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Collin, Niklas. "Thermo-mechanical fatigue of castiron for engine applications." Thesis, KTH, Maskinkonstruktion (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156880.
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In an engine component the repeated start-stop cycles cause temporal and local inhomogeneous temperatures, which in turn lead to a type of low-frequency loading, plastic deformation and eventually failure due to thermo-mechanical fatigue. Simultaneously, high-frequency mechanical loading arises from the cyclic combustion pressure and from road induced vibrations. These types of loadings that mainly are in the elastic region are usually denoted high cycle fatigue (HCF). In order to improve efficiency, power density and to reduce emissions, future truck engines will be subjected to higher temperatures and higher combustion pressures which will affect the service life of the different engine components. As a consequence, there is a need to determine the limitations of the used alloys under these service conditions as exactly as possible. In this master thesis work the fatigue properties of one grey iron (EN-GJL 250) and one compacted graphite iron (EN-GJV 400) has been investigated under realistic loading conditions. The results show that a change from the grey iron to the compacted graphite iron will result in a significant increase of the fatigue life. The investigation also reveal that the life will increase significantly if the maximum temperature can be decreased tens of degrees. Further, the results indicate that addition of a relatively small HCF load may give a large decrease of the fatigue life.Motorkomponenter utsätts för upprepade start och stopp, vilka skapar tillfälliga och lokala temperaturvariationer. Dessa resulterar i lågfrekventa lastväxlingar, plastiska deformationer och eventuella brott i form av termodynamisk utmattning (TMF). Det sker dessutom en högfrekvent mekanisk last, genererad av förbränningen och från vägvibrationer. Dessa laster är mestadels elastiska och benämns högcykelutmattning (HCF). För att kunna förbättra verkningsgrad och minska emissioner kommer framtida lastbilsmotorer att utsättas för högre förbränningstryck och högre temperaturer, vilket kommer påverka motorernas livslängd. För detta krävs det att materialens begränsningar utreds under ett verklighetstroget förhållande. I detta exjobb kommer utmattningsegenskaperna för ett gråjärn (EN-GJL 250) och ett kompaktgrafikjärn (EN-GJV 400) utredas under realistiska lastförhållanden. Resultatet påvisar att ett byte från gråjärn till kompaktgrafitjärn ger en signifikant ökad livslängd. Det framkommer också att livslängden kan ökas genom att sänka den maximala temperaturen ett tiotal grader. Analysen påvisar även att en relativt liten HCF last kan ge kraftigt förkortad livslängd.
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Brookes, Stephen Peter. "Thermo-mechanical fatigue behaviour of the near-g-titanium." Berlin BAM, 2009. http://d-nb.info/999495747/34.
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Adair, Benjamin Scott. "Thermo-mechanical fatigue crack growth of a polycrystalline superalloy." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/46027.
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A study was done to determine the temperature and load interaction effects on the fatigue crack growth rate of polycrystalline superalloy IN100. Temperature interaction testing was performed by cycling between 316°C and 649°C in blocks of 1, 10 and 100 cycles. Load interaction testing in the form of single overloads was performed at 316°C and 649°C. After compiling a database of constant temperature, constant amplitude FCGR data for IN100, fatigue crack growth predictions assuming no load or temperature interactions were made. Experimental fatigue crack propagation data was then compared and contrasted with these predictions. Through the aid of scanning electron microscopy the fracture mechanisms observed during interaction testing were compared with the mechanisms present during constant temperature, constant amplitude testing. One block alternating temperature interaction testing grew significantly faster than the non-interaction prediction, while ten block alternating temperature interaction testing also grew faster but not to the same extent. One hundred block alternating testing grew slower than non-interaction predictions. It was found that as the number of alternating temperature cycles increased, changes in the gamma prime morphology (and hence deformation mode) caused changes in the environmental interactions thus demonstrating the sensitivity of the environmental interaction on the details of the deformation mode. SEM fractography was used to show that at low alternating cycles, 316°C crack growth was accelerated due to crack tip embrittlement caused by 649°C cycling. At higher alternating cycles the 316°C cycling quickly grew through the embrittled crack tip but then grew slower than expected due to the possible formation of Kear-Wilsdorf locks at 649°C. Overload interaction testing led to full crack retardation at 2.0x overloads for both 316°C and 649°C testing. 1.6x overloading at both temperatures led to retarded crack growth whereas 1.3x overloads at 649°C created accelerated crack growth and at 316°C the crack growth was retarded.
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Colombo, Francesco. "Service-like thermo-mechanical fatigue characteristics of 1CrMoV rotor steel /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17070.
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Elschich, Ahmed. "Thermo-mechanical Fatigue of Electrical Insulation System in Electrical machine." Thesis, Karlstads universitet, Avdelningen för maskin- och materialteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-62579.
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Electrical machines in electrified heavy-duty vehicles are subjected to dynamic temperature loadings during normal operation due to the different driving conditions. The Electrical Insulation System (EIS) in a stator winding is aged as an effect of these dynamic thermal loads. The thermal loads are usually high constant temperatures and thermal cycling. The high average constant thermal load is well-known in the electrical machine industry but little is known about the effect of temperature cycling. In this project, the ageing of the EIS in stator windings due to temperature cycling is examined. In this project, computational simulations of different simplified models that represent the electrical insulation system are made to analyse the thermo-mechanical stresses that is induced due to thermal cycling. Furthermore, a test object was designed and simulated to replicate the stress levels obtained from the simulations. The test object is to ease the physical testing of electrical insulation system. Testing a complete stator takes time and has the disadvantage of having a high mass, therefore a test object is designed and a test method is provided. The results from the finite element analysis indicate that the mechanical stresses induced will affect the lifetime of the electrical insulation system. A sensitivity study of several thermal cycling parameters was performed, the stator core length, the cycle rate and the temperature cycle amplitude. The results obtained indicate that the stator core length is too short to have a significant effect on the thermo-mechanical stresses induced. The results of the sensitivity study of the temperature cycle rate and the temperature cycle amplitude showed that these parameters increase the thermo-mechanical stresses induced. The results from the simulations of the test object is similar to the results from the simulations of the stator windings, which means that the tests object is valid for testing. The test method that is most appropriate is the power cycling test method, because it replicates the actual application of stator windings. The thermally induced stresses exposing the slot insulation exceeds the yield strength of the material, therefore plastic deformation may occur only after one thermal cycle. The other components in the stator are exposed to stresses below the yield strength. The thermally induced stresses exposing the slot insulation are high enough to low cycle fatigue the electrical insulation system, thus thermo-mechanical fatigue is an ageing factor of the electrical insulation system.
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Stekovic, Svjetlana. "Low Cycle Fatigue and Thermo-Mechanical Fatigue of Uncoated and Coated Nickel-Base Superalloys." Doctoral thesis, Linköpings universitet, Konstruktionsmaterial, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9820.
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High strength nickel-base superalloys have been used in turbine blades for many years because of their superior performance at high temperatures. In such environments superalloys have limited oxidation and corrosion resistance and to solve this problem, protective coatings are deposited on the surface. The positive effect of coatings is based on protecting the surface zone in contact with hot gas atmosphere with a thermodynamically stable oxide layer that acts as a diffusion barrier. During service life, mechanical properties of metallic coatings can be changed due to the significant interdiffusion between substrate and coating. There are also other degradation mechanisms that affect nickel-base superalloys such as low cycle fatigue, thermo-mechanical fatigue and creep. The focus of this work is on a study of low cycle fatigue and out-of-phase thermo-mechanical fatigue behaviour of three uncoated and coated nickel-base superalloys. Polycrystalline IN792 and two single crystals CMSX-4 and SCB were coated with four different coatings; an overlay coating AMDRY997 (NiCoCrAlYTa), a platinum aluminide modified diffusion coating RT22 and two innovative coatings with a NiW interdiffusion barrier in the interface called IC1 and IC3. A low cycle fatigue and thermo-mechanical fatigue device was designed and set-up to simulate service loading of turbine blades and vanes. The low cycle fatigue tests were run at 500oC and 900oC while the thermo-mechanical fatigue tests were run between 250oC and 900oC.To simulate long service life, some coated specimens were exposed at 1050oC for 2000 h before the tests. The main conclusions are that the presence of the coatings is, in most cases, detrimental to LCF lives of the superalloys at 500oC while the coatings do improve the LCF lives of the superalloys at 900oC. Under TMF loading conditions, the coatings have negative effect on the lifetime of IN792. On single crystals, they are found to improve TMF life of the superalloys, especially at lower strains. The tests also indicate that long-term aging influences the fatigue and fracture behaviour of coated superalloys by oxidation and diffusion mechanisms when compared to non-aged specimens. The aged specimens exhibit longer life in some cases and shorter life during other test conditions. Fatigue cracks were in most cases initiated at the surface of the coatings, growing transgranularly perpendicular to the load axis.
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Šteković, Svjetlana. "Low cycle fatigue and thermo-mechanical fatigue of uncoated and coated nickel-base superalloys /." Linköping : Department of Managenet and Engineering, Linköping University, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9820.
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Barker, Vincent Mark. "Thermo-mechanical fatigue crack growth modeling of a nickel-based superalloy." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44714.
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A model was created to predict the thermo-mechanical fatigue crack growth rates under typical engine spectrum loading conditions. This model serves as both a crack growth analysis tool to determine residual lifetime of ageing turbine components and as a design tool to assess the effects of temperature and loading variables on crack propagation. The material used in the development of this model was a polycrystalline superalloy, Inconel 100 (IN-100).
The first step in creating a reliable model was to define the first order effects that influence TMF crack growth in a typical engine spectrum. Load interaction effects were determined to be major contributors to lifetime estimates by influencing crack growth rates based upon previous load histories. A yield zone model was modified to include temperature dependent properties that controlled the effects of crack growth retardation and acceleration based upon overloads and underloads, respectively. Multiple overload effects were included in the model to create enhanced retardation compared to single overload tests. Temperature interaction effects were also considered very important due to the wide temperature ranges of turbine engine components. Oxidation and changing temperature effects were accounted for by accelerating crack growth in regions that had been affected by higher temperatures. Constant amplitude crack growth rates were used as a baseline, upon which load and temperature interaction effects were applied. Experimental data of isolated first order effects was used to calibrate and verify the model.
Experimental data provided the means to verify that the model was a good fit to experimental results. The load interaction effects were described by a yield zone model, which included temperature dependent properties. These properties were determined experimentally and were essential in the model's development to include load and temperature contributions. Other interesting factors became apparent through testing. It was seen that specific combinations of strain rate and temperature would lead to serrated yielding, discovered to be the Portevin-Le Chatelier effect. This effect manifested itself as enhanced hardening, leading to unstable strain bursts in specimens that cyclically yielded while changing temperature.
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Koernig, Andreas, and Nicke Andersson. "Thermo-mechanical fatigue crack propagation in a single-crystal turbine blade." Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-153876.
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Simulation of crack growth in the internal cooling system of a blade in a Siemens gas turbine has been studied by inserting and propagating cracks at appropriate locations. The softwares used are ABAQUS and FRANC3D, where the latter supports finite element meshing of a crack and calculation of the stress intensities along the crack front based on the results from an external finite element program. The blade is subjected to thermo-mechanical fatigue and the cracks are grown subjected to in-phase loading conditions. The material of the blade is STAL15SX, a nickel-base single-crystal superalloy. The <001> crystalline direction is aligned with the loading direction of the blade, while the secondary crystalline directions are varied to examine how it affects the thermo-mechanical crack propagation fatigue life of the blade. The finite element model is set up using a submodeling technique to reduce the computational time for the simulations. Investigations to validate the submodeling technique are conducted. From the work it can be concluded that a crack located at a critical location in the cooling lattice reach above the crack propagation target life. Cracks located at noncritical locations have crack propagation lives of a factor 5.2 times the life of the critical crack.
