• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 6
  • 2
  • 2
  • Tagged with
  • 10
  • 10
  • 7
  • 6
  • 6
  • 5
  • 5
  • 4
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Power Fingerprinting for Integrity Assessment of Embedded Systems

Aguayo Gonzalez, Carlos R. 20 January 2012 (has links)
This dissertation introduces Power Fingerprinting (PFP), a novel technique for assessing the execution integrity of embedded devices. A PFP monitor is an external device that captures the dynamic power consumption of a processor using fine-grained measurements at the clock-cycle level and applies anomaly detection techniques to determine whether the integrity of the system has been compromised. PFP uses a set of trusted signatures from the target code that are extracted during a pre-characterization process. PFP provides significant visibility into the internal execution status, making it extremely robust against evasion. Because of its independence and physical separation, PFP prevents attacks on the monitor itself and introduces minimal overhead on platforms with resource constraints. Due to its anomaly detection operation, PFP is effective against unknown (zero-day) attacks. This dissertation demonstrates the feasibility of PFP on different platforms with different configurations and architectural complexities. Experimental results demonstrate the feasibility of PFP in a basic deterministic embedded platform for radio applications in two different areas: security and regulatory certification. For more complex, non-deterministic platforms, this works presents feasibility results for monitoring the execution integrity of complex software on a high-performance Android platform, including the ability to detect a real privilege escalation attack. In addition, the dissertation develops several general techniques to implement and integrate PFP into embedded platforms such as a general monitoring architecture, a methodology to characterize software modules and extract signatures, and an approach to perform board characterization and improve monitoring sensitivity. / Ph. D.
2

Investigation of decommissioned reactor pressure vessels of the nuclear power plant Greifswald

Viehrig, Hans-Werner, Altstadt, Eberhard, Houska, Mario, Mueller, Gudrun, Ulbricht, Andreas, Konheiser, Joerg, Valo, Matti 05 June 2018 (has links) (PDF)
The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald nuclear power plant representing the first generation of Russian-type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs of 4 units represent different material conditions as follows: • Irradiated (Unit 4), • irradiated and recovery annealed (Units 2 and 3), and • irradiated, recovery annealed and re-irradiated (Unit1). The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam. Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall. This report presents test results measured on the trepans from the beltline welding seam No. SN0.1.4. and forged base metal ring No. 0.3.1. of the Units 1 2 and 4 RPVs. The key part of the testing is focussed on the determination of the reference temperature T0 of the Master Curve (MC) approach following the ASTM standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined: • The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed. • KJc values of the weld metals generally followed the course of the MC though with a large scatter. • There was a large variation in the T0 values evaluated across the thickness of the multilayered welding seams. • The T0 measured on T-S oriented SE(B) specimens from different thickness locations of the welding seams strongly depended on the intrinsic structure along the crack front. • The reference temperature RT0 determined according to the “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs - VERLIFE” and the fracture toughness lower bound curve based thereon are applicable on the investigated weld metals. • A strong scatter of the fracture toughness KJc values of the recovery annealed and re-irradiated and the irradiated base metal of Unit 1 and 4, respectively is observed with clearly more than 2% of the values below the MC for 2% fracture probability. The application of the multimodal MC-based approach was more suitable and described the temperature dependence of the KJc values in a satisfactory manner. • It was demonstrated that T0 evaluated according to the SINTAP MC extension represented the brittle fraction of the data sets and is therefore suitable for the nonhomogeneous base metal. • The efficiency of the large-scale thermal annealing of the Greifswald WWER 440/V230 Unit 1 and 2 RPVs could be confirmed.
3

Assessment of White Matter Integrity in Bonnet Macaque Monkeys using Diffusion-weighted Magnetic Resonance Imaging

