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St, Clair Gibson Alan. "Fatigue, aging and the neuromuscular system". Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/3205.
Pełny tekst źródłaThe aim of this thesis was to investigate the relationship between chronic exercise activity, aging, the neuromuscular system and the symptom of fatigue in a series of studies. The hypothesis of the thesis was that in contrast to the accepted dogma that exercise is beneficial to an individual, increasing longevity and improving quality of life, excessive or chronic exercise activity may accelerate the aging process, lead to neuromuscular damage, and cause the development of pathological symptoms or levels of fatigue.
Narynbek, Ulu Kubat. "Fatigue of HNBR - Effects of formulation and thermal aging". Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0006/document.
Pełny tekst źródłaThe present PhD thesis is devoted to investigation of fatigue in elastomers, andmore particularly of carbon black-filled hydrogenated nitrile butadiene rubber (HNBR).HNBR is a high performance elastomer classically used for high temperature industrial applications, where high resistance to industrial solvents is also required.The thesis is divided into three main parts.First, major improvements of testing procedures utilized in fatigue life testing ofelastomers are proposed. An original method to prescribe the true stress throughout fatigue experiments is developed; it permits to plot the first “true” Wöhler curve, i.e. true stress vs.number of cycles, for elastomers. Then,statistical tools, widely applied in medical research, are adopted for a comprehensive probabilistic analysis of fatigue life results that exhibit high scatter and censored lifetimes.Second, these novel tools are used to investigate the effect of chemical formulation -acrylonitrile content, percent hydrogenation,and of a composite blend - on fatigue resistance of HNBR at the service temperature of 120 oC. In addition to these fatigue life tests,fatigue crack propagation experiments and microscopic fatigue damage analysis are carried out. Third, the influence of thermal aging on fatigue performances of HNBR is investigated.To this end, two additional fatigue life tests are carried out: simultaneous aging and fatigue experiments, and fatigue experiments on preaged samples.Additionally, strain-induced crystallization in HNBR is studied; for the first time, quantitative relationships between crystallization, strain,and stress are established for unfilled HNBR blends
Che, Yunxiang, i S3145469@student rmit edu au. "Aging structure life prediction and reliability assessment". RMIT University. SAMME, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20091113.114541.
Pełny tekst źródłaVarli, Aziz Egemen. "Fatigue Crack Growth Behaviour Of Aa6013 Aluminum Alloy At Different Aging Conditions". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607440/index.pdf.
Pełny tekst źródłaC for 90 minutes, water quenched and aged in room temperature for 96 hours, and one group of samples were overaged at 245 º
C for 12 hours after T42 condition was achieved. Hardness and conductivity measurements were achieved for all conditions after the heat treatments. Fatigue crack growth tests were performed at as received condition T651, T42 and 245 º
C aged samples in laboratory air with sinusoidal loading of stress ratio R=0.1 and at a frequency of 1 Hz. The highest fatigue crack growth resistance is observed for T651 T-L and 245 º
C overaged L-T condition.
Avin, Keith Gerard. "Moderators of fatigue: the complexity of interactions". Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/2815.
Pełny tekst źródłaAli, Mahdi. "Study of the bitumen aging effects on the rheological properties and fatigue behavior". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16255/.
Pełny tekst źródłaYassierli, Yassierli. "Muscle Fatigue during Isometric and Dynamic Efforts in Shoulder Abduction and Torso Extension: Age Effects and Alternative Electromyographic Measures". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29509.
Pełny tekst źródłaPh. D.
Cavuoto, Lora Anne. "Evaluating obesity-related differences in upper extremity and trunk muscular capacity". Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/28345.
Pełny tekst źródłaPh. D.
Colas, Damien. "Approche multi-échelle du vieillissement et du comportement cyclique dans le tantale". Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2013. http://pastel.archives-ouvertes.fr/pastel-00957882.
Pełny tekst źródłaBisson, Etienne. "Influence of Neuromuscular Fatigue of the Lower Limb on Postural Control and Associated Central Processes in Young and Older Adults". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23612.
Pełny tekst źródłaSmet, 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.
Pełny tekst źródłaThis 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
Rahbar-Rastegar, Reyhaneh. "Cracking in Asphalt Pavements| Impact of Component Properties and Aging on Fatigue and Thermal Cracking". Thesis, University of New Hampshire, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10622119.
Pełny tekst źródłaCracking in asphalt pavements is one of the most common and critical pavement distresses. Cracks let the water penetrate from the surface to underlying layers resulting in shorter pavement service life and poor riding quality. There are various factors that affect the cracking potential of asphalt mixtures including the properties of asphalt components, mix design factors, loading time and loading mode, temperature, stress state, and aging. While several researchers have conducted studies investigating the cracking of asphalt mixtures, the effective parameters are not all well understood to allow engineers to design and construct more resistant pavements against cracking.
The work presented in this dissertation provides some additional insights into the effects of component properties and aging condition on asphalt cracking. The cracking susceptibility of hot mix asphalt (HMA) is evaluated through the experimental testing and numerical modeling on mixtures produced either in design (laboratory) or production (plant) stage. Various criteria and approaches for the prediction of cracking in asphalt binder and asphalt mixture are assessed and their correlation are discussed. Different levels of aging in laboratory are simulated, and the effects of long term oven aging (LTOA) on linear viscoelastic parameters, fatigue and fracture characteristics of asphalt mixtures are explored. The uniaxial tensile fatigue testing based on simplified viscoelastic continuum damage (SVECD) approach is conducted to characterize fatigue behavior, and semi circular bending (SCB), disc-shaped compact tension (DCT) testing and cohesive zone model are used to evaluate thermal cracking in asphalt mixtures.
This dissertation makes a good contribution in improvement of available approaches for evaluation of cracking potential of asphalt pavements and allows for assessment of different mixtures at early stage of material selection. The results of this study can lead to develop a new parameter to predict fatigue and thermal cracking susceptibility of flexible pavements in performance-based specifications, resulting in a better ride quality and cost saving for contractors and taxpayers.
Bryanton, Megan. "The Influence of Muscular Fatigue on Human Multi-Joint Movement: Determinants of Sit-to-Stand Capacity with Aging". Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35369.
Pełny tekst źródłaRobert, Mylène. "Impact of degradation and aging on properties of PFSA membranes for fuel cells". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0004.
