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Showing 111 to 119 of 119 (0.128 seconds)Spelling suggestions: "subject:"8tress corrosion cracking"" "subject:"_stress corrosion cracking""
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Wasserstoffinduzierte Spannungsrisskorrosion: Ein Beitrag zur Beurteilung der Zuverlässigkeit von Spannbetonbrücken mit Hennigsdorfer SpannstahlWilhelm, Tobias 04 November 2014 (has links)
Bei dem Prozess einer Wasserstoffinduzierten Spannungsrisskorrosion (H-SpRK) handelt es sich um einen zeitabhängigen Vorgang, der zu einer Reduzierung der Duktilität und Widerstandskraft des Spannstahls führt und daraus resultierend ein sprödes und schlagartiges Versagen eines Spannbetonbauwerkes zur Folge haben kann. Der Prozess selbst und insbesondere auch die ihn beeinflussenden Parameter sind für die im Bauwesen verwendeten hochfesten Spannstähle älterer Produktion weitestgehend unerforscht. Die Relevanz für bestehende Bauwerke ist jedoch nicht zuletzt durch einzelne dokumentierte und untersuchte Schadensfälle nachgewiesen.
Ziel der vorliegenden Arbeit war es, die zur Verfügung stehenden Bauwerksuntersuchungen aus den zurückliegenden ca. 10 Jahren statistisch zu analysieren und auszuwerten. Auf dieser Basis war ein Berechnungsmodell wahrscheinlichkeitstheoretischer Basis zu entwickeln, mit dem die Gefahr eines spröden Bauwerksversagens für das Gesamttragwerk beurteilt und hinsichtlich der Auswirkungen auf das einzuhaltende Sicherheitsniveau bewertet werden kann.
Es wurden insgesamt 31 Bauwerksuntersuchungen statistisch ausgewertet und beurteilt. Die zur Verfügung stehenden Daten wurden analysiert und hinsichtlich der Prüfqualität sowie der Quantität der Proben bewertet. Dabei war festzustellen, dass aufgrund fehlender konkreter Vorgaben im Regelwerk eine sehr heterogene Datenbasis vorliegt. Nicht alle Untersuchungsergebnisse konnten in die weitere Auswertung einbezogen werden. Die in ausreichender Datenqualität und Datenumfang geeigneten Untersuchungen wurden hinsichtlich ihrer Relevanz für den Prozess einer H-SpRK analysiert und die Auswirkungen einzelner Parameter bewertet.
Im Ergebnis der materialtechnischen Untersuchungen und statistischen Auswertung der Bauwerksuntersuchungen wurde ein Berechnungsmodell vorgestellt, das den gleichzeitigen Ausfall von Spannstahl in allen Bereichen des Bauwerkes berücksichtigt. Zusätzlich zum Standardverfahren des beschriebenen Vorgehens wird das Modell um den Ansatz eines korrelierten Spannstahlausfalls erweitert. Außerdem wird für Bauwerke mit einem statisch unbestimmten Anteil der Vorspannung sowie für Konstruktionen mit gestaffelter Spannstahlbewehrung die Anwendung des Verfahrens konkretisiert.
Neben der Erstellung des Berechnungsmodells wurden Vorschläge zu Vorgaben für die Bauwerksprüfung vorgestellt. Dazu zählen insbesondere die Festlegung von Prüfintervallen sowie einheitliche Vorgaben zu den verwendeten Prüfmethoden und -verfahren. Bezüglich der Festlegung von Mindestumfängen von Proben wird zwischen bestehenden und auch weiter zu nutzenden Bauwerken einerseits sowie Probennahmen im Rahmen von Rückbaumaßnahmen unterschieden.
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| 112 |
Modeling and Analysis for Atmospheric Galvanic Corrosion of Fasteners in AluminumYoung, Paul S. 29 May 2015 (has links)
No description available.
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| 113 |
Corrosion Study Of Interstitially Hardened SS 316L AND IN718 In Simulated Light Water Reactor ConditionsNiu, Wei January 2017 (has links)
No description available.
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| 114 |
Weldability and Corrosion of 7xxx Series Aluminum AlloysBorchers, Tyler Edward January 2016 (has links)
No description available.
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| 115 |
Scaling Effects on Damage Development, Strength, and Stress-Rupture Life on Laminated Composites in TensionLavoie, J. André 04 April 1997 (has links)
The damage development and strength of ply-level scaled carbon/epoxy composite laminates having stacking sequence of [+Tn/-Tn/902n]s where constraint ply angle, T, was 0, 15, 30, 45, 60, and 75 degrees, and size was scaled as n=1,2,3, and 4, is reported in Part I. X-radiography was used to monitor damage developments. First-ply failure stress, and tensile strength were recorded. First-ply failure of the midplane 90 deg. plies depended on the stiffness of constraint plies, and size. All 24 cases were predicted using Zhang's shear-lag model and data generated from cross-ply tests. Laminate strength was controlled by the initiation of a triangular-shaped local delamination of the surface angle plies. This delamination was predicted using O'Brien's strain energy release rate model for delamination of surface angle plies. For each ply angle, the smallest laminate was used to predict delamination (and strength) of the other sizes.