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Johansson, Johnny. "Weld Analysis in Combustion Chambers Subjected to Thermo-Mechanical Fatigue Load Conditions." Thesis, Linköpings universitet, Hållfasthetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69482.
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At cyclic operation of gas turbines, components are subjected to thermo-mechanical fatigue (TMF) due to the high temperature gradients that arises. In this thesis life assessment of welds in combustion chambers are at focus. Siemens Industrial Turbomachinery AB uses a method they call the HQ-method to estimate the TMF life of components, but how well this estimation work with welds have not been investigated before and is therefore unclear. Because of this unclearness, an additional reduction factor is used take this into account. The goal of this thesis is to conduct a study of welds in the combustion chambers to get an overview of welds that are present, and to identify eventual problems with those. Furthermore, an analysis of a selected weld is performed and the results are evaluated by using the HQ-method. For this analysis, a TIG weld on a test specimen of Hastelloy X is selected as both the weld method and the material are commonly used in combustion chambers. The specimen is chosen due to the possibility to verify the results using a test rig designed for TMF-tests. The results show that the HQ-method, with the assumptions made today, yields a life of welds considered very low compared with the base metal. Also the location of the most severely loaded point is questionable. Further investigations also show that residual stresses in the weld relax quickly and the creep rate of the weld does not make any particular difference to expected life. To verify the results and clarify some questions it is therefore suggested that the commenced investigation continues with real tests on the weld. As the results show that the creep rate is unimportant to the fatigue life, the parameter should be ruled out from the investigation and the objective should instead be to find the accurate yield strength of the weld, and study if failure occurs in or outside the weld.Vid cyklisk drift av gasturbiner utsätts komponenterna för termomekanisk utmattning (TMF) på grund av de höga temperaturgradienter som uppkommer. I detta arbete är livslängdsbedömningen av svetsar i brännkammare i fokus. Siemens Industrial Turbomachinery AB använder en metod som de kallar för HQ-metoden för att bedöma livslängden av komponenter utsatta för TMF men hur väl denna bedömning stämmer på svetsar är oklart. På grund av denna oklarhet används en extra reduceringsfaktor för att ta hänsyn till detta. Målet med detta arbete är att göra en undersökning av svetsar i brännkammare för att få en överblick av vilka svetsar som finns samt att identifiera eventuella problem med dessa. Vidare ska en analys på en utvald svets utföras och resultaten ska utvärderas med HQ-metoden. Till denna analys väljs en TIG-svets på en provstav av Hastelloy X då både svetsmetoden och materialet är vanligt förekommande i brännkammare. Provstaven valdes eftersom den ger en möjlighet att verifiera resultaten i en provrigg avsedd för TMF-prov. Resultaten visar att HQ-metoden, med de antaganden som görs idag, ger en livslängd på svetsar som är väldigt låg i förhållande till grundmaterialet. Också placeringen av den mest påkända punkten kan ifrågasättas. Vidare visar även undersökningen att restspänningar i svetsen relaxerar snabbt och att kryphastigheten i svetsen inte gör någon speciell skillnad på den förväntade livslängden. För att verifiera resultaten samt klargöra vissa frågetecken föreslås därför att den påbörjade undersökningen fortsätter med riktiga tester på svetsar. Eftersom resultaten visar att kryphastigheten endast är av ringa betydelse ska den parametern uteslutas ur undersökningen och målet ska istället vara att finna den korrekta sträckgränsen i svetsen samt studera om brott uppkommer i eller utanför svetsen.
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Drew, G. L. "Thermo-mechanical fatigue of the single crystal nickel based superalloy CMSX-4." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598651.
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This thesis has been to develop the understanding of, and capability to accurately model, the response of the commercial single crystal nickel-based superalloy turbine blade material CMSX-4TM1, and like-alloys, under thermo-mechanical fatigue, for the range of near-<001> orientation corresponding to the primary turbine blade axis. Thermo-mechanical fatigue (TMF) testing was conducted together with creep and isothermal low cycle fatigue (LCF) testing, and analysed in order to investigate inelastic deformation, microstructural evolution, crack growth and oxidation damage phenomena. Based on the results obtained selected contemporary semi-empirical and mechanistic approaches to material behaviour and lifetime modelling were assessed. Isothermal uniaxial tensile creep tests were performed and compiled for orientation q>20°, at 750°C under a constant nominal stress of 750 MPa, in parallel with uniaxial tensile creep tests stepped in temperature and stress between 950°C/500 MPa and 750°C/750 MPa conditions. The interaction of high and low temperature creep deformation mechanisms, as may be expected during TMF under constant varying temperature and stress, and the orientation dependent phenomenological behaviour were discussed in light of a detailed microstructural analysis. This work was used in the assessment of a continuum damage mechanics approach to modelling of the stress-relaxation behaviour during TMF. Isothermal LCF test specimens deformed between 550°C and 950°C over a wide range of loading conditions were analysed to determine the temperature and stress dependence of fatigue crack initiation and propagation, and the role of oxidation in these processes. Quantitative parameters were determined for use in an oxidation-fatigue crack growth model, which was shown to compare well with both 950°C LCF and TMF fatigue crack growth rate and life to failure data. In-Phase (IP), Clockwise (CW) and Counter-Clockwise (CCW) TMF cycles, chosen to simulate the behaviour at critical locations in the turbine blade, were performed between 500-950°C. The phenomenological behaviour was discussed in conjunction with fractographic, morphological and microstructural analysis, and compared with the continuum damage mechanics and oxidation-fatigue models for material behaviour and life prediction.
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Alagbada, Adefemi Samuel. "Thermo-Mechanical Fatigue Assessment of Marine Boiler : Using linear Finite Element Analyses." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-95439.
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This thesis is on fatigue crack growth assessments of a thermomechanical loaded Marine Boiler- Sunrod CPDB12. The installation position of the marine boiler in the ship in relation to its fatigue life under mode 1 loading is investigated. Thermomechanical loading embodies pressures, temperatures, RAO, subjected to the rigid body dynamic of ship in the marine environment. Linear elastic fracture mechanics (LEFM) method was used is predicting the growth rates of the welding flaws at the joint based on stress range of the Paris law relationship. FEA Numerical simulation delivered better crack growth rate assessments and life predictions of the smallest detectable flaws in the boiler. The identified smallest detestable flaws at the welding joint diminishing the designed safe life of the boiler significantly. Also, installation position within the ship do affect the fatigue life of the boiler.
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Kliemt, Christian. "Thermo-mechanical fatigue of cast aluminium alloys for engine applications under severe conditions." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2529.
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The increase in target performance of engines and hence the loading of their structural materials has dictated the need for more information about the behaviour of cast aluminium alloys under severe conditions up to 400°C. This study was therefore conducted in order to determine how different cooling rates, different pre-treatments and different alloying elements can improve the performance of cast aluminium (Al) alloys under thermo-mechanical fatigue (TMF) loading compared to a reference alloy and condition, AlSi6Cu4-T6. An existing TMF test rig was modified to allow an investigation of temperature gradients corresponding to those prevailing in real cylinder heads. The measured data were implemented in a Chaboche damage model and in an FEM tool in order to simulate low cycle fatigue (LCF) and TMF behaviour. These models provide a possibility to simulate LCF and TMF behaviour taking into account microstructural changes. On metallographic examination, a dependence of crack initiation on secondary dendrite arm spacing (SDAS) and on porosity was observed. Here, a smaller SDAS and a HIP modified microstructure led to a longer lifetime. Furthermore, clusters of brittle Si particles, decohesion or intermetallic phases were also found to initiate cracks. Stage I crack behaviour was seen at low strain amplitudes, where the crack propagates along the interface between the Al matrix and the intermetallic phases. Stage II behaviour was observed for higher strain amplitudes with crack propagation taking place along intermetallic phase boundaries such as Al2Cu, α-phase and β-phase or through pores. An increasing proportion of matrix cracks was observed for low strain amplitudes. Investigation of the decohesion behaviour revealed decohesion under high strain amplitudes and in areas with a high particle fracture volume attributable to high notch stresses. A refinement of the microstructure, particularly the particles, was found with increased Si content, associated with an increase in particle density. Following all TMF tests, an orientation of particles dependent on the loading conditions was observed, and this seemed to have had an influence on crack behaviour. A drift of stress was also found after long term high temperature exposure for strain amplitudes of 0.2%, attributed to creep.
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Adair, Benjamin Scott. "Characterization and modeling of thermo-mechanical fatigue crack growth in a single crystal superalloy." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52191.
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Turbine engine blades are subjected to extreme conditions characterized by significant and simultaneous excursions in both stress and temperature. These conditions promote thermo-mechanical fatigue (TMF) crack growth which can significantly reduce component design life beyond that which would be predicted from isothermal/constant load amplitude results. A thorough understanding of the thermo-mechanical fatigue crack behavior in single crystal superalloys is crucial to accurately evaluate component life to ensure reliable operations without blade fracture through the use of "retirement for cause" (RFC). This research was conducted on PWA1484, a single crystal superalloy used by Pratt & Whitney for turbine blades. Initially, an isothermal constant amplitude fatigue crack growth rate database was developed, filling a void that currently exists in published literature. Through additional experimental testing, fractography, and modeling, the effects of temperature interactions, load interactions, oxidation and secondary crystallographic orientation on the fatigue crack growth rate and the underlying mechanisms responsible were determined. As is typical in published literature, an R Ratio of 0.7 displays faster crack growth when compared to R = 0.1. The effect of temperature on crack growth rate becomes more pronounced as the crack driving force increases. In addition secondary orientation and R Ratio effects on crack growth rate were shown to increase with increasing temperature. Temperature interaction testing between 649°C and 982°C showed that for both R = 0.1 and 0.7, retardation is present at larger alternating cycle blocks and acceleration is present at smaller alternating cycle blocks. This transition from acceleration to retardation occurs between 10 and 20 alternating cycles for R = 0.1 and around 20 alternating cycles for R = 0.7. Load interaction testing showed that when the crack driving force is near KIC the overload size greatly influences whether acceleration or retardation will occur at 982°C. Semi-realistic spectrum testing demonstrated the extreme sensitivity that relative loading levels play on fatigue crack growth life while also calling into question the importance of dwell times. A crack trajectory modeling approach using blade primary and secondary orientations was used to determine whether crack propagation will occur on crystallographic planes or normal to the applied load. Crack plane determination using a scanning electron microscope enabled verification of the crack trajectory modeling approach. The isothermal constant amplitude fatigue crack growth results fills a much needed void in currently available data. While the temperature and load interaction fatigue crack growth results reveal the acceleration and retardation that is present in cracks growing in single crystal turbine blade materials under TMF conditions. This research also provides a deeper understanding of the failure and deformation mechanisms responsible for crack growth during thermo-mechanical fatigue. The crack path trajectory modeling will help enable "Retirement for Cause" to be used for critical turbine engine components, a drastic improvement over the standard "safe-life" calculations while also reducing the risk of catastrophic failure due to "chunk liberation" as a function of time. Leveraging off this work there exists the possibility of developing a "local approach" to define a crack growth forcing function in single crystal superalloys.
