Cette thèse s’inscrit dans le cadre général de l’étude de la tolérance au dommage des pièces tournantes dans les turbomachines d’hélicoptères et porte sur la résistance à la propagation de fissures courtes 2D.Pour mener à bien cette étude, l’effet de la température est d’abord étudié sur les seuils de propagation de fissures longues à R=0,1 sur deux alliages TA6V et Ti6242 de microstructure bimodale (20°C et 400°C pour le TA6V et 20°C, 200°C et 500°C pour le Ti6242). Au voisinage du seuil, le comportement effectif(après correction de la fermeture) est sensiblement identique pour les deux alliages aux températures testées. La fermeture est principalement induite par l’oxyde à haute température et par la rugosité des surfaces de rupture à température ambiante.L’évolution du seuil de propagation en fonction de la longueur de fissure a ensuite été étudiée à R=0,1. Un outil de détermination automatique du niveau de fermeture a été mis en place afin d’améliorer la mesure pour des fissures très courtes (80 μm). La fermeture mesurée pour différentes longueurs de fissure obtenues par usinage progressif du sillage plastique est comparable à celle obtenue au cours de la propagation d’une fissure courte 2D au seuil, sauf pour les hautes températures où la fermeture induite par l’oxyde se développe rapidement. Les différences de comportement entre fissure longue et fissure courte sont expliquées par une contribution réduite de la fermeture lorsque le sillage de la fissure est réduit.Un critère de non-propagation s’inspirant du formalisme initialement proposé par Kitagawa et une loi de propagation adaptée permettent de mieux prédire la résistance à la propagation des fissures physiquement courtes. / Damage tolerance analyses of rotating parts, containing 2D-short crack, in turbomachines of helicopters is the main focus of this thesis.Fatigue crack propagation tests were performed at R=0.1 on two bimodal Titanium alloys at different temperatures (20°C and 400°C for TA6V and 20°C, 200°C and 500°C for Ti6242). Near-threshold effective behaviors (after crack closure correction) were approximately the same for the two alloys attested temperatures. Crack closure was principally due to oxide layer at high temperatures and to fracture surface roughness at ambient temperature.Then the variations of the crack propagation threshold with crack length was studied at R=0.1 and different temperatures. A numerical tool was developed to automatically detect crack closure level more precisely for, as short as, 80μm cracks. Crack closure levels measured at different crack lengths obtained from progressive machining of the plastic wake were quite similar to the ones obtained during propagation of 2D-short cracks near the threshold, except at high temperatures where oxide-induced crack closure developed rapidly. Differences in behavior of long cracks and short cracks were explained by a reduction of crack closure level when crack wake was not fully developed.A non-propagation criterion based on formalism initially proposed by Kitagawa and a modified-Paris propagation law allow to give a better description of physically 2D-short crack propagation resistance.

A large-area electronics (LAE) strain sensor, termed soft elastomeric capacitor (SEC), has shown great promise in fatigue crack monitoring. The SEC is capable to monitor strain changes over a large structural surface and undergo large deformations under cracking. Previous tests verified that the SEC can detect and localize fatigue cracks under low-cycle fatigue loading. In this paper, we further investigate the SEC's capability for monitoring high-cycle fatigue cracks, which are commonly seen in steel bridges. The peak-to-peak amplitude (pk-pk amplitude) of the SEC measurement is proposed as an indicator of crack growth. This technique is is robust and insensitive to long-term capacitance drift. To overcome the difficulty of identifying the pk-pk amplitude in time series due to high signal-to-noise ratio, a signal processing method is established. This method converts the measured SEC capacitance and applied load to power spectral densities (PSD) in the frequency domain, such that the pk-pk amplitudes of the measurements can be accurately extracted. Finally, the performance of this method is validated using a fatigue test of a compact steel specimen equipped with a SEC. Results show that the crack growth under high-cycle fatigue loading can be successfully monitored using the proposed signal processing method.