Pełny tekst źródłaAlthough proton-exchange membrane fuel cells (PEMFC) are nowadays considered as a safe and clean energy technology, they still suffer from durability and reliability issues restricting their widespread commercialization. Innumerable studies have already led to a better understanding of aging phenomena and highlighted membrane degradation as one of the main factors limiting PEMFC lifetime. This study aims at bringing some clarifications on the chemical and mechanical degradation mechanisms of membranes through ex-situ aging protocols as well as understanding the impact of these degradations on the membrane structure and functional properties. First, it was necessary to clarify the influence of Fenton’s reaction, an ex-situ aging protocol widely recognized in the literature, on the chemical degradation of Nafion™ membranes. The results confirmed that Fenton’s reagents concentration significantly influenced polymer chemical decomposition, both from a chemical and morphological point of view. Subsequently, we chose to monitor the evolution of pure chemical degradation of Nafion™ membranes as a function of time and to study its impact on the membrane structure, water sorption and diffusion properties, as well as operability in fuel cells. In that respect, various characterization techniques such as 19F or 1H-NMR as well as FTIR spectroscopies allowed us to correlate physico-chemical properties of the membrane to its structural characteristics and to thus highlight several indicators of chemical degradation. Finally, a custom-made device has been developed to study the impact of conjoint mechanical and chemical stress on Nafion™ membranes. The objective of this device was to replicate aging conditions close to those encountered during fuel cell operation
Abdessalem, Abir. "Etude et modélisation de l'endommagement mécanique des matériaux composites sous l'effet de l'humidité : Couplage hydrolyse et endommagement". Thesis, Paris, ENSAM, 2019. http://www.theses.fr/2019ENAM0042.
Pełny tekst źródłaThe present study deals with the wet durability and fatigue damage of organic matrix composite (OMC) materials. The diffusion of water in a SMC material (polyester matrix reinforced with glass fibers and particles of chalks) is first analyzed experimentally. Then it is modeled numerically under different conditions of hygrothermal aging in immersion. The physical mechanisms causing the hygrothermal damage are then identified. Decreases of different mechanical properties as a function of time and of the absorbed water content are highlighted with the identified damage phenomena. The effect of hygrothermal damage on fatigue life is then studied experimentally. A predictive model that takes into account the effects of waterborne and mechanical damage is then proposed. A coupled diffusion / mechanical calculation makes it possible to determine the overall behavior of the material. It is shown that it is possible to simulate and to follow continuously the evolution of the fatigue life of the aged material whatever the time and temperature
Walubita, Lubinda F. "Comparison of fatigue analysis approaches for predicting fatigue lives of hot-mix asphalt concrete (HMAC) mixtures". Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/3898.
Pełny tekst źródłaDavidson, Bradley. "Experimental and simulation-based assessment of the human postural response to sagittal plane perturbations with localized muscle fatigue and aging". Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29361.
Pełny tekst źródłaPh. D.
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.
Pełny tekst źródłaChoubey, Anupam. "Microstructural changes under isothermal aging and their influence on thermal fatigue reliability for tin-lead and lead-free solder joints, including microstructural changes under isothermal aging in mixed solder joints". College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7712.
Pełny tekst źródłaThesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
Crozatier, Mathilde. "Étude de la durabilité d'un matériau composite bobiné sous chargements sévères". Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0008/document.
Pełny tekst źródłaComposites materials have been studied for decades. Indeed, the association between lightness and resistance of these structures leads to the development of their use. Their characterization remains an essential point in most researches.This work is part of Sollicitern project, which aims to design a composite water treatment truck, financed by a single interministerial fund. The aim is to study the durability of the composite material retained under severe loads. It thus offers tools to industrialists for adjusting parameters in the tank optimization and the estimation of the lifetime under these various loadings.In the first stage, attention is focused on the integration of the curvature of the structure and therefore of the material in the study. Indeed, it is manufactured by filament winding, which necessarily generates a tubular structure. In a second step, a static characterization is carried out. This part includes, in particular, radial compression tests on the whole tubular structure where an experimental protocol is developed. By coupling the results of these tests with a numerical simulation reproducing the test, the elastic properties of the unidirectional ply are obtained by optimization. In a third and final stage, more specific durability is discussed. Fatigue, impact, wear and aging tests are first carried out independently of one another. The final objective is to associate these different loadings and thus to apprehend their combined effect
Mansour, Mustafa. "Effects of Mix, Aging, and Production Types on the I-FIT and IDEAL-CT Cracking Indices". University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1597147736637553.
Pełny tekst źródłaEmerson, Nadia. "The Effects of 6-weeks of Resistance Training on the Neuromuscular Fatigue Threshold in Older Adults". Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5631.
Pełny tekst źródłaM.S.
Masters
Child, Family, and Community Sciences
Education and Human Performance
Sport and Exercise Science; Applied Exercise Physiology
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.
Pełny tekst źródłaUnder 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
Ng, Andressa Ka Yan. "Evaluation of the fatigue damage behavior of fine aggregate matrices prepared with modified asphalt binders". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18143/tde-03012018-122026/.
Pełny tekst źródłaO processo de trincamento por fadiga ocorre devido ao carregamento dinâmico repetido do tráfego de veículos pesados. Este fenômeno tem o início por meio de microtrincas e se propaga por meio de duas condições: (i) após a ruptura adesiva, quando a trinca ocorre na interface entre agregado e mástique, e/ou (ii) após a ruptura coesiva, quando o processo de trincamento ocorre no mástique. Com base nesta interpretação para o trincamento por fadiga em mistura asfáltica, pesquisadores vêm usando matrizes de agregado fino (MAFs) para estimar o comportamento da mistura asfáltica completa quanto ao dano por fadiga. Boa correlação é observada entre as propriedades da MAF e da mistura asfáltica completa (MAC) em estudos relacionados ao dano por umidade, fadiga e deformação permanente. Com relação a resistência de pavimentos flexíveis, é importante avaliar o efeito do uso de ligantes asfálticos modificados e do envelhecimento do ligante nas propriedades da mistura asfáltica, uma vez que ligantes modificados podem melhorar o comportamento da mistura asfáltica quanto ao dano por fadiga, e o envelhecimento do ligante asfáltico pode enrijecer o material tornando-o mais frágil, reduzindo a vida de fadiga das misturas asfálticas. Levando em consideração as evidências apresentadas, este estudo tem por objetivo avaliar o efeito de ligantes asfálticos modificados e o nível de envelhecimento na vida de fadiga das MAFs, mástiques e ligantes asfálticos. Estas três escalas da mistura asfáltica completa foram compostas por quatro ligantes asfálticos (CAP 50/70, CAP+PPA, CAP+SBS e CAP+borracha) envelhecidos a curto e a longo prazo. As propriedades das três escalas quanto ao dano por fadiga foram avaliadas por meio dos conceitos da teoria do dano contínuo em meio viscoelástico (VECD), uma vez que esta teoria é capaz de prever o comportamento da mistura asfáltica independentemente do modo de carregamento (uniaxial ou torsional, tensão ou deformação controlada) e da amplitude do carregamento aplicado ao material para induzir o dano. De modo geral, os resultados indicaram que o uso de ligantes asfálticos modificados melhoram o comportamento das MAFs quanto ao dano por fadiga e o envelhecimento é capaz de comprometer o desempenho das MAFs quanto ao trincamento por fadiga. Na escala do ligante e do mástique asfáltico, o CAP+borracha apresentou o melhor desempenho à fadiga, ocupando o primeiro lugar no ordenamento final, e o CAP+SBS o pior desempenho, ocupando a última posição. Entretanto, na escala da MAF, as MAFs preparadas com CAP+SBS apresentaram o melhor desempenho à fadiga, ocupando o primeiro lugar no ordenamento final, e as MAFs preparadas com CAP 50/70 apresentaram o pior desempenho, ocupando o último lugar no ordenamento final. A melhor correlação entre as três escalas com relação ao envelhecimento a curto e a longo prazo, foi obtido entre os ligantes asfálticos e mástiques envelhecidos no PAV com as MAFs envelhecidas a longo prazo por 30 dias.
