In aerospace industry and other major mechanical industry systems, engineering components that are subjected to cyclic loads often lead to progressive crack growth that eventually results in struc-tural fracture. The damage tolerance design which is based on the assumption of pre-existed flaws in a structure is an important approach in aircraft industry since it is impossible to have flaw-free manufactured components.In this thesis work, an evaluation of crack propagation models was carried out. Fatigue crack growth threshold and fatigue crack growth rate models were evaluated. A method to present ex-perimental data available was developed to evaluate uncertainties in fatigue life models for more accurate predictions. Currently, a software that is used for predicting crack propagation life is NASGRO. The study has been made for two types of materials: a nickel-iron-based alloy (Inconel 718 forging) and titanium alloys (Ti 6-4 both forging and casting).A threshold model is in the normal case developed for each temperature. A method to model fatigue threshold (ΔKth) has been suggested by assuming temperature independence of ΔKth. In this method, a new threshold model was created by making use of an A/P (Actual/Predicted) plot so that all measured threshold values are on the conservative side of the minimum model. With this method, an understanding of fatigue threshold model was improved over the other method due to the possibilities to model ΔKth with average and minimum threshold values for each load ratio (ΔKth, R).Moreover, a method to investigate which set of parameters that best represent the crack growth behaviour has been suggested. In this method the best set of parameters were chosen to be the set of parameters giving the best fit to the available (da/dN, ΔK) points. The comparison between this method and the method with the set of parameters that give minimum scatter in the A/P values was done.Crack growth rate da/dN log curves were plotted as function of stress intensity range ΔK for R-ratio values ranging from -2 to 0.9 for the two different methods. A distinctive difference between the two methods was observed in Paris region at high temperatures (5500C-6500C) which becomes more obvious at lower R-ratios. Predicting crack propagation rate model with set of parameters giving minimum standard deviation in da/dN points was shown to be less conservative than that of parameter sets giving lowest scatter in A/P. Using both evaluation methods, da/dN versus ΔK plots of Inconel718forging were compared to da/dN (ΔK) plots for the pre-existing data at 5500C for R-ratios ranging from 0 to 0.8. An overall R-ratio influence was observed throughout for both ΔKth and da/dN.

Les motoristes aéronautiques doivent répondre à de nouvelles demandes de certifications en tolérance aux dommages. Ils doivent en particulier démontrer que la présence de petites anomalies de surface, pouvant être introduites lors d’opérations de maintenance, ne mène pas à la rupture des pièces les plus critiques de leurs moteurs. Cette étude concerne la caractérisation de la nocivité d’anomalies de surface de type rayure et choc sur la tenue en fatigue du superalliage à base Nickel Inconel 718 sous sa version Direct Aged. Une campagne d’essais expérimentaux a permis d’évaluer l’influence de la contrainte maximale, de la température, du type et de la profondeur des anomalies de surface sur leur durée de vie en fatigue. Une étude expérimentale et numérique approfondie de la méthode de suivi de la différence de potentiel a conduit à une bonne maîtrise de cet outil de détection de l’amorçage et de suivi de la fissuration. Son utilisation a ainsi révélé que l’amorçage de fissure est très rapide à partir de rayures et de chocs mais que la vitesse de propagation dans les premiers stades de fissuration est ralentie. Des essais spécifiques ont alors été développés pour identifier la source physique des phénomènes observés. L’utilisation d’un traitement thermique a notamment permis de mettre en avant l’influence prédominante des contraintes résiduelles de compression générées lors de l’introduction des anomalies. Différentes méthodes expérimentales et numériques ont été testées pour les quantifier et des pistes de modélisations ont été mises en avant pour prédire de manière fiable la durée de vie en fatigue d’anomalies de surface de type rayure et choc. / Aircraft engine manufacturers have to meet with new certification requirements in damage tolerance. In particular they have to demonstrate that the presence of small surface anomalies introduced on engine parts during maintenance operations in critical areas do not lead to failure during service life. This study was undertaken to characterize the harmfulness of scratch and dent type surface anomalies on the fatigue life of the Nickel based superalloy Direct Aged Inconel 718.The influence of maximal stress, temperature, type and depth of surface anomalies was evaluated in a large series of experiments. An experimental and numerical in-depth study of the potential drop technique led to a good control of this tool and allowed to efficiently detect crack initiation and to measure the crack propagation. Indeed, the use of this technique has revealed that the crack initiation from scratches and dents is very rapid but that the first stages of crack growth are delayed.Specific tests were then performed to identify the physical origin of the observed phenomenon. A heat treatment was used to show that the compressive residual stresses created during the introduction process of surface anomalies have a great influence on the fatigue life. Different experimental and numerical techniques were used to quantify these residual stresses and some directions were identified to establish a new model able to predict the fatigue life of scratch and dent type surface anomalies.