Umapathy, Lavanya, Umapathy, Lavanya January 2016 (has links)
Diffusion-weighted magnetic resonance imaging (dMRI) has been used to non-invasively investigate the integrity of white matter and the connectivity of the brain. In this work, high angular resolution diffusion imaging (HARDI), an advanced dMRI methodology was developed and employed in bonnet macaque monkeys to study the connectivity of the orbitofrontal cortex (OFC) and amygdala, two gray matter regions involved in making reward-guided decisions. With age, it is believed that there is a decline in the white matter connectivity between these two regions, also known as uncinate fasciculus (UF), and that this affects reward-value assignment and feedback learning in older adults. The analysis pipeline involved correction for distortions due to eddy currents and field inhomogeneity, noise reduction using a local principal component analysis based technique and subsequent registration to the high-resolution T1-weighted images. Gray matter regions corresponding to OFC and amygdala were identified on the T1-weighted images and probabilistic tractography was carried out to delineate the tracts belonging to UF. The output connectivity map from tractography was used to extract imaging parameters of interest such as fractional anisotropy, axial and radial diffusivity along the UF. A significant reduction in the fractional anisotropy index and the axial diffusivity index along the UF tract was observed with increased age of monkeys. Compared to the left hemisphere, stronger trends were observed in the right hemisphere of the monkeys, indicating possible laterality.
4

Structural Integrity Assessment of Nuclear Energy Systems / 原子力エネルギーシステムの構造健全性評価

Ruan, Xiaoyong 25 May 2020 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22672号 / エネ博第404号 / 新制||エネ||77(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)准教授 森下 和功, 教授 星出 敏彦, 教授 今谷 勝次 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM
5

Investigation of decommissioned reactor pressure vessels of the nuclear power plant Greifswald

Viehrig, Hans-Werner, Altstadt, Eberhard, Houska, Mario, Mueller, Gudrun, Ulbricht, Andreas, Konheiser, Joerg, Valo, Matti 05 June 2018 (has links)
The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald nuclear power plant representing the first generation of Russian-type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs of 4 units represent different material conditions as follows: • Irradiated (Unit 4), • irradiated and recovery annealed (Units 2 and 3), and • irradiated, recovery annealed and re-irradiated (Unit1). The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam. Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall. This report presents test results measured on the trepans from the beltline welding seam No. SN0.1.4. and forged base metal ring No. 0.3.1. of the Units 1 2 and 4 RPVs. The key part of the testing is focussed on the determination of the reference temperature T0 of the Master Curve (MC) approach following the ASTM standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined: • The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed. • KJc values of the weld metals generally followed the course of the MC though with a large scatter. • There was a large variation in the T0 values evaluated across the thickness of the multilayered welding seams. • The T0 measured on T-S oriented SE(B) specimens from different thickness locations of the welding seams strongly depended on the intrinsic structure along the crack front. • The reference temperature RT0 determined according to the “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs - VERLIFE” and the fracture toughness lower bound curve based thereon are applicable on the investigated weld metals. • A strong scatter of the fracture toughness KJc values of the recovery annealed and re-irradiated and the irradiated base metal of Unit 1 and 4, respectively is observed with clearly more than 2% of the values below the MC for 2% fracture probability. The application of the multimodal MC-based approach was more suitable and described the temperature dependence of the KJc values in a satisfactory manner. • It was demonstrated that T0 evaluated according to the SINTAP MC extension represented the brittle fraction of the data sets and is therefore suitable for the nonhomogeneous base metal. • The efficiency of the large-scale thermal annealing of the Greifswald WWER 440/V230 Unit 1 and 2 RPVs could be confirmed.
6

Application of the Master Curve approach to fracture mechanics characterisation of reactor pressure vessel steel

Viehrig, H.-W., Kalkhof, D. 22 September 2010 (has links) (PDF)
The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C. SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.
7

Application of the Master Curve approach to fracture mechanics characterisation of reactor pressure vessel steel

Viehrig, H.-W., Kalkhof, D. January 2010 (has links)
The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C. SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.
8

Formalisation d'un environnement d'analyse des données basé sur la détection d'anomalies pour l'évaluation de risques : Application à la connaissance de la situation maritime / Formalisation of a data analysis environment based on anomaly detection for risk assessment : Application to Maritime Domain Awareness

