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1
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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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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Yazdanpanah, Amir. "Computer aided fatigue design." Thesis, Sheffield Hallam University, 1990. http://shura.shu.ac.uk/20587/.
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Today's competitive market requires engineers to produce reliable light weight products at low cost. This can be achieved by more effective use of computer aided engineering tools during early stages of the design process. A research programme has been undertaken to investigate the data requirements of integrating commercially available software packages (finite element analysis and fatigue life evaluation) to evaluate the integrity and durability of engineering components at the conceptual design stage. A real engineering component, in the form of a steering arm, supplied by a European truck manufacturer was used as a basis for the investigation. This is a typical vehicle component, in which, under service loading conditions, a multiaxial state of stress occurs. A geometric model of the component was created using the Prime "MEDUSA" software suite. The model was used to locate the boundary co-ordinates necessary for the development of a PAFEC Finite Element model. By imposing the conditions experienced during the service, the critical areas of the component were identified by analysing the F.E. model and a detailed description of the elastic stress/strain fields were also established. These were incorporated in an energy density approach and Neuber's uniaxial analysis to predict total local elastic/plastic strains at these critical- locations. These were compared with strain gauge measurements. The calculated results were used to plot a number of load/local strain calibration curves for the development of a load history, suitable for experimental fatigue life assessment. Fatigue crack initiation tests were performed on the steering arm using a computer controlled DARTEC multiaxial fatigue testing machine. Fatigue life assessment based on full service loading was carried out using a software package based on the critical location approach. A comparison of computerised, experimental and actual test circuit fatigue lives has been made. The work enabled a specification to be produced for the integration of the two items of software. This integrated software was developed by third parties and used to produce a computerised life map of the steering arm.
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Jethwa, Jagdish K. "The fatigue performance of adhesively-bonded metal joints." Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/7526.
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Larsson, Tobias. "Material and fatigue properties of old metal bridges." Licentiate thesis, Luleå : Luleå University of Technology, 2006. http://epubl.ltu.se/1402-1757/2006/26/.
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Dear, Matthew Nicholas. "Fatigue in SiC fibre reinforced titanium metal matrix composites." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6603/.
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The fatigue and interfacial characteristics of a unidirectional, SiC (SCS 6), fibre reinforced Ti 6Al 4V metal matrix composite have been investigated using a series of fatigue crack propagation, total life, and interfacial characterisation techniques. A room temperature crack arrest to catastrophic failure (CA/CF) transition was quantified using the initial stress intensity factor range ΔKapp. This transition occurred between 21 and 18 MPa√m in the three point bend geometry, and was found to be dependent on volume fraction of intact fibres bridging the crack. Increasing the test temperature to 300˚C had different effects on the resistance to fatigue crack growth depending on crack opening displacements and test piece stiffness. Total life fatigue tests revealed that the dominant failure mechanism was matrix fatigue cracking and fibre bridging. The extent of fatigue crack growth and fibre bridging was dependant on the applied stress and test temperature. The introduction of a dwell period at maximum load resulted in a small reduction in the total fatigue life. Post fatigue fibre push out tests identified that fatigue caused a reduction of interfacial properties below the as received levels. This reduction of interfacial properties was dependent on fatigue test temperature and initial loading conditions.
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Dinsley, Christopher Paul. "Fatigue properties of dissimilar metal laser welded lap joints." Thesis, Sheffield Hallam University, 2004. http://shura.shu.ac.uk/19561/.
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This work involves laser welding austenitic and duplex stainless steel to zinc-coated mild steel, more specifically 1.2mm V1437, which is a Volvo Truck Coiporation rephosphorised mild steel. The work investigates both tensile and lap shear properties of similar and dissimilar metal laser welded butt and lap joints, with the majority of the investigation concentrating on the fatigue properties of dissimilar metal laser welded lap joints. The problems encountered when laser welding zinc-coated steel are addressed and overcome with regard to dissimilar metal lap joints with stainless steel. The result being the production of a set of guidelines for laser welding stainless steel to zinc-coated mild steel. The stages of laser welded lap joint fatigue life are defined and the factors affecting dissimilar metal laser welded lap joint fatigue properties are analysed and determined; the findings suggesting that dissimilar metal lap joint fatigue properties are primarily controlled by the local stress at the internal lap face and the early crack growth rate of the material at the internal lap face. The lap joint rotation, in turn, is controlled by sheet thickness, weld width and interfacial gap. Laser welded lap joint fatigue properties are found to be independent of base material properties, allowing dissimilar metal lap joints to be produced without fatigue failure occurring preferentially in the weaker parent material, irrespective of large base material property differences. The effects of Marangoni flow on the compositions of the laser weld beads are experimentally characterised. The results providing definite proof of the stirring mechanism within the weld pool through the use of speeds maps for chromium and nickel. Keywords: Laser welding, dissimilar metal, Zinc-coated mild steel, Austenitic stainless steel, Duplex stainless steel, Fatigue, Lap joint rotation, Automotive.
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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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Marrow, Thomas James. "Fatigue mechanisms in an embrittled duplex stainless steel." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386998.
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Beheshti, Milad. "Fatigue life prediction of threaded pipe connection." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15588.