No description available.

In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.

The main goal of this thesis is to get an insight into a field of non-destructive testing using potential drop techniques that have nowadays become the standard not only in the fatigue and loading tests but also in the industry. These methods can serve to non-destructively and continuously measure material specimens, thickness, corrosion losses, deformations, spectroscopy and detection and analysis of crack geometry. They can help to identify materials and measure material changes over time. The second part of this thesis deals with designing the aperture for detection of cracks in steam and product piping using potential drop technique modified by Ing. Ladislav Korec, CSc. Last part deals with extensive testing, experimenting and evaluation of the aperture.

Este trabalho apresenta o desenvolvimento e aplicação de espécimes SE(T) em aço API X60 para avaliação de integridade estrutural em dutos condutores de gás e petróleo, o qual consiste na implantação de três técnicas que forneçam as curvas de resistência à propagação dútil de trincas, curvas J-Rs. As metodologias utilizadas foram a da variação da flexibilidade elástica, da queda de potencial elétrico e da normalização linear da carga, nas quais duas análises são verificadas para obtenção da área plástica abaixo da curva de carregamento. A primeira, através da medida do deslocamento da linha de carga e a segunda, pelo deslocamento do extensômetro colocado na boca da trinca. Foram ensaiados corpos de prova SE(T) com trincas rasa (a/W = 0,2) e profunda (a/W = 0,5) e os resultados obtidos permitiram observar a iniciação da propagação por rasgamento dúctil e discutir os limites das metodologias aplicadas. Os resultados mostraram que é possível obter as curvas J-Rs medindo o deslocamento na boca da trinca, podendo-se converter os deslocamentos de CMOD em deslocamentos do LLD. Foi constatada também que a técnica de normalização linear da carga é a que possibilitou o menor tempo de preparação e execução do ensaio, por utilizar apenas a medição do CMOD e não necessitar da realização dos descarregamentos. A variação da flexibilidade elástica é uma técnica rápida e confiável e não sofre alterações devido às delaminações. Já a técnica de queda do potencial elétrico se mostrou a mais consistente para o caso de a/W = 0,5, porém no caso de trincas curtas, a plasticidade desenvolvida na frente da trinca influencia nas medições causando imprecisões. As curvas J-Rs são deslocadas para a esquerda quando o tamanho inicial de trinca é reduzido, isto é, ocorre um aumento na energia de iniciação da propagação, JIC. / This work presents the development and application of SE(T) type specimen for structural integrity evaluation of pipeline steels used for gas and oil transportation, and it consists of the implementation of different techniques to provide the crack growth resistance curves, J-R curves. The methodologies used for crack growth measurement were: the elastic compliance, the electrical potential drop and the linear normalization techniques. Two techniques to provide the plastic area, Apl under the load versus displacement curve were used to evaluate Jpl, one based on the load line displacement, LLD, and the other based on the crack mouth opening displacement, CMOD. SE(T) specimens with two different initial crack size, denominate as shallow crack (a0/W = 0.2) and deep crack (a0/W = 0.5). The obtained results allowed the determination of the ductile tearing initiation point and to discuss the limits of the methodologies applied. It was proved be possible to get J-R curves using only one extensometer to measure the CMOD, which provides both crack size and Apl. The linear normalization technique is the one that provided the lower preparation and testing time, since there is no need of multiples unloading for crack growth measurement. The elastic compliance is a very easy, fast and reliable technique, and it is not sensible to the effect of the occurrence of delaminations, as it was the linear normalization technique. The electrical potential drop technique proved to very consistent for a0/W = 0.5, however in the case of shallow cracks the developed plasticity at the crack tip affected the measurements. The J-R curves were displaced to the left as the initial crack size is reduced, this is, there is an increase in the energy for crack tearing initiation, JIC.

