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The main objective of the thesis was to gain better understanding of key parameters associated with Cold Work (CW) and their possible effects on Stress Corrosion Cracking (SCC) susceptibility of Austenitic Stainless Steels (ASS) cold rolled to different degrees. The microstructural characterisation of the cold rolled ASS was carried out using optical microscopy to determine and correlate the average grain size with the level of CW. The assessment of martensite development during the CW was carried out using the neutron diffraction technique. The effects of CW levels and strain paths on the lattice strain evolution during the in-situ loading and on the mechanical failure of cold worked ASS were studied. The electrochemical behaviour of cold rolled ASS was also studied. Finally, The SCC susceptibility of ASS was investigated using the Slow Strain Rate Testing (SSRT) techniques. The post-mortem analyses of the failed samples were carried using the optical and Scanning Electron Microscopy (SEM). The study showed that the average grain size decreases with CW and reaches minimum at 20%CW. The smallest and the largest grain size occurred consistently on the Longitudinal (L) and Short-transverse (S) plane respectively. Evidence of martensite development was only found during the plastic deformation at cryogenic temperature and none was observed at ambient temperature. The study showed that the strength of material increases with the level of CW. The Bauschinger effect occurred when the strain path is reversed and its magnitude is independent on whether the tensile or compressive prestraining comes first or last but rather dependent on the amount of CW. The correlation between the CW levels and the lattice strain evolution during the in-situ loading showed that, the lattice strain increases with prestrain and reaches saturation in the material prestrained to 20%CW.The result of the mechanical failure test showed that, 20% cold rolled material loaded along the L and Transverse (T) directions showed a gradual failure, whilst the material loaded along the S direction exhibited a rapid failure. The SEM micrographs suggest that materials loaded along the L and T direction failed with the characteristic features of pure ductile failure while the specimen loaded along S direction showed mixed features of the ductile and brittle failure. The electrochemical properties of the cold rolled materials are more affected by sample orientation than the levels of CW. The short-transverse plane was observed to be most noble whilst the longitudinal plane was the least noble. The results of the SSRT in the chloride environment showed that the plastic elongation, the ultimate tensile strength and the time to failure decrease as the applied potential increases. The post-mortem analysis of the failed samples with the SEM showed that, the fracture surface contained region of ductile failure characterised by dimples, and region of SCC with secondary cracks along the loading axis. Whilst the cross sectional analysis, showed evidence of predominant transgranular stress corrosion cracks. The study found that SCC susceptibility of the ASS is directly linked to strain heterogeneity and directional anisotropy caused by cold working.

Titanium is a widely used metal in industrial and commercial applications. It retains anisotropic mechanical properties at room temperature due to its HCP crystal structure. The effects of crystal orientation have been studied theoretically and through modeling though there is a lack of empirical data available on the topic. The work presented here uses laser-machined voids along with EBSD analysis to study the ductility of grains in different orientations to better understand the microscale fracture process in α-titanium. Experimental results show that hard grains with their c-axis parallel to the tensile direction behave in a less ductile manner than grains with their c-axis oriented away from the tensile direction. This is due to the basal slip systems activating in the former case and prismatic slip systems in the latter. Models utilized include the McClintock model for void growth, Brown-Embury model for void coalescence and FEM crystal plasticity simulations