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Mai, Ronny. "Thermo-mechanical fatigue investigations on Nickel base superalloys and creep of NiAl thin films." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2492.
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In service, many components and structures of aero jet engines, are exposed to a complex superposition of varying mechanically and thermally induced forces. This cyclic loading is most pronounced during the start-up and the shut-down sequence of the engine, usually combined with high temperature transients, and is responsible for a serious reduction in lifetime, compared to isothermal operating conditions. A detailed knowledge of this interaction between varying temperatures and loads is of considerable importance for precise lifetime calculations. In order to characterise and scientifically describe the material behaviour under thermo-mechanical fatigue (TMF) exposure, laboratory experiments are performed under strictly defined conditions. The main challenge for experimental investigations is the precise temperature control required to simulate the fast thermal transients under operating conditions. In any component, the lifetime behaviour is dominated by three different damage mechanisms: fatigue, oxidation and creep. In order to protect the component surface against oxidising atmosphere in gas turbines the substrate material is coated with different protective coating systems. This work compares the thermal mechanical fatigue behaviour of two different substrate materials, Nimonic 90 as the “classic” matrix and PM1000, an oxide dispersoide strengthened powder metallurgical superalloy under TMF loadings. Additionally, the creep behaviour and the lifetime analysis of a b−nickel aluminide diffusion coating system is described.
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O'Rourke, Matthew Daniel. "Effects of specimen geometry and coating on the thermo-mechanical fatigue of PWA 1484 superalloy." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52192.
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The single crystal superalloy PWA 1484 is used in hot section turbine blade applications due to its performance at high temperatures. In practice, the turbine blades are often coated in order to protect them from environmental degradation. However, under repeated cyclic loading, the coating may serve as a site for crack initiation in the blades. Fundamental out-of-phase (OP) thermo-mechanical fatigue (TMF) studies, primarily using uncoated solid cylindrical test samples, have previously examined both crack initiation and propagation in PWA 1484. In this work, mechanical strain-controlled OP TMF tests were performed on coated and uncoated specimens of a hollow cylindrical geometry in order to study the effects of both geometry and coating on the TMF crack initiation behavior. To accomplish this, it was necessary to create and analyze a modified gripping mechanism due to the unique geometry of the test samples, and as predicted by hand calculations and finite element analysis, these modifications proved to be successful. The TMF test results for the uncoated material were compared to those from previous studies under the same testing conditions, and it was found that the differences in geometry had a minimal impact on fatigue life. Comparisons of the results for the coated and uncoated material suggested that the coating may have offered a slight improvement in life, although insufficient results were available to determine whether these differences were statistically significant. Damage mechanisms resulting from different test conditions were also observed through microscopy on failed specimens.
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Sofia, Wännman. "Influence of Nitrocarburization on Thermo-Mechanical Fatigue Properties : Material Characterization of Ductile Cast Iron for Exhaust Components." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-69160.
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The large number of vehicles operating on the roads cause high emissions and consequently a negative effect on the environment. When developing and optimizing internal combustion engines, certain requirements must be considered, which are environmental regulations, reduced fuel consumption and increased specific power. In order to meet these demands, an increase of the engine combustion pressure will occur usually accompanied with a temperature increase. During start-up and shut-down of an engine, it is subjected to cyclic thermo-mechanical fatigue (TMF) loads. The turbo manifold and exhaust manifolds connected to the engine is also subjected to these thermo-mechanical fatigue loads and thereby exposed to alternating tensile and compression loads. As these TMF loads will increase in the near future due to the development and optimization of internal combustion engines, it is important to understand the limitations of the material for these loads. In collaboration with Scania CV AB in Södertälje, this thesis covers the investigation of influence of nitrocarburizing (NC) on TMF properties of three ductile irons (DCI) labelled HiSi, SiMo51 and SiMo1000 intended to be used for components in the exhaust system. Nitrocarburizing is a thermo-chemical process where nitrogen and carbon diffuses from the process medium into the surface zone of a ferrous metal. The purpose of the NC is to increase the wear properties in contact areas between different parts. The oxidation with and without nitrocarburizing are studied both after isothermal and stress free oxidation tests at 780 °C and after TMF loads with combined cyclic variation of mechanical and thermal loads. In addition, the properties such as hardness, defects, porosity, microstructure, composition of both the materials and of the oxide layer have been investigated. For SiMo1000+NC cracks formed during nitrocarburizing were positioned parallel to the surface edge in the diffusion zone and consequently an increased diffusion of nitrogen into the material, i.e. deeper diffusion depth. SiMo1000+NC showed highest hardness, highest compressive residual stresses and thickest oxide layer. SiMo1000 showed highest resistance against oxidation due to the protective aluminum oxide layer. Oxide crack initiations after thermo-mechanical tests with a protective silicon oxide layer around the cracks for HiSi and SiMo51 and a protective aluminum oxide layer around the cracks for SiMo1000. In materials with nitrocarburizing, these protective layers of either silicon oxide or aluminum oxide were more distributed into the material. In SiMo1000+NC, crack initiations were not oxidized.
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Benoit, à. la Guillaume Aurélie. "Prédiction de la durée de vie de structures mécanosoudées soumises à des chargements thermiques anisothermes : application aux collecteurs d'échappement en tôle." Thesis, Paris, ENMP, 2012. http://www.theses.fr/2012ENMP0023/document.
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Traditionnellement, les collecteurs d'échappement sont fabriqués en fonte, d'un seul tenant. En raison de l'augmentation des performances des moteurs, des tôles d'acier mécano-soudées sont maintenant utilisées pour améliorer la tenue mécanique du collecteur à haute température. Cette technologie permet de réduire la masse du collecteur et de répondre ainsi favorablement aux normes de dépollution les plus sévères. L'objectif de la thèse est de proposer un modèle numérique de soudure et un critère de ruine associé permettant de prédire la durée de vie de ces structures mécano-soudées soumises à des chargements thermiques anisothermes. La procédure de dimensionnement consiste à simuler plusieurs cycles de chargements et à évaluer le critère de fatigue sur le dernier cycle simulé, considéré comme stabilisé.Dans un premier temps, une étude théorique est menée sur la caractérisation des différents états asymptotiques (adaptation, accommodation et rochet). Elle permet, d'une part de vérifier que l'état stabilisé est effectivement atteint et éventuellement d'estimer le nombre de cycles nécessaires pour l'atteindre, d'autre part de déterminer la nature de l'état limite. Dans un second temps, des essais de durée de vie isothermes, réalisés sur des éprouvettes en tôle, en tôle soudée et en tôle soudée arasée (abrasion du cordon puis polissage de la zone utile) mettent en évidence l'influence de la géométrie et de la microstructure au niveau de la soudure sur la durée de vie de ces structures. Enfin, des essais de durée de vie anisothermes, inspirés de chargements effectivement observés sur le collecteur, ont été réalisés sur des éprouvettes en tôle et en tôle soudée.La rigidité du cordon de soudure est modélisée à l'aide d'éléments coques dimensionnés de sorte à reproduire la déformée des éprouvettes en tôle soudée observée expérimentalement. Différents critères de ruine sont mis au point sur le matériau de base pour caractériser l'endommagement induit par des chargements anisothermes puis sont adaptés à la zone soudée. Enfin, la simulation d'un essai de choc thermique sur un collecteur d'échappement permet de valider le modèle de soudure proposé et de tester la pertinence des critères vis-à-vis de l'application industrielleExhaust manifolds are classically designed in cast-iron. However, the engine performance increasing, the output gas reaches higher temperature, and other types of material like welded steel plates are considered to design exhaust manifolds. These components are subjected to complex thermomechanical loadings which must be taken into account in fatigue design. To limit the computational costs, only a few loading cycles are simulated and a fatigue criterion is used to estimate the lifetime of the structure. This study proposes a junction model combined with a fatigue criterion to assess the lifetime of a welded structure. The model is simple enough to be integrated into a computation on a complete structure and the fatigue criterion is available for anisothermal loadings.The theoretical characterization of the asymptotic states (elastic or plastic shakedown, ratchetting) is studied and adapted to anisothermal loadings in order to check whether the structure reaches a stabilized behaviour and to find the trend line of the evolution of the structure. Then isothermal low cycle fatigue tests are completed up to specimen crack initiation on plate, butt-welded plate and butt-welded plate after smoothing out the weld bead. The geometry and the microstructure of the weld have significant influence on strain localization and on the fatigue lifetime of the specimens. Finally anisothermal tests were completed on welded specimens to reproduce the typical loading seen by welds on exhaust manifolds.The stiffness of the weld is modelled thanks to additional shell elements calibrated to reproduce the deflected shapes of the welded specimens. Various fatigue criteria are developed on the base material to characterize anisothermal damage, and are then adapted to welded zones. The junction model is finally validated thanks to the simulation of a thermal shock on an exhaust manifold and the relevance of the criteria is estimated in relation to the industrial application
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Larsson, Karl. "Influence of nitrocarburization on the thermomechanical fatigue properties of ductile iron for exhaust components : Analysis and comparisons of TMF-properties." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-72033.
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New stricter environmental legislation requires lower emissions and fuel consumption of automotive engines. Therefore the fuel efficiency must be increased but this leads to higher loads in the engine. As for the exhaust system it is affected by higher thermomechanical loads. Until today the turbo manifold has been nitrocarburized in order to increase the wear resistance in slip joints with other exhaust components. The problem is that there is no knowledge of how the nitrocarburizing affects the thermomechanical properties of the material. The purpose of this thesis work is to examine the difference in thermomechanical properties with and without nitrocarburizing on the three different ductile irons High Silicon, SiMo51 and SiMo1000 intended for exhaust components. Thermo-mechanical fatigue (TMF) experiments were performed on test rods to evaluate difference in number of cycles to failure. In each cycle the test-rod was affected by a combination of mechanical loads and thermal loads resembling those found on exhaust components. Light optical microscopy, scanning electron microscopy and x-ray radiography were used to examine microcracks and damage mechanisms of the materials. It was found that the nitrocarburizing did not affect the number of cycles to failure in any large extent. Further, it was also found that SiMo1000 on average has the longest lifetime followed by SiMo51 and High Silicon. Although, the difference is small for many loadings and taking a 95% confidence band into account the curves overlap for many loading cases.
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Lopez, Santaella Mauricio [Verfasser]. "Thermo-mechanical fatigue of hot forging tools – prediction, analysis and optimization methods through six-sigma / Mauricio Lopez Santaella." Aachen : Shaker, 2014. http://d-nb.info/1051572908/34.
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Engler, Pinto Carlos Carvalho Engler Pinto Carlos Carvalho Engler Pinto Carlos Carvalho. "Etude de l'endommagement en fatigue thermo-mécanique de superalliages à base de nickel = [Study of thermo-mechanical fatigue damage of nickel base superalloys] = [Estudo do dano por fadiga termo-mecânica de superligas à base de níquel] /." [S.l.] : [s.n.], 1996. http://library.epfl.ch/theses/?nr=1496.
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Rombo, Oskar. "Software Benchmark and Material Selection in an Exhaust Manifold : Thermo-mechanical fatigue simulation of an exhaust manifold in AVL Fire M." Thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik (from 2013), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-68662.
