Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Primary goal of this thesis is to present proposed method for fatigue life evaluation applicable to light composite aircraft. The first chapter of this thesis is focused on certification specifications and requirements for fatigue life proof of structure. Significant part of this thesis is dedicated to fatigue life evaluation and guideline how to proceed in evaluation of fatigue data. Thesis also points out on possible methods of statistical fatigue data analysis and critical parts of structure in means of fatigue life. The last part of thesis is focused on design of experimental evaluation of structure including test rig and load sequence. This chapter also provides inside into possible means of introducing artificial defects into the structure.

La courbe S-N est le moyen le plus courant d'analyse et de prédiction de la durée de vie d'un matériau, d'un composant ou d'une structure. Cependant, les modèles standards, qu'ils soient basés sur la théorie de la rupture ou sur des modèles probabilistes n'ajustent pas la courbe dans la totalité sans information sur la microstructure du matériau. Or, cette information provient d'analyses fractographiques souvent coûteuses et rarement disponibles dans le cadre d'une production industrielle. D'un autre côté, les modèles statistiques ne proposent pas d'interprétation matériau et ne peuvent pas être utilisées pour réaliser des prévisions. Les résultats d'un test de fatigue sont par ailleurs très dispersés, plus particulièrement pour les fortes durées de vie, lieu d'apparition d'un phénomène de bi-modalité. Ces constats sont la raison de la proposition d'un nouveau modèle probabiliste. Celui-ci est composé d'un modèle de mélange spécifique, prenant en compte l'approche apportée par la mécanique de la rupture sans nécessiter de d'information supplémentaire sur la microstructure du matériau. Il utilise le fait que la fatigue peut être vue comme la somme d'un amorçage de fissure suivi de sa propagation. Les paramètres du modèle sont estimés à l'aide d'un algorithme EM, où la phase de maximisation combine une méthode d'optimisation de Newton-Raphson et une intégration de type Monte-Carlo. Le modèle "amorçage-propagation" offre une représentation parcimonieuse des courbes $S-N$ dont les paramètres peuvent être facilement interprétés par des ingénieurs matériau. Ce modèle a été testé à l'aide de simulations et appliqué à des données réelles (données sur l'Inconel 718). Ceci nous a permis de mettre en évidence le bon ajustement du modèle à nos données, et ce, pour toutes les déformations disponibles. / S-N curve is the main tool to analyze and predict fatigue lifetime of a material, component or structure. But, standard models based on mechanic of rupture theory or standard probabilistic models for analyzing S-N curves could not fit S-N curve on the whole range of cycles without microstructure information. This information is obtained from costly fractography investigation rarely available in the framework of industrial production. On the other hand, statistical models for fatigue lifetime do not need microstructure information but they could not be used to service life predictions because they have no material interpretation. Moreover, fatigue test results are widely scattered, especially for High Cycle Fatigue region where split $S-N$ curves appear. This is the motivation to propose a new probabilistic model. This model is a specific mixture model based on a fracture mechanic approach, and does not require microstructure information. It makes use of the fact that the fatigue lifetime can be regarded as the sum of the crack initiation and propagation lifes. The model parameters are estimated with an EM algorithm for which the maximisation step combines Newton-Raphson optimisation method and Monte Carlo integrations. The resulting model provides a parsimonious representation of S-N curves with parameters easily interpreted by mechanic or material engineers. This model has been applied to simulated and real fatigue test data sets. These numerical experiments highlight its ability to produce a good fit of the S-N curves on the whole range of cycles.