Babadopulos, Lucas Feitosa de Albuquerque Lima. "A Contribution to couple aging to hot mix asphalt (HMA) mechanical characterization under load-induced damage". reponame:Repositório Institucional da UFC, 2014. http://www.repositorio.ufc.br/handle/riufc/11164.
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Although aging simulation in binder is performed through RTFO and PAV tests, n o considerations of asphalt mixture aging are made in regular laboratory characterization. T he present work is focused in incorporating aging to the modeling of the mechanical behavior of hot mix asphalt (HMA) during load - induced damage. This is accomplished by combining existing models and the adaptation of mixture aging procedures . The aging model used is based on the evolution of an internal state v ariable, associated to oxygen availability, aging temperature a nd four material parameters. The se parameters are related to aging susceptibility , reaction kinetics and dependency on aging history and on aging temperature. The model allows to establish relation ship s between different aging processes. Results at four aging states (using two different temperatures) we re analyzed and the aging model parameters w ere estimated. Capturing aging dependency on temperature constitutes a contribution of the presen t work with respect to previous results reported in the literature . T he aging model is coupled to viscoplasticity and damage, comparing the behavior observed at the different aging states. Concerning the damage models, t his thesis used mechanical models de rived from Schapery's work potential theory to model fatigue behavior . T he Simplified Viscoelastic Continuum Damage (S - VECD) model was selected . U nconfined dynamic creep tests were used to evaluate the effect of aging in the mixture resistance to permanent deformation. In addition to the state - of - the - art modeling of HMA, the characterization methods currently in use in Brazil (tensile strength, resilient modulus and controlled force indirect tensile fatigue tests) were also conducted . T he possibility to sim ulate the material behavior for various loading conditions constitutes a n advantage of the state - of - the - art model over the state - of - the practice method for fatigue characterization, used primarily to rank mixtures. It was concluded that, depending on pavem ent conditions and layer geometry, aging not necessarily affects negatively the fatigue behavior, while certainly improving the permanent deformation characteristics. That happens de s pite the fact that aging produces less damage tolerant materials, i.e., m aterials that fail for less evolved damage states. T he framework ( testing and analysis) for damage characterization of asphalt mixtures was implemented and it is expected to contribute to further developments in aging modeling of asphalt mixtures
Apesar de simulação de envelhecimento ser realizada em ligantes asfálticos através dos ensaios de RTFOT e PAV, nenhuma consideração sobre envelhecimento de misturas é feita na caracterização laboratorial comum. O presente trabalho se concentra na incorporação do envelhecimento na modelagem do comportamento mecânico de concretos asfálticos (CA) para carregamentos que induzem dano. Isto é feito através da combinação de modelos e da adaptação de procedimentos de envelhecimento existentes. O modelo de envelhecimento utilizado se baseia na evolução de uma variável interna de estado e é associado à disponibilidade de oxigênio, à temperatura e a quatro parâmetros materiais. Estes parâmetros são relacionados à susceptibilidade ao envelhecimento, à cinética de reação e à dependência sobre o histórico e sobre a temperatura de envelhecimento. O modelo permite estabelecer relações entre diferentes processos de envelhecimento. Resultados em quatro estados de envelhecimento (em duas temperaturas diferentes) foram analisados, e os parâmetros do modelo estimados. Capturar a dependência do processo quanto à temperatura constitui uma contribuição do trabalho quanto a resultados da literatura. O modelo de envelhecimento é acoplado à resposta viscoplástica e ao dano, comparando-se o comportamento nos diferentes estados. Quanto aos modelos de dano, esta dissertação trata dos derivados da teoria do potencial de trabalho de Schapery para análise da fadiga. O modelo simplificado de dano contínuo em meio viscoelástico (S-VECD) foi selecionado. Ensaios de Creep Dinâmico não confinado foram utilizados para avaliar o efeito do envelhecimento na resistência à deformação permanente. Além da modelagem mecânica do comportamento do CA usando modelos do Estado da Arte, também foram executados métodos de caracterização em uso no Brasil (resistência à tração, módulo de resiliência e ensaios de fadiga por compressão diametral). A possibilidade de se simular a resposta do material em várias condições de carga constitui uma vantagem do método do Estado da Arte sobre o do Estado da Prática, usado principalmente para comparar misturas. Concluiu-se que, dependendo das condições do pavimento e da geometria das camadas, o envelhecimento não necessariamente diminui a resistência à fadiga, embora certamente melhore a resistência à deformação permanente. Isso acontece apesar de o envelhecimento produzir materiais menos tolerantes ao dano, i.e., materiais que rompem para estados de dano menos evoluídos. O procedimento para a caracterização do dano em misturas asfálticas foi implementado e espera-se ter contribuído para um maior desenvolvimento da modelagem de misturas quanto ao envelhecimento.
Libura, Tomasz. "Étude de la tenue à l’impact après vieillissement en fatigue, des composites stratifiés à base d’acrylique". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0259.