The influences of a superheated steam environment and temperature on the nearthreshold crack growth behaviour of mild steel during rotating bending fatigue were investigated. A fatigue machine in which rotating bending is simulated was designed and built to allow continuous crack growth measurement. Experiments compared the threshold stress intensities (∆Kth ) for air at 24 °C, air at 160 °C and steam at 160 °C.Air at 160 °C yielded the lowest threshold stress intensity in both cases. Oxide thicknesses in the vicinity of the threshold were estimated from temper colours. The difference in threshold stress intensities can be explained by the concept of oxideinduced crack closure. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / MEng / unrestricted

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Orientador: Renata Cruz Soares de Azevedo / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-27T12:58:53Z (GMT). No. of bitstreams: 1 Oliveira_KarinaDiniz_D.pdf: 1545858 bytes, checksum: fc5c6d38466b6c63873474240fcefa4d (MD5) Previous issue date: 2015 / Resumo: Objetivos: descrever o perfil sociodemográfico e o padrão de uso de substâncias psicoativas (SPA) em pacientes admitidos em unidade de emergência (UE) por traumas. Além disso, relacionar a detecção laboratorial de SPA com a gravidade e o mecanismo de trauma. Métodos: Estudo quantitativo, de corte transversal e longitudinal realizado com sujeitos maiores de 18 anos, admitidos em UE em decorrência de traumas. Os instrumentos utilizados foram: questionário com dados sociodemográficos e de padrão de consumo de SPA, e as seções J e K do "Mini International Neuropsychiatric Interview", para avaliação de abuso e dependência. Os pacientes que apresentaram uso nocivo ou dependência de SPA foram submetidos à intervenção breve. Foram coletadas amostras de sangue e urina para pesquisa laboratorial de álcool, cocaína, crack, cocaetileno e canabinóides. Dos prontuários médicos, foram levantados os dados de mecanismo e gravidade do trauma (avaliado pelos escores RTS ¿ Revised Trauma Score ¿ e ISS ¿ Injury Severity Score). O seguimento foi realizado através de contato telefônico um ano após o evento trauma para avaliação do padrão de uso de SPA. Resultados: Foram incluídos no estudo 453 indivíduos, em sua maioria homens, com média de idade 36,1 anos, 8 anos de escolaridade, com filhos e laboralmente ativos. 348 pacientes responderam ao questionário. Padrão de poliuso e dependência foram detectados em 147 e 37 sujeitos respectivamente, principalmente em homens jovens. Houve predomínio de acidentes de trânsito e maior proporção de homens nos mecanismos ferimentos com arma branca, acidentes de moto e ferimentos por projétil de arma de fogo. Das 435 amostras de sangue e urina coletadas, 169 foram positivas para a presença de SPA: álcool (21,2%), cocaína (19,8%), canabinóides (13%), crack (11%), cocaetileno (15,9%). Houve diferença significativa na comparação da análise laboratorial de SPA com o mecanismo de trauma, com correlação negativa para cocaína/crack no acidente de trânsito e correlação positiva para todas as SPA no trauma de violência. Os pacientes com análises positivas para álcool, cocaína, crack e cocaetileno apresentaram traumas mais graves (RTS<7,84). Quando considerado o ISS, os traumas mais graves foram apresentados por sujeitos cujas amostras foram positivas para cocaetileno e crack (ISS>16). A maior letalidade foi causada por atropelamentos, responsável por 13/41 (31,7%) dos óbitos. Intervenção breve não interferiu na mudança de padrão de uso de SPA relatado no seguimento de um ano. Conclusões: Homens, jovens, com 4 a 8 anos de escolaridade, sem companheira fixa, com filhos e laboralmente ativos foram a maioria dos sujeitos do estudo. O padrão de consumo de SPA nas vítimas de trauma mostrou início de uso antes dos 18 anos de idade e grande proporção de abuso e dependência. A presença de álcool e drogas ilícitas na análise laboratorial em vítimas de trauma foi elevada, com destaque para cocaína e crack. O mecanismo de trauma mais comum foi acidente de trânsito, com maior letalidade no atropelamento. A presença de álcool, crack e cocaetileno esteve associada a maior gravidade do trauma. Em relação a outros mecanismos, trauma de violência esteve associado a maior detecção positiva de SPA / Abstract: Objectives: describing sociodemographic profile and pattern of psychoactives substances (PSA) use in patients treated for injuries in an Emergency Unit. Furthermore, unite the PSA laboratorial detection with the severity and injury mechanism. Methods: quantitative study, transversal and longitudinal, with subjects older than 18, admitted in ER for trauma. The instruments applied were a sociodemographic questionnaire and the J and K sections of Mini International Neuropsychiatric Interview (M.I.N.I.) to evaluate PSA abuse and dependence. Blood and urine samples were collected to detect alcohol, cocaine, crack, cocaethylene and THC. Data from injury mechanism and lesions severity (evaluated through RTS ¿ Revised Trauma Score ¿ and ISS ¿ Injury Severity Score) were found in medical records. The following were made by phone contact to evaluate pattern of PSA use one year after trauma. Results: 453 subjects, male, average age 36,3 years, 8 years of scholarity, with kids and working. 348 answered the questionnaire. Polyuse and poly-dependance pattern were detected in 147 and 37 patients respectively, mainly young men. The predominant trauma mechanism was traffic-related injuries. In young men the main mechanisms were motocycle accidents, cold steal and firearm perforation. From 435 urine and blood samples collected, 169 (38,8%) detected some PSA: alcohol (21,2%), cocaine (19,8%), THC (13%), crack (11%), cocaethylene (15,9%). There was a significant correlation between the sample analysis and the trauma mechanism. Negative correlation for crack and cocaine in traffic related injuries and positive correlation for all PSA in violence-related injuries. Subjects whose samples were positive to alcohol, cocaine, crack and cocaethylene showed more severe traumas according to RTS. When ISS is considered, more severity in the patients whose samples were positive to crack and cocaethylene (ISS>16). Major lethality caused by tramplings (31,7% of the 41 deaths). Brief intervention didn't change the pattern of PSA use one year after trauma. Conclusions: Most subjects were men, young, 4 to 8 years of scholarity, without partner, with kids and working. Trauma patients began the use of PSA during the youth and showed great percentages of abuse and dependence. Positive samples percentages were high, specially crack and cocaine. Predominant trauma mechanism was traffic accident, and trampling was the most lethal mechanism. Positive samples for alcohol, crack and cocaethylene were associated to major severity of trauma. Violence-related traumas were associated to positive samples more than other mechanisms / Doutorado / Saude Mental / Doutora em Ciências Médicas