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In the oil and gas industry, threaded pipe connection is frequently used to connect the casing string, drill pipe strings or production and transportation risers and pipelines. The connection is normally preloaded in order to maintain a sealed and secure connection while in service and avoid leakage. Tapered thread are a common connection and in order to introduce preload to the threaded connection when they are assembled a certain make-up torque is going to be applied. The make-up torque plus external loads result in a multiaxial stress distribution over the connection, where the threaded connections act as stress risers. Environment such as waves and currents cause dynamic loads acting on the pipe line and offshore structures. The weakest point in offshore structure is the pipe connection because of fatigue crack initiated in the connection's threads. Researchers and engineers developed a variety of patented threaded pipe connection which all claiming to improve a connection's fatigue life. The experimental data for patented designs, available in literature, is limited. Most published studies usually comprise experiments on a single connection type. For detailed fatigue analysis those published studies cannot be used since there is no uniformity in testing setup, loading conditions and damage detection technique exist. Moreover, current design curves in codes and standards lead to overly conservative or inaccurate results. The aim of this work is to provide a better understanding of the fatigue mechanisms of threaded pipe connections and to study the effect of different design features on a connection's fatigue life. The final goal is to formulate guidelines for new fatigue resistant connection designs. API connection is used as a reference in this study. Several modifications and design features are applied to the connection type. To simulate the effect of these modifications, a parametric 2D axisymmetric finite element model, ABAQUS is used. 2D finite element result are compared with a 3D model to prove its validity for both make-up. In addition, the results of the 2D axisymmetric simulation are validated by static strain gauge measurements during a make-up test and an axial tension test. The validated model is then used to evaluated the influence of the connection properties and design features on the threaded connection's behaviour. Test rigs were designed to perform axial fatigue experiment on two scales: the small-scale experiments on 1" (33.4 mm outer diameter) connections are performed in axial fatigue testing, the medium scale tests on 4.5" (114.3 mm) connections are carried out under axial tension for which a setup is developed. The majority of the performed fatigue tests are small scale experiments. Several modified configurations are tested. The S-N curve is constructed, so that the effect of certain configuration on the connection's fatigue life can be quantified. The local modification of the threaded connection's geometry as well as the connection's contact condition's contact conditions can have an important influence on the fatigue life of the connection. A beach marking technique is used to visualized the crack fronts at different moments during the tests so that exact crack shape can be seen during post-mortem analysis. The result shown that a crack initiates at the root of the last engaged thread of the male part of the connection, and propagates slowly over a large segment of the circumference, forming a long shallow crack. When the crack penetrates the pipe wall, it rapidly increases in size along two crack fronts. The shape of crack observed in beach mark analysis do not have a semi-elliptical shape as commonly used in fracture mechanics. A fatigue crack growth analysis that considers the crack as an annular flaw, is effective in describing the crack growth behaviour. The experimentally obtained S-N curves and the result from the finite element simulations are combined in multiaxial damage evolution law. The observed trend in fatigue lives of the configuration are explained by using the fatigue analysis. Using a connection's thread load distribution as a measure for its fatigue life is proven to be inaccurate. The main reason for this is that the load distribution is related to axial stresses over the connection. The fatigue life of a threaded connection is determined by the local multiaxial stress distribution and strain range around the root of the last engaged thread. These local conditions are not only the result of the load distribution, but they are also affected by the hoop stress introduced during make-up, which can additionally be affected by a changed connection stiffness. The multiaxial damage evolution law is used to analyse the influence of several features on a connection's fatigue life. It is not for all patented modifications that an increased fatigue life is predicted when applied to the API connection. The final conclusion reached is that, in order to optimize a fatigue resistant connection, several design features must be combined together. The thread shape can be optimized to obtained a low stress concentration factor and reduce the local strains at the thread root. The connection's global geometry and make-up conditions can be optimized to improve the load distribution over the threads and reduce local stresses and strains at the threads.
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Guzek, John S. (John Stephen). "Fatigue crack propagation along polymer-metal interfaces in microelectronic packages." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41401.
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Sugiman. "Combined environmental and fatigue degradation of adhesively bonded metal structures." Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548357.