Pełny tekst źródłaImpact resistance is one of the most critical features of the composite structures, and therefore, its examination for a new material has a fundamental importance. This thesis is devoted to the characterization of the fully recyclable thermoplastic ELIUM Acrylic resin reinforced by glass fabric woven that belongs to a new category of materials requiring advanced testing before their application in responsible elements of engineering structures. Its high strength, low weight as well as low production cost give an excellent opportunities to its wide application in the automotive industry as a replacement of the thermoset-based laminates. The study presents an experimental work concerning the effect of damage due to low and high cyclic fatigue aging of two groups of specimens with two different woven fabric orientations in relation to the acting load: [0°/90°]4 and [45°/45°]4, on their low and high impact velocity properties. Subsequently, a comparison of the experimental data with the results of numerical simulations predicted by the macroscopic model proposed for the non-aged GFRE [0°/90°]4 specimens of 1.8 mm thickness are shown. A response of the materials on fatigue loading was evaluated in terms of the stiffness variation analysis. The fatigue aging program was interrupted at a given value of the stiffness drop, prior to the specimen failure. The initial stiffness was reduced by about 17 % for the GFRE [0°/90°]4, after either LCF or HCF tests. Such reduction was much more pronounced in the case of GFRE [45°/45°]4. It was equal to 48 %. The low velocity impact resistance was measured in terms of load peak, absorbed energy and penetration threshold, while the high velocity impact resistance using the ballistic limit and total energy dissipation. The non-aged specimens impacted at energy of 5 J, 10 J and 30 J were not perforated and showed a great ability to rebound the impactor. The composites subjected to low cyclic fatigue (LCF) demonstrated the greatest decrease of the initial slope of the force-displacement characteristics. It results from the significant reduction of stiffness caused by the matrix cracking and interface debonding taking place between the fibers and matrix. The maximum force reduction for tests carried out at the impact energy of 50 J for GFRE [0°/90°]4 and GFRE [45°/45°]4 was equal to 11% and 19%, respectively. Analysis of the absorbed energy during impact tests confirmed, that the aged materials containing the woven fabric oriented at the angle of 45° exhibited the weakest impact resistance. Similarly to the tests at low velocity impact, the analysis of the energy dissipation and evolution of the impact force during perforation tests confirmed, that GFRE [0°/90°]4 plates subjected to uniaxial fatigue loading had better ballistic performance and higher energy dissipation than GFRE [45°/45°]4 targets. It was also observed that specimens of GFRE [45°/45°]4 aged by cyclic loading at the stress either below or above the yield point had 20 m/s lower ballistic limits compared to those of GFRE [0°/90°]4. Therefore, one can conclude that the fibers orientation, fatigue aging, and glass fibers concentration significantly affect the elastic properties, and as a consequence, lead to the stiffness reduction and decrease of the energy absorbed and ballistic limit. The results are in agreement with the analyzes of damage phenomena. The numerical predictions of the ballistic limits, residual velocities as well as the analysis of energy absorption performed using the finite element software ABAQUS/Explicit exhibited a good agreement with the experimental data and confirmed the relevance of the approach proposed
Kirka, Michael. "Thermomechanical behavior of a directionally solidified nickel-base superalloys in the aged state". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53458.
Pełny tekst źródłaRednour, Allison. "A Nutritional Shopping System for Senior Citizens". University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1491227694091354.
Pełny tekst źródłaHuang, Zhiyong. "Endommagement des aciers au C-Mn en fatigue oligocyclique et gigacyclique". Thesis, Paris 10, 2010. http://www.theses.fr/2010PA100088.
Pełny tekst źródłaIn steam generators of nuclear power plants, typical pipes components are subjected to thermal and mechanical loading which are variable and divided into two different regimes: low cycle fatigue and gigacycle fatigue. Carbon-manganese steels A42, A48 and Tu48 steels (French standards) are often used in such applications. The material properties manifest some special characters in mechanics and metallurgy such as Dynamic Strain Aging, increasing UTS values in 200℃ temperature domain. The LCF and VHCF behaviors are investigated respectively by test method at room temperature and 200℃. The cumulative fatigue tests are implemented through referencing the load as prior LCF following gigacycle fatigue from the steam generator pipes thermal loads in order to obtain the performance of material under accumulated fatigue damage. All the test results are analyzed by using plastic mechanics, continuums damage mechanics and microscopic analysis. Hysteresis loops are due to plastic deformation in LCF which is the effect of kinematic hardening and they can be described by Armstrong – Frederick form models; the isotropy hardening is used to predict the evolution of stress amplitude in LCF. But with rising of accumulated plastic deformation, the damage can not be neglected. The Chaboche fatigue damage model is applied to describe the damage evolution of LCF and extended to VHCF regime. The cumulative fatigue damage model is extended from Chaboche model and applies to the estimation cumulative fatigue damage. The constitutive relationship and isotropy rule are coupled with fatigue damage model that can describe the whole fatigue behavior. In 200℃ for LCF, A48 is sensitive to dynamic strain aging and its secondary hardening behavior is important which can be predicted by dislocation theory and is simulated in the paper. The fractographic analysis is performed by SEM for LCF, VHCF and cumulative fatigue tests. The LCF crack is initiated in surface. Some of cracks of VHCF are given birth from the inclusions located at interior of sample
Hoche, François-Xavier. "Vers une prise en compte du vieillissement thermique dans la filière de dimensionnement des structures pour la fatigue thermomécanique". Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM051.
Pełny tekst źródłaCylinder heads of automotive engines are produced by casting of precipitation strengthened Al-Si alloys.The cylinder head quickly reaches a steady state temperature but the succession of starts and stops generates thermomechanical fatigue in the area between the valve seats. At service temperature, the precipitation microstructures evolve from their state after precipitation hardening heat treatment to an aged state, which results in the reduction of their mechanical properties. The increase of thermomechanical stresses in new engines requires taking thermal aging into account for sizing. To that end, the precipitation microstructures (precipitates crystal structures, composition, morphology, and distribution) have been analyzed by Transmission Electron Microscopy (TEM) for various aging conditions and the corresponding cyclic least-viscoplastic behavior has been determined. The effect of plastic deformation on the kinetics of precipitate growth has been studied throughout loadings representative of engine operation. The morphological characteristics of the precipitation microstructure resulting from the thermomechanical aging were determined by TEM for different numbers of cycles and compared with those resulting from the mere thermal aging in order to assess the effect of plastic deformation on the kinetics of precipitate growth. As micro hardness is a good indicator of the aging of precipitation strengthened aluminium alloys, micro hardness evolution models have been developed to calculate its decrease in the cylinder head during a test simulating in service conditions. The simulations give us a better understanding of the in-service aging of these alloys
Shabani, Amin. "Thermal and radiochemical of neat and ATH filled EPDM : establishment of structure/properties relationships". Phd thesis, Paris, ENSAM, 2013. http://pastel.archives-ouvertes.fr/pastel-00941289.
Pełny tekst źródłaPu, Xiaoxue. "Thermomechanical study of the gigacycle fatigue behavior of pure iron and carbon-manganese steels : influence of chemical composition and microstructure on damage and crack initiation mechanism". Thesis, Paris 10, 2019. http://www.theses.fr/2019PA100051.