Foram estudadas as propriedades de fadiga em dois grupos de soldas de alta resistência e baixa liga com diferentes composições microestruturais. As soldas do grupo A apresentaram microestruturas compostas de ferrita acicular, ferrita alotriomórfica e ferrita de Widmanstätten, com limite de escoamento de aproximadamente 460 MPa, enquanto que as soldas do grupo B apresentaram microestruturas compostas de martensita de baixo carbono, bainita e ferrita acicular, com limite de escoamento de aproximadamente 850 MPa. A partir do ensaio de trincas longas, foi obtida a taxa de crescimento por ciclos de carregamento, da/dN, de da/dN=1,18·10-12·DeltaK2,91 e da/dN=1,34·10-11·DeltaK2,64, respectivamente para as soldas dos grupos A e B. Como pode ser observado a partir destas equações, a taxa de crescimento foi mais alta para o grupo B. Da análise do fechamento da trinca pode ser concluído que o principal fator determinante de uma menor taxa de propagação para as soldas do grupo A foi a plasticidade desenvolvida pela estrutura. Dos ensaios de trincas curtas foi observado que no caso das soldas do grupo A, uma vez nucleada a trinca, esta se propagava até o colapso do corpo de prova. Para as soldas do grupo B foi observado que não bastava a existência de uma trinca para que esta se propagasse até a fratura total do corpo de prova e que o fator controlador foi a granulomentria associada a uma determinada composição microestrutural. / The fatigue properties of two groups of high strength low alloy steel weld metals with different microstructural composition were studied. Weld metals from group A presented microstructures composed of acicular ferrite, Widmanstätten ferrite and allotriomorphic ferrite, with yield strength of 460 MPa. Weld metals from group B exhibited a microstructural composition of low carbon martensite, bainite and acicular ferrite, with a yield strength of 850 MPa. The fatigue crack growth per cycle of loading, da/dN, for weld metals from groups A and B is obtained from the relationships, da/dN=1,18·10-12·DeltaK2,91 and da/dN=1,34·10-11·DeltaK2,64, respectively. As can be seen from these equations, the crack growth rate was higher for group B. From the crack growth closure analysis, it may be concluded that the lower crack growth rate obtained for weld metals from group A was mainly due to the higher crack tip plasticity developed in this type of microstructure. From the short crack fatigue tests, it was observed for weld metals from group A, that once a crack was nucleated, it propagated until the testpiece plastic collapsed. For weld metals from group B, it was observed that the existence of a crack was not sufficient to cause the complete testpiece failure, and the association of the grain size with the local microstructure was the main factor controlling the failure process.