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Today, there is a great focus on downsizing the engines, this means that the engines are made smaller in size but retain the same power. This in combination with the drive to increase the power of the engines has led to the engine components being exposed to high thermal loads. Today’s engines also use very high cylinder pressure. The high thermal loads in combination with the high cylinder pressure have led to that the engine components are often very close to their material limits, so close that damage is common. This places high requirements on the materials, which makes the material selection a critical part of the engineering process.The main focus in this thesis work has been to develop and investigate a FEM model that can be used to quickly evaluate materials in an exhaust manifold that is exposed to thermo-mechanical fatigue (TMF). The model was then used to verify a material selection made for an existing exhaust manifold. One of AVL’s own software programs has also been evaluated, to see if it is a viable alternative to ABAQUS when preforming TMF simulations.The material selection made in this master thesis had the restriction that the exhaust manifold should not fail due to low cycle fatigue (LCF) when exposed to TMF. The goal has been to minimize the mass of the exhaust manifold by selecting a strong material with low density. The reason for this is because today there is a big focus on energy efficient cars with low emission levels. The simplest way to achieve this is to minimize the mass of the vehicle.The simulations conducted in this work has been performed in two different software’s, ABAQUS and AVL Fire M. In AVL Fire M flow simulations and steady-state heat transfer simulations have been performed. In ABAQUS, steady-state and transient heat transfer simulations and stress-strain simulations have been performed.The material selection process showed that Inconel 601 is the most suitable material for an exhaust manifold exposed to TMF. The simulations using Inconel 601 showed that this material will not fail due to LCF.The FEM model that was developed in this thesis was a lot faster compared to the existing TMF model used at AVL.CPU time for the existing model: 14 days 13 hours 14 minutes and 30 seconds (Core time).CPU time for the model developed in this thesis: 1 day 6 hours 37 minutes and 49 seconds (Core time).Two alternative models have been proposed for TMF simulations, one that uses the model developed in this thesis and one that is a combination of the existing model and the model developed in this work.
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Soulignac, Romain. "Prévision de la durée de vie à l’écaillage des barrières thermiques." Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0087/document.
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Cette étude porte sur la modélisation de la durée de vie à l'écaillage des barrières thermiques pour aubes de turbines aéronautiques. La caractérisation expérimentale de l'adhérence du revêtement combine l'identification de la durée de vie - qualifiée par l'écaillage macroscopique de la céramique - à une caractérisation de l'endommagement à l'échelle de la microstructure du revêtement et en particulier à la dégradation des interfaces céramique / oxyde / métal. Des essais de compression uniaxiale sur des éprouvettes en AM1 revêtues NiAlPt et YSZ par EB-PVD, vieillies en fatigue thermique et mécano-thermique permettent d'estimer l'adhérence du revêtement. Ces essais sont complétés par des essais de propagation du délaminage interfacial par compression. Un essai original de compression in situ en laminographie aux rayons X a également permis d'analyser l'écaillage et la propagation du front de délaminage. Tous ces essais sont instrumentés et équipés de moyens d'observation permettant de réaliser des mesures de surfaces délaminées ou écaillées et de déterminer leur évolution en fonction des déformations locales mesurées.Une analyse microstructurale complète l'étude afin de comprendre l'influence du vieillissement thermique ou mécano-thermique sur l'évolution de l'endommagement du système. Cette analyse porte sur les mécanismes d'oxydation, de diffusion, de changement de phase principalement dans l'oxyde et la sous-couche. Elle est complétée par l'étude de l'ondulation de surface au cours du cyclage thermique, phénomène de « rumpling », et de ses conséquences, notamment au niveau de l'endommagement global de l'interface et de son adhérence. Le lien entre endommagement de l'interface à l'échelle d'imperfections de rugosité (quelques microns) et de la propagation d'une fissure d'interface (quelques dizaines à quelques centaines de microns) est analysé numériquement par la méthode des zones cohésives.Ces deux études complémentaires ont permis d'établir un modèle phénoménologique de durée de vie à l'écaillage. Celui-ci se base sur une estimation de l'énergie contenue dans la couche de céramique comparée à la valeur théorique d'énergie critique à rupture obtenue par un modèle d'endommagement, fonction de l'oxydation et des paramètres de chargement mécano-thermique. Ce modèle est implémenté en post-processeur d'un calcul par éléments finis facilitant son utilisation industrielleThis study aims to model lifetime of thermal barrier coating (TBC) used on aircraft turbine blades. Experimental characterization of the coating adherence combines the lifetime identification – described by macroscopic spallation of the ceramic – with damage estimation trough the analysis of the influence of the microstructure of the coating and evolutions of interfaces ceramic / oxide / metal.Adherence of the ceramic is assessed using uniaxial mechanical compressive tests on AM1 specimen coated with NiAlPt bond coat and EB-PVD yttria stabilized zirconia varying the thermal and thermo-mechanical fatigue ageing conditions. Those tests are completed with analysis of interfacial crack propagation. A pioneering in situ compressive test using X-ray laminography has also been developed to analyze spallation and further delamination. The use of in-situ surface imaging by CCD cameras has enabled measurement of delaminated or spalled areas as function of measured local strain.The influence of thermal or thermo mechanical ageing on damage evolution of TBCs is studied through a microstructural analysis. Oxidation, diffusion and phase transformation mechanisms in the alumina and the bond coat are main parts of this analysis. Moreover the oxide rumpling and its consequences have been detailed, particularly through the measurement of global interfacial damage and adherence evolution. The link between interfacial damage at the scale of local defects (few microns) and the propagation of an interfacial crack (from tens to hundreds of microns) is numerically analyzed with a cohesive zone model.Those two spatial length of analysis were used to build a phenomenological lifetime model to spallation. This model was based on the assessment of the elastic strain energy stored in the ceramic layer and it comparison to fracture energy. A damage model is used to model the fracture strain energy evolution as a function of oxidation and thermo mechanical loading. This model is implemented in post processor of a FEM analysis, making its industrial use easier
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Eftekhari, Mohammadreza. "Creep, Fatigue, and Their Interaction at Elevated Temperatures in Thermoplastic Composites." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1470388940.
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RACCA, ALBERTO. "Turbocharger Design Optimization by Adjoint Method Coupled with CHT Analysis." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2933754.
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Smet, Vanessa. "Aging and failure modes of IGBT power modules undergoing power cycling in high temperature environments." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20075/document.
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Cette thèse a pour objet l'étude de la fiabilité de modules de puissance triphasés à IGBTs 200 A - 600 V, destinés à la construction d'onduleurs de traction pour des applications automobiles hybrides ou électriques. Ces travaux visent à évaluer la tenue de ces modules de puissance en régime de cyclage thermique actif à hautes température, en mettant l'accent sur leur résistance à la fatigue thermomécanique. Deux approches complémentaires ont été mises en oeuvre dans ce but: tests de vieillissement accéléré et modélisation numérique. Une compagne d'essais de vieillissement par cyclage actif a été menée avec des profils de température variés, définis par la température ambiante et la variation de température de jonction des IGBTs, utilisés comme facteurs d'accélération des contraintes. Au cours de ces tests, les composants ont électriquement fonctionné dans des conditions semblables à une application réelle (commande MLI). L'objectif était d'identifier les modes de défaillance, d'estimer l'influence des facteurs d'accélération du vieillissement, et d'évaluer la pertinence des indicateurs de défaillance classiques dans ces conditions de stress thermiques sévères. Aussi, afin de mieux comprendre les mécanismes de défaillance responsables de la fatigue de l'assemblage des modules considérés, une modélisation thermomécanique visant à déterminer l'impact des modèles de comportement mécanique sur la durée de vie estimée des brasures, a été développée. La réponse de l'assemblage à des contraintes de cyclage actif similaires à celles appliquées durant les essais a été évaluée par analyse numérique. Les différentes lois de comportement ont été comparées en termes de contraintes, déformations plastiques, et densité d'énergie plastique dans les brasuresThis thesis is dedicated to reliability investigations led on three-phase 200~A~--~600~V IGBT power modules, designed for building drive inverters for hybrid or electric automotive traction applications. The objective was to evaluate the durability of the studied modules when they withstand power cycling in high temperature environments, and especially their resistance to thermo-mechanical fatigue. Two complementary approaches were considered: accelerated aging experiments and numerical modeling.A series of power cycling tests was carried out over a large range of temperature profiles, defined by the ambient temperature and IGBT junction temperature excursion. These quantities are used as thermal stress acceleration factors. Those experiments were led in realistic electrical conditions (PWM control scheme). They aimed at identifying the failure modes of the target devices, assessing the impact of the acceleration factors on their aging process, and evaluating the suitability of standard aging indicators as damage precursors in such harsh loading conditions. Besides, to better understand the failure mechanisms governing the fatigue life of the modules assembly, a thermo-mechanical modeling focusing on solder joints was built. Our simulation efforts concentrated on the appraisal of constitutive modeling effects on solder joints lifetime estimation. Numerical analysis of the assembly response to power cycling in similar operating conditions as practiced in experiments were performed. Behavior laws were then compared on stress, plastic strain, and strain energy density developed within the joints
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Degeilh, Robin. "Développement expérimental et modélisation d’un essai de fatigue avec gradient thermique de paroi pour application aube de turbine monocristalline." Thesis, Cachan, Ecole normale supérieure, 2013. http://www.theses.fr/2013DENS0019/document.
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Les aubes de turbine haute pression en superalliage monocristallin sont refroidies, à la fois par un réseau de canaux internes, ainsi que par des perforations débouchantes. Soumises à des cycles thermo-mécaniques complexes, elles subissent des endommagements de type fatigue, fluage et oxydation. Pour valider les chaînes de prévision de durée de vie en conditions réelles d'utilisation, il a été nécessaire d’étudier des configurations d’essais technologiques reproduisant les conditions d'un cycle moteur en laboratoire. Pour cela, une installation d'essai de fatigue à gradient thermique de paroi est développée. Le gradient thermique est généré par chauffage de la surface externe et refroidissement interne par une circulation d’air. L’installation a ainsi permis la réalisation d'essais selon une complexité croissante, allant de l’essai isotherme jusqu'au cycle thermo-mécanique complexe, sur éprouvette tubulaire lisse ou multi-perforée. Afin d’analyser finement ces essais, deux méthodes de mesures sont étudiées. La méthode du potentiel électrique pour la détection et le suivi de fissure appliquée à des géométries complexes et la corrélation d’images, dont l’utilisation est étendue à la haute température. Le point-clé de la modélisation de ces essais est l'estimation du champ thermique. L'impossibilité de le mesurer sur éprouvette, a conduit à le déterminer numériquement, notamment par des simulations couplées aéro-thermiques. La chaîne de prévision de durée de vie intégrant l'aspect non-local, a ainsi pu être confrontée aux mesures expérimentales en termes de réponse mécanique, localisation de l'endommagement et durée de vie à amorçageMonocrystalline high pressure turbine blades are booth cooled by an internal channel network and side-wall crossing holes. As they undergo complex thermo-mechanical cycles they suffer fatigue, creep and oxidation damages. In order to validate lifetime prediction chain under real conditions of use, the study of technological test configurations reproducing turbine cycle conditions was necessary. For that, a thermal gradient mechanical fatigue facility is developed. Thermal gradient is generated through an external surface heating and an internal air cooling. As a result, tests could be conducted following a growing complexity on smooth and multi-perforated tubular specimens going from isothermal test up to thermo-mechanical complex cycle. The need of in-depth analysis of these tests led to the study of two measurement methods. The electrical potential drop method for crack detection and crack following applied to complex shapes and digital image correlation which use was extended to high temperatures. Simulation key issue is the thermal field estimation. Measurement complexity led us to numerically determine it by various methods including aero-thermal coupled calculations. Finally lifetime prediction chain including non-local coverage was confronted with experimental measurements in terms of mechanical response, damage localisation and crack initiation lifetime
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Bouchenot, Thomas. "A Simplified Approach to Thermomechanical Fatigue and Application to V-shaped Notches." Honors in the Major Thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/939.