Pełny tekst źródłaThis work attempts to a better understanding of the fatigue damage in ferrite-pearlite steels in the Very High Cycle Fatigue (VHCF) domain. The influences of two parameters, pearlite phase percentage and free interstitial atoms percentage in solid solution, are investigated to understand dissipative mechanisms under 20 kHz high frequency fatigue loading. In-situ infrared thermography is carried out to record the temperature changes, while fractography studies and microscope observations are conducted to investigate the dissipative mechanism on the surface of specimens.For body centered cubic (BCC) materials, under high stress amplitudes, a sudden increase of the temperature occurs without a crack initiation and fracture. The inevitable temperature increase up to hundreds of degrees at high stress amplitudes, is caused mainly by the screw dislocations mobility, which is the key to explaining the observed fatigue behavior and thermal response of BCC structure under high frequency loading. Therefore, PSBs on surface and micro-voids in matrix emerge massively, accompanying with this abrupt temperature increase. These phenomena are considered as transition of deformation mechanism from thermal regime to athermal regime. At low amplitudes, few PSBs or surface roughness are still observed on the specimen surface. Through the cycles of PSB appearance on armco-iron, it’s found that PSBs are inclined to appear before 1x10(7)cycles, and PSB threshold lies below the conventional fatigue limit. The increase of pearlite phase content weakens the temperature elevation, and strengthens the fatigue properties. The presence of free interstitial atoms in steels results in appearence of a secondary temperature increase in the stabilized temperature part (100-200 degree). This behavior seems to be related to the interaction of edge dislocations with free interstitial atoms. Moreover, the remarkable hardening-softening-hardening phenomenon after the sudden temperature elevation to above 300 degree is thought as the interaction of multiplicated screw dislocations and free interstitial atoms
Tout, Firas. "Étude expérimentale des éléments structuraux multi-matériaux collés sollicités en flexion : effet du fluage, fatigue et durabilité". Phd thesis, Université Claude Bernard - Lyon I, 2014. http://tel.archives-ouvertes.fr/tel-01064338.
Pełny tekst źródłaDeshayes, Maxime. "Influence des stéréotypes sexués et des stéréotypes liés à l’âge sur la performance d’endurance non-technique : un effet positif de l’induction d’un stéréotype négatif ?" Thesis, Université Côte d'Azur (ComUE), 2019. http://www.theses.fr/2019AZUR4108.
Pełny tekst źródłaThe stereotype threat theory (Steele, 1997) suggests that when a negative stereotype toward one group is induced, in a context where this stereotype is susceptible to be applied, a decrease in performance would be observed. After being replicated in various domains, this negative effect on performance was generalized to the physical domain. Most studies investigated this effect during technical tasks such as soccer-dribbling tasks (for a meta-analysis, see Gentile, Boca, & Giammusso, 2018). Although technical abilities are major factors in physical performance, other factors also regulate physical performance such as physical abilities with, for example, endurance (Weineck, 1983). The objective of this thesis was to examine the influence of inducing sex stereotypes and aging stereotypes on women’s and older adults’ non-technical endurance performance. The integrated process model (Schmader, Johns, & Forbes, 2008), widely used in the literature, explains performance modifications after a negative stereotype was induced during technical tasks. However, this model makes no assumptions about its effect during non-technical tasks. The mere effort account (Jamieson & Harkins, 2007), recently validated in the physical domain, could be applied during this type of task. This account suggests that inducing a negative stereotype could lead to an increase in threatened participants’ performance during non-technical endurance tasks. In line with these predictions, studies 1, 2, 3 and 4 showed an increase in women’s endurance performance after inducing a negative stereotype toward them during tasks at submaximal and maximal intensities, and on different muscle groups. These studies especially observed that threatened women were more motivated to outperform men (study 4) and they put more effort into the tasks. This performance increase could also be due to a lower central fatigue (study 3) and a greater planning of the central motor command over the prefrontal cortex (study 4). These four studies strengthen the hypothesis that the effects of sex stereotypes would be task-dependent and that the mere effort account appears to be relatively robust to explain the effects of sex stereotypes during non-technical endurance tasks. Interestingly, these positive results were not fully replicated in older adults. Inducing a negative aging stereotype did not influence participants’ maximal performance (studies 5 and 6). An increase in performance was nonetheless observed when the intensity of the task was reduced (study 6). When investigating aging stereotypes, the mere effort account seems to be imperfect and needs to be completed to explain their effects in the physical domain. The results of this thesis enrich the stereotype threat literature by showing that inducing a negative stereotype can, contrary to the predictions of the initial stereotype threat theory (Steele, 1997), lead to an improvement of women’s performances and under certain conditions for older adults
Ruffilli, Roberta. "Modes de fatigue des métallisations à base d'aluminium dans les composants MOSFET de puissance". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30256/document.
Pełny tekst źródłaThis thesis, a collaboration between CEMES-CNRS, Satie laboratory (ENS Cachan) and NXP Semiconductors is motivated by the comprehension of the failure mechanisms of low voltage power MOSFET devices produced for ap- plications in the automotive industry. A limiting factor for the long-term reliability of power modules is the electro- thermal and/or thermo-mechanical aging of the metallic parts of the source: Al metallization and bonding wires. At the temperature reached during the on-off operating cycles (few hundred degrees), the difference in the coefficient of thermal expansion between the metallization and the oxide and semicon- ductor parts induces an inevitable plastic deformation in the metal, which is the softest material in the complex MOSFET architecture. We have characterized the metal microstructure before and after accelerated electro-thermal aging tests, by using specific techniques from the field of the physical metallurgy: electron and ion microscopy, grain orientation and chem- ical composition mapping. For the first time the source metallization has been characterized both away and under the bonding connections, which are one hundred times thicker than the metallization layer. The latter is a critical loca- tion for the reliability assessment because the ultrasonic bonding process may weaken the initial metallization microstructure by adding an important plas- tic deformation prior to aging. This is, however, poorly stated in the literature because of the difficulty to access the metallization under the wires without damaging their bonding, which is known to be particularly weak in case of aged modules. In order to investigate the wire-metallization interface, we have set up origi- nal sample preparations, based on ion polishing, that allowed us to disclose the metallization under the bonding wires without introducing preparation artifacts in the microstructure. The bonding process induces a severe and non- uniform plastic deformation in the metallization under the wires without re- creating a good electrical contact: small cavities and native oxide residues, have been systematically observed at the Al/Al interface, in all the analyzed mod- ules, before and after aging. The main mechanism behind the device failure is the generation and propa- gation of fatigue cracks in the aluminum metallization, associated to a local Al oxidation that prevents these crack from closing. Away and under the wire bonds, they run perpendicularly from the surface down to the silicon substrate following the grain boundaries, due to an enhanced intergranular diffusion of aluminum atoms. In the bonding area, the phenomenon of parallel cracking is favored by the initial imperfections in the wire-metallization bonding. Ion to- mography experiments have shown that these cracks are confined to the wire- metal interface and do not propagate in the wire despite its lower strength (pure Al, larger grain structure). Crack propagation along the Al/Al interface can cause a contact reduction between the wire and the source metallization and eventually its failure. Such discontinuities in the metal can explain the lo- cal increase in the device resistance and temperature that accelerates the aging process until failure. This study settled new, dedicated techniques and quantification methods to as- sess the aging of the metal parts of MOSFET devices. The full characterization of the intrinsically defective interface generated by the bonding process and the metallization degradation during electro-thermal aging indicated paths to possible improvements of current technologies and potential developments of new processes
Pereira, Andressa Busch Rocha. "Efeito do uso do sistema âncora no controle postural após a fadiga dos músculos flexores plantares em idosos". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/17/17152/tde-29032018-104533/.
