Some researchers have suggested that the weakest link of dental composites is thefiller-matrix bond. However, due to incompleteness of information dealing with this bond and its stability in a humid environment, it was considered desirable to investigate the effect of water on this region, as well as the influence of filler bonding and filler fraction on compressive strength and therm al expansion. Experimental composites containing different filler fractions of either silane-treatedor untreated fillers were made. Compressive strength and coefficient of thermalexpansion were determined using routine methods, while the hydrolytic degradation was investigated by measuring changes in concentrations of elements in the storagewater using atomic absorption spectrophotom etry. Scanning electron microscopicinvestigations were made on fractured samples. The diffusion coefficient of a representative resin system was determined gravimetrically. Seven commercial composites were investigated regarding hydrolyticdegradation. The filler compositions of these composite materials were determined by emission spectroscopy or energy-dispersive x-ray analysis before storage in distilledwater. This water was replaced and analyzed m onthly using plasma spectrophotom etryor atomic absorption spectrophotom etry. After completed water storage the samples were fractured and investigated by useof scanning electron microscopy.From the results of these studies the following conclusions were drawn: 1. The compressive strength of composites changes linearly with increased fillerfraction. Contrary to bonded fillers, composites containing unbonded fillers loststrength with increased filler fraction. 2. Water diffuses through the polymer m atrix and attacks the filler particles. This degradation is most pronounced for untreated fillers containing glass modifying elements such as sodium, barium and strontium. 3. The resin, used as a matrix, influences the speed with which the hydrolyticdegradation of the filler proceeds. 4. The hydrolytic degradation of the filler seemed to be associated w ith micro-crackform ation occurring in the matrix. Of the investigated composites, the micro-filledresin showed the lowest frequency of such crack formations. 5. The coefficient of ther al expansion decreases linearly with increased fillerfraction. Silane treatment did not influence this coefficient. 6. Using a simplified model to predict stresses in a particle filled composite indicatesthat rather high stress levels are induced in the polymer m atrix due to polym erizationshrinkage. This shrinkage induces radial compressive and tangential tensilestresses with respect to the filler surface. Increased filler fraction increases thetangential tensile stresses but reduces the compressive radial stresses. / <p>S. 1-66: sammanfattning, s. 67-168: 6 uppsatser</p> / digitalisering@umu