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A vast array of high value parts in land- and air-based turbomachinery are subjected to non-isothermal cycling in the presence of mechanical loading. Crack initiation, growth and eventual failure more significantly reduce life in these components compared to isothermal conditions. More accurate simulation of the stress and strain evolution at critical locations of components, as well as test specimens, can lead to a more accurate prediction of remaining life to a structural integrity specialists. The focus of this thesis is to characterize the effects of thermomechanical fatigue (TMF) on generic turbomachinery alloy. An expression that can be used to estimate the maximum and minimum stress under a variety of loading conditions is formulated. Analytical expressions developed here are modifications of classic mechanics of materials methods (e.g. Neuber's Rule and Ramberg-Osgood). The novel models are developed from a collection of data based on parametric finite element analysis to encompass the complex load history present in turbine service conditions. Relevance of the observations and formulated solutions are also explored for the case of a tensile specimen containing a v-shaped notch. Accurate estimations of non-isothermal fatigue presented here endeavor to improve component lifing and decrease maintenance costs.B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical Engineering
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Brookes, Stephen Peter [Verfasser], Birgit [Gutachter] Skrotzki, and Gunther [Gutachter] Eggeler. "Thermo-mechanical fatigue behaviour of the near-γ-titanium aluminide alloy TNB-V5 under uniaxial and multiaxial loading / Stephen Peter Brookes ; Gutachter: Birgit Skrotzki, Gunther Eggeler." Berlin : Bundesanstalt für Materialforschung und -prüfung (BAM), 2009. http://d-nb.info/1122835736/34.
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Pocheron, Mickaël. "Life-time prediction of solder joints used in surface mount assemblies during thermo-mechanical and isothermal aging." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0245.
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Les directives ROHS et WEEE banniront, dans les années qui viennent, le plomb de l’industrie électronique. Seulement, les assemblages électroniques de Schlumberger destinés à des applications hautes températures, tels que les ceux faisant intervenir des composants montés en surface, font intervenir des brasures à forte teneur en plomb. C’est pourquoi, Schlumberger investit énormément afin de trouver de nouvelles brasures sans plomb pour les remplacer. Ce projet, qui s’inscrit dans ce cadre, a pour objectif de prédire la durée de vie d’assemblages utilisant ces nouvelles brasures avec un substrat et des composants en céramique. Cette prédiction se fait en deux étapes. La première est expérimentale. Les assemblages sont soumis à des vieillissements accélérés thermomécaniques et isothermes. En plus de la durée de vie, ces tests apportent des connaissances sur les effets du vieillissement, sur les mécanismes et les zones de défaillances, sur l’interaction de ces brasures avec les finitions du substrat et des composants et enfin sur l’évolution de la microstructure et des phases d’intermétalliques créées lors du vieillissement.La seconde étape est la modélisation de ces assemblages afin de comprendre leur comportement sous sollicitations thermomécaniques. Les simulations aident à comprendre les phénomènes locaux qui apparaissent dans l’assemblage et à extraire des paramètres de fatigue pour diverses conditions thermomécaniques. Enfin, une corrélation entre les résultats de défaillance expérimentaux et la fatigue calculée grâce à la simulation va permettre d’estimer la durée de vie des assemblages pour différentes sollicitations thermomécaniques. Les simulations permettent donc de diminuer le nombre d’essais expérimentaux souvent chers et longs. Seulement, pour faire des simulations fiables, il est nécessaire de connaitre les paramètres mécaniques de tous les matériaux. Pour la brasure, cela veut dire le comportement élastique, plastique et en fluage. Donc, un bénéfice supplémentaire pour Schlumberger est la détermination de ses paramètres pour les nouvelles brasuresBecause of ROHS or WEEE directives, in a close future, lead materials will be banned from electronicindustry. Unfortunately, Schlumberger is using high-lead content solders for surface mount devices forhigh temperature applications. Considering this issue, Schlumberger puts in place high amount of investments to replace these solders by lead-free solders. The topic of the work is to study lead free candidates destined to support Schlumberger high temperature mission profiles. The device under test chosen for this project is a surface mount device composed of a passive component connected to a ceramic substrate by solder joints. The predictive study of reliability of these new assemblies for high temperature applications needs two complementary analyses. The first study is to characterize, experimentally, the life time of surface mount assemblies using these new lead free solders submitted to accelerated thermomechanical and isothermal aging tests. Hence, the first benefits for Schlumberger are knowledge on thecompatibility of these new alloys with their current finishes with the microstructure and intermetallic compounds evolution. More over, the main effects due to aging are investigated like failure sites and mechanisms. The second goal of the project is to perform thermo-mechanical simulations of surface mount assembly under thermal cycling. Simulations help to understand local phenomena and estimatefatigue parameters under other thermal conditions. Then, a correlation between experimental results about failure and calculated fatigue leads to an estimation of the life time of the assemblies. Thus, simulations have the advantage to reduce the number of time-consuming and expensive thermo-mechanical agingtests. To perform a simulation, the physical parameters of each solder material are needed like elastic,plastic and creep data. Additional benefits for Schlumberger involve mechanical properties which are, at the moment, unknown for these new high temperature lead free materials
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Abu-Ragheef, Basil. "Polymer Aging Mechanics : An investigation on a Thermoset Polymer used in the Exterior Structure of a Heavy-duty Vehicle." Thesis, Linnéuniversitetet, Institutionen för skog och träteknik (SOT), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-88887.
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The use of plastic materials in the design of vehicle components is primarily driven by the need for vehicle weight and cost reduction. Additionally, these materials give design engineers freedom in creating appealing exterior designs. However, creating self-carrying exterior structures with polymers must fulfill long-term strength, creep and fatigue life requirements. Thus, the polymer polyDicyclopentadiene (pDCPD) has been chosen for this purpose. Its aging mechanics need to be understood by the design engineers to make the right decisions. This thesis has carried out mechanical tests such as uniaxial tensile testing, fatigue, and creep testing. Digital image correlation (DIC) system has been used to capture strain data from tensile tests. In the final analysis, DIC measurements proved more accurate than extensometer data retrieved from the testing machine. The rise in temperature has been captured using thermal imaging. Several degradation processes have been explored including physical aging, thermo-oxidation, photo-oxidation, chemical- and bio- degradations. Test results showed significant changes in mechanical properties after 17 years of aging. Additionally, severe thermal degradation has been observed in one of the tested panels of pDCPD. Temperature can rise to significant levels during cyclic loading at high stresses, which could have an impact on physical aging effects. Viscoelastic behavior has been explored and changes in dynamic and creep properties have been observed. The investigation also reviled that different defects caused by flawed manufacturing also can affect the material severely as one case has proved in this research.
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Taina, Fabio. "Optimisation of microstructure and fatigue properties of Inconel 718 for extrusion die applications." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0087/document.
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Ce travail est une contribution à une étude de recherche et développent, proposée par Hydro Aluminium, dans le domaine des mécanismes d'endommagement de filières d'extrusion et. L'originalité du travail de thèse est basée sur le développement d'un alliage Inconel 718 optimisé pour l'application spécifique de filière d’extrusion, ce qui représente un saut technologique dans l'emploi de ce superalliage dans le domaine des outils. L'impact des paramètres du procédé d'extrusion, appelés paramètres extrinsèques, - tels que la vitesse d'extrusion, la longueur de billette, le chargement thermo-mécanique - sur le comportement mécanique du matériau a été analysé. Les cycles traction-compression sont simulés à l'aide d’essais isothermes de fatigue oligocyclique (LCF) qui donnent des informations sur les différents mécanismes d'endommagement survenant dans la filière. Du point de vue scientifique, la sollicitation de fatigue oligocyclique isotherme (LCF) est considérée comme la plus représentative des conditions thermomécaniques agissant sur l'outil. Les résultats montrent que la vitesse de déformation et de temps de maintien ont un impact significatif sur la durés de vie en fatigue. Le développent du matériau, enfin, a été atteint en modifiant les paramètres intrinsèques au matériau - tels que la taille des grains et la morphologie des précipités intermétalliques. Des traitements thermiques alternatifs, permettant d'adapter le matériau aux conditions spécifiques imposées par le procédé d'extrusion, ont été formulés. Des essais de fatigue LCF supplémentaires, ont permit de comparer la réponse cyclique de ces nouvelles nuances à celle du traitement original. Un de ces traitement, élaboré au travers d’une approche pluridisciplinaire incluant les aspects métallurgie, chimie et mécanique, a été retenu comme la nouvelle procédure standard pour le traitement des matrices d'extrusion en Inconel 718This present work is a contribution to an extensive development study, promoted by Hydro Aluminium, in the field of the damage mechanisms of extrusion dies. The originality of the present work is based on the development of an optimized Inconel 718 alloy as bulk material for extrusion die., which corresponds to a new application of this alloy in the field of tools: The investigation of the impact of the so called “Material Extrinsic Parameters”, such as extrusion speed, billet length and thermo-mechanical loading on the mechanical behaviour of the material is proposed. The cyclic tensile and compressive stresses, acting on the die, are simulated by isothermal Low Cycle Fatigue (LCF) tests. Results show that strain rate and holding time have a significant impact on fatigue life. These considerations represent the “Input Data” for the design of an optimized Inconel 718 in order to adapt the material to the specific conditions imposed by the extrusion process. This objective is achieved by modifying the “Material Intrinsic Parameters” such as grain size or precipitates morphology through the formulation of alternative thermal treatments. Additional LCF tests, are carried out to compare the cyclic response of the alternative Inconel 718 grades. One of this treatment, elaborated by a multidisciplinary approach including metallurgical, chemical and mechanical experiments that has been implemented in the industrial production practice as the new standard procedure for the thermal treatment of the Inconel 718 extrusion dies
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Brookes, Stephen Peter [Verfasser]. "Thermo-mechanical fatigue behaviour of the near-γ-titanium [near-gamma-titanium] aluminide alloy TNB-V5 under uniaxial and multiaxial loading / von Stephen Peter Brookes. [Hrsg.: BAM, Bundesanstalt für Materialforschung]." Berlin : BAM, 2009. http://d-nb.info/999495747/34.
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Mahalingam, Sakethraman. "Study of Interfacial Crack Propagation in Flip Chip Assemblies with Nano-filled Underfill Materials." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7215.
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No-flow underfill materials that cure during the solder reflow process is a relatively new technology. Although there are several advantages in terms of cost, time and processing ease, there are several reliability challenges associated with no-flow underfills. When micron-sized filler particles are introduced in no-flow underfills to enhance the solder bump reliability, such filler particles could prevent the solder bumps making reliable electrical contacts with the substrate pads during solder reflow, and therefore, the assembly yield would be adversely affected. The use of nano-sized filler particles can potentially improve assembly yield while offering the advantages associated with filled underfill materials.