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The main objective of this research is to investigate the effect of moisture on the degradation of adhesively bonded aluminium joints under both static and fatigue loading. This has been achieved through a combination of experimentation and progressive damage finite element modelling (using a cohesive zone approach). Moisture uptake behaviour in the adhesive was studied to obtain the coefficient of moisture diffusion and of moisture expansion. The coefficient of thermal expansion was also measured to provide the data for the finite element modelling, which included residual stresses due to cooling from cure temperature and swelling of the adhesive layer. The moisture dependent properties of the adhesive were obtained from bulk adhesive tensile tests. The joints investigated included monolithic single lap joints loaded in tension and laminated doublers loaded in bending and tension. Various widths were used to get the full and partial saturation of the adhesive layer. Under both static and fatigue loading, the degradation increased with increasing moisture content and tended to level out when the moisture content approached the saturation level. Most of the failures were cohesive in the adhesive layer, showing that the degradation was due to adhesive, rather than interfacial degradation. Calibration of the cohesive properties was achieved by combining backface strain and load data measured in the monolithic single lap joint. These were then utilised to predict the residual strength of the doublers in bending. In fatigue, the calibrated cohesive zone properties were integrated with a strain-based fatigue damage model to simulate the fatigue response of the monolithic single lap joint and doubler loaded in bending both in the unaged and aged condition. The backface strain technique has been successfully used to monitor the fatigue damage evolution in the joints considered, to calibrate the parameters in the strain based fatigue model, and also to study the effect of adhesive fillet on the fatigue damage evolution in the doubler loaded in bending. Doublers loaded in tension exhibited an entirely different failure mechanism including rupture of both the adhesive and aluminium layer. The effect of moisture on the 11 degradation of this joint was not significant. The butts between aluminium sheets that inevitably exist in laminates were shown to affect the strength of the joint. For these joints, the progressive damage modelling used a cohesive zone approach for the adhesive layer and the butt, and continuum damage for the aluminium layer. In fatigue, the cohesive zone and the continuum damage were integrated with the strain-based fatigue damage model to predict the response. The predicted response under both static and fatigue loading was found to be in good agreement with the experimental data. Finally, experimental and numerical studies have been undertaken on hybrid fibre-metal (aluminium-Glare) laminate (FML) doubler joints to investigate their response under static and fatigue tension loading. The specimens had fibres either parallel to the loading direction (spanwise) or perpendicular to the loading direction (chordwise). Again, the effect of the butt position was investigated. The spanwise specimen was found to have the highest strength followed by chordwise specimens without butts and finally chordwise specimens with butts. The most critical position for a butt was found to be adjacent to the doubler end. Without butts, the static strength for spanwise and chordwise specimens was controlled by the failure in the Glare layer whilst the fatigue failure was precipitated by failure in the aluminium sheet. Where butts are present, they significantly influence the joint response. A progressive damage numerical analysis was undertaken and was found to be in good agreement with the experiment data in terms of both the strength and the failure mechanisms.
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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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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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Hammond, D. W. "Fatigue fracture in the presence of shot peening residual stresses : initiation, propagation and relaxation phenomena." Thesis, Cranfield University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233342.
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Rodopoulos, C. A. "Fatigue studies under constant and variable amplitude loading in MMCs." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245575.
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Fleming, William. "Prediction of the fatigue of metal matrix composites using theory of cells." Thesis, Northumbria University, 2006. http://nrl.northumbria.ac.uk/1960/.
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Discontinuous and particulate metal matrix composites have emerged as a set of materials which has found increasing niche areas of use. They are now widely used in both diesel and petrol internal combustion engines, as well as in sports bicycles and other areas where their combination of unique properties can be exploited to advantage. The inclusion of fibres into a base matrix produces a complex material both in its make up and mechanical properties and it would be an advantage to be able to predict a candidate metal matrix composite material's mechanical and thermal properties prior to that material's development. One such approach, the so called Theory of Cells, is a micromechanical approach which uses the analysis of repeating cells within the composite to make prediction of the composite's mechanical properties. In the present study, this approach has been employed to predict the fatigue life of a series of different metal matrix composites at ambient temperature. These composites include some materials with SiC fibres and some with Al203 fibres. Using data obtained from the monolithic matrix material and the individual fibres theoretical S/N and Strain/N curves were produced. This was possible by assuming that the matrix material in the composite fails at the same fatigue stress level as does the monolithic matrix material or, if fibres fail, this will be at the failure level of the individual fibres. These curves were then compared to experimental data for all metal matrix composites and good agreement was obtained for all but the low cycle fatigue regime. A finite element programme was employed to predict fatigue life in the low cycle fatigue regime and the results were compared to the predictions made by the Theory of Cells. It was found that the finite element was no better at predicting the fatigue life of the composite than the Theory of Cells. Both systems however predicted an area of high stress in front of the fibre in the direction of loading. Fatigue tests were carried out on one particular material at both 200°C and 300°C and the fatigue life was compared to that predicted by the Theory of Cells. It was found that the predictions became increasingly inaccurate with increasing temperature.
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Xia, Ji. "TENSION AND FATIGUE BEHAVIOR OF AL-2124/SIC-PARTICULATE METAL-MATRIX COMPOSITES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1548169132710822.
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Upton, David Mark. "An automated monitoring system for the production and measurement of metal fatigue." Master's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/8324.
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Includes bibliography.New equipment for producing and following the fatigue process, in metals, has been developed. The specimens, which must be in the shape of tuning forks, are resonated at high amplitudes. This is achieved by attaching small, powerful, samarium-cobalt magnets to the ends of the tynes, enabling them to be driven efficiently by a "U"-core electromagnet. A small, piezoceramic strain gauge provides a method of picking up the vibrations. To maintain resonance, the signal is used in a positive feedback loop, which incorporates an analogue multiplier to provide AGC. This also keeps the amplitude constant at any desired level, throughout the duration of an experiment.
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Chang, Po-Yu. "Modeling of fatigue behavior and damage tolerance/durability in fiber metal laminates." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1608577901&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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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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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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Santos, Luciano Valdomiro dos. "Análise de falha de estruturas metal-polímero: enrijecedores à flexão." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-26082014-105410/.