The in-situ tensile strength of the 0 deg. plies within different cross-ply, and quasi-isotropic laminates of varying size and stacking sequence is reported in Part II. No size effect was observed in the strength of 0 deg. plies for those lay-ups having failure confined to the gauge section. Laminates exhibiting a size-strength relationship, had grip region failures for the larger sizes. A statistically significant set of 3-point bend tests of unidirectional beams were used to provide parameters for a Weibull model, to re-examine relationship between ultimate strength of 0 deg. plies and specimen volume. The maximum stress in the 0 deg. plies in bending, and the tensile strength of the 0 deg. plies (from valid tests only) was the same. Weibull theory predicted loss of strength which was not observed in the experiments. An effort to model the durability and life of quasi-isotropic E-glass/913 epoxy composite laminates under steady load and in an acidic environment is reported in Part III. Stress-rupture tests of unidirectional coupons immersed in a weak hydrochloric acid solution was conducted to determine their stress-life response. Creep tests were conducted on unidirectional coupons parallel and transverse to the fibers, and on ±45°. layups to characterize the lamina stress- and time-dependent compliances. These data were used in a composite stress-rupture life model, based on the critical element modeling philosophy of Reifsnider, to predict the life of two ply-level thickness-scaled quasi-isotropic laminates. / Ph. D.
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Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects / Propagação de trinca por fadiga na liga AA7050-T7451 considerando o efeito do meio ambiente, razão de tensões, direção de laminação e forma de ondaCárdenas Barbosa, José Fernando 17 March 2017 (has links)
Main extrinsic and intrinsic modifiers factors of crack growth rate in AA7050-T7451 were assessed in order to provide tools for aeronautical structures designers. These tools cover most necessary information to project aircraft\'s structures using the studied alloy, under damage tolerance philosophy. The experimental methodology consisted of use CT specimens, on TL and LT rolling direction to test its behavior under different conditions of stress ratio, force waveform, and the environment. The stress ratio values were 0.1 and 0.5, the force waveform used were sine and trapezoidal or Dwell under normal air laboratory conditions and salt fog 3.5%NaCl weight in order to simulate the marine environment. In Dwell tests, results were checked with the electrical potential drop technique (DCPD) in addition to the crack opening displacement (COD) method. Using the Walker coefficients, calculated on the present research, could be projected accurately the crack propagation behavior on Paris region and do fatigue life predictions using da/dN and S-N diagrams for different stress ratio values. The corrosion environment increases both crack growth rate and ΔKth due to oxides formation on the crack path that generates a crack closure effect. Dwell carrying makes decrease the crack growth rate by decreasing the slope of the Paris line on log (da/dN) versus log (ΔK) curve, instead of shifting down the line as occurs on titanium alloys. Rolling direction change from LT to TL increase the FCG rate in both threshold and Paris region, where the rate change use to be small. / Os principais fatores modificadores extrínsecos e intrínsecos da taxa de propagação de trincas na liga AA7050-T7451 foram avaliados para fornecer subsídios para projetistas de estruturas aeronáuticas, com base na filosofía de tolerância ao dano. A metodologia experimental consistiu em ensaiar corpos de prova do tipo compact tension (CT) da liga nas direções de laminação TL e LT, para verificar seu comportamento sob diferentes razões de tensões, forma de onda e condição ambiente. Os valores de razão de tensão estudados foram 0,1 e 0,5, as formas de onda foram senoidal e trapezoidal ou de Dwell, em condições normais de laboratório, ao ar, e névoa salina 3,5% NaCl, em massa, para simular um ambiente marinho. No caso dos ensaios Dwell, os resultados foram conferidos pelo método de queda de potencial eléctrico (QPE), além do método de flexibilidade elástica. Usando os coeficientes de Walker calculados a partir dos resultados obtidos, pôde-se projetar com precisão o comportamento da propagação de trinca na região de Paris e prever a vida em fadiga usando os diagramas da/dN e S-N para diferentes valores da razão de tensões. O ambiente corrosivo aumenta tanto a taxa de propagação de trinca, quanto o valor de ΔKth por causa da formação de óxidos na trajetória da trinca, que geram um efeito de fechamento sobre a mesma. Quanto à forma de onda, verificou-se que o carregamento Dwell diminui a taxa de propagação de trinca, diminuindo a inclinação das curvas log (da/dN) versus log (ΔK) na região de Paris, ao invés de deslocá-la paralelamente como ocorre com ligas de titânio. A mudança da direção de laminação de LT para TL aumenta a taxa de propagação de trinca por fadiga (PTF) tanto na região de threshold, quanto na região de Paris, onde a mudança de taxa é pequena.