Nuclear Reactor Pressure Vessels (RPV) are manufactured from medium strength low alloy ferritic steel, specifically selected for its high toughness and good weldability. The ability of the RPV material to resist crack growth is crucial given that it is one of the fundamental containment safety systems of nuclear power plants. For most of their lifetime, the RPV operates at sufficiently elevated temperatures to ensure the material is ductile. However, the development of ductile damage, in the form of voids, and the ability to predict ductile tearing in RPV materials using a mechanistically-based model remains difficult. The Gurson-Tvergaard-Needleman (GTN) model of ductile tearing provides one such tool for predicting ductile damage development in RPV materials. The difficulty in using the GTN model lies in the ability to calibrate the model parameters in a robust manner. The parameters are typically calibrated data, derived from fracture tests and relying on an iterative “trial and error” procedure of numerical simulations and comparison with test data until the model reproduces the experimental behaviour with sufficient accuracy. This research has addressed the development of a mechanistically-based approach to the calibration of the GTN model by developing a new understanding of the ductile fracture mechanism in RPV material through conventional metallography and 3D X-ray computed tomography to image the initiation, growth and coalescence of ductile voids. The metallographic and tomographic data were analysed in a quantitative manner to establish a direct link between the microstructural features and void evolution and the key parameters of the GTN model. This approach has established a more robust mechanistically based method for the calibration of the GTN model that will enhance the conventional iterative calibration procedure. The calibrated model was applied to predict ductile tearing behaviour in compact-tension and notched-tensile specimens. The results showed good agreement with test data and also reproduced the morphology and branching of crack extension observed in practise. Whilst these observations were due, in part, to the numerical solving procedure, they enabled new insights to be gained regarding the development of non-uniform void volume fraction distributions in tested specimensThe results from this research will strengthen the guidance provided to structural integrity engineers in industry regarding the calibration and application of ductile damage mechanics models such as the GTN model for predicting ductile initiation and growth in RPV materials.

O processo de roleteamento é um tratamento superficial, comumente utilizado em peças fabricadas em aços e ferros fundidos nodulares, em regiões onde há concentradores de tensões, com o intuito de melhorar as propriedades de resistência à fadiga. Este processo endurece e introduz tensões residuais compressivas na camada superficial do material, através de deformação controlada, provocando uma redução das tensões de tração que atuam na superfície da peça submetida a carregamentos cíclicos. Este trabalho teve como principal objetivo o estudo do efeito do roleteamento superficial sobre o comportamento em fadiga de um ferro fundido nodular de matriz perlítica, utilizado na fabricação de virabrequins pela indústria automobilística. Foram realizados ensaios de fadiga por flexão rotativa em corpos de prova lisos e com entalhe. Os corpos de prova com entalhe foram divididos em dois grupos, com e sem roleteamento superficial. Foi utilizado entalhe com geometria semicircular com raio de 1,20mm e profundidade de 0,70mm. Para o processo de roleteamento foi utilizado um rolete com diâmetro de 15,00mm e com raio de curvatura de 1,30mm e aplicada uma força de compressão de 2390N. A introdução de tensões residuais compressivas pelo trabalho a frio, dificultou a nucleação e a propagação de trincas na camada superficial dos entalhes roleteados. Isto ficou evidenciado pelo aumento do valor do limite de fadiga para 483MPa obtido para o material entalhado e roleteado, enquanto que para o material nas condições de sem entalhe e somente entalhado estes valores foram de 300MPa e 168Mpa, respectivamente. / Surface rolling is a mechanical treatment commonly used in parts fabricated with steel and ductile cast iron, specifically in stress concentration regions, to improve fatigue properties. This process hardens and introduces compressive residual stresses to the surface of the material through the application of controlled strains, thus provoking a reduction of resulting tensile stress at its surface under cyclic loading. This work deals with the effect of surface rolling on high cycle fatigue behavior of a pearlitic ductile cast iron used in crankshaft by automotive industries. Rotating bending fatigue tests were performed in both smooth and notched specimens. The notched specimens were divided into two groups: with and without surface rolling treatment. The specimens notch geometry was semicircular with radius of 1.20mm and depth of 0.70mm. The rolling treatment was carried out using a roller with diameter of 15,00mm, curvature radius of 1.30mm and a compression force of 2390N. The introduction of compressive residual stresses under cold work made difficult the nucleation and propagation of the crack on the rolled surface of the notch. It was confirmed by the increase of the endurance limit of the surface rolled specimens to 483MPa in comparison with the smooth and notched specimens, respectively, 300MPa and 168 MPa.