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Este trabalho apresenta um novo modelo de análise de falha em estruturas metal-polímero que, além de considerar a falha independente no metal ou no polímero, leva em consideração a falha na região de interface metal-polímero em decorrência de desgaste por deslizamento, quando existe movimento relativo entre as superfícies. Inicialmente, o estudo apresenta as principais características dos metais e polímeros e os mecanismos de falha mais relevantes. Faz a proposta do modelo de análise de falha e por último, apresenta a análise completa de falha de enrijecedores à flexão, uma estrutura metal-polímero utilizada pela indústria de óleo e gás. O modelo proposto permite fazer a previsão da taxa de desgaste de polímeros por deslizamento em função do ângulo da aspereza da superfície metálica, em situações onde a falha é gerada por fadiga de alto ciclo.This work presents a new model for evaluating the failure in polymer-metal structures that, besides considering the isolated failure in metal or polymer, considers the failure in the polymer-metal interface region due to sliding wear, when there is relative movement between the surfaces. Initially, the study presents the main characteristics of metals and polymers and the most relevant failure mechanisms. Makes the proposed failure analysis model and, finally, shows the complete analysis of failure in bending stiffeners, a polymer-metal structure used by the oil and gas industry. The proposed model allows the prediction of the wear rate of polymers by sliding a function of asperity´s angle of the metal surface in situations where failure is generated by high cycle fatigue.
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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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Qi, Dong-Mei. "Assessment and improvement of aeroengine disc structural integrity." Thesis, Cranfield University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328601.
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Harrison, David John. "Eddy-current imaging of cracks." Thesis, University of Surrey, 1985. http://epubs.surrey.ac.uk/847494/.
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As a consequence of metal fatigue, cracks can develop and grow in operational aircraft. Periodic inspections must be made in order to detect and repair them before they reach a dangerous length. Cracks which grow from holes are a significant problem for aircraft since the wings and fuselage can contain many thousands of fasteners, or rivets. Since it is impractical to remove them all, inspection must be made with them installed. Research into the application of eddy currents to this problem has led to the development of a scanning procedure in which a small coil is moved around the circumference of the fastener while its impedance is repeatedly measured at different positions. This set of data constitutes an image which can be analvsed using pattern recognition techniques to identify the presence of a crack. A self-contained automated instrument has been built on these principles. It incorporates a microprocessor which controls all aspects of the systems operation, including analysis and display of results. Tests show that it can detect the presence of simulated radial cracks as small as 0.2 mm long beneath the heads of fasteners. The natural extension of these ideas leads to the concept of eddy-current imaging in which a 3D picture of a defect is reconstructed from measurements of the surface magnetic field. The feasibility of implementing this, using techniques such as tomography, is discussed.
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Lewis, Adam Miles. "The modelling of electromagnetic methods for the nondestructive testing of fatigue cracks." Thesis, University College London (University of London), 1991. http://discovery.ucl.ac.uk/1317503/.
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This thesis describes a theoretical and experimental investigation of electromagnetic methods for the detection and measurement of metal fatigue cracks. The available methods are reviewed, with particular attention being paid to mathematical models, and a new model of the electromagnetic field near a metal fatigue crack for small skin-depths is presented which uses a surface impedance boundary condition with the addition of a line source to represent the crack. This leads to a coupled system of two magnetic scalar potentials, one on the crack face which obeys the two-dimensional Laplace equation and one outside the test-piece which obeys the three-dimensional Laplace equation. The behaviour of the field is governed by a parameter m =l/(μ, δ), where l is the size of the field perturbation, μ, is the relative permeability and δ is the skin-depth. When m is small, almost all the flux is concentrated inside the metal and the exterior potential also obeys the two-dimensional Laplace equation, on the test-piece surface. When m is large, the perturbation part of the exterior field has a negligible effect on the field inside the crack so that the crack-face potential may be found by the Born approximation. The general m problem is solved for rectangular and semi-elliptical cracks in flat plates, interrogated by uniform fields, and the solution is verified experimentally. A method for calculating the crack depth from the magnetic field is given, with descriptions of industrial applications. The theory is further developed to find the impedance change in an air-cored circular coil caused by a crack, to find the field near overlapping cracks and to find the field near a crack in an interior corner. Finally, a semi-empirical analysis is presented for a ferrite-cored measuring coil.
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Allison, Paul Galon. "STRUCTURE-PROPERTY RELATIONS FOR MONOTONIC AND FATIGUE LOADING CONDITIONS FOR A POWDER METAL STEEL." MSSTATE, 2009. http://sun.library.msstate.edu/ETD-db/theses/available/etd-07082009-170520/.
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Developing a multi-scale math-based model for powder metallurgy (PM) component design and performance prediction requires experimental calibration and validation. Monotonic tension, compression and torsion tests were performed at various porosity and temperatures to obtain the set of plasticity and damage constants required for model calibration. Uniaxial fatigue experiments were performed to determine the constants required for capturing the low cycle and high cycle fatigue characteristics of a PM steel. Tension tests on two different Bridgman notched specimens were undertaken to study the damage-triaxiality dependence for model validation. Validation of the model is further being performed by monotonic component testing using PM bearing caps. Fracture surface analysis was performed using Scanning Electron Microscopy (SEM) to quantify the void nucleation and void sizes of the different specimens. The developed model will be used for optimizing component performance and design for PM parts.
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Bradley, Gareth Richard. "Fatigue properties of metal inert gas and friction stir welded aluminium alloy 5383-H321." Thesis, University of Plymouth, 2003. http://hdl.handle.net/10026.1/2359.
