculations. The maximum relieved stress in the parent material was compressive in nature having a magnitude of 11percent of the “as manufactured” yield strength (265 MPa). For the mechanical formed material compressive residual stresses were measured on the outer surface while tensile stresses were measured on the inner surface. The difference between actual number of cycles to failure to that calculated using the standard mathematical models for the parent material, ranged between 48 percent and 18 percent and for the mechanical formed samples between 35 percent and 1percent, depending on the strain amplitude used. An important aspect of this study was to determine the criteria required for mathematical modelling of the parent material as testing occurred between the limit of proportionality and yield point. Although this aspect requires further investigation the mathematical results obtained during this study were considered to be acceptable.
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Walker, Simon Valentin. "Characterization of fatigue damage in A36 steel specimens using nonlinear Rayleigh surface waves". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42753.
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A36 steel is a commonly used material in civil engineering structures where fatigue damage can lead to catastrophic failure. In this research, nonlinear Rayleigh surface waves are used to characterize damage in A36 steel specimens caused by monotonic tension and low cycle fatigue. Fatigue damage produces the increased acoustic nonlinearity that leads to the generation of measurable higher harmonics in an initially monochromatic Rayleigh wave signal. One specimen is subjected to static tension and four specimens are used for low cycle fatigue tests in the tension-tension mode with a constant stress amplitude. The fatigue tests are interrupted at
different numbers of cycles for the nonlinear ultrasonic measurements. Tone burst Rayleigh wave signals are generated and detected using a pair of oil coupled wedge transducers. The amplitudes of the first and second harmonic are measured at varying propagation distances to obtain the nonlinearity parameter for a given damage state.
The experimental results show an increase of acoustic nonlinearity in the early stages of fatigue life. Furthermore, a close relationship between plastic deformation and the acoustic nonlinearity is found, which indicates that the acoustic nonlinearity is indeed a measure of microplasticity in this material.
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Ilic, Slobodan Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Methodology of evaluation of in-service loads applied to the output shafts of automatic transmissions". Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/30172.
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This work presents a novel methodology for evaluation of in service loads applied to the output shafts of automatic transmissions. It also presents a novel methodology of data reduction for shaft load signals as an alternative to the cycle counting methods. Current durability testing of automatic transmission output shafts uses 50 000 stall torque cycles from zero to wide open throttle. In the majority of cases, these requirements lead to an over design that can result in an unnecessarily bulky transmission system. As a solution to this problem a novel methodology for evaluation of loads applied to the output shafts of automatic transmissions was developed. The methodology is based on real world loading conditions and therefore leads to a more realistic estimation of the fatigue life of shafts. The methodology can be used as a tool for shaft optimisation in different drive conditions. Using the developed methodology the effects of different road conditions on the fatigue life of a transmission output shaft were compared. Four routes having differing driving conditions were investigated and of those routes, the route with most stop-start events resulted in the greatest reduction in fatigue life. A novel methodology of data reduction for shaft load signals was also developed. The methodology is based on knowledge of the bandwidth and dynamic range of the expected in-service load signal. This novel methodology allows significant reduction of the volume of data to be acquired. It preserves the time sequence of peaks and valleys of the signal, which is vital in the case of fatigue analysis. This is in contrast to current methods based on cycle counting. Cycle counting methods achieve high data reduction but do not preserve the time sequence of the signal. The developed novel methodology has been validated on the newly developed data acquisition system capable of real time data acquisition and compression of shaft torque signal. The performed tests show that the proposed one-channel low cost system equipped with 1 GB compact flash card can store well over 10 000 hrs of load history.
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Funk, Matthias Friedrich [Verfasser]. "Microstructural stability of nanostructured fcc metals during cyclic deformation and fatigue / Matthias Friedrich Funk". Karlsruhe : KIT Scientific Publishing, 2012. http://d-nb.info/1185580980/34.
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Estes, Matthew J. "Corrosion of composite tube air-ports in kraft recovery boiler: Cr₂O₃, Fe₂O₃, NiO solubility in molten hydroxide". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/7027.
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Seyed, Hossein Hesamedin Sadeghi. "Study of electromagnetic field distributions around cracks in metals, induced by u-shaped current-carrying wires". Thesis, University of Essex, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280900.
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February, Eugene J. "Analysis of fatigue crack properties of the weld metal of gas metal Arc welded 300WA steel". Thesis, Cape Peninsula University of Technology, 2006. http://hdl.handle.net/20.500.11838/1278.