Pełny tekst źródłaThe fatigue of the planta flexor muscles disturbs postural control. On the other hand, the use of the anchor system reduces postural sway. However, it is unknown whether the use of this tool would compensate for the increase of the body sway caused by muscle fatigue of the plantar flexor muscles. The additional haptic information provided by light touch and taping was able to compensate for the disturbing effect of fatigue in young adults. However, it is unknown how the old adults would respond to this disturbance with the use of additional haptic information. The purpose of this study was to investigate whether the use of the anchor system is able to compensate for the increase of the body sway due to fatigue of the plantar flexor muscles in young and old adults. The groups of participants were tested barefoot and with eyes closed in four conditions in upright posture: with and without the anchor system, before and after the fatigue protocol. The anchor system consists of two flexible cables with a light load (125 g) attached to one end of each cable. Participants should hold one cable in each hand and the keep the cable taut without removing the loads from the ground. The fatigue protocol consisted of performing a single series of bilateral plantar flexion of the ankles repeatedly and continuously and uninterrupted. As expected, the fatigue protocol increased body sway in both groups. Both groups benefited from the use of anchors with reduction of body sway. However, this effect was independent of fatigue. We conclude that the anchor system contributed to the reduction of body sway in young and old adults. However, the anchor system was not able to compensate for the disturbing effect in postural control created by fatigue of the plantar flexor muscles.
Ruffilli, Roberta. "Modes de fatigue des métallisations à base d'aluminium dans les composants MOSFET de puissance". Electronic Thesis or Diss., Toulouse 3, 2017. http://www.theses.fr/2017TOU30256.
Pełny tekst źródłaThis thesis, a collaboration between CEMES-CNRS, Satie laboratory (ENS Cachan) and NXP Semiconductors is motivated by the comprehension of the failure mechanisms of low voltage power MOSFET devices produced for ap- plications in the automotive industry. A limiting factor for the long-term reliability of power modules is the electro- thermal and/or thermo-mechanical aging of the metallic parts of the source: Al metallization and bonding wires. At the temperature reached during the on-off operating cycles (few hundred degrees), the difference in the coefficient of thermal expansion between the metallization and the oxide and semicon- ductor parts induces an inevitable plastic deformation in the metal, which is the softest material in the complex MOSFET architecture. We have characterized the metal microstructure before and after accelerated electro-thermal aging tests, by using specific techniques from the field of the physical metallurgy: electron and ion microscopy, grain orientation and chem- ical composition mapping. For the first time the source metallization has been characterized both away and under the bonding connections, which are one hundred times thicker than the metallization layer. The latter is a critical loca- tion for the reliability assessment because the ultrasonic bonding process may weaken the initial metallization microstructure by adding an important plas- tic deformation prior to aging. This is, however, poorly stated in the literature because of the difficulty to access the metallization under the wires without damaging their bonding, which is known to be particularly weak in case of aged modules. In order to investigate the wire-metallization interface, we have set up origi- nal sample preparations, based on ion polishing, that allowed us to disclose the metallization under the bonding wires without introducing preparation artifacts in the microstructure. The bonding process induces a severe and non- uniform plastic deformation in the metallization under the wires without re- creating a good electrical contact: small cavities and native oxide residues, have been systematically observed at the Al/Al interface, in all the analyzed mod- ules, before and after aging. The main mechanism behind the device failure is the generation and propa- gation of fatigue cracks in the aluminum metallization, associated to a local Al oxidation that prevents these crack from closing. Away and under the wire bonds, they run perpendicularly from the surface down to the silicon substrate following the grain boundaries, due to an enhanced intergranular diffusion of aluminum atoms. In the bonding area, the phenomenon of parallel cracking is favored by the initial imperfections in the wire-metallization bonding. Ion to- mography experiments have shown that these cracks are confined to the wire- metal interface and do not propagate in the wire despite its lower strength (pure Al, larger grain structure). Crack propagation along the Al/Al interface can cause a contact reduction between the wire and the source metallization and eventually its failure. Such discontinuities in the metal can explain the lo- cal increase in the device resistance and temperature that accelerates the aging process until failure. This study settled new, dedicated techniques and quantification methods to as- sess the aging of the metal parts of MOSFET devices. The full characterization of the intrinsically defective interface generated by the bonding process and the metallization degradation during electro-thermal aging indicated paths to possible improvements of current technologies and potential developments of new processes
Klass, Malgorzata. "Contribution à l'étude de l'effet du vieillissement sur la fonction neuromusculaire". Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209224.
Pełny tekst źródłaL’objectif de nos investigations a été d’étudier, chez le sujet humain, les mécanismes responsables de l'altération des performances motrices au cours du vieillissement. La première étude était destinée d’une part, à comparer la diminution maximale de force observée dans les différents régimes de contraction et, d’autre part, à contribuer à la compréhension des mécanismes à l’origine de la meilleure préservation de force pour le régime excentrique. Etant donné que jusqu’à présent, seuls des facteurs musculaires avaient été proposés afin d’expliquer les différences existant en fonction du régime de contraction, nous nous sommes plus particulièrement intéressés à une éventuelle participation de facteurs nerveux.
Dans la seconde étude, nous avons testé de manière indirecte (via l’enregistrement d’activités réflexes) l’efficacité des afférences périphériques au cours du vieillissement. En effet, sous le contrôle de la commande centrale, celles-ci contribuent également à réguler le niveau d’excitabilité des motoneurones. Une moindre efficacité de celles-ci pourrait donc être un facteur supplémentaire responsable de l’altération de la fonction motrice.
Nous avons ensuite analysé (études III et IV) les propriétés contractiles et le comportement des unités motrices lors de contractions lentes et très rapides (contractions balistiques). Cela nous a permis de vérifier s’il existait chez les seniors une relation entre la diminution de force, de sa vitesse d’installation, et la stratégie d’activation des unités motrices.