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The following dissertation details the development of a simple defect-tolerant based model for determining the fatigue properties of a 5383-H321 aluminium alloy and metal inert gas and friction stir welded butt joints in the same alloy. The model considers the fatigue life to consist of three regimes, crack initiation and short and long crack growth, in contrast to the typical defect-tolerant approaches which only consider the long crack growth period. Crack initiation was considered to consist of an initial short crack, present prior to fatigue loading, identical in length to the crack initiator. The short crack growth rate was considered to be a function of the crack length and stress amplitude, whilst the long crack growth regime was described through the Paris equation, dcldN = C(AK)m. The model also considers the effect on the crack initiation and growth rates of the microstructure, macrostructure and residual stresses, with the latter being determined both through the conventional hole-drilling approach and the emerging technique of synchrotron strain scanning. The accuracy of the model was verified through integration of the short and long crack growth regimes, with the predicted lifespan being compared to results obtained from S-N testing of identical welded specimens. A good correlation between the experimental and theoretical results was observed for the parent material and friction stir welded joints for lives in the region 105-106 cycles, although the approach, in its current format, appeared less suitable for determining the fatigue properties of the MIG welded joints. 2
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Kirwan, M. A. Q. "Diamond machining in 5 wt% Y2O3 sinter hipped silicon nitride." Thesis, University of Surrey, 1992. http://epubs.surrey.ac.uk/843045/.
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A collaborative research project was set up to study peripheral diamond wheel machining damage in silicon nitride ceramics. The objective of the work to be carried out at the University of Surrey was to study the nature and depth of machining damage in 3 point flexural rupture test bars made from 5 wt% Y2O3 sintered hot isostatically pressed silicon nitride. The bars were machined to three surface finishes. The work carried out at Rolls-Royce by Mr R Quinn concentrated on the effects the machining damage had on the fracture strengths of the test bars. Work at the University of Surrey has identified in detail the nature and depth of machining damage in "coarse" 0. 4mum centre line average roughness surfaces. Deep grooves up to 2mum depth, 18mum width are found to have been superimposed on the general surface roughness by singularly large diamonds in the 350 grit diamond wheel. Sub-surface median cracks normal to the machining direction were clearly identified in bar cross-sections using oblique, diffuse "penumbra" illumination in an optical microscope, an as yet undocumented technique. Cross-section views of the machined surface and sub-surface were made possible by the very difficult and delicate technique of producing sandwich cross-sections of the machined bars. An analysis of machining-induced median cracks has not been carried out in such detail before. Semi-elliptical in shape the median cracks extend from 6mum - 45mum below the machined surface, and range from 19mum to 101mum in length parallel to the machining direction. They initiate at the focal point of a tributary system of microcracks at an average depth of 4mum - 5mum below the machined surface. It is believed that the median cracks initiate at the plastic/elastic boundary of a plastically deformed surface layer. Therefore a residual compressive layer, formed by the overlap of localised residual stresses from multi-particle contact events. and bound by an underlying tensile field, is thought to have an average depth of 4mum - 5mum. A very innovative technique was used to reveal sub-surface deformation, where TEM X-ray microdiffraction spots were distorted by mechanical damage in the ceramic grain structure. The "arcing" or "streaking" of the diffraction spots tended to disappear at a depth of 4mum - 5mum below the machined surface. This is further evidence of the existence of a thin layer in residual compression, which has an average depth of 4mum - 5mum. This technique is not known to have been used before. Fine diamond machining with a 600 grit wheel produced a centre line average roughness of 0.01/0.02 mum. However, evidence of machining damage is still present in the form of "remnant tracks" which lie parallel to the machining direction and consist of material pull-out. They are remnants of machining damage under grinding grooves introduced in previous machining stages. Single point Vickers pyramid diamond scratches were implemented at different loads on a polished surface. The morphology of the grooves and material fragmentation and the sub-surface median cracks were examined. Many features were found to resemble the deformation/fracture formed under a deep grinding groove in the coarse machined surface. Work carried out at Rolls-Royce by R Quinn showed that an increase in the quality of surface finish is accompanied by an increase in the mean strength and Weibull modulus of the machined bars. Furthermore a distinct anisotropy in the fracture strengths parallel and normal to the "coarse" machining direction is evidence of anisotropy in machining damage formed by a peripheral diamond grinding wheel. X-ray diffraction tests carried out at the CEGB by P E J Flewitt showed that machining damage produces a long range biaxial residual compressive field with the highest component acting normal to the machining direction. These results are consistent with the nature of machining damage identified at the University of Surrey, namely the strength-controlling median cracks which lie parallel to the machining direction and the residual compressive stress which exists as a thin 4mum - 5mum layer below the machined surface. Processing flaws were discovered in the as-hipped billets received for the project. Their elemental composition and likely origin were examined. A three dimensional "cellular network" flaw ranging from 400mum to 2.1mm in size (in different production batches) is believed to have been formed as a result of flocculation clustering during processing. Clusters of 1mum - 3mum metallic particles were also identified. They range from 5mum - 45mum in size. The contaminant particles are steel and were introduced as a result of the original ceramic powder ball milling process which employed a steel ball mill.
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Xin, Xiaojiang. "Experimental and theoretical aspects of microstructural sensitive crack growth in Al-Li 8090 alloy." Thesis, University of Sheffield, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295521.