Iphar, Clément 22 November 2017 (has links)
Il existe différents systèmes de localisation de navires en mer qui favorisent une aide à la navigation et une sécurisation du trafic maritime. Ces systèmes sont également utilisés en tant qu’outils de surveillance et d’aide à la décision par les centres de surveillance basés à terre. Le Système d’Identification Automatique (AIS) déployé par l’Organisation Maritime Internationale, bien qu’étant le système de localisation de navires le plus utilisé de nos jours, est faiblement sécurisé. Cette vulnérabilité est illustrée par des cas réels et détectés tels que des usurpations d’identité ou des disparitions volontaires de navires qui sont sources de risques pour les navires, les infrastructures offshores et côtières et l’environnement.Nous proposons dans cette thèse une démarche méthodologique d’analyse et d’évaluation des messages AIS fondée sur les dimensions de la qualité de la donnée, dont l’intégrité considérée comme la plus importante de ces dimensions. Du fait de la structure complexe de l’AIS, une liste d'indicateurs a été établie, afin d’évaluer l'intégrité de la donnée, sa conformité avec les spécifications techniques du système et la cohérence des champs des messages entre eux et au sein d’un seul ou plusieurs messages. Notre démarche repose également sur l’usage d’informations additionnelles telles que des données géographiques ou des registres de navires afin d’évaluer la véracité et l’authenticité d’un message AIS et de son expéditeur.Enfin, une évaluation des risques associés est proposée, permettant une meilleurecompréhension de la situation maritime ainsi que l’établissement de liens de causalité entre les vulnérabilités du système et les risques relevant de la sécurité et sûreté de la navigation maritime. / At sea, various systems enable vessels to be aware of their environment and on the coast, those systems, such as radar, provide a picture of the maritime traffic to the coastal states. One of those systems, the Automatic Identification System (AIS) is used for security purposes (anti-collision) and as a tool for on-shore bodies as a control and surveillance and decision-support tool.An assessment of AIS based on data quality dimensions is proposed, in which integrity is highlighted as the most important of data quality dimensions. As the structure of AIS data is complex, a list of integrity items have been established, their purpose being to assess the consistency of the data within the data fields with the technical specifications of the system and the consistency of the data fields within themselves in a message and between the different messages. In addition, the use of additional data (such as fleet registers) provides additional information to assess the truthfulness and the genuineness of an AIS message and its sender.The system is weekly secured and bad quality data have been demonstrated, such as errors in the messages, data falsification or data spoofing, exemplified in concrete cases such as identity theft or vessel voluntary disappearances. In addition to message assessment, a set of threats have been identified, and an assessment of the associated risks is proposed, allowing a better comprehension of the maritime situation and the establishment of links between the vulnerabilities caused by the weaknesses of the system and the maritime risks related to the safety and security of maritime navigation.
9

Avaliação da estabilidade de trincas em componentes estruturais por meio do parâmetro elasto-plástico integral-J e comparação com resultados obtidos via mecânica da fratura elástica-linear / Crack stability assessment on structural components by using elastic-plastic J-integral parameter and comparison to results obtained from linear-elastic fracture mechanics