All systems are unreliable in the sense that they degrade with age and usage and eventually fail. The degradation depends on the load (or stress) on the system and the maintenance actions. With higher load the productivity increases but this is achieved at the expense of faster degradation and more frequent failures. This in turn reduces the availability of the system. The yield (expected output per unit time), expected operational cost and the expected profit are functions of the load and the availability. The relationship between load and yield is a complicated function and depends on system reliability and maintenance actions. The thesis deals with determining the optimal load and maintenance actions to maximise the yield (or expected profit) or to minimise the expected cost. The thesis comprises of two parts (Parts I and II). Part I is theoretical in nature and looks at the modelling, analysis and optimisation issues. Part II deals with a real case study involving a dragline used in open cut mining. Part I starts with stress-life models which link the load on the system with the reliability of the system. It examines the empirical data in the form of S-N and P-S-N curves, and as WPP plots reported in the literature. The salient features are identified so as to assess the suitability of different models to model the stress-life data. Various Weibull models are assessed to determine their suitability to model stress-life data at the component level. This is followed by a discussion of the modelling at the system level. Optimal maintenance actions are derived based on component level and system level stress-life models. For the component level models, the optimal maintenance actions are derived for a variety of maintenance strategies (such as the age, block and periodic policies) for a specified load to minimise the asymptotic expected cost per unit time. Following this, the joint optimal choice of load and maintenance is examined. For the system level model, the optimal load is obtained to minimise the expected cost per unit time over the life of the system taking into account different actions such as minor and major preventive maintenance actions and corrective maintenance actions. Part II deals with a case study involving a BE1370W dragline. The dragline is used in open cut coal mining to remove the dirt (overburden) on top of the coal seam. This involves dragging the bucket, which is suspended from the boom, through the muckpile until full and then hoisting and swinging the bucket to the dumping point. The capacity of the bucket size determines the load on the dragline. The system level model studied in Part I is used to determine the optimal load to maximise the yield. The dragline was modelled as comprising of 25 components (or sub-systems). Each component was modelled using a system level model of Part I. The model parameters were estimated using real operating and maintenance data over two years. The optimal load to maximise the yield was derived and a sensitivity study carried out.

This theses presents the synthesis and characterization of Cd(II)-, Pb(II)- and Hg(II)-aminoethanethiolates in aqueous media. 2-Aminoethanethiolate, a versatile sulfur andnitrogen (S/N) based ligand was used due to its resemblance to the naturally occurringamino acid, cysteine. The work is presented in four major parts: first, backgroundinformation on the versatile structural chemistry of Cd, Pb and Hg-thiolates with S/Ncontaining ligands; second, synthesis and characterization of Cd(II) with 2-aminoethanethiolates; third, synthesis and characterization and structural chemistry ofPb(II) with 2-aminoethanethiolates; and fourth, synthesis and characterization of Hg(II)-2-aminoethanethiolates in solution- and solid-state with emphasis on the mechanisticpathways for the formation of clusters.The compounds reported here are synthesized by direct addition of the metal saltsand the ligand in deionized water. For Cd(II)-thiolates, insoluble products (77 - 80 and 82- 84) due to the formation of oligomers and polymers were obtained. In Pb(II)-thiolates(85 - 89), the structural chemistry is variable due to the extensive array of coordinationenvironments Pb can acquire. This can be related to the stoichiometry of the reaction aswell as the reaction conditions. The structural trends in Cd(II)- and Pb(II)-thiolates arenot observed in the Hg(II)-thiolates. Rather the halide influences the formation ofmolecular as well as non-molecular structures. Systematic pathways for the formation ofthe compounds based on a variety of commonly observed structural 'building blocks' arepresented. For Cl, Br derivatives, a four-coordinate intermediate, [Hg(SR)2X2] (88 - 96)and for I derivatives three-coordinate intermediates, [HgI(SR)2] and [HgI2(SR)] (97 -100) can be considered as building units. The compounds were characterized withIR/Raman, NMR, MS, Uv-Vis and X-ray crystallography.

No description available.