This thesis deals with the monitoring of buildings disorders caused by surrounding con-struction activity. The first section describes the methods of monitoring failures, from the detailed inspection to the result evaluation, there is also given an overview of measuring instruments. The second part describes the methodology of passports implementation and contains an example of the object repassport that was violated by tunneling. There is a comparison of passport and repassport. The third largest section describes a practical ex-ample of monitoring object cracks around which the building activity took place. There is a documentation of failures, a description of the measuring spots choise, installation of the bases, monitoring, processing of results and conclusion.

Les divers composants d'un réacteur d'avion sont soumis à des chargements de fatigue mécaniques et thermiques fortement variables. Afin de prédire au mieux leurs durées de vie, il est alors nécessaire de prendre en compte l'ensemble de ces variations. Pour ce faire, un modèle représentant de façon incrémentale l'évolution de la plasticité en pointe de fissure a été développé. Celui-ci permet de prédire la vitesse de propagation d'une fissure tout en prenant en compte les effets d'histoire provenant de la plasticité produite lors de surcharges ou de sous-charges. Dans cette étude, ce modèle condensé de plasticité a été exprimé plus simplement à partir du facteur d'intensité des contraintes et l'identification automatisée de ses divers paramètres a été redéveloppée. Dans ce but, un essai de fissuration stable a été conçu pour déterminer simplement le seuil de non-propagation du matériau. Par ailleurs, les éventuelles fissures se propageant dans un composant sont en général amorcées en surface à partir de chocs ou de rayures. Ces fissures passent la majeure partie de leur vie dans un régime de propagation de fissure courte, différant de celui d'une fissure longue. En effet, à facteur d'intensité des contraintes équivalent, une fissure courte se propagera plus rapidement qu'une fissure longue. La prise en compte de ce comportement dans la prédiction de durée de vie est donc primordiale. En outre, il a été observé qu'une fissure longue subissant une contrainte T négative se propage de façon analogue à une fissure courte. Il a donc été choisi de développer un nouveau modèle adapté aux fissures courtes en prenant en compte l'influence de la contrainte T sur la vitesse de propagation. Enfin, à partir des essais de fissuration stable, un protocole a été développé pour réaliser des éprouvettes comportant fissure courte. Une campagne d'essais multiaxiaux pour différentes valeurs de contrainte T a été menée en régime permanent et transitoire afin d'étudier les similitudes entre effet de fissure courte et influence de la contrainte T. / The various components of an aircraft engine undergo strong changes in mechanical and thermal fatigue loadings. All these variations must be taken into account in order to anticipate the components' total fatigue life to the best. An incremental model showing the changes in plasticity at the crack tip has therefore been developed. It allows us to foresee the crack growth rate with history effects by modelling the plastic behaviour produced when overloads or underloads occur. In this study, the plasticity condensed model has been represented in an easier way, using the stress intensity factor and the automated identification of its parameters has been redeveloped. A stable crack growth test has been designed to determine easily the fatigue crack growth threshold of the material. Cracks usually grow from scratches or impacts on the surface of the component. These cracks spend much of their fatigue life growing with a short crack behaviour, differing from the long crack one. As a matter of fact, a short crack grows faster than a long crack for a same stress intensity factor. This behaviour must therefore be taken into account while modelling the crack growth to accurately predict the total fatigue life of the component. It appeared furthermore that a long crack undergoing a negative T-stress grows the same way as a short crack. It has consequently been chosen to develop a short crack growth model using the influence of T-stress on the crack growth rate. Finally, using the stable crack growth specimens, an experimental protocol has been designed to produce new specimens containing a short crack. A multiaxial tests campaign was carried out for various values of T-stress in permanent and transitional regimes in order to compare short crack and T-stress effects.

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