Tarpani, José Ricardo 17 October 1995 (has links)
Neste trabalho são comparados os resultados analíticos de previsão de falha de um vaso nuclear PWR destinado à propulsão naval, contendo oito diferentes tipos de trinca, obtidos segundo a Mecânica da Fratura Elástica-Linear (MFEL) e a correspondente Elasto-Plástica (MFEP). Os resultados são fornecidos em termos da pressão interna e do gradiente de deformações ao longo da espessura da parede do componente estrutural, sendo diretamente aplicáveis às condições impostas e desenvolvidas em ensaios isotérmicos de hidro-pressurização. O elevado nível de conservativismo dos resultados derivados segundo a MFEL, via critério KIC de disparo de clivagem, quando comparados àqueles obtidos por meio da MFEP, através do critério de iniciação de rasgamento dúctil, Ji, e em especial dos critérios J50 e Jinstab.dúctil de falha com base na Teoria da Instabilidade do Rasgamento Dúctil ou Elasto-Plástico (TIRD/TIREP) por intermédio de diagramas J x T (integral-J versus módulo de rasgamento), foi avaliado e quantificado. O intenso efeito das dimensões dos corpos de prova nos resultados obtidos a partir de ambas abordagens, assim como o papel determinante dos entalhes laterais nos ensaios da MFEP foram definitivamente comprovados. Foi também demonstrado o saudável conservativismo das previsões segundo o critério J50 para projeto e serviço seguros de plantas nucleares frente às condições reais em que se verifica analiticamente a instabilidade dúctil do componente trincado, tais como definidas por Jinstab.dúctil, assim como das previsões decorrentes dos processos de extrapolação linear de curvas J-R no espaço J x T quando comparadas às resultantes de extrapolações não-lineares mais frequentemente utilizadas. Com relação aos efeitos exercidos nos resultados de previsão de falha pelo tipo, profundidade e comprimento da trinca contida na parede do vaso de pressão, ficou demonstrado que as trincas de superfície são muito mais críticas que as sub-superficiais de idênticas profundidade e comprimento, assim como que as avaliações de integridade são muito mais sensíveis a mudanças na profundidade da trinca relativamente a alterações no seu comprimento. As aproximações entre os resultados obtidos via J50 e através de Jinstab.dúttil, e entre os resultados obtidos pelos procedimentos de extrapolação linear e não-linear de curvas JMAT-TMAT, são muito mais nítidas para as trincas de superfície menos profundas e, em especial para as embutidas, mesmo aquelas mais críticas. Deste modo, a metodologia aqui aprimorada, destinada em última instância a avaliações de integridade estrutural de vasos PWR em transientes de potência durante a sua vida em serviço, se mostrou absolutamente efetiva no caso das trincas mais prováveis em tais circunstâncias, quais sejam, as de pequenas dimensões e situadas superficialmente na parede do vaso. Ainda, foi verificada a tendência da ocorrência do vazamento do meio pressurizante anteriormente à falha do vaso por instabilidade dúctil nos casos da presença das trincas mais profundas, independentemente de serem elas de superfície ou sub-superficiais e, novamente, de seu comprimento, contribuindo assim para a percepção visual da iminência da falha bem como para eventos de freamento de trinca dúctil, impedindo a falha catastrófica do vaso PWR. Por outro lado, trincas rasas ou meno·s profundas tendem a entrar no regime de instabilidade dúctil muito precocemente, com a essência da propagação se dando de modo instável, causando fratura rápida ou súbita do vaso sem sinal anterior. Finalmente, foi comprovada nesse estudo a aplicabilidade da técnica analítica de normalização linear para o levantamento de curvas J-R, e como consequência JMAT-TMAT, para a avaliação de integridade estrutural de componentes robustos falhando de modo dúctil após considerável, e mensurável, crescimento estável de trinca; também, foi aqui proposto o ajuste logarítmico de dados de curvas J-R, em oposição ao hoje consensualmente utilizado via lei de potência, de modo a computar os efeitos do fenômeno de saturação de J, permitindo assim extrapolações conservativas e seguras para as condições em que se verifica a falha do componente nuclear. / In this work the analytical results related to a nuclear pressure vessel failure conditions as obtained by Linear Elastic Fracture Mechanics (LEFM) and the Elastic-Plastic Fracture Mechanics (EPFM) were compared for eigth different crack types. The results are supplied in terms of internal pressure and strain gradient through the wall thickness of the structural component, and might be directly applied to isothermal hydrotests experiments. The high conservatism of LEFM approach, by using KIC criterion of cleavage triggering, as compared to results obtained via Ji of ductile crack initiation from EPFM approach, and specially to the J50 and Jduct.instab. criteria based on ductile Tearing Instability Theory through J x T (J-integral x tearing modulus) diagrams, was evaluated and quantified. The overriding effect of specimens size over LEFM and EPFM results were definitely proved, as well as the very strong influence of side-grooving the EPFM specimens. It was demonstrated the healthy conservatism of the predictions following the J50 criterion for safe design and service in the nuclear industry facing the real conditions where ductile instability takes place as analytically defined by Jduct.instab.. In the same way the conservatism of the predictions from the linear extrapolation procedure of J-R curves on J x T space, as compared with the most common non-linear process was proved as well. With respect to the effect exerted by type, depth and length of the crack over the results it was demonstrated that surface cracks are more critical than the embedded ones with identical dimensions, being the analytical evaluation much more sensitive to changes in the crack depth than in its length. The approximations among the results obtained from J50 and Jduct.instab. criteria as well as among the results from the linear and non-linear extrapolation procedure are best verified for the less depth surface cracks and specially for the embedded cracks even the largest ones. So, the methodology here improved, aimed in last instance to structural integrity assessment of PWR vessels on power transients during their service life has been shown to be a powerful tool in evaluating the most expected cracks under such circunstances, that is, those having small dimensions and located on surface wall. Still, it was demonstrated the trend for leak-before-ductile instability in the presence of the deepest surface and internal cracks, allowing the visual perception of the threshold of the vessel failure and the development of crack arrest events avoiding catastrofic rupture of the component. Otherwise, shallow cracks are prone to get very fast in the unstable regime of growth, with the essence of the propagation occuring under this condition, conducting to suddenly fracture of the vessel without any prior evidence. Finally, it was proved in this study the accuracy of the linear normalization technique in deriving J-R curves for the assessment of structural integrity of massive components which fail in a ductile way after undergo large stable crack extensions; it was suggested here the logarithmic fit of J-R data points taking in account more properly the J-saturation phenomena and leading to more safe and conservative extrapolation results when compared to resulting from power-law fit.
10