The objective of this thesis is to study the thermo-mechanical reliability of nano-filled epoxy underfills (NFU) through experiments and theoretical modeling. In this work, the thermo-mechanical properties of NFUs with 20-nm filler particles have been measured. An innovative residual stress test method has been developed to measure the interfacial fracture toughness. Using the developed residual stress method and the single-leg bending test, the mode-mixity-dependent fracture toughness for NFU-SiN interface has been determined. In addition to such monotonic interfacial fracture characterization, the interface crack propagation under thermo-mechanical fatigue loading has been experimentally characterized, and a model for fatigue interface crack propagation has been developed. A test vehicle comprising of several flip chips was assembled using the NFU material and the reliability of the flip-chip assemblies was assessed under thermal shock cycles between -40oC and 125oC. The NFU-SiN interfacial delamination propagation and the solder bump reliability were monitored. In parallel, numerical models were developed to study the interfacial delamination propagation in the flip chip assembly using conventional interfacial fracture mechanics as well as cohesive zone modeling. Predictions for interfacial delamination propagation using the two approaches have been compared. Based on the theoretical models and the experimental data, guidelines for design of NFUs against interfacial delamination have been developed.
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Taher, Bilal. "Analyse et modélisation de l'endommagement dû au couplage thermomécanique des multi-matériaux cylindriques." Phd thesis, Université de Technologie de Belfort-Montbeliard, 2012. http://tel.archives-ouvertes.fr/tel-00977567.
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Un grand nombre de systèmes thermomécaniques industriels se trouve confronté à des régimes transitoires plus ou moins rapides suivant la fréquence de fonctionnement. L'amélioration de leurs performances nécessite l'utilisation de nouvelles structures du type multimatériaux ou barrière thermique. En effet, ces matériaux peuvent être de type multicouche en associant plusieurs couches rangées de façon à améliorer le comportement mécanique et thermique d'un système ou alors constitués d'un substrat revêtu d'une succession de couches minces obtenues par projection thermique par exemple.Dans un système donné, ces matériaux subissent généralement des sollicitations cycliques qui peuvent être d'origine thermique et/ou mécanique. Il est donc nécessaire de mieux connaître leur comportement thermomécanique en régimes élastique et plastique. Ainsi, l'étude présentée dans ce travail, limitée ici à des conditions périodiques uniquement d'origine thermique, traite de l'évolution de l'endommagement d'un matériau sous une ou plusieurs formes de fatigue thermique.L'origine de la sollicitation imposée provient d'une condition de flux périodique (sous forme d'échelon, de triangle ou de sinus) prenant en compte les pertes par convection. Sur le plan mécanique, le matériau est supposé fixe sur l'une de ses deux extrémités et libre de se déformer sur l'autre. Les contraintes et les déformations mécaniques dans le matériau proviennent essentiellement des différences des coefficients de dilatation thermique et des gradients de température dans le matériau. La nature variable et transitoire du comportement thermique du matériau permet de suivre l'évolution de la distribution des contraintes et des déformations au sein du matériau.L'étude de son endommagement est menée selon les cas, soit sur des modèles établis directement à partir du comportement thermo élastique soit sur des modèles nécessitant l'étude thermo-élastoplastique. Dans les deux cas, comme la plupart des modèles d'endommagement (Lemaître et Chaboche) rencontrés dans la littérature ne sont valides que sur des matériaux uniformes et homogènes, une recherche de matériau équivalent du multi-matériau étudié était nécessaire. L'équivalence entre le matériau réel et le matériau équivalent repose sur un critère d'équivalence thermique. Les modèles étudiés fournissent dans les deux cas, l'évolution de l'endommagement du matériau, en fonction des paramètres géométriques et aussi de la forme des sollicitations thermiques imposées telles que le coefficient d'échange par convection, l'amplitude et la période du flux imposé.Une application de ces modèles sur un exemple de moteur à combustion interne est proposée à la fin de ce mémoire. Elle montre une prédiction du nombre de cycles (durée de vie) du cylindre moteur en fonction des conditions de fonctionnement utilisées.
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CAIVANO, RICCARDO. "Design for Additive Manufacturing: Innovative topology optimisation algorithms to thrive additive manufacturing application." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2957748.
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Akkaoui, Abdessamad. "Bétons de granulats de bois : étude expérimentale et théorique des propriétés thermo-hydro-mécaniques par des approches multi-échelles." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1169/document.
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Les bétons végétaux, composés de particules végétales et d'un liant minéral ou organique, constituent une solution à explorer pour limiter l'impact environnemental du bâtiment. Utilisés principalement pour leurs performances thermiques, ces matériaux suscitent l'intérêt de plusieurs organismes de recherche ainsi que de plusieurs entreprises industrielles. La généralisation de leur utilisation dans la construction ne sera pas possible sans résoudre certains problèmes liés à leurs techniques de mise en œuvre, à leur certification et à leur durabilité. Le présent travail a pour objectif de contribuer à la caractérisation de ces matériaux complexes. Il s'agit en particulier d'étudier les comportements mécanique, thermique et hydromécanique du béton de granulats de bois. La stratégie utilisée consiste à combiner l'expérience et la modélisation pour mieux comprendre les mécanismes mis en jeu. Le module de Young et la résistance en compression ont été mesurés expérimentalement à l'aide de la technique de corrélation d'images numériques. L'évolution de ces propriétés dépend des conditions de conservation, de la durée de séchage ainsi que de la teneur en ciment. En raison de l'orientation aléatoire des granulats de bois, le comportement mécanique du béton est isotrope. Un modèle d'homogénéisation basé sur le schéma autocohérent a été développé pour prédire le module de Young du béton et ses résultats sont très satisfaisants. Les mesures de la conductivité thermique montrent que celle-ci reste constante en conditions endogènes. La modélisation de cette propriété par le schéma autocohérent conduit à des résultats cohérents avec les mesures expérimentales. En conditions de dessiccation, la conductivité thermique dépend linéairement de la densité du béton. L'évolution de la conductivité thermique des granulats de bois et de la pâte de ciment au cours du séchage a été modélisée grâce au schéma de Mori-Tanaka. Ces évolutions ont été intégrées dans le modèle autocohérent qui fournit ainsi des résultats satisfaisants, mais qui pourrait être amélioré si l'on disposait des courbes de sorption/désorption des constituants du béton. Les variations dimensionnelles du béton au cours du temps dépendent des conditions de conservation, mais pas de la direction de mesure, ni de la teneur en ciment. Un modèle reposant sur une combinaison des déformations induites par la désorption de l'eau par des constituants et le transfert d'humidité entre ceux-ci a été proposé et a permis de capturer les tendances des déformations du béton sauf au jeune âge. À l'échelle locale, l'étude a montré que les déformations du béton sont du même ordre de grandeur que celles de la pâte de ciment. Elle a aussi mis en évidence un endommagement partiel de l'interface granulat/liant qui mériterait à être pris en compte dans la modélisationEnvironmentally-friendly concretes, made up of plant-based particles and mineral or organic binder, are solutions worth exploring to reduce the environmental impact of buildings. Mainly used for their thermal performance, these materials have aroused interest of many research organisations and industrial companies. Their widespread use in construction is not possible without resolving some technical problems related to their implementation, certification and durability. This work aims to contribute to characterize these complex materials, in particular to study the mechanical, thermal and hydromechanical behaviors of wood-aggregate concrete. Modeling and experiments have been used to understand the complex mechanisms involved. The Young's modulus and the compressive strength were experimentally measured using digital image correlation. The evolution of these properties depends on the conditions of storage, the drying time and the cement content. Because of the random orientation of the wood aggregates, the material exhibits isotropic behavior. A homogenization model based on a self-consistent scheme was developed to predict the Young's modulus. The results were satisfactory. Measurements show that thermal conductivity remains constant under sealed conditions. The modeling of this property with the self-consistent scheme gives results consistent with experimental measurements. In desiccation conditions, the thermal conductivity depends linearly on the density of concrete. The evolution of the thermal conductivity of the wood aggregates and the cement paste during drying was modeled with the Mori-Tanaka scheme. These evolutions were integrated into the self-consistent model, which yielded satisfactory results, but could be improved if sorption/desorption curves of the phases were available. The macroscopic dimensional variations of the wood-aggregate concretes depended on the storage conditions, but not on the measurement direction, nor on the cement content. A model based on the combination of the strains induced by the desorption of water from the phases and the moisture transfer between them was proposed. It allowed us to capture the trends of the strains of our concrete except at early age. At a local scale, the study showed that the strains of concrete were close to those of the cement paste. The study also shed light on a significant damage of the aggregate/binder interfaces, which would deserve to be taken into account into the modeling
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Stitt, Alice C. "A physics-based maintenance cost methodology for commercial aircraft engines." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/13134.
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A need has been established in industry and academic publications to link an engine's maintenance costs throughout its operational life to its design as well as its operations and operating conditions. The established correlations between engine operation, design and maintenance costs highlight the value of establishing a satisfactory measure of the relative damage due to different operating conditions (operational severity). The methodology developed in this research enables the exploration of the causal, physics-based relationships underlying the statistical correlations in the public domain and identifies areas for further investigation. This thesis describes a physics-based approach to exploring the interactions, for commercial aircraft, of engine design, operation and through life maintenance costs. Applying the "virtual-workshop" workscoping concept to model engine maintenance throughout the operating life captures the maintenance requirements at each shop visit and the impact of a given shop visit on the timing and requirements for subsequent visits. Comparisons can thus be made between the cost implications of alternative operating regimes, flight profiles and maintenance strategies, taking into account engine design, age, operation and severity. The workscoping model developed operates within a physics-based methodology developed collaboratively within the research group which encompasses engine performance, lifing and operational severity modelling. The tool-set of coupled models used in this research additionally includes the workscoping maintenance cost model developed and implements a simplified 3D turbine blade geometry, new lifing models and an additional lifing mechanism (Thermo-mechanical fatigue (TMF)). Case studies presented model the effects of different outside air temperatures, reduced thrust operations (derate), flight durations and maintenance decisions. The use of operational severity and exhaust gas temperature margin deterioration as physics based cost drivers, while commonly accepted, limit the comparability of the results to other engine-aircraft pairs as the definition of operational severity, its derivation and application vary widely. The use of a single operation severity per mission based on high pressure turbine blade life does not permit the maintenance to vary with the prevalent lifing mechanism type (cyclic/steady state).
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Košťál, Josef. "Posouzení tepelně-mechanické únavy výfukového potrubí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-418196.
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Tato diplomová práce se zabývá posouzením tepelně-mechanické únavy výfukového potrubí. Nejprve byla provedena rešeršní studie, ve které je rozebrán fenomén tepelně-mechanické únavy. Byly prezentovány hlavní mechanismy poškození a přístupy k jejich modelování. Diskutována byla i specifická chování materiálu vystavenému tepelně-mechanickému zatěžování. Byl vypracován přehled vhodných modelů materiálu a modelů únavové životnosti společně s algoritmem predikce tepelně-mechanické únavy komponenty. Poté byl tento teoretický základ aplikován na praktický případ výfukového potrubí podléhajícího tepelně-mechanickému zatěžování. Dva tepelně závislé elasto-plastické modely materiálu byly nakalibrovány a validovány na základě experimentálních dat. Byl vytvořen diskretizovaný konečnoprvkový model sestavy výfukového potrubí. Model tepelných okrajových podmínek byl předepsán na základě výpočtů ustáleného sdruženého přestupu tepla. Slabě sdružená tepelně-deformační úloha byla vyřešena metodou konečných prvků pro oba modely materiálů. Bylo použito paradigma nesvázaného modelu únavy, které je vhodné pro nízkocyklovou únavu. Životnost byla tedy vyhodnocena jako součást post-procesoru. Použity byly dva modely únavové životnosti – energeticky založený model a deformačně založený model. Získané hodnoty životnosti byly porovnány vzhledem k použitým modelům materiálu a modelům únavové životnosti. Nakonec jsou diskutovány závěry této práce, oblasti dalšího výzkumu a navrženy možnosti na zlepšení použitých přístupů.