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Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2006.Welded joints are major causes for concern in the engineering arena for two basic reasons. In the first instance the weld is known to be a region of weakness within a structure and is caused by residual and applied stress concentrations. Secondly, the behaviour of the stress patterns is somewhat difficult to predict accurately due to the difficulty of conforming to the geometry and process parameters. The experimental procedure in this work commenced with specimens being welded with a technique very commonly used in industry. The residual stresses generated by thermal fluctuations from the welding process cannot be predicted easily and is viewed as a problem as increased stress levels promotes failure. Residual stresses were then determined with the use of an ultrasonic stress measuring device. Strain gauges were used to measure strains in the welded specimens and these strains converted to stresses. The results of the two methods were compared and analysed. Compact tensile specimens were used to perform fatigue testing. The results confirmed findings from earlier research such as the proportion of cyclic life spent on initiating the crack. Hardness tests were performed to determine if any relationship existed between fatigue failure, yield strength and hardness. Finally metallurgical analysis revealed the phases and structures of the weld and heat-affected zones. The findings of this research indicate that close relationships exist between the cycles to crack initiation and ultimate fracture, the hardness, yield stress and the fatigue life of the weld as well as between the grain diameter and the yield stress. Furthermore it is shown that there was not enough information gathered in this research to conclude that the life expectancy of 300WA welded steel can be predicted. However recommendations are made for future research in the prediction of failure of the 300WA welded steel.
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Calderon, Jose Guadalupe. "Comparison of 43Sn/43Pb/14Bi Solder and Standard 60Sn/40Pb Solder by Thermocyclic Fatigue Analysis". Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc501128/.
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The thermocyclic fatigue behavior of the low-melting solder 43Sn/43Pb/14Bi has been investigated and compared to that of standard 60Sn/4OPb solder via metallographic analysis (using scanning electron microscopy) and evaluation of the degree of fatigue development (using a fatigue scale as a function of thermocycles). Specimens were subjected to shearing strains imposed by several hundred fatigue thermocycles. Both solder types fatigue by the same microstructural failure mechanism as described by other workers. The mechanism is characterized by a preferential coarsening of the solder joint microstructure at the region of maximum stress concentration where cracks originate.
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Findley, Kip Owen. "Physically-based models for elevated temperature low cycle fatigue crack initiation and growth in Rene". Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-04292005-092902/.
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Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2006.McDowell, David, Committee Member ; Gokhale, Arun, Committee Member ; Saxena, Ashok, Committee Chair ; Johnson, Steven, Committee Member ; Sanders, Thomas, Committee Member.
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Solanki, Kiran N. "TWO AND THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF PLASTICITY-INDUCED FATIGUE CRACK CLOSURE ? A COMPREHENSIVE PARAMETRIC STUDY". MSSTATE, 2002. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11102002-143748/.
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Finite element analyses are frequently used to model growing fatigue cracks and the associated plasticity-induced crack closure. Two-dimensional, elastic-perfectly plastic finite element analyses of middle-crack tension (M(T)), bend (SEB), and compact tension (C(T)) geometries were conducted to study fatigue crack closure and to calculate the crack opening values under plane-strain and plane-stress conditions. The loading was selected to give the same maximum stress intensity factor in both geometries, and thus similar initial forward plastic zone sizes. Mesh refinement studies were performed on all geometries with various element types. For the C(T) geometry, negligible crack opening loads under plane-strain conditions were observed. In contrast, for the M(T) specimen, the plane-strain crack opening stresses were found to be significantly larger. This difference was shown to be a consequence of in-plane constraint. Under plane-stress conditions, it was found that the in-plane constraint has negligible effect, such that the opening values are approximately the same for the C(T), SEB, and M(T) specimens. Next, the crack opening values of the C(T), SEB and M(T) specimens were compared under various stress levels and load ratios. The effect of a highly refined mesh on crack opening values was noted and significantly lower crack opening values than those reported in literature were found. A new methodology is presented to calculate crack opening values in planar geometries using the crack surface nodal force distribution under minimum loading as determined from finite element analyses. The calculated crack opening values are compared with values obtained using finite element analysis and more conventional crack opening assessment methodologies. It is shown that the new method is independent of loading increment, integration method (normal and reduced integration), and crack opening assessment location. The compared opening values were in good agreement with strip-yield models.