Les prévisions alarmistes en ressources naturelles encouragent la recherche de solutions alternatives au niveau mondial. Le recyclage devient alors un défi majeur pour la société, en particulier pour les produits dérivés du pétrole comme les huiles de transformateur. Cette étude est basée sur la recherche de nouvelles voies de revalorisation de ces huiles, par l’analyse critique du contexte concurrentiel, des segments de marché potentiels, ainsi que des propriétés physico-chimiques de ces huiles. Nous nous sommes attachés à déterminer l’adéquation des performances et caractéristiques des huiles de transformateur régénérées aux exigences propres au marché de l’usinage et de la mise en forme des métaux. L’usure des matériaux dans le cadre de la lubrification limite et au-delà, est un domaine d’étude complexe combinant la mécanique, la physique du solide, la chimie ainsi que la thermodynamique des phénomènes irréversibles. Dans le cadre de cette étude les performances d’hydrocarbures neufs, usagés (pollué par les Polychlorobiphényls) et régénérés, ayant des propriétés physico-chimiques et rhéologiques proches, sont comparés dans le cadre d’essais sclérométriques et tribométriques sur une fonte à graphite sphéroïdal, matériau de frottement largement employé dans l’industrie du transport. Une séquence de techniques d’analyse de surface est développée afin de caractériser les morphologies des surfaces et quantifier les déformations de matières résultantes du frottement. La complémentarité des essais sclérométriques et tribométriques, qui permettent d’étudier les performances des hydrocarbures dans différents états de contraintes, respectivement de compression et de cisaillement, révèlent les bonnes performances des huiles de transformateurs régénérées. En quantifiant spécifiquement les performances des huiles revalorisée à travers la détermination de paramètres tribologiques classiques, comme les taux de déformations, les coefficients de frottements ou encore les temps d’initiation au grippage. La composition finale de l’huile régénérée, à savoir la longueur des chaines hydrocarbonées, les teneurs en eau et en PCB, conditionne son comportement tribologique. Suite à ce bilan positif portant sur les performances des huiles de transformateur régénérées en usure abrasive et catastrophique, la mise en forme des métaux peut être identifiée comme une nouvelle voie de valorisation matière de ces huiles. / The alarming forecasts of natural resources encourage worldwide the search for alternative solutions. Hence recycling becomes a major challenge for society, especially for petroleum products such as transformer oils. This study is based on finding new ways of valorizing these oils, which is a complex problem that must meet the economic, political, regulatory, environmental and scientific constraints and challenges. A critical analysis of the competitive environment, of the potential market segments, as well as physic-chemical properties of these oils is the basis to determine new ways of revalorization. In this study, we attempted to determine the suitability and performance characteristics of transformer oil regenerated to the specific requirements of the machining and shaping of metals. The wear of materials under boundary lubrication and beyond this regime, is a complex area of study combining mechanics, solid state physics, chemistry and thermodynamics of irreversible processes. In this study the performance of new, used ( polluted by polychlorinated biphenyls ) and regenerated oils with close physic-chemical and rheological properties are compared in scratch test and tribometric with a ductile cast iron, which is friction material widely used in the transportation industry. A sequence of surface analysis techniques is developed to characterize the morphologies of the surfaces and quantify the resulting deformation of the friction material. The complementarity of scratch an tribometric tests for the study of the performance of hydrocarbons in different stress states, respectively compression and shear, reveals the good performances of regenerated transformer oils. This study has allowed discriminating the behavior of various origins oils under conditions of extreme friction, and specifically quantifying the performance of the regenerated oils through the determination of classical tribological parameters such as rate of deformation, friction coefficients or time to seizure. The final composition of the regenerated oils, ie the length and nature of the hydrocarbon chains, the water and PCBs content and the presence of polar molecules, determines its tribological behavior. Thus, the study showed that the performance of regenerated oils increases with the water and PCB content. Following this positive assessment on the regenerated oil performances in case of abrasive and catastrophic wear, machining and shaping of metals can be identified as a new way for regenerated transformers oils.