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Kenningley, Scott David Peter. "High temperature thermal and mechanical load characterisation of a steel fibre reinforced aluminium metal matrix composite (AlMMC) for automotive diesel pistons." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/high-temperature-thermal-and-mechanical-load-characterisation-of-a-steel-fibre-reinforced-aluminium-metal-matrix-composite-almmc-for-automotive-diesel-pistons(5cc789fc-d64e-4905-bc1c-beb0e3b9c0df).html.
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In modern automotive engines, the vast majority of light vehicle diesel (LVD) pistons are made from gravity die cast monolithic AlSi based alloy systems. Presently, the market drivers for reduced emissions, more efficient fuel consumption and increased specific power output are providing cyclic thermal and mechanical fatigue loading above the safe life durability threshold for the current AlSi based alloy systems. Peak temperatures in the diesel piston’s fatigue critical combustion bowl region are presently 420 °C for the AlSi based alloys, which represents a homologous TH value in excess of 0.8. In combination with peak temperatures of 420 C, the pistons are subject to cylinder pressures up to 220 bar, inducing mechanical stress amplitudes 15-20% greater than the allowable component fatigue strength for 1x108 cycles, in some applications. This durability deficit naturally leads to a requirement for new material and process solutions aimed at improving thermal and mechanical fatigue resistance at temperatures in excess of 420 C.One solution to this problem is to locally reinforce the pistons combustion bowl edge with a metal matrix composite (MMC) system. In this study, an aluminium based metal matrix composite (AlMMC) has been investigated and has shown some promise with increases in iso-thermal high cycle (1x 107) fatigue strength of 50 % compared to standard monolithic piston alloys. The AlMMC consists of a premium AlSi based LVD piston alloy matrix reinforced with 0.15 Vf of an interconnected network of 2-4 mm long Fe based fibres. The AlMMC is manufactured by pressure assisted infiltration of a sintered metallic fibre preform with as cast materials having a pore density of 0.2 %. In contrast to the use of ceramic fibre reinforcement systems generally requiring high pressure infiltration techniques, preform infiltration is considered possible with a comparably inexpensive manufacturing route. The Fe based fibre preforms can be infiltrated at lower pressure due to the reactivity between the Fe based fibres and the AlSi based matrix alloy. Unfortunately, this increased reactivity, although an advantage for preform infiltration, can result in (FeAlXX)Si(+X) interfacial reaction products forming between the fibre and matrix at operating temperatures of greater than 440 °C. These interfacial reactions result in a 15-20 m interfacial intermetallic layer after prolonged periods of exposure (>500 hrs), resulting in depleted fibre Vf and void formations on the matrix side of the interface.
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Uygur, I. "Environmentally assisted fatigue response of Al-Cu-Mg-Mn with SiC particulate metal matrix composites." Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639290.
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Experimental research has been carried out with the purpose of evaluating the tensile properties, stress and strain control fatigue properties and, crack propagation behaviour of a particulate reinforced metal matrix composite. Fractographic examination has also been undertaken of the powder metallurgy processed 2124 Al-alloy with two volume fractions (17 and 25vol%) and different particle sizes (2.5μm and 15μm) silicon carbide particles (SiCp). The present study shows that tensile properties of composites significantly improve with the incorporation of hard, brittle ceramic particles. The composite materials were cyclically deformed over a range of constant stress amplitudes at R=0.1 and R=0.5 using a variety of notch geometries in air and elevated temperatures. Results indicated that for a given aged condition (T4), load controlled fatigue lives of the composites are significantly improved compared with the unreinforced base alloy. However the severity of a notch, i.e. increased stress concentration factor and elevated temperatures shift down the S-N curves of the 2124 25vol% SiCp (AMC225) composite material. The effects of particle size and volume fraction on strain controlled fatigue behaviour were evaluated for a variety of composite materials at different strain range levels. An increased volume fraction of particles reduces fatigue lives due to the lower monotonic ductility of the AMC225 composite which showed some degree of softening at R=-1, but stable behaviour at the R=0 conditions under strain loading. At R=0.5 the composite cyclically hardened. On the basis of these results, fatigue life predictions for the notch geometries have been made by using a critical strain approach.
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Kauffmann, Hans. "A digital image analysis method for monitoring crack growth in metal fatigue testing / H. Kauffmann." Thesis, North-West University, 2005. http://hdl.handle.net/10394/976.
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Metal fatigue tests are an everyday occurrence that updates existing fatigue libraries, ensuring
that structures and components do not fail when in use. The American Society for Testing and
Materials (ASTM) provides standard tests whereby certain material properties are obtained by
the exact same method for each test, providing designers the information to prevent premature
failure. The Fatigue Crack Growth Rate (FCGR) of a standard specimen provides information
for situations where a crack may exist in components. The critical size of the crack determines
when it is safe to use a component and when to discard it.
Testing methods relating to fatigue crack growth propagation rates vary with respect to
requirements and conditions. A wide variety of test methods can be utilised to find reliable data.
One such a method uses a travelling microscope. It has been extensively used with success,
but requires constant stoppages for measurements and user attention to make interval
measurements. Alternative measurement methods have solved these disadvantages but have
generally been of the contact and indirect types. Contact to the specimen may in some cases
influence the results negatively, while indirect methods generally require previously obtained
data to calibrate the results.
The presented digital image analysis method has in principle the same functioning as that of the
travelling microscope whilst eliminating constant user attention and stoppages. The process
was automated and provided a cost saving alternative to similar products available on the
market. The standard test method for measurement of fatigue crack growth rates as outlined by
ASTM E647 (2002) was employed to provide standardised results.