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| 117 |
Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects / Propagação de trinca por fadiga na liga AA7050-T7451 considerando o efeito do meio ambiente, razão de tensões, direção de laminação e forma de ondaJosé Fernando Cárdenas Barbosa 17 March 2017 (has links)
Main extrinsic and intrinsic modifiers factors of crack growth rate in AA7050-T7451 were assessed in order to provide tools for aeronautical structures designers. These tools cover most necessary information to project aircraft\'s structures using the studied alloy, under damage tolerance philosophy. The experimental methodology consisted of use CT specimens, on TL and LT rolling direction to test its behavior under different conditions of stress ratio, force waveform, and the environment. The stress ratio values were 0.1 and 0.5, the force waveform used were sine and trapezoidal or Dwell under normal air laboratory conditions and salt fog 3.5%NaCl weight in order to simulate the marine environment. In Dwell tests, results were checked with the electrical potential drop technique (DCPD) in addition to the crack opening displacement (COD) method. Using the Walker coefficients, calculated on the present research, could be projected accurately the crack propagation behavior on Paris region and do fatigue life predictions using da/dN and S-N diagrams for different stress ratio values. The corrosion environment increases both crack growth rate and ΔKth due to oxides formation on the crack path that generates a crack closure effect. Dwell carrying makes decrease the crack growth rate by decreasing the slope of the Paris line on log (da/dN) versus log (ΔK) curve, instead of shifting down the line as occurs on titanium alloys. Rolling direction change from LT to TL increase the FCG rate in both threshold and Paris region, where the rate change use to be small. / Os principais fatores modificadores extrínsecos e intrínsecos da taxa de propagação de trincas na liga AA7050-T7451 foram avaliados para fornecer subsídios para projetistas de estruturas aeronáuticas, com base na filosofía de tolerância ao dano. A metodologia experimental consistiu em ensaiar corpos de prova do tipo compact tension (CT) da liga nas direções de laminação TL e LT, para verificar seu comportamento sob diferentes razões de tensões, forma de onda e condição ambiente. Os valores de razão de tensão estudados foram 0,1 e 0,5, as formas de onda foram senoidal e trapezoidal ou de Dwell, em condições normais de laboratório, ao ar, e névoa salina 3,5% NaCl, em massa, para simular um ambiente marinho. No caso dos ensaios Dwell, os resultados foram conferidos pelo método de queda de potencial eléctrico (QPE), além do método de flexibilidade elástica. Usando os coeficientes de Walker calculados a partir dos resultados obtidos, pôde-se projetar com precisão o comportamento da propagação de trinca na região de Paris e prever a vida em fadiga usando os diagramas da/dN e S-N para diferentes valores da razão de tensões. O ambiente corrosivo aumenta tanto a taxa de propagação de trinca, quanto o valor de ΔKth por causa da formação de óxidos na trajetória da trinca, que geram um efeito de fechamento sobre a mesma. Quanto à forma de onda, verificou-se que o carregamento Dwell diminui a taxa de propagação de trinca, diminuindo a inclinação das curvas log (da/dN) versus log (ΔK) na região de Paris, ao invés de deslocá-la paralelamente como ocorre com ligas de titânio. A mudança da direção de laminação de LT para TL aumenta a taxa de propagação de trinca por fadiga (PTF) tanto na região de threshold, quanto na região de Paris, onde a mudança de taxa é pequena.
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| 118 |
Performance characterisation of duplex stainless steel in nuclear waste storage environmentOrnek, Cem January 2016 (has links)
The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.
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An Analysis of Microstructure and Corrosion Resistance in Underwater Friction Stir Welded 304L Stainless SteelClark, Tad Dee 30 June 2005 (has links) (PDF)
An effective procedure and parameter window was developed for underwater friction stir welding (UWFSW) 304L stainless steel with a PCBN tool. UWFSW produced statistically significant: increases in yield strengths, decreases in percent elongation. The ultimate tensile strength was found to be significantly higher at certain parameters. Although sigma was identified in the UWFSWs, a significant reduction of sigma was found in UWFSWs compared to ambient FSWs. The degree of sensitization in UWFSWs was evaluated using double loop EPR testing and oxalic acid electro-etched metallography. Results were compared to base metal, ambient FSW, and arc welds. Upper and lower sensitization localization bands were identified in the UWFSWs. Although higher sensitization levels were present in UWFSWs compared to the arc weld, ambient FSW, and heat treated base metals, the UWFSWs were found less susceptible to corrosion than arc welds due to the subsurface location of the sensitization bands. A SCC analysis of UWFSWs relative to base metal and arc weldments was performed. U-bends were exposed to two 3.5% NaCl cyclic immersion experiments at 21 °C and 63 °C for 1000 hours each. A tertiary test was conducted in a 25% NaCl boiling solution. The UWFSW u-bends were no more susceptible to SCC than base metal in the cyclic immersion tests. In the boiling NaCl test, the SCC of the UWFSWs showed significant improvement over the SCC of arc welds. Arc u-bends cracked entirely within the weld bead and HAZ, while SCC in the UWFSWs showed no cracking localization.
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