Avaliação da estabilidade de trincas em componentes estruturais por meio do parâmetro elasto-plástico integral-J e comparação com resultados obtidos via mecânica da fratura elástica-linear / Crack stability assessment on structural components by using elastic-plastic J-integral parameter and comparison to results obtained from linear-elastic fracture mechanics

José Ricardo Tarpani 17 October 1995 (has links)
Neste trabalho são comparados os resultados analíticos de previsão de falha de um vaso nuclear PWR destinado à propulsão naval, contendo oito diferentes tipos de trinca, obtidos segundo a Mecânica da Fratura Elástica-Linear (MFEL) e a correspondente Elasto-Plástica (MFEP). Os resultados são fornecidos em termos da pressão interna e do gradiente de deformações ao longo da espessura da parede do componente estrutural, sendo diretamente aplicáveis às condições impostas e desenvolvidas em ensaios isotérmicos de hidro-pressurização. O elevado nível de conservativismo dos resultados derivados segundo a MFEL, via critério KIC de disparo de clivagem, quando comparados àqueles obtidos por meio da MFEP, através do critério de iniciação de rasgamento dúctil, Ji, e em especial dos critérios J50 e Jinstab.dúctil de falha com base na Teoria da Instabilidade do Rasgamento Dúctil ou Elasto-Plástico (TIRD/TIREP) por intermédio de diagramas J x T (integral-J versus módulo de rasgamento), foi avaliado e quantificado. O intenso efeito das dimensões dos corpos de prova nos resultados obtidos a partir de ambas abordagens, assim como o papel determinante dos entalhes laterais nos ensaios da MFEP foram definitivamente comprovados. Foi também demonstrado o saudável conservativismo das previsões segundo o critério J50 para projeto e serviço seguros de plantas nucleares frente às condições reais em que se verifica analiticamente a instabilidade dúctil do componente trincado, tais como definidas por Jinstab.dúctil, assim como das previsões decorrentes dos processos de extrapolação linear de curvas J-R no espaço J x T quando comparadas às resultantes de extrapolações não-lineares mais frequentemente utilizadas. Com relação aos efeitos exercidos nos resultados de previsão de falha pelo tipo, profundidade e comprimento da trinca contida na parede do vaso de pressão, ficou demonstrado que as trincas de superfície são muito mais críticas que as sub-superficiais de idênticas profundidade e comprimento, assim como que as avaliações de integridade são muito mais sensíveis a mudanças na profundidade da trinca relativamente a alterações no seu comprimento. As aproximações entre os resultados obtidos via J50 e através de Jinstab.dúttil, e entre os resultados obtidos pelos procedimentos de extrapolação linear e não-linear de curvas JMAT-TMAT, são muito mais nítidas para as trincas de superfície menos profundas e, em especial para as embutidas, mesmo aquelas mais críticas. Deste modo, a metodologia aqui aprimorada, destinada em última instância a avaliações de integridade estrutural de vasos PWR em transientes de potência durante a sua vida em serviço, se mostrou absolutamente efetiva no caso das trincas mais prováveis em tais circunstâncias, quais sejam, as de pequenas dimensões e situadas superficialmente na parede do vaso. Ainda, foi verificada a tendência da ocorrência do vazamento do meio pressurizante anteriormente à falha do vaso por instabilidade dúctil nos casos da presença das trincas mais profundas, independentemente de serem elas de superfície ou sub-superficiais e, novamente, de seu comprimento, contribuindo assim para a percepção visual da iminência da falha bem como para eventos de freamento de trinca dúctil, impedindo a falha catastrófica do vaso PWR. Por outro lado, trincas rasas ou meno·s profundas tendem a entrar no regime de instabilidade dúctil muito precocemente, com a essência da propagação se dando de modo instável, causando fratura rápida ou súbita do vaso sem sinal anterior. Finalmente, foi comprovada