The designed and assembled test facility was put to test when a FCGR test was conducted.
The set-up consisted of an lnstron 1603 Electromagnetic Resonance machine, a Nikon D70 and
a PC with acquired and custom written software. The digital image analysis method provided
crack growth measurements with a difference of less than 1% from the actual values.
Furthermore, the end result provided a Paris equation for a mild steel specimen.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2006.
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Mlikota, Marijo [Verfasser], and Siegfried [Akademischer Betreuer] Schmauder. "Multiscale modelling and simulation of metal fatigue and its applications / Marijo Mlikota ; Betreuer: Siegfried Schmauder." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1225743885/34.
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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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Boselli, Julien. "Quantification of the effects of reinforcement distribution and morphology on fatigue in Al-SiCâ†p composites." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310572.
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Willens, David C. "Improving the Fatigue Life of Cylindrical Thread Rolling Dies." Digital WPI, 2020. https://digitalcommons.wpi.edu/etd-dissertations/602.
Full textAbstract:
Thread rolling is a unique metal forming process which is commonly used to form screw threads on threaded fasteners and precision leadscrews at relatively high rates of speed. Threads are formed on a cylindrical blank by flat or cylindrical dies having the reverse form on them, which rotate and penetrate the blank simultaneously, to plastically deform it into a precise geometry. Thread rolling dies are exposed to a complex state of cyclical contact stresses that eventually cause the dies to fail by fatigue and wear. The stress state is not easily ascertained through standard analytical models due to complex geometry and process conditions. This research seeks to better understand the state of contact stresses present in cylindrical thread rolling dies as they form material, to aid in identifying and testing economical methods of improving thread rolling die fatigue life. Some work has been published on using FEA simulation software to model the thread rolling process, but no work has been published on using FEA software to analyze the stresses in thread rolling dies. DEFORM®-3D Forming Simulation Software by Scientific Forming Technologies Corporation in Columbus, Ohio was used to simulate the throughfeed thread rolling process and model the state of stresses in the dies. The results were compared to the Hertzian contact stress model and the Smith Liu equations for rolling and sliding friction. Fatigue life prediction methods involving S-N curves, surface fatigue strength, and Weibull probability distributions were tested using the simulation data against field results. An optimized die design was generated from a design of experiments simulating different die design geometry. Findings show that field failures correlate well to the DEFORM® simulation results. The Hertz model with Smith Liu equations improved correlation with the simulation. Fatigue life prediction models correlated reasonably well to field results using the simulation data for inputs. These findings can aid in selecting appropriate die materials, design parameters, and fatigue life treatments.
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Griffin, David. "Studies of and modelling of the fracture behaviour of composite materials." Thesis, Northumbria University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245214.
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Lindmark, Terese. "Welding parameter window for Tandem gas-shielded metal arc welding and fatigue in welded T-joints." Thesis, University West, Department of Technology, Mathematics and Computer Science, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-828.
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Ledoux, Laurence. "Effets de la porosité et d'un traitement de surface, le traitement à la vapeur d'eau, sur les propriétés mécaniques statistiques et cycliques du fer fritté." Châtenay-Malabry, Ecole centrale de Paris, 1989. http://www.theses.fr/1989ECAP0103.
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Etude de la tenue en fatigue et du comportement à la rupture sous sollicitation quasi-statique du fer fritté réalisée sur deux types de poudres de morphologies différentes avec un domaine de variation des porosités de 5 a 20%. Étude de l'influence d'un traitement de surface a la vapeur d'eau formant l'oxyde FE3 O4
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Aytekin, Oguz. "Numerical And Experimental Investigation Of Fatigue Life In Deep Drawn Parts." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12607386/index.pdf.
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Sheet metal forming has an important place among metal forming processes. As the usage of sheet metal increases, the fatigue simulation and optimization of these parts become more important. This thesis study examines the change of the fatigue life of a sheet metal part after forming. A sphere-like shape is deep drawn and change in thickness and residual stresses are analyzed. To understand the effect of residual stresses, deep drawn parts with and without residual stress tested against the fatigue failure. In parallel, the forming process is simulated with an implicit finite element method (FEM). The success of forming simulation is discussed in the study. Thickness changes and residual stresses calculated with FEM are included in computer aided fatigue analysis. The effect of thickness changes is examined with the results of FEM analysis. The effectiveness of the whole simulation process is discussed by comparing the outputs of experiments and computational analysis.
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Couch, P. D. "Fatigue and fracture of an aluminium-lithium based metal matrix composite at both ambient and elevated temperatures." Thesis, University of Birmingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499904.
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Gaudette, Frederick G. "The influence of alloy composition and interfacial segregants on the fracture and fatigue of metal/ceramic interfaces." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9412.
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Harrison, M. "Fracture studies in aluminium alloys : An investigation of the effect of manganese-bearing and zirconium-bearing dispersoids on the fatigue properties of peak aged Al-Zn-Mg alloys." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376914.
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Åstrand, Erik. "A Framework for optimised welding of fatigue loaded structures : Applied to gas metal arc welding of fillet welds." Doctoral thesis, Högskolan Väst, Forskningsmiljön produktionsteknik(PTW), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-9339.