L’IASCC est un mécanisme de fissuration intergranulaire par corrosion sous contrainte (IGCSC) induite par l'irradiation. C’est un phénomène complexe qui peut avoir une influence significative sur le temps et le coût de maintenance des composants internes du coeur des réacteurs à eau pressurisée (REP) et est donc un sujet d'intérêt. Des études récentes ont proposé d'utiliser l'irradiation aux ions (protons) comme une alternative à l'irradiation neutronique afin d’améliorer la compréhension du mécanisme. L'objectif de cette thèse est d’étudier la sensibilité à la fissuration de l’acier austénitique SA 304L irradié aux ions ainsi que les facteurs contribuant à cette fissuration. Deux types d’irradiations aux ions ont été menées (fer et aux protons). Ces deux irradiations ont générées des défauts ponctuels dans la microstructure représentatifs de ceux crées par les neutrons provoquant ainsi le durcissement de l’acier austénitique 304L. Matériel (non irradié et le fer irradié) n'a montré aucune sensibilité à la fissuration intergranulaire sur la soumission à un essai de traction lente SSRT (Slow Strain Rate Test) commencer avec une vitesse de déformation de 5 × 10-8 s-1 jusqu'à 4% de déformation plastique dans un environnement inerte. Il est montré que les deux types d’irradiation aux ions (fer et protons) augmentent la sensibilité à la fissuration intergranulaire du matériau après un essai de SSRT dans un environnement simulé de REP à 340 ° C. La corrélation entre la sensibilité de fissuration et le degré de localisation de la déformation plastique a été étudiée. L’impact de l'irradiation aux ions fer sur l'oxydation du 304L a été aussi étudié grâce à des essais effectués pendant 360 h dans un milieu REP à 340 ° C. Les résultats de cette thèse indiquent que la fissuration intergranulaire de l'acier inoxydable 304L en milieu REP peut être étudiée en utilisant l'irradiation Fe malgré sa faible profondeur de pénétration dans le matériau. Par ailleurs, il est montré que le comportement vis-à-vis de la fissuration est similaire entre une irradiation aux protons et au fer, et ceux malgré une localisation de la déformation moins importante pour ces derniers. Par conséquent, l’irradiation au fer est utilisée pour étudier l'impact de la préparation de surface et des chemins de déformation sur la sensibilité de la fissuration intergranulaire de l’acier 304L. / IASCC is irradiation – assisted enhancement of intergranular stress corrosion cracking susceptibility of austenitic stainless steel. It is a complex degrading phenomenon which can have a significant influence on maintenance time and cost of PWRs’ core internals and hence, is an issue of concern. Recent studies have proposed using ion irradiation (to be specific, proton irradiation) as an alternative of neutron irradiation to improve the current understanding of the mechanism. The objective of this study was to investigate the cracking susceptibility of irradiated SA 304L and factors contributing to cracking, using two different ion irradiations; iron and proton irradiations. Both resulted in generation of point defects in the microstructure and thereby causing hardening of the SA 304L. Material (unirradiated and iron irradiated) showed no susceptibility to intergranular cracking on subjection to SSRT with a strain rate of 5 × 10-8 s-1 up to 4 % plastic strain in inert environment. But, irradiation (iron and proton) was found to increase intergranular cracking severity of material on subjection to SSRT in simulated PWR primary water environment at 340 °C. Correlation between the cracking susceptibility and degree of localization was studied. Impact of iron irradiation on bulk oxidation of SA 304L was studied as well by conducting an oxidation test for 360 h in simulated PWR environment at 340 °C. The findings of this study indicate that the intergranular cracking of 304L stainless steel in PWR environment can be studied using Fe irradiation despite its small penetration depth in material. Furthermore, it has been shown that the cracking was similar in both iron and proton irradiated samples despite different degrees of localization. Lastly, on establishing iron irradiation as a successful tool, it was used to study the impact of surface finish and strain paths on intergranular cracking susceptibility of the material.

L’objectif de ce travail est d’améliorer la compréhension des phénomènes de Corrosion Sous Contrainte (CSC) susceptibles d’être rencontrés sur les fils d’armures des conduites flexibles, faits d’aciers ferrito-perlitiques. Dans l’annulaire des conduites flexibles, l’environnement chimique des aciers est constitué d’une « eau de mer » confinée et saturée en CO2. Celui-ci favorise la formation d’une couche protectrice de sidérite qui semble avoir un effet déterminant sur la vitesse de corrosion de l’acier. Les conditions de service entrainant des fluctuations de l’environnement ou des contraintes appliquées s’ajoutant à des contraintes résiduelles peuvent provoquer la rupture des conditions d’équilibre entre l’acier et son environnement protecteur, et amorcer ainsi la CSC.Les paramètres microstructuraux et mécaniques qui gouvernent l’amorçage et la propagation de fissures par CSC dans les aciers ferrito-perlitiques dans un milieu confiné simulé sont identifiés au moyen d’essais de traction lente menés sous différents potentiels électrochimiques sur des éprouvettes lisses et micro-entaillées. La phase d’amorçage met en jeu des effets de synergie entre la localisation de la plasticité et la dissolution de l’acier. Cependant, des effets de l’hydrogène doivent être pris en compte dans la propagation des fissures. L’hydrogène, au travers d’interactions hydrogène/plasticité, entraine l’avancée des fissures. Il a été également démontré que l’emploi de microstructures particulières peut favoriser ou retarder les effets de l’hydrogène sans pour autant affecter la limite d’élasticité de la même manière. / In confined solutions containing dissolved CO2, ferrito-pearlitic steels can suffer Stress Corrosion Cracking (SCC). We could find such situations in the annulus of flexible pipes. In these conditions, a protective corrosion product, the siderite FeCO3, is formed on the steel surface decreasing the corrosion rate. In service, environment fluctuation (such as pH, potential…) and/or an addition of applied stress can disturb the balance between the steel and this protective film, causing the fracture of the latter and leading to SCC.The objective is to understand the mechanism of SCC in such environments and to identify the parameters controlling the initiation and the propagation of cracks. Slow strain rate tensile tests in confined solution are carried out on smooth and notched specimens to study crack initiation and propagation. Crack initiation is controlled by synergistic effects between localized plasticity and the dissolution processes. However, hydrogen effects must be considered to explain crack propagation. Through hydrogen/plasticity interactions, hydrogen ingress leads to crack propagation. It is also demonstrated that the design and use of specific microstructures may promote or delay hydrogen effects, without affecting the yield strength in the same manner. Finally, the influence of a torsional pre-strain on the susceptibility to Environmentally-Assisted Cracking of a cold-worked ferrito-pearlitic steel is studied.