Enfin, dans l’étude V, nous avons analysé la fatigabilité neuromusculaire chez les seniors, comparativement aux sujets jeunes. Plus spécifiquement, nous avons étudié les contractions concentriques et excentriques maximales fatigantes. La fatigue n’a en effet pas encore été étudiée lors de ces deux types de contraction chez les adultes jeunes et âgés. L’objectif de cette dernière étude était surtout d’analyser la part relative des mécanismes nerveux et musculaires à l’origine de la fatigue ainsi que leur décours dans le temps en fonction de l’âge des sujets.
L’approche méthodologique utilisée nous a permis d’analyser les modifications fonctionnelles du muscle et de ses unités motrices avec l’âge. Un intérêt tout particulier a été porté aux ajustements de la commande nerveuse et à la compréhension des mécanismes sous-jacents. L’ensemble de nos résultats expérimentaux documentent de manière originale l’interaction étroite entre les adaptations nerveuses et musculaires au cours du vieillissement. Plus largement, notre travail doctoral contribue à une meilleure connaissance de la remarquable plasticité du système neuromusculaire chez l’homme.
Résumé en anglais :\
Doctorat en Sciences de la motricité
info:eu-repo/semantics/nonPublished
Solignac, Marie-Paul. "Etude du comportement a la fissuration en fluage et en fatigue d'aciers inoxydables austenitiques z2 cnd 17-12 (316 l) a 550 c". Paris 6, 1986. http://www.theses.fr/1986PA066540.
Pełny tekst źródłaKhoury, Georges. "Investigation de l'évolution de la microstructure et de la plasticité des joints de brasure SAC sous effets du vieillissement thermomécanique". Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0124.
Pełny tekst źródłaNowadays, SAC alloys are widely used as soldering materials. The SAC solder joints have a dynamic microstructure which evolve excessively under different aging conditions. The characteristic of visco-plasticity of the SAC being extremely sensitive to its microstructure complicates the evaluation and the estimation of the life expectancy of the joints.This work is aimed at improving the predictions of SAC solder joints reliability by contributing to expand knowledge on the evolution of the microstructure and the mechanical characteristic of visco-plasticity of SAC. This work consists in studying separately the evolution of microstructure and plasticity under the effect of aging.The study of the microstructure allowed the gain of new knowledge on the coarsening under different aging conditions. This study also allowed the evaluation of the hypothesis of linear damage accumulation on the microstructural analysis basis and on the basis of a thermal cycle with all the different conditions that it presents.The study of plasticity allowed the assessment of the effect of aging by thermal cycling on the mechanical strength of the SAC. This study also allowed the evaluation of the effect of not taking into account the evolution of the mechanical characteristic of plasticity on the estimation of the life expectancy of the solder joints using finite element simulations
Naanani, Soumaya. "Etude du comportement à hautes températures d'un alliage TiAl performant densifié par frittage flash". Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30359.
Pełny tekst źródłaOne of the major challenges of the aircraft industries is to develop more effective and lighter systems. This will fits, among others, in a process of reducing fuel consumption by airplanes. Titane aluminum based alloys present a remarkable creep resistance and a high level of resistance to oxidation and low density. These properties are conductive to industrial manufacturing parts, as low pressure turbine for aircraft engines and turbocharger wheels for automotive engines. IRIS alloy (Ti49.92-Al48-W2-B0.08) has been developed by a CEMES team in 2013 in order to meet these industrial expectations. It is processed by Spark Plasma Sintering, a powder metallurgy technique which allows a fast processing with parts near to the final dimensions and a precise control of the microstructure. First tensile and creep tests on IRIS show interesting results which lead us in this work to explore more mechanical properties at a considerable service temperature of 800°C, which is considered as the ultimate operating temperature of TiAl alloys. For this purpose, we explored a new chapter in IRIS' life: the low cycle fatigue behavior. These studies have been supplemented by tensile and creep tests at the same level of temperature. In order to understand and explain these mechanical behaviors, plasticity studies have been performed on each type of solicitation. Finally, we achieve a final study on aged microstructures, to complete our understanding of the impact of the temperature on the alloy
Nuñez, Javier Yesid Mahecha. "Caracterização à fadiga de ligantes asfálticos modificados envelhecidos a curto e longo prazo". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18143/tde-19112013-171029/.
Pełny tekst źródłaFatigue cracking is a major mechanism of deterioration of flexible pavements, and even then, it is still one of the defects that are more difficult to control. One alternative to improve fatigue characteristics of asphalt mixtures is the use of modified asphalt binders; however, there is no doubt that the stiffening caused by the addition of modifiers can influence the fatigue resistance of asphalt mixture. In order to measure characteristics of asphalt binders that are related to the fatigue cracking of asphalt mixture, some laboratory tests have been recently developed such as the time sweep and the linear amplitude sweep (LAS) test. The objective of this study is to characterize the fatigue behavior of 12 modified asphalt binders with the same high-temperature performance grade (PG 76-xx). The formulations AC+PPA, AC+SBS, AC+SBS+PPA, AC+Rubber, AC+Rubber+PPA, AC+PE, AC+PE+PPA, AC+EVA, AC+EVA+PPA, AC+SBR, AC+SBR+PPA and AC+Elvaloy+PPA were prepared with a 50/70 base asphalt binder graded as PG 64-xx in the Superpave specification. Based on the characterization made in this study, the main conclusions are the following: (a) the material that showed better fatigue life was the AC+EVA; (b) the material that is less sensitive to deformation was the neat AC; (c) the less sensitive one to temperature was the AC+PPA; (d) the effect of PPA in asphalt binders prepared with other additives caused a reduction in the fatigue life for many formulations, an increase in the sensitivity levels of deformation for all formulations, a reduction in the sensitivity to temperature and an increase in the sensitivity to aging for several formulations; (e) on the final ranking of the characteristics of asphalt binders according to the parameters analyzed in this research study, the AC+Rubber showed the best overall performance
Castro, Danilo Borges Villarino de. "Estudo do comportamento em fadiga do aço ASTM A297 Gr HP modificado com nióbio em altas temperaturas". Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-20122012-092456/.