nesse estudo a aplicabilidade da técnica analítica de normalização linear para o levantamento de curvas J-R, e como consequência JMAT-TMAT, para a avaliação de integridade estrutural de componentes robustos falhando de modo dúctil após considerável, e mensurável, crescimento estável de trinca; também, foi aqui proposto o ajuste logarítmico de dados de curvas J-R, em oposição ao hoje consensualmente utilizado via lei de potência, de modo a computar os efeitos do fenômeno de saturação de J, permitindo assim extrapolações conservativas e seguras para as condições em que se verifica a falha do componente nuclear. / In this work the analytical results related to a nuclear pressure vessel failure conditions as obtained by Linear Elastic Fracture Mechanics (LEFM) and the Elastic-Plastic Fracture Mechanics (EPFM) were compared for eigth different crack types. The results are supplied in terms of internal pressure and strain gradient through the wall thickness of the structural component, and might be directly applied to isothermal hydrotests experiments. The high conservatism of LEFM approach, by using KIC criterion of cleavage triggering, as compared to results obtained via Ji of ductile crack initiation from EPFM approach, and specially to the J50 and Jduct.instab. criteria based on ductile Tearing Instability Theory through J x T (J-integral x tearing modulus) diagrams, was evaluated and quantified. The overriding effect of specimens size over LEFM and EPFM results were definitely proved, as well as the very strong influence of side-grooving the EPFM specimens. It was demonstrated the healthy conservatism of the predictions following the J50 criterion for safe design and service in the nuclear industry facing the real conditions where ductile instability takes place as analytically defined by Jduct.instab.. In the same way the conservatism of the predictions from the linear extrapolation procedure of J-R curves on J x T space, as compared with the most common non-linear process was proved as well. With respect to the effect exerted by type, depth and length of the crack over the results it was demonstrated that surface cracks are more critical than the embedded ones with identical dimensions, being the analytical evaluation much more sensitive to changes in the crack depth than in its length. The approximations among the results obtained from J50 and Jduct.instab. criteria as well as among the results from the linear and non-linear extrapolation procedure are best verified for the less depth surface cracks and specially for the embedded cracks even the largest ones. So, the methodology here improved, aimed in last instance to structural integrity assessment of PWR vessels on power transients during their service life has been shown to be a powerful tool in evaluating the most expected cracks under such circunstances, that is, those having small dimensions and located on surface wall. Still, it was demonstrated the trend for leak-before-ductile instability in the presence of the deepest surface and internal cracks, allowing the visual perception of the threshold of the vessel failure and the development of crack arrest events avoiding catastrofic rupture of the component. Otherwise, shallow cracks are prone to get very fast in the unstable regime of growth, with the essence of the propagation occuring under this condition, conducting to suddenly fracture of the vessel without any prior evidence. Finally, it was proved in this study the accuracy of the linear normalization technique in deriving J-R curves for the assessment of structural integrity of massive components which fail in a ductile way after undergo large stable crack extensions; it was suggested here the logarithmic fit of J-R data points taking in account more properly the J-saturation phenomena and leading to more safe and conservative extrapolation results when compared to resulting from power-law fit.

Page generated in 0.0967 seconds