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22067号 / 工博第4648号 / 新制||工||1725(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 安田 秀幸, 教授 辻 伸泰, 教授 宇田 哲也 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The Grängesberg Mining District (GMD) is located in the western part of the Bergslagen province in south central Sweden, and is the only known apatite-iron oxide mineralization south of Norrbotten. The Grängesberg deposit is the largest of the mineralizations along GMD and consists of a line of steeply to moderately dipping 20-100 m wide lenses extending to a depth of 1.7 km. It is hosted by felsic volcanic rocks that are phyllosilicate altered in the vicinity of the ore. Field relationships indicate that a competent granitoid was structurally emplaced on top of the ore during D2, and that the less competent phyllosilicate-rich host rocks accommodated large parts of the strain. These D2 structures described from the area around the ore bodies in Grängesberg include stretching lineation at the tapering edges of the lenses, asymmetric folds with opposite vergence along strike, sheath folds and possibly fold interference patterns. These structures are proposed to have formed in response to the competence contrast and the reverse movements on a large scale. The hypothesis is that the competence contrast between the competent ore and granitoid and the less competent host rocks could explain the formation and location of the key D2-structures in Grängesberg. To test the hypothesis, four analogue tectonic models were run in the centrifuge at the Hans Ramberg Tectonic Laboratory (HRTL), Uppsala University. The competent bodies were represented by an acrylic glass wedge with two lenses corresponding to the ore lenses, with an inclination of either 60° or 45° mimicking the approximate dip of the ore. Plasticine was used as the less competent host rocks. On the top surface, circles and squares were printed and used as strain markers. The models were run at c. 300-400 G until penetrative deformation and shortening ranging from 32.5 to 39.2% was reached. During centrifuging, the wedge indented the plasticine, resembling the possible deformation during thrusting of the deep granitoid. The models were then cut to reveal the structures formed, and one model was digitalized using the software Move. After shortening, the strain markers had deformed to show a change in direction of strain around the lenses. Vertical sections perpendicular to the shortening direction showed that stretching lineation developed between the lenses. Horizontal sections revealed asymmetric non-cylindrical folds with opposite vergence along strike and fold interference patterns. These results show that the observed field relationships were reproducible with the model setup, and that the competence contrast between the ore bodies, the granitoid and the host rocks could be the controlling factor for localization of shear and sites of stretching in the area.

The primary goals of this project were to examine the amount of lateral force resisted by a single-bay mortise-tenon connected timber moment frame, and to introduce ductile behavior into the mortise-tenon connections by adding a steel sleeve around a traditional wood peg. This research aimed to provide proof that traditional timber frames are capable of ductile racking while reliably complying with ASCE 7-10 building code drift speci! cations, implying an increase in the ASCE 7-10 ductility factor (R) for wood frames when used as lateral force resisting elements. A secondary goal was to promote traditional heavy timber framing as a main structural system. Modern structural framing is dominated by light-wood, steel, and concrete framing. The exploration in this project aspires to demonstrate that heavy timber frames can achieve comparable lateral performance and frame behavior to other current lateral systems, reassuring the reliability of traditional timber frames.

The diploma thesis deals with the modification and inoculation of cast iron with spheroidal graphite, the influence of the chemical composition on the shape and size of the graphite nodules and ferrite/perlite ratio in the structure. The aim of the practical part was to determine the effect of inoculant containing bismuth (SMW 605) on microstructure and mechanical properties of ferritic ductile cast iron GJS 400-15. The dissolving time of mold inoculant was further investigated. The samples were subjected to a tensile test, Charpy impact test, hardness test and graphite morphology and ferrite/perlite examination using standard ČSN EN ISO 945-1.