[pt] Esta pesquisa teve como objetivos promover variações microestruturais em um ferro fundido nodular ferrítico tipo ASTM A536 60-40-18, pelo do uso de resfriadores durante a solidificação do material e pela adoção de tratamentos térmicos pós-fundição, bem como avaliar a influência de tais variações microestruturais sobre as propriedades mecânicas e vida em fadiga do material. Inicialmente, amostras do material foram fundidas em areia com e sem o uso de resfriadores. Após a fundição, algumas amostras de ambas as condições de resfriamento sofreram normalização, enquanto outras foram recozidas, perfazendo seis diferentes condições microestruturais: sem resfriador bruta de fundição (SRB); sem resfriador normalizada (SRN); sem resfriador recozida (SRR); com resfriador bruta de fundição (CRB); com resfriador normalizada (CRN) e com resfriador recozida (CRR). Em seqüência, corpos de prova de todas as condições mencionadas acima foram ensaiados em tração e, posteriormente, sofreram análises metalográficas qualitativas e quantitativas. Dando continuação a etapa experimental, levantaramse as curvas tensão versus número de ciclos para a falha das condições microestruturais SRB, SRR, CRB e CRR, por meio de ensaios de fadiga em flexão rotativa. A vida em fadiga do material também foi relacionada com às características metalúrgicas de cada condição. / [en] The objectives of the present work were to promote microstructural variations in an ASTM A 536 60-40-18 ferritic nodular cast iron, making use of cast coolers during and adopting heat treatments after casting, as well as to evaluate the influence of the microstructural variations on the mechanical properties and fatigue life of the material. Initially, samples of the material were cast in sand moulds with and without internal coolers. After casting, a number of samples in both cooling conditions were subjected to normalizing and annealing heat treatments and, therefore, six different microstructural conditions were obtained: as- cast without cooler (SRB), normalized without cooler (SRN), annealed without cooler (SRR), as-cast with cooler (CRB), normalized with cooler (CRN) and annealed with cooler (CRR). Tensile test were carried out on specimens representing the above mentioned conditions and their microstructures were analysed by qualitative and quantitative metallography. In the sequence of the experimental procedure, rotating bend fadigue test were performed in order to establish the stress-life curves for the SRB, SRR, CRB and CRR microstructural conditions. The fadigue life of the material was also related to the metallurgical characteristics of each condition. The metallographic analysis has indicated that the use of coolers increases the number of graphite nodules, reduces the graphite nodule size and otimizes the spherical morphology. However, these microstructural modifications seam to have no significant influence on the mechanical properties of the material. As to the effect of normalizing annealing, boht treatments not imply in significant changes in the mechanical properties of the as-cast conditions. Regarding the fadigue resistance of the material in the as-cast conditions, the CRB sample showed a longer fatigue life than the SRB samples and this performance under cyclic loading was attributed to the fact that the CRB condition is characterized by a higher number of graphite nodules of class VI. A comparison between the as-cast and annealed conditions indicated that the microstructural conditions SRR and CRR presented a lower fatigue resistance than the conditions SRB and CRB, respectively. This behaviour was associated with the microstructural features of the as-cast conditions, namely the smaller graphite nodule size, the higher microhardness of the matrix and the presence of the bull`s-eye structure. Finally, the experimental stress-life curves were modelled by means of Coffin-Manson law, which was considered efficient in the fadigue life data of ferritic nodular cast iron.

Le phénomène de défaillance par fatigue peut apparaitre à des niveaux de contraintes éloignés du seuil de dimensionnement statique de mécanique des milieux continus, tout simplement du fait que l’endommagement suit un processus complexe et de longue haleine. Disposer d’outils performants de prévision de durée de vie en fatigue est donc une nécessité de conception pour le dimensionnement des machines, composants, structures, par natures soumises à des sollicitations variables dans le temps, liée à leur utilisation en service. Pour contribuer à cet objectif nous nous sommes attachés à une conception concernant les outils les plus fréquemment utilisés pour ces prévisions en fatigue : les critères multiaxiaux de fatigue et les lois d’endommagement et de cumul en fatigue. La première partie du travail effectué a consisté en une étude de validité et d’analyse de nouveaux critères de fatigue multiaxiaux proposés depuis une dizaine d’années. Cette validité est comparée vis-à-vis de celle des critères implantés dans l’industrie. L’approche intégrale dont le principe est l’établissement du caractère endommageant d’un cycle multiaxial par la contribution des sollicitations présentes sur tous les plans physiques et non un seul comme le cas de l’approche « plan critique », est la plus efficace en règle générale pour traduire correctement le comportement en fatigue sous chargement multiaxial. L’intégration d’une démarche probabiliste proposée permet d’associer la probabilité de survie aux résultats de calcul d’un critère. La seconde partie de cette thèse a conduit à proposer de nouveaux modèles différentiels d’endommagement permettant de retrouver, dans le cas d’un chargement d’amplitude constante, le formalisme classique des courbes S-N des matériaux (Wöhler, Basquin, Bastenaire et Stromeyer). L’influence de l’ordre d’apparition des cycles de contraintes, les valeurs moyennes, l’évolution non linéaire du dommage par fatigue sont ainsi prises en compte. Le problème de sensibilité du modèle et donc ses prévisions de durée de vie en fatigue uniaxiale d’amplitude variable, comme cela est rencontré dans le modèle de Chaboche, est ainsi écarté. La confrontation du modèle proposé pour les courbes S-N de Basquin et Bastenaire est prometteuse en terme de prévision de duré de vie. Une étude comparative par rapport à la loi de Miner, prise comme référence, avec celles proposée et de Mesmacque & Amrouche à donnée des résultats concluants pour les lois à évolution non linéaire. / The phenomenon of failure by fatigue can apparaitre at levels of stress remote from the threshold of static dimensinnaly of mechanics of the continuous medium, simply because the damage follows a complex and longterm process. Have successful tools of forecast of life expectancy in fatigue is thus a necessity of conception forthe dimensionnly of machines, components, structures, by natures subjected to requests time-varying, connected to their use in service. To contribute to this objective we became attached to a conception concerning tools most frequently used for these forecasts in fatigue: The multiaxial criteria of fatigue and the laws of damage and of cumul in fatigue. The first part of the made work consisted of a study of validity and analysis of new multiaxial criteria of fatigue proposed since around ten years. This validity is compared towards that of the criteria implanted in the industry. The integral approach the principle of which is the establishment of the character damaging of a multiaxial cycle by the contribution of the sollicitation on all the physical plans and not the only one as the case of the approach " critical plan", is the most effective as a general rule to translate correctly the behavior into fatigue under multiaxial load. The integration of a proposed probability approach allows to associate the probability of survival with the results of calculation of a criterion. The second part of this thesis led to propose new differential models of damage allowing to find, in the case of a load of constant amplitude, the classic formalism of the curves S-N of materials (Wöhler, Basquin, Bastenaire and Stromeyer). The influence of the order of appearance of cycles of stress, the mean values, the not linear evolution of the damage by fatigue are so taken into account. The problem of sensibility of the model and thus its forecasts of life in fatigue uniaxiale of variable amplitude, as it is met in the model of Chaboche, is so pushed aside. The confrontation of the model proposed for the curves S-N of Basquin and Bastenaire is promising in term of forecast of the life. A comparative study with regard to the law of Miner, taken as reference, with those proposed and of Mesmacque and Amrouche with datum of the decisive results for the laws with not linear evolution.