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Broudin, Morgane. "Vieillissement thermo-oxydatif d'un élastomère industriel pour applications automobiles antivibratoires : caractérisations, compréhension, outils de dimensionnement." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0079.
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Dans les conditions réelles d’utilisation, de multiples facteurs sont à l’origine de l’évolution des propriétés mécaniques des caoutchoucs (température, oxygène, conditions de chargement mécaniques…). Les pièces en élastomère pour l’antivibratoire automobile sont généralement massives (plusieurs millimètres d’épaisseur), le vieillissement conduit alors à des évolutions de propriétés hétérogènes. Ceci peut être induit par plusieurs mécanismes de dégradation liés, par exemple, à la présence ou non d’oxygène. Pour comprendre et identifier les mécanismes de dégradation prépondérants, une campagne de vieillissement accéléré a été menée pour une large gamme de températures représentative des conditions de service rencontrées sur véhicule (de 40°C à 120°C). De nombreux échantillons de géométries différentes (films minces, éprouvettes de caractérisation et éprouvettes de structure) ont été utilisés afin, d’une part, de faciliter l’interprétation, et d’autre part, de viser la transposition des résultats à l’échelle des pièces industrielles. L’étude présentée ici vise à identifier les mécanismes physico-chimiques et/ou évolutions microstructurales à l’origine du processus de dégradation, et de quantifier les conséquences de ceux-ci sur le comportement mécanique et les propriétés en fatigue. Ces résultats permettront de fournir les éléments nécessaires à la modélisation et la prise en compte fine des effets du vieillissement dans le processus de conception de pièces antivibratoires automobilesUnder service conditions, many factors are responsible for the evolution of the mechanical properties of rubber parts (temperature, oxygen, mechanical loadings, etc.). Automotive anti-vibration parts using rubber-like materials are usually massive and ageing can therefore lead to heterogeneous properties. To understand the degradation process and especially the effect of oxygen, aerobic and anaerobic ageing conditions have been studied for a wide range of temperatures (from 40°C to 120°C). Numerous samples have been used with different geometries (from thin films to massive structural samples) to ease the interpretation but also to remain as close as possible from the final applications. The mechanical consequences of the ageing have been investigated for both static and fatigue properties throughout a wide experimental database (about 1000 specimens tested in fatigue, for example). The study aims at identifying the physicochemical mechanisms and/or microstructural evolution that cause the processes of degradation and to quantify the consequences on the mechanical behavior and the fatigue properties. These results will provide the necessary elements needed for the integration of thermo-oxidative effects in the fatigue design loop of automotive anti-vibration parts
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Mussault, Cécile. "Temperature-induced phase transition of grafted hydrogels : from primary structure to mechanical properties." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS216.
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Afin d’étudier spécifiquement le rôle des processus de séparation de phase sur le renforcement des propriétés mécaniques des hydrogels, nous avons travaillé en conditions isochores en développant des architectures non seulement thermosensibles mais également capables de conserver un taux d’hydratation très élevé de part et d’autre de la température de transition de phase. Pour cela, des gels greffés ont été préparés à partir d’un réseau réticulé de polymère hydrophile en introduisant des chaînes latérales thermosensibles de type LCST (PNIPAm). A partir de cette structure primaire, et en maintenant fixe le rapport massique des précurseurs hydrophile/thermosensible, nous montrons que les caractéristiques thermodynamiques de la transition de phase (température et variation d’enthalpie) restent pratiquement indépendantes de la masse molaire des greffons de même que leur processus d’auto-assemblage qui conduit à la formation de domaines cylindriques concentrés en greffons PNIPAm. A l’instar des matériaux composites, la formation de ces domaines denses en polymère stabilisés par des interactions physiques vont ainsi largement augmenter la rigidité des gels à haute température ainsi que leur résistance à la fracture en jouant le rôle de dissipateur d’énergie. Nous montrons que ce renforcement thermo-contrôlé augmente avec la taille des chaînes à LCST. Dans le cas où l’on fait varier la composition massique hydrophile/thermosensible, tout en maintenant constante la masse molaire des greffons, on démontre des comportements opposés à basse et haute températures avec de bonnes propriétés à froid lorsque le réseau est riche en matrice hydrophile réticulée (élasticité d’origine entropique) et de très bonnes propriétés à chaud lorsque le comportement mécanique est contrôlé par les domaines concentrées en greffons à LCST (élasticité d’origine enthalpique). Le phénomène de séparation de phase des greffons PNIPAm étant thermo-réversible par nature, et les interactions entre ces mêmes chaînes peu dynamiques à haute température, nous montrons que ces hydrogels greffés cumulent, respectivement, des propriétés d’auto-adhésion et de mémoire de forme. Enfin, en généralisant le processus de séparation de phase, nous montrons que le remplacement du réseau hydrophile par un réseau thermosensible de type UCST, permet d’obtenir un double phénomène de séparation de phase, à basse et à haute température. Si les températures de transition sont parfaitement corrélées avec les caractéristiques thermodynamiques de chacun des polymères, le renforcement mécanique dépend plus quant à lui des énergies d’interaction qui se développent lors de la transition de phase au sein du réseau à UCST (liaisons-H) ou entre les greffons à LCST (interactions hydrophobes + liaisons-H)To specifically study the impact of phase-separation processes on hydrogels mechanical reinforcement, we worked under isochoric conditions developing architectures not only thermo-responsive but also able to keep a high level of hydration on both sides of the phase-separation temperature. For this purpose, grafted hydrogels have been formulated from a chemically cross-linked hydrophilic polymer network grafted with thermo-sensitive side-chains of LCST type (PNIPAm). From this primary structure and keeping constant the weight ratio between the hydrophilic and thermo-responsive parts, we demonstrate that the thermodynamic characteristics of the phase transition (enthalpy and temperature transitions) are only very weakly dependent on the molar mass of PNIPAm grafts as well as their self-assembly process which leads to cylindrical domains concentrated in PNIPAm grafts. Like the nanocomposite materials, the formation of these dense polymer domains stabilized by physical interactions highly enhances both the gels stiffness and fracture resistance at high temperature by dissipating energy. We show that this temperature-controlled reinforcement increases with the molar mass of the PNIPAm grafts. Varying the hydrophilic/thermo-responsive parts weight ratio while keeping constant the molar mass of the grafts, opposite behaviours at low and high temperatures were established. When the hydrophilic cross-linked network weight is high compared to the one of thermo-responsive grafts, the hydrogels exhibit good properties at low temperature (entropic elasticity) whereas at high temperature, their mechanical behaviour is controlled by the phase-separated domains concentrated in PNIPAm grafts (energetic elasticity). The phase-separation phenomenon of PNIPAm grafts being thermo-reversible by nature and the interactions between these chains being weakly dynamic at high temperature, we demonstrate that these grafted hydrogels exhibit both adhesive and shape-memory properties. Finally, expanding the phase-separation concept, we show that replacing the hydrophilic network by a UCST type thermo-responsive one allows getting a dual thermo-response with phase-separation occurring at both low and high temperatures. While these transition temperatures are perfectly correlated to the thermodynamic characteristics of each polymer, the mechanical reinforcement is more dependent on the energy due to the nature of interactions developing inside the UCST network (H-bonds) or between the LCST grafts (H-bonds and hydrophobic interactions) during the phase-separation process
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Chen, Kun-Yi, and 陳坤毅. "Thermo-Mechanical Fatigue Properties of Joints in Solid Oxide Fuel Cell." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/13871138440685045580.
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碩士國立中央大學
機械工程學系
104
The objective of this study is to investigate thermo-mechanical fatigue (TMF) behavior and relevant fracture mode of a joint between a glass-ceramic sealant and an interconnect steel in solid oxide fuel cell (SOFC) operating environments. The materials used are a GC-9 glass-ceramic sealant developed at the Institute of Nuclear Energy Research (INER) and a commercial Crofer 22 H ferritic stainless steel. TMF test is conducted by applying a cyclic combined thermal and mechanical loading (shear or tensile mode) on the joint. TMF life of shear specimen is increased with a decrease in applied stress level at peak temperature (800 °C) and is dominated by the applied stress level at peak temperature in both oxidizing environment (air) and reducing environment (humidified hydrogen). For applied shear stress of 0.2 joint strength ratio, the sample can run more than 50 TMF cycles. The accumulated time at high temperature (795-800 °C) in TMF test is comparable with the creep rupture time at 800 °C in both oxidizing and reducing environments for shear loading specimens. Based on the observation of fracture surface, fracture mainly occurred at the interface between barium chromate layer and glass-ceramic layer for the shear sample tested in oxidizing environment, while it mainly took place at the interface between chromia layer and glass-ceramic layer in reducing environment. For tensile specimens, TMF life is also increased with a decrease in applied stress level at peak temperature (800 °C) in both oxidizing and reducing environment. However, TMF life under tensile loading is controlled not only by the stress level applied at peak temperature (800 °C) but also by the stress level applied at low temperature (40 °C). It might be due to that brittle glass-ceramic sealant is more sensitive to tensile stress at low temperature. For tensile specimens tested in oxidizing environment with a TMF life of several cycles, fracture occurred in the glass-ceramic layer and at the interface between BaCrO4 chromate layer and Cr2O3 chromia layer on the periphery of joint. For those tested in reducing environment, fracture all took place within the glass-ceramic and at the interface of Cr2O3 chromia layer and glass-ceramic layer. The environmental effect on TMF life is insignificant due to a limited exposure time at high temperature in both given environments.
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(10716387), Abhilash Anilrao Gulhane. "Physics-based Thermo-Mechanical Fatigue Model for Life Prediction of High Temperature Alloys." Thesis, 2021.
Find full textAbstract:
High temperature alloys have been extensively used in many applications, such as furnace muffles, fuel nozzles, heat treating fixtures and fuel nozzles. Due to such conditions these materials should have resistance to cyclic loading, oxidation and high heat. Although there are numerous prior experimental and theoretical studies, there is insufficient understanding of application of the unified viscoplasticity theory to finite element software for fatigue life
prediction.
Therefore, the goal of this research is to develop a procedure to implement unified viscoplasticity
theory in finite element (FE) model to model the complex material deformation pertaining to thermomechanical load and implement an incremental damage lifetime rule to
predict thermomechanical fatigue life of high temperature alloys.
The objectives of the thesis are:
1. Develop a simplified integrated approach to model the fatigue creep deformation
under the framework of ‘unified viscoplasticity theory’
2. Implement a physics - based crack growth damage model into the framework
3. Predict the deformation using the unified viscoplastic material model for ferritic
cast iron (Fe-3.2C-4.0Si-0.6Mo) SiMo4.06
4. Predict the isothermal low cycle fatigue (LCF) and LCF Creep life using the damage model
In this work, a unified viscoplastic material model is applied in a FE model with a combination of Chaboche non-linear kinematic hardening, Perzyna rate model and static recovery
model to model rate dependent plasticity, stress relaxation, and creep-fatigue interaction.
Also, an incremental damage rule has been successfully implemented in a FE model. The calibrated viscoplastic model is able to correlate deformations pertaining to isothermal LCF, LCF-Creep and thermal-mechanical fatigue (TMF) experimental deformations. The life predictions
from the FE model have been fairly good at room temperature (20°C), 400°C and 550°C under Isothermal LCF (0.00001/s and 0.003/s) and LCF-Creep tests.