Com a implementação do Programa Nacional do Álcool (Proálcool), Protocolo de Quioto e substituição do MBTE (metil-terci-butil eter) em alguns países nos últimos anos, houve um aumento significativo da produção de etanol. Os dois maiores produtores mundiais de etanol são os Estados Unidos e o Brasil, sendo o etanol oriundo do Milho e da Cana-de-açucar, respectivamente. Transporte por dutos é a forma mais econômica para grandes quantidades, porém, há evidências de que esses dutos de transporte, e também fundo de tanques de armazenamento, possam ser susceptíveis ao fenômeno de corrosão sob tensão quando operam com etanol. Este fenômeno pode ser avaliado, por exemplo, por ensaios de baixa taxa de deformação (BTD) e de tenacidade à fratura, com corpos de prova definidos em normas já conhecidas internacionalmente. Este trabalho tem por objetivo avaliar a susceptibilidade do aço API X70 em diferentes meios de etanol (Etanol combustível simulado (SFGE), Milho e Cana) através de ensaios de mecânica da fratura. Foram preparados corpos de prova pré-trincados do tipo C(T) (Compact Tension), de acordo com a norma ASTM E647-08. A análise dos resultados foi realizada através das equações da mecânica da fratura linear elástica. Nos ensaios de curvas K-R, apesar de somente o etanol de Milho apresentar uma queda de tenacidade, o K de iniciação aparente e as análises fractográficas, confirmam a fragilização do material nos meios etanol SFGE e Milho. Ensaios de baixa taxa de deformação (BTD) interrompidos e os de step loading com carga flutuante também confirmam estes resultados. / In recent years, there have been significant increases in ethanol production due to Brazilian Alcohol Program (Proálcool) implementation, Kyoto Protocol and replacement MBTE in some countries. The world’s largest producers of ethanol are United States and Brazil, being produced from Corn and Sugar Cane, correspondingly. Pipeline transportation is the most cost effective in large volumes, although, there are evidences that these pipelines and the bottom of ethanol storage tanks might be susceptible to the stress corrosion cracking phenomenon. This phenomenon can be assessed, for example, by slow strain rate tests (SSRT) and fracture toughness tests, with specimens well defined by international standards. This study aims to evaluate the susceptibility of steel API X70 in different ethanol environment (Simulated fuel-grade ethanol (SFGE), Corn and Sugar Cane) through fracture mechanics specimens. The tests were carried out on pre-cracked C(T) (Compact Tension) specimens, according to ASTM E647-08. The analysis of results was performed using linear elastic fracture mechanics equations. The analysis of K-R curves initially presented a decrease in toughness only in Corn environment, however the K for crack initiation apparent and fractography investigation confirm the material embrittlement in both SFGE and Corn ethanol environments. Tests of the slow strain rate test (SSRT) interrupted and loading step with fluctuating load also confirm these results.