No description available.

This thesis aims to reveal the correlation between stress corrosion cracking propagation behavior and Schmid and Taylor factor mismatch using EBSD analysis. <div><br></div><div>Chloride induced stress corrosion cracking (CISCC) is one of the most vulnerable weaknesses for the widely used austenitic stainless steel in many industries. The complex nature of CISCC involves mechanical, electrochemical, and microstructural perspectives. The objective of this thesis is to assess CISCC phenomenon in austenitic stainless steel from the mechanical and crystallographic perspective, specifically on the effect of local strain and stress and anisotropic plastic deformation. Austenitic stainless steel 304L test coupons are bent in four-point bending fixtures to obtain tensile stress for CISCC, followed by corrosion experiment in boiling magnesium chloride solution. Stress state of the sample is evaluated by finite element analysis (FEA) and X-ray Diffraction Crystallography (XRD) prior corrosion test. Cross section of the cracked region are analyzed with Electron Backscatter Diffraction (EBSD) to analyze the relationship between CISCC behaviors and crystallographic features in the sample. Schmid factor and Taylor factor are used to quantitatively evaluate CISCC initiation and propagation behavior. It is learned that in polycrystalline FCC stainless steel, mismatch of Schmid factor and Taylor factor values in adjacent grains along crack path governs CISCC propagation susceptibility and path selection. Crack propagation factor competition model is proposed based on observations from EBSD maps, incorporating Schmid factor and Taylor factor mismatch, electrochemical condition of crack tip, and anisotropic properties. <br></div>

In this work, Slow Strain Rate Test (SSRT) testing, Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) were used to study the effect of micro-structure, corrosive environments and cathodic polarisation on stress corrosion cracking (SCC) of two grades of high strength steels, Type A and Type B. Type A is manufactured by quench and tempered (Q&amp;T) method. Type B, a normalize steel was used as reference. This study also supports electrochemical polarisation resistance method as an effective testing technique for measuring the uniform corrosion rate. SSRT samples were chosen from base metal, weld metal and Heat Affected Zone (HAZ). SSRT tests were performed at room temperature under free corrosion potential and cathodic polarisation using 4 mA/cm2 in 1 wt% and 3.5 wt% NaCl solutions. From the obtained corrosion rate measurements performed in 1 wt% and 3.5 wt% NaCl solutions it was observed that increased chloride concentration and dissolved oxygen content enhanced the uniform corrosion for all tested materials. Moreover, the obtained results from SSRT tests demonstrate that both Q&amp;T and normalized steels were not susceptible to SCC in certain strain rate(1×10-6s-1) in 1 wt% and 3.5 wt% NaCl solutions under free corrosion potential. It was con-firmed by a ductile fracture mode and high reduction in area. The weld metal of Type A with acicular ferrite (AF), pro-eutectoid (PF) and bainite microstructure showed higher susceptibility to hydrogen assisted stress corrosion cracking compared to base metal and HAZ. In addition, typical brittle intergranular cracking with small reduction in area was observed on the fracture surface of the Type A due to hydrogen charging.