The material calibration techniques proposed for calibrating the model parameters resulted in a fairly good correlation of FE model derived hysteresis loops with experimental hysteresis, pertaining to Isothermal LCF (ranging from 0.00001/s to 0.003/s), Isothermal LCF-Creep tests (with hold time) and TMF responses. In summary, the method and models developed in this work are capable of simulating material deformation dependency on temperature, strain-rates, hold time, therefore, they are capable to modeling creep-stress relaxation and fatigue interaction in high-temperature alloy design.
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Gulhane, Abhilash Anilrao. "Physics - based Thermo - Mechanical Fatigue Model for Life Prediction of High Temperature Alloys." Thesis, 2021. http://dx.doi.org/10.7912/C2/16.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)High-temperature alloys have been extensively used in many applications, such as furnace muffles, fuel nozzles, heat-treating fixtures, and fuel nozzles. Due to such conditions, these materials should have resistance to cyclic loading, oxidation, and high heat. Although there are numerous prior experimental and theoretical studies, there is insufficient understanding of application of the unified viscoplasticity theory to finite element software for fatigue life prediction. Therefore, the goal of this research is to develop a procedure to implement unified viscoplasticity theory in finite element (FE) model to model the complex material deformation pertaining to thermomechanical load and implement an incremental damage lifetime rule to predict the thermomechanical fatigue life of high-temperature alloys. The objectives of the thesis are: 1. Develop a simplified integrated approach to model the fatigue creep deformation under the framework of ‘unified viscoplasticity theory’ 2. Implement a physics - based crack growth damage model into the framework 3. Predict the deformation using the unified viscoplastic material model for ferritic cast iron (Fe-3.2C-4.0Si-0.6Mo) SiMo4.06 4. Predict the isothermal low cycle fatigue (LCF) and LCF-Creep life using the damage model In this work, a unified viscoplastic material model is applied in a FE model with a combination of Chaboche non-linear kinematic hardening, Perzyna rate model, and static recovery model to model rate-dependent plasticity, stress relaxation, and creep-fatigue interaction. Also, an incremental damage rule has been successfully implemented in a FE model. The calibrated viscoplastic model is able to correlate deformations pertaining to isothermal LCF, LCF-Creep, and thermal-mechanical fatigue (TMF) experimental deformations. The life predictions from the FE model have been fairly good at room temperature (20°C), 400°C, and 550°C under Isothermal LCF (0.00001/s and 0.003/s) and LCF-Creep tests. The material calibration techniques proposed for calibrating the model parameters resulted in a fairly good correlation of FE model derived hysteresis loops with experimental hysteresis, pertaining to Isothermal LCF (ranging from 0.00001/s to 0.003/s), Isothermal LCF-Creep tests (withhold time) and TMF responses. In summary, the method and models developed in this work are capable of simulating material deformation dependency on temperature, strain rates, hold time, therefore, they are capable of modeling creep-stress relaxation and fatigue interaction in high-temperature alloy design.
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Wang, Yung-Wen, and 王湧文. "Thermo-mechanical Finite Element Model in BGA Solder Joints Fatigue Life Analysis." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/nx2v84.
Full textAbstract:
碩士國立中山大學
機械與機電工程學系研究所
102
As the microelectronic package develops technologies for fabrication smaller, faster and economical, thermal management play an important role. Temperature variation caused by either environmental changes or power consumption, and the coefficient of thermal expansion (CTE) mismatch between different packages material lead to stress and strain in package assemblies especially in solder joint. This research builds up the viscoplastic finite element model to analyze thermal-mechanical behavior of solder joint under temperature cycling loading. The finite element software ANASYS is used to calculate the accumulative strain energy density of solder joint. Furthermore, a design of experiment (DoE) with factorial analysis is used to investigate the reliability impact of the design parameters, including solder material properties and geometry. Finally, we use the analysis of variance (ANOVA) to obtain the regression model and to find out optimization factors. The purpose of this research is to provide a quickly experimental design assessment to improve reliability of the solder joint. The assessment model can be used to predict the accumulative strain energy density and fatigue life of the solder joint in terms of cycles to failure. The smaller plastic strain can be achieved through a better combination of material properties and geometry parameters, which is helpful of packaging design before to manufacturing.
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Abrokwah, Emmanuel. "Microstructural studies on failure mechanisms in thermo-mechanical fatigue of repaired DS R80 and IN738 Superalloys." 2012. http://hdl.handle.net/1993/5195.
Full textAbstract:
Directionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.
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Durocher, Jonathan. "Thermo-mechanical fatigue of polycrystalline, directionally solidified and single crystal nickel base superalloys repaired by laser beam welding." 2013. http://hdl.handle.net/1993/18486.
Full textAbstract:
The low cycle thermo-mechanical fatigue of laser beam welded conventionally cast Inconel 738, directionally solidified René 80 and single crystal René N5 has been evaluated. Results have been compared to gas tungsten arc and baseline alloy conditions. Metallographic examination of laser beam welds and the associated heat affected zone were conducted by scanning electron microscopy and energy dispersive spectroscopy. The impact of laser beam welding on thermo-mechanical fatigue properties of Inconel 738, René 80 and René N5 has been evaluated and recommendations for improvements and areas of further research have been presented.
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Chiu, Yung-Tang, and 邱泳棠. "Creep and Thermo-Mechanical Fatigue Properties of Ferritic Stainless Steels for Use in Solid Oxide Fuel Cell Interconnect." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/62931511095112857876.
Full textAbstract:
博士國立中央大學
機械工程研究所
100
Creep and thermo-mechanical fatigue (TMF) properties of newly developed ferritic stainless steels (Crofer 22 APU and Crofer 22 H) are investigated at 25oC-800oC for use in planar solid oxide fuel cell (pSOFC) interconnect. Tensile properties of both Crofer 22 APU and Crofer 22 H steels are evaluated at temperatures of 25oC to 800oC. Creep properties of the given steels are evaluated by constant-load tests at 650oC to 800oC. Several creep lifetime models are applied to correlate the creep rupture time with applied stress or minimum creep rate. Comprehensive comparisons between Crofer 22 APU and Crofer 22 H steels are made on the tensile strength and creep resistance so as to characterize the influence of additions of refractory elements (Nb and W). Out-of-phase TMF tests as well as TMF-creep interaction tests under various combinations of cyclic mechanical and thermal loadings are conducted at a temperature range of 25oC-800oC for Crofer 22 H to study its long-term durability for applications in pSOFCs. Experimental results show the variation of yield strength with temperature in Crofer 22 APU can be described by a sigmoidal curve for different deformation mechanisms. According to the creep stress exponent, activation energy, and microstructural observations, a diffusion-controlled dislocation creep mechanism is involved in the creep behavior of Crofer 22 APU steels at 650oC-800oC, while a power-law dislocation creep mechanism interacting with an in-situ precipitation strengthening mechanism is involved in the creep behavior of Crofer 22 H steels at 650oC-800oC. A significantly improved tensile and creep strength of Crofer 22 H over Crofer 22 APU for pSOFC interconnect is observed and attributed to a precipitation strengthening effect of the Laves phase. A significant coarsening of the Laves phase is responsible for a reduced improvement of creep resistance in Crofer 22 H at the low-stress, long-term region of 800oC. In addition, creep rupture time of the Crofer 22 APU and Crofer 22 H steels can be described by a Monkman-Grant relation. The relation between creep rupture time and normalized stress for both steels is well fitted by a universal simple power law for all of the given testing temperatures. Larson-Miller relationship is also applied and shows good results in correlating the creep rupture time with applied stress and temperature for both steels. Fractographic and microstructural observations indicate a ductile, dimpled fracture pattern with considerable necking is identified for the Crofer 22 APU and Crofer 22 H specimens after creep test. Experimental results of Crofer 22 H steels under TMF loadings show the number of cycles to failure for non-hold-time TMF loading is decreased with an increase in the minimum stress applied at 800oC. There is very little effect of maximum stress applied at 25oC on the number of cycles to failure. The non-hold-time TMF life is dominated by a fatigue mechanism involving cyclic high-temperature softening plastic deformation. A hold-time of 100 h for the minimum stress applied at 800oC causes a significant drop of number of cycles to failure due to a synergistic action of fatigue and creep. Creep and creep-fatigue interaction mechanisms are the two primary contributors to the hold-time TMF damage. The creep damage ratio in the hold-time TMF damage is increased with a decrease in applied stress at 800oC and an increase in number of cycles to failure.
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Li, Zhi-Hao, and 李志豪. "Cyclic Thermo-mechanical Behavior of Sn/Ag/Cu Solder Alloys and Evaluation of Fatigue Initiation Life Using The Endochronic Viscoplasticity with Damage." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/42893962526238908408.
Full textAbstract:
碩士國立成功大學
工程科學系碩博士班
95
In this paper, the kernel function and the strain rate sensitive function in the Endochronic viscoplasticity were established by using Sn/3.9Ag/0.6Cu experimental cyclically steady hysteresis loops of Wei et. al., in the temperature range (298K to 373K) and strain rateThen, the mechanical behavior of solder under thermal cycle(298K to 373K) and strain rate was computed. The results and the experimental data were in very good agreement under In-phase condition, and had almost the same trend with that of the Damage-Coupled Constitutive Model of Wei et. al. under Out-phase condition. To define the cyclic damage factor, the reducing rate of maximum cyclic stress was used. The critical cyclic damage could be found by combining experimental vs. data and the Percolation theory. The Endochronic viscoplasticity with damage was used to simulate Sn/3.8Ag/0.7Cu cyclic stress-strain hysteresis loops with damage under strain amplitude 0.8% provided by Zeng et. al. in temperature 298K. The results were in very good agreement with data. Employed the evolution equation of intrinsic damage proposed by Lee and Chen and the computed cyclic stress-inelastic strain relation, modified Coffin-Manson relationship was derived and used to predict the data of fatigue initiation life very effectively.
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"Effects of Foreign Object Damage on Fatigue Behavior of Two Metallic Materials used in a Concentrating Solar Power Plant." Master's thesis, 2016. http://hdl.handle.net/2286/R.I.40776.
Full textAbstract:
abstract: Structural stability and performance of structural materials is important for energy production, whether renewable or non renewable, to have uninterrupted energy supply, that is economically feasible and safe. High temperature metallic materials used in the turbines of AORA, an Israel-based clean energy producer, often experience high temperature, high stress and foreign object damage (FOD). In this study, efforts were made to study the effects of FOD on the fatigue life of these materials and to understand their failure mechanisms. The foreign objects/debris recovered by AORA were characterized using Powder X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) to identify composition and phases. To perform foreign object damage experiment a gas gun was built and results of XRD and EDS were used to select particles to mimic FOD in lab experiments for two materials of interest to AORA: Hastelloy X and SS 347. Electron Backscattering Diffraction, hardness and tensile tests were also performed to characterize microstructure and mechanical properties. Fatigue tests using at high temperature were performed on dog bone samples with and without FOD and the fracture surfaces and well as the regions affected by FOD were analyzed using Scanning Electron Microscopy (SEM) to understand the failure mechanism. The findings of these study indicate that FOD is causing multiple secondary cracks at and around the impact sites, which can potentially grow to coalesce and remove pieces of material, and the multisite damage could also lead to lower fatigue lives, despite the fact that the FOD site was not always the most favorable for initiation of the fatal fatigue crack. It was also seen by the effect of FOD on fatigue life that SS 347 is more susceptible to FOD than Hastelloy X.Dissertation/Thesis
Masters Thesis Materials Science and Engineering 2016