Com a implementação do Programa Nacional do Álcool (Proálcool), Protocolo de Quioto e substituição do MBTE (metil-terci-butil eter) em alguns países nos últimos anos, houve um aumento significativo da produção de etanol. Os dois maiores produtores mundiais de etanol são os Estados Unidos e o Brasil, sendo o etanol oriundo do Milho e da Cana-de-açucar, respectivamente. Transporte por dutos é a forma mais econômica para grandes quantidades, porém, há evidências de que esses dutos de transporte, e também fundo de tanques de armazenamento, possam ser susceptíveis ao fenômeno de corrosão sob tensão quando operam com etanol. Este fenômeno pode ser avaliado, por exemplo, por ensaios de baixa taxa de deformação (BTD) e de tenacidade à fratura, com corpos de prova definidos em normas já conhecidas internacionalmente. Este trabalho tem por objetivo avaliar a susceptibilidade do aço API X70 em diferentes meios de etanol (Etanol combustível simulado (SFGE), Milho e Cana) através de ensaios de mecânica da fratura. Foram preparados corpos de prova pré-trincados do tipo C(T) (Compact Tension), de acordo com a norma ASTM E647-08. A análise dos resultados foi realizada através das equações da mecânica da fratura linear elástica. Nos ensaios de curvas K-R, apesar de somente o etanol de Milho apresentar uma queda de tenacidade, o K de iniciação aparente e as análises fractográficas, confirmam a fragilização do material nos meios etanol SFGE e Milho. Ensaios de baixa taxa de deformação (BTD) interrompidos e os de step loading com carga flutuante também confirmam estes resultados. / In recent years, there have been significant increases in ethanol production due to Brazilian Alcohol Program (Proálcool) implementation, Kyoto Protocol and replacement MBTE in some countries. The world’s largest producers of ethanol are United States and Brazil, being produced from Corn and Sugar Cane, correspondingly. Pipeline transportation is the most cost effective in large volumes, although, there are evidences that these pipelines and the bottom of ethanol storage tanks might be susceptible to the stress corrosion cracking phenomenon. This phenomenon can be assessed, for example, by slow strain rate tests (SSRT) and fracture toughness tests, with specimens well defined by international standards. This study aims to evaluate the susceptibility of steel API X70 in different ethanol environment (Simulated fuel-grade ethanol (SFGE), Corn and Sugar Cane) through fracture mechanics specimens. The tests were carried out on pre-cracked C(T) (Compact Tension) specimens, according to ASTM E647-08. The analysis of results was performed using linear elastic fracture mechanics equations. The analysis of K-R curves initially presented a decrease in toughness only in Corn environment, however the K for crack initiation apparent and fractography investigation confirm the material embrittlement in both SFGE and Corn ethanol environments. Tests of the slow strain rate test (SSRT) interrupted and loading step with fluctuating load also confirm these results.

Com a implementação do Programa Nacional do Álcool (Proálcool), Protocolo de Quioto e substituição do MBTE (metil-terci-butil eter) em alguns países nos últimos anos, houve um aumento significativo da produção de etanol. Os dois maiores produtores mundiais de etanol são os Estados Unidos e o Brasil, sendo o etanol oriundo do Milho e da Cana-de-açucar, respectivamente. Transporte por dutos é a forma mais econômica para grandes quantidades, porém, há evidências de que esses dutos de transporte, e também fundo de tanques de armazenamento, possam ser susceptíveis ao fenômeno de corrosão sob tensão quando operam com etanol. Este fenômeno pode ser avaliado, por exemplo, por ensaios de baixa taxa de deformação (BTD) e de tenacidade à fratura, com corpos de prova definidos em normas já conhecidas internacionalmente. Este trabalho tem por objetivo avaliar a susceptibilidade do aço API X70 em diferentes meios de etanol (Etanol combustível simulado (SFGE), Milho e Cana) através de ensaios de mecânica da fratura. Foram preparados corpos de prova pré-trincados do tipo C(T) (Compact Tension), de acordo com a norma ASTM E647-08. A análise dos resultados foi realizada através das equações da mecânica da fratura linear elástica. Nos ensaios de curvas K-R, apesar de somente o etanol de Milho apresentar uma queda de tenacidade, o K de iniciação aparente e as análises fractográficas, confirmam a fragilização do material nos meios etanol SFGE e Milho. Ensaios de baixa taxa de deformação (BTD) interrompidos e os de step loading com carga flutuante também confirmam estes resultados. / In recent years, there have been significant increases in ethanol production due to Brazilian Alcohol Program (Proálcool) implementation, Kyoto Protocol and replacement MBTE in some countries. The world’s largest producers of ethanol are United States and Brazil, being produced from Corn and Sugar Cane, correspondingly. Pipeline transportation is the most cost effective in large volumes, although, there are evidences that these pipelines and the bottom of ethanol storage tanks might be susceptible to the stress corrosion cracking phenomenon. This phenomenon can be assessed, for example, by slow strain rate tests (SSRT) and fracture toughness tests, with specimens well defined by international standards. This study aims to evaluate the susceptibility of steel API X70 in different ethanol environment (Simulated fuel-grade ethanol (SFGE), Corn and Sugar Cane) through fracture mechanics specimens. The tests were carried out on pre-cracked C(T) (Compact Tension) specimens, according to ASTM E647-08. The analysis of results was performed using linear elastic fracture mechanics equations. The analysis of K-R curves initially presented a decrease in toughness only in Corn environment, however the K for crack initiation apparent and fractography investigation confirm the material embrittlement in both SFGE and Corn ethanol environments. Tests of the slow strain rate test (SSRT) interrupted and loading step with fluctuating load also confirm these results.