Heat exchanger tubes are commonly made from stainless steel.In a heat exchanger both the process fluid and the cooling orheating media can be corrosive. It is therefore important to beable to select materials that do not suffer from corrosion.Current methods in this area, however, suffer from limitationsand shortcomings. This thesis concerns corrosion tests forgeneral corrosion, dewpoint corrosion and stress corrosioncracking, respectively. For evaluation of general corrosion ofsuperduplex stainless steels in hydrochloric acid and sulphuricacid the importance of activation was studied. The results showthat activation has a great influence on the test result.Further the results indicate that experimental differences canbe the explanation for previously reported differences incorrosion resistance of superduplex stainless steel that havebeen attributed to the alloying with Cu and W. Furthermore, asimple test loop for testing stainless steels under dew formingconditions with a formed condensate of 1 % hydrochloric acidhas been developed. In the work constant strain and constantload test result have been compared and the observationsindicate that the differences can be explained by differencesin the relaxation properties of the materials. <b>Key words:</b>corrosion testing, heat exchanger, stainlesssteel, general corrosion, immersion tests, activation, stresscorrosion cracking, constant load, u-bends, relaxation,dewpoint corrosion / NR 20140805

Visualization is used for stainless steel container wall and lid cross section characterization. Two specific types of containers are examined: 3013 and SAVY. The container wall examined is from a sample of the inner container of a 3013 container. The inner lid cross section examined is from a SAVY container. Laser confocal microscope data and photographic data are used to determine features of the surfaces. The surface features are then characterized by various feature statistics, such as, maximum depth, area, eccentricity, and others. The purpose of this pilot study is to demonstrate the effectiveness of using the methodology to detect potential corrosion events on the inner container surfaces. The features are used to quantify these corrosion events. An automatic image analysis system uses this methodology to classify images for possible further human analysis by flagging possible corrosion events. A manual image analysis methodology is used to determine the amount of MnS on the SAVY container lid cross section. Visualization is an integral component of the analysis methodology.

No description available.

In this work, Slow Strain Rate Test (SSRT) testing, Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) were used to study the effect of microstructure, corrosive environments and cathodic polarisation on stress corrosion cracking (SCC) of two grades of high strength steels, Type A and Type B. Type A is manufactured by quench and tempered (Q&amp;T) method. Type B, a normalize steel was used as reference. This study also supports electrochemical polarisation resistance method as an effective testing technique for measuring the uniform corrosion rate. SSRT samples were chosen from base metal, weld metal and Heat Affected Zone (HAZ). SSRT tests were performed at room temperature under Open Circuit Potential (OCP) and cathodic polarisation using 4 mA/cm2 in 1 wt% and 3.5 wt% NaCl solutions. From the obtained corrosion rate measurements performed in 1 wt% and 3.5 wt% NaCl solutions it was observed that increased chloride concentration and dissolved oxygen content enhanced the uniform corrosion for all tested materials. Moreover, the obtained results from SSRT tests demonstrate that both Q&amp;T and normalized steels were not susceptible to SCC in certain strain rate (1×10-6 s-1) in 1 wt% and 3.5 wt% NaCl solutions under OCP condition. It was confirmed by a ductile fracture mode and high reduction in area. The weld metal of Type A with acicular ferrite (AF), pro-eutectoid (PF) and bainite microstructure showed higher susceptibility to hydrogen assisted stress corrosion cracking compared to base metal and HAZ. In addition, typical brittle intergranular cracking with small reduction in area was observed on the fracture surface of the Type A due to hydrogen charging.