This thesis deals with fatigue behaviour of magnesium alloy AZ91E produced by extrusion. In the frame of this work, basic mechanical characteristics and data from performed fatigue tests were obtained. Further metallographic analysis of microstructure and fractographic analysis of broken specimens after fatigue tests were carried out.

Os aços de alta resistência e baixa liga (ARBL) utilizados em tubos para linhas de transmissão, ou seja, transferência e transporte de petróleo e gás, são especificados pela American Petroleum Institute (API) através da norma API 5L. Neste trabalho foi realizado um estudo da influência da têmpera e da nitretação no comportamento mecânico do aço API 5L X56. A microestrutura, os compostos formados com a nitretação e os mecanismos de fratura foram analisadas usando microscopia óptica, difração de raios X e microscopia eletrônica de varredura respectivamente. As amostras foram caracterizadas mecanicamente por testes de microdureza, tração, impacto e fadiga. Os resultados revelaram que apenas a têmpera promoveu modificações severas na microestrutura em relação à como recebida, formando bainita, martensita e constituinte M-A. A camada nitretada apresentou profundidade de 25 ?m e formação dos nitretos Fe3N e Fe4N. Houve aumento da microdureza, resistência mecânica com os tratamentos, juntamente com a diminuição da tenacidade e também houve um melhoramento na vida em fadiga para as duas amostras tratadas termicamente e superficialmente. Os mecanismos de fratura variaram de dúctil à frágil e em fadiga foi observado que as trincas nuclearam a partir da superfície para todas as amostras. / The high strength and low alloy steel (HSLA) used in pipeline for line transmission, there is transference and transportation of oil and gas, they are specified by American Petroleum Institute (API) through norm API 5L. In this work it was conducted a study of the nitriding and quenching influence on the mechanical behavior of API 5L X56. The microstructure, compounds made with the nitriding and the mechanisms failure were analyzed using optical microscopy, X-ray diffraction and scanning electron microscopy respectively. The samples were mechanical characterized by microhardness, tensile, impact and fatigue test. The results revealed that only quenching treatment promoted severe modifications in microstructure in relation to as received, making up bainite, martensite and M-A constituent. The nitriding layer showed depth of 25 ?m and formation of Fe3N e Fe4N nitrides. There was an increasing of microhardness and mechanical strength with the treatments, along with the decreasing of toughness and there was also an improvement in fatigue life for the two samples heat e surface treated. The failure mechanisms varied from ductile to brittle and in fatigue was observed that the cracks nuclear from the surface to all samples.