Pełny tekst źródłaThis work aims to study the mechanical behavior at high temperatures of ASTM A-297 Gr HP steel changed with niobium. This type of steel is used for pipe supports that remain exposed long periods of time at operating temperatures near 900°C. In this study, was studied the microstructural composition, the mechanical strength, impact toughness and fatigue resistance, considering the effect of temperature test. To evaluate the effect of temperature and residence time in the microstructure and hence the mechanical properties were performed hardness, tensile and impact test for each of the conditions presented. All conditions of the aged material showed the presence of precipitates in the interdendritic boundaries and secondary precipitates within the austenitic matrix, causing the material to elevate its mechanical strength, compared to CR condition. After this step was studied the mechanical properties at elevated temperatures only for the conditions CR and T1000 (aged at 927°C for 1000 hours). Tensile, impact and fatigue tests (E-N and da/dN-\'delta\'K), were performed at the following temperatures: 25°C, 871ºC, 899ºC, 927ºC, 954ºC and 982°C. To evaluate the impact tests, were used Charpy specimens of the conventional type (presence of the notch) and pre-cracked (pre crack more notch). In all test temperatures of traction, it was observed that the T1000 condition resulted in an increase of the value of mechanical strength and reduction of its ductility, compared to CR conditions. In tests at elevated temperatures, it was observed that the precipitation of carbides in the austenitic matrix of the secondary condition T1000 is able to avoid a sharp decline in mechanical strength compared with the proviso CR. The two conditions (CR and T1000) were sensitive to the presence of a stress raiser (notch further pre-crack) when subjected to impact tests. The results of tensile and impact fractographies corroborate the evidence found for each condition, indicating a greater share of ductile fracture in testing samples at elevated temperatures than at room temperature. Regarding the fatigue behavior of the material, it was found that the fatigue life of the material tested at 25°C was much greater than 927°C, especially in the region of high cycle fatigue. This fact can be attributed to two factors dependent on the time: premature nucleation due to a significant reduction in yield strength and due to the effect of surface oxidation of permanent slip bands. The tests of crack propagation by fatigue showed that the rate da/dN was greater at a temperature of 927°C than at 25°C, because of higher ductility that the material exhibits at high temperatures associated with the effects of oxidation and creep.
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.
Pełny tekst źródłaOlivier, Nelson Cárdenas. "Análise de falha da camada polimérica externa de cabos umbilicais". Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-14012008-111221/.
Pełny tekst źródłaIn the present work is proposed a method to establish a failure criterion of the polymeric external layer of umbilical cables used in offshore operations. The proposed method is based on the determination of the increment of the quantity of absorbed water by the polymeric external layer of the cable due to deterioration caused by cyclic loads and the aging process originated by the marine environment. The method proposes to carry out a uniaxial fatigue test on the polymer that composes the external layer of the cable. This test is made simulating the cyclical deformation that the external layer is submitted in the umbilical during the fatigue test done, according to the API 17E standard, during the process of cable homologation. It is also intended to make an artificial aging test in the polymeric external layer simulating the service conditions of the cable in the marine environment. In order to evaluate of the cyclical loads and the sea set aging influence on the properties of the polymer, carry out water absorption test according to the ASTM D 570 standard, traction test according to the ASTM D 638 standard, hardness test according to the ASTM D 2240 standard and observations in an scanning electron microscopy. Finally starting from the mass increment suffered by the polymer in the water absorption test it was estimated the damage in the external layer material of the cable. The results obtained in this work showed that the cyclical loads and marine environment accelerated the degradation process of polymeric external layer of umbilical cable demonstrating the efficiency of the proposed method.
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.
Pełny tekst źródłaBecause 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
Mrozowski, Nicolas. "Mécanismes de propagation de fissure dans un superalliage base nickel polycristallin en régime d’interaction fatigue-fluage-oxydation-vieillissement métallurgique Aging of γ′ precipitates at 750°C in the nickel-based superalloy AD730TM: a thermally or thermo-mechanically controlled process?" Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0010.
Pełny tekst źródłaThe 750°C crack propagation behavior in the polycristalline nickel-base superalloy AD730TM is studied. This study falls within the overall objectives of optimizing the “microstructure – mechanical properties” relations in nickel-base superalloys used for example in turbine disks. The deceleration of the crack propagation with the increase in ΔK value is specifically at the core of the PhD thesis work. Via a crack propagation test campaign, this phenomenon is systematically identified when dwell-fatigue loading are performed. The influence of the thermomechanical history of the material in investigated by varying several experimental parameters such as the initial microstructural state (γ’ precipitates), the initial value of ΔK, the environment or the dwell durations. The origin of the deceleration phenomenon is therefore shown to be linked with combined and protective effects of stress relaxation, oxide growth and metallurgical aging at the crack tip. To improve the understanding of the crack propagation results, complementary analysis of the 750°C γ’ precipitates aging is performed. One of the main outcomes is that aging kinetics (γ’ growth, carbide precipitation) are enhanced thanks to a cyclic loading. Besides, the more the microstructure is aged, the higher the stress relaxation rate at 750°C
Burch, Judith Gulliver. "Dementia garden design: a framework to facilitate Kaplans’ attention restoration theory (A.R.T.) in environments of care". Thesis, Kansas State University, 2012. http://hdl.handle.net/2097/13665.
Pełny tekst źródłaDepartment of Landscape Architecture/Regional and Community Planning
Timothy D. Keane
This thesis documents an exploratory design process that examines the efficacy of a framework for designing dementia gardens based on: theory, Stephen and Rachel Kaplan’s Attention Restoration Theory (A.R.T.), (Kaplan and Kaplan, 1989) and Roger Ulrich’s Theory of Supportive Gardens (Ulrich, 1999); John Zeisel’s (2007) process for designing dementia gardens; and design details, Claire Cooper Marcus’ Garden Audit Tool (2007) and Moore’s analysis of exemplary dementia gardens (2007). It documents the integration of theory that is not specific to dementia gardens (Kaplans’ A.R.T. and Ulrich’s Theory of Supportive Gardens) with process (Zeisel) and programming elements that are specific to dementia gardens (Cooper Marcus’ Garden Audit Tool Kit and Moore’s exemplary dementia gardens). The framework was developed during an illustrative courtyard design project for a retirement center whose clientele included patients with varying need levels. Throughout the illustrative design project, knowledge of the four A.R.T. characteristics (Being Away, Fascination; Compatibility and Extent) guided design decision-making in an effort to create an engaging environment, where improved health outcomes and restorative person-environment interactions could occur.
Douzi, Chawki. "Effet du vieillissement par fatigue électrothermique sur la compatibilité électromagnétique des composants de puissance à base de SiC". Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR002/document.
Pełny tekst źródłaThis research work focuses on the electrothermal aging effect on the electromagnetic compatibility of power components based on silicon carbide SiC. It focuses on two major parts ; an experimental part and another more oriented modelization. Experimentally, this thesis studies the aging effect of SiC transistors used in static converters on the electromagnetic interferences EMI generated by these converters. The second part deals with the modeling of these transistors in order to emulate the effect of their aging on the EMI of the modules they compose. This step made it possible to validate the methodology developed for the simulation of the conducted EMI of a healthy SiC MOFSET at first and of an aged SiC MOSFET in a second time. Overall, this innovative modeling approach developed in this work helps the designers of static converters to predict the conducted EMI before and after aging without going through the measurement. This provides additional information on the evolution of the EMC signatures of such modules during its lifetime and thus to estimate the risk associated with the aging of the components
Gualandi, Mattia. "Fatigue response of CFRP subjected to hygroscopic ageing". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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