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Welding is a key process for heavy steel structures, but it is also a weak link in the structure since fatigue fractures in welds are a common cause of failure. This thesis proposes several changes in order to improve the fatigue properties in acost effective way, enabling reduced weight and reduced cost of welded structures. The main idea is to adapt the weld requirements and welding procedures to the load conditions of the weld. This approach ensures that the main focus in the welding process is the critical characteristics of the welds fatigue life properties. The fatigue life critical properties are most often related to the geometrical factors of the weld such as the radius at the weld toe or the penetration in the root. The thesis describes a holistic view of the subject and covers fatigue, weld quality, weld requirements and welding procedures. It becomes evident that the traditional way of working without a direct connection to fatigue is not the best. With an adaptation to the load conditions and fatigue, it is possible to enhance the fatigue life and reduce the welding cost. The main challenge is to connect the welding process, weld requirements and fatigue life properties. It is needed for an optimised welding process of heavy structures subjected to fatigue and toget a predictable fatigue life. Welds optimised for enhanced fatigue life properties are not necessary accepted according to the requirements in a current standard. Several welding procedures are proposed for improving the fatigue life properties of the weld, which indicate a high potential for enhanced fatigue lifeof fillet welds. The idea is to replace the "standard" fillet weld with three different weld types: (i) Welds with deep penetration, (ii) Welds with large weld toe radius and (iii) Welds produced with low cost. Together with customised requirements and reduced over-welding there is a vast potential for reduced weight, reduced cost and increased productivity.The main contribution of this thesis work is the cross-functional studies including design, analysis, production and quality control. This gives a framework for improvements supporting reduced cost and reduced weight of VIII welded structures without reducing the fatigue strength. Many shortcomings have been highlighted to change the welding from a state where welds are done in a way as they "always" have, by tradition, to a more contemporary situation where weld requirements and welding procedures are actively chosen to match the load conditions of the weld. This result in requirements and welding procedures which actually are connected to the fatigue properties as defined by the loading conditions, and where auditors with high probability can say that an accepted weld actually is better than a rejected weld.
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Friend, Gareth William. "The effect of defects on the mechanical properties of fibre reinforced titanium metal matrix composites under fatigue loading." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5438/.
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Applications for titanium metal matrix composites (TiMMCs) are currently being developed by Rolls-Royce plc in gas turbine engine components. With any component manufacturing process there is a probability of defects, as much of the work on TiMMCs to date has been laboratory scale there is as yet no study that looks specifically at the defects that can arise in full scale components. This work set out to investigate the influence of a selection of defects on the fatigue properties of titanium diffusion bonds – an integral joint type in TiMMC components – using conditions derived from TiMMC component stress analysis. The study found that cladding material microstructure and texture greatly affected the fatigue life of the bond. This was characterised by a new technique called Spatially Resolved Acoustic Spectroscopy (SRAS). Airborne debris and residual degreasing agent staining were found to be contaminants the most detrimental to fatigue life and methods of modifying the manufacturing process have been suggested to eliminate them. A number of other methods have been discussed for reducing the sensitivity of the TiMMC components to defects of this type through the control of residual stresses microstructure and texture.
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Malpertu, Jean-Louis. "Fatigue mecano-thermique d'un superalliage a base de nickel." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0075.
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Etude sur une eprouvette tubulaire en alliage in100 soumise simultanement a un cycle de temperature (600 a 1050c) et a un cycle de deformation. Determination experimentale des lois de comportement anisotherme. Influence de divers parametres sur l'amorcage et le debut de propagation des fissures. Analyse des mecanismes d'endommagement lies a la fragilisation de l'alliage par la diffusion de l'oxygene. Proposition d'un modele d'endommagement prenant directement en compte l'interaction fatigue-oxydation. Prevision de la duree de vie en fatigue isotherme a 1000c et en fatigue mecano-thermique
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Shukla, Shivakant. "Understanding the Micromechanism of Cyclic Loading Behavior of Ultrafine Grained Alloys." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538796/.
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In the current study, we have investigated the cyclic loading behavior of conventional as well as novel alloy system exhibiting fine and ultrafine-grained structure. While in case of conventional alloy systems (here aluminum alloy AA5024), the effect of three different grain sizes was investigated. Improvement in fatigue properties was observed with decreasing grain size. The unique microstructure produced via Friction stir processing was responsible for the improved fatigue response. Additionally, microstructures consisting of a high fraction of special boundaries within the fine and ultrafine-grained regime were also subjected to cyclic loading. The hierarchical features introduced in the eutectic high entropy alloy deflected the persistent slip bands, responsible for fatigue cracking, thus resulted in delayed crack initiation and improved fatigue life. The selective nature of fatigue was learnt in the fine grain Al0.5CoCrFeNi, where the introduction of hierarchical features did not result in improved fatigue properties. The weak links in the microstructure, while not affecting the tensile properties, got exposed during cyclic loading. Further study on the medium entropy alloy revealed the inherent reason for the improved fatigue properties. The medium entropy alloys utilized the benefit of UFG single-phase FCC matrix. The UFG matrix showed signs of transformation of FCC phase into the HCP phase during fatigue deformation and hence exhibited improved work-hardening. Alongside atomic scale transformation, stacking faults and nano-twins can also be attributed for obtained cyclic properties.
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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
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Mestre em Engenharia Automobilistica