Este trabalho apresenta o desenvolvimento e aplicação de espécimes SE(T) em aço API X60 para avaliação de integridade estrutural em dutos condutores de gás e petróleo, o qual consiste na implantação de três técnicas que forneçam as curvas de resistência à propagação dútil de trincas, curvas J-Rs. As metodologias utilizadas foram a da variação da flexibilidade elástica, da queda de potencial elétrico e da normalização linear da carga, nas quais duas análises são verificadas para obtenção da área plástica abaixo da curva de carregamento. A primeira, através da medida do deslocamento da linha de carga e a segunda, pelo deslocamento do extensômetro colocado na boca da trinca. Foram ensaiados corpos de prova SE(T) com trincas rasa (a/W = 0,2) e profunda (a/W = 0,5) e os resultados obtidos permitiram observar a iniciação da propagação por rasgamento dúctil e discutir os limites das metodologias aplicadas. Os resultados mostraram que é possível obter as curvas J-Rs medindo o deslocamento na boca da trinca, podendo-se converter os deslocamentos de CMOD em deslocamentos do LLD. Foi constatada também que a técnica de normalização linear da carga é a que possibilitou o menor tempo de preparação e execução do ensaio, por utilizar apenas a medição do CMOD e não necessitar da realização dos descarregamentos. A variação da flexibilidade elástica é uma técnica rápida e confiável e não sofre alterações devido às delaminações. Já a técnica de queda do potencial elétrico se mostrou a mais consistente para o caso de a/W = 0,5, porém no caso de trincas curtas, a plasticidade desenvolvida na frente da trinca influencia nas medições causando imprecisões. As curvas J-Rs são deslocadas para a esquerda quando o tamanho inicial de trinca é reduzido, isto é, ocorre um aumento na energia de iniciação da propagação, JIC. / This work presents the development and application of SE(T) type specimen for structural integrity evaluation of pipeline steels used for gas and oil transportation, and it consists of the implementation of different techniques to provide the crack growth resistance curves, J-R curves. The methodologies used for crack growth measurement were: the elastic compliance, the electrical potential drop and the linear normalization techniques. Two techniques to provide the plastic area, Apl under the load versus displacement curve were used to evaluate Jpl, one based on the load line displacement, LLD, and the other based on the crack mouth opening displacement, CMOD. SE(T) specimens with two different initial crack size, denominate as shallow crack (a0/W = 0.2) and deep crack (a0/W = 0.5). The obtained results allowed the determination of the ductile tearing initiation point and to discuss the limits of the methodologies applied. It was proved be possible to get J-R curves using only one extensometer to measure the CMOD, which provides both crack size and Apl. The linear normalization technique is the one that provided the lower preparation and testing time, since there is no need of multiples unloading for crack growth measurement. The elastic compliance is a very easy, fast and reliable technique, and it is not sensible to the effect of the occurrence of delaminations, as it was the linear normalization technique. The electrical potential drop technique proved to very consistent for a0/W = 0.5, however in the case of shallow cracks the developed plasticity at the crack tip affected the measurements. The J-R curves were displaced to the left as the initial crack size is reduced, this is, there is an increase in the energy for crack tearing initiation, JIC.