Structural integrity assessment of nuclear components assessed using the R6 Failure Assessment Diagram approach requires an understanding of the limiting condition in terms of both fracture and plastic collapse. For ductile materials, such as stainless steels used for nuclear components, including the primary pipe-work of a Pressurised Water Reactor (PWR), the limiting condition defined by plastic collapse is likely to occur prior to the initiation of fracture. This is due to the relatively low yield stress of the material and the high fracture toughness. If this is the case, structural integrity may be solely assessed on plastic collapse criteria, with little or no reference to fracture toughness; thus considerably simplifying the assessment procedure, whilst maintaining the integrity of the plant. Nevertheless, an in-depth understanding of fracture under plastic collapse conditions is required to make a robust case for single parameter assessments based on a plastic collapse criterion alone. The challenge in this project lay in understanding and predicting ductile fracture initiation under large-scale yielding conditions, i.e. outside the normal validity limits of conventional elastic-plastic fracture mechanics as plastic collapse conditions are achieved. The approach developed in this research has explored three fracture assessment methods: (a) two parameter fracture mechanics based on the J-integral and a refined Q-parameter calculated closer to the crack-tip under widespread plasticity than is conventionally the case, (b) two local approach methods based on critical void growth ratio defined by Rice and Tracey, and (c) a local approach method based on the critical work of fracture. All three methodologies were found to adequately describe failure across a range of constraint conditions. The fracture toughness constraint dependence of 304(L) stainless steel was studied experimentally and analytically. Significant constraint loss was shown to occur in nominally high constraint fracture toughness specimens due to extensive plastic deformation at fracture initiation. Furthermore, significant fracture toughness constraint dependence was observed experimentally. An analytical method using local approach criteria was developed to predict high constraint fracture toughness, required for structural integrity assessments, and to quantify the constraint dependence fracture toughness as a function of two parameter fracture mechanics based on the J-integral and the refined Q-parameter. The influence of constraint on the prediction of failure in a stainless steel pipe containing a fully circumferential crack of various depths was investigated analytically for a range of loading conditions. A refined constraint independent failure assessment methodology was developed using local approach analyses. Using this methodology, the pipe component was shown to consistently fail by plastic collapse irrespective of the crack depth or loading condition. The conservatism of the conventional structural integrity assessment was quantified and shown to vary with crack depth and with loading conditions. This research has suggested that failure in a 304(L) stainless steel pipe will be by plastic collapse prior to ductile initiation for a limited range of defects and loading conditions. Further analytical studies and experimental work will be required to demonstrate whether this observation is general for a wider range of defects and loading conditions.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / Pectin obtained from cocoa husks has recently been investigated because of its gelling and stabilizing properties that have great potential for the food, cosmetic and pharmaceutical industries. However, its production at the industrial level has not been studied or developed in Peru. A fundamental part of the extraction process is the stage of hydrolysis and filtering of the cocoa shell. Because of this, an automated system for acid-thermal hydrolysis and shell filtration is proposed. The control of both processes is of great importance because the quality and efficiency of the extracted pectin will depend on it. The tests will be carried out in a cylindrical taper with a 100 L capacity which is adapted to contain a 20 L cylindrical filter, both made of AISI 304 stainless steel. The filter has a motor to homogenize the temperature and pH of the mix. The pH of the process is 2 and the temperature is 90 ± 2 °C, since in these ranges the pectin is released more easily from the cocoa shell. The method consists of the structural design of the tank and the filter, and in the design of the pH regulator and the heating system. The yield of the extraction process was achieved by 10%. / Revisión por pares

No description available.

In response to the extensive energy demands on national and global levels, concentrated solar power (CSP) plants are designed to harness and convert solar energy to electricity. For such green energy application, robust, reliable and durable materials for CSP constructions are required. The corrosion resistance is among many parameters to consider in these thermalelectrical stations such as for pipes and storage tanks in CSP. In this investigation, the corrosion behavior of AISI 304 stainless steel (18 wt. % Cr, 8 wt. % Ni) with the heat transfer fluid, also known as solar salt, has been examined. The ternary eutectic salt mixture with the composition, 53 wt. % KNO3, 40 wt. % NaNO2, and 7 wt. % NaNO3, that melts at 142°C, has a potential use in CSP as a heat transfer fluid. The solar salt was prepared for this corrosion study from reagent grades of high purity nitrites and nitrates. Samples of AISI 304 stainless steel were sectioned from a sheet stock of the alloy and exposed to solar salt at 530°C in air at 1 atmospheric pressure. After test intervals of 250, 500, and 750 hours in total immersion condition, AISI 304 stainless steel samples have developed a scale of corrosion products made up of multiple oxides. X-ray diffraction and scanning electron microscopy with X-ray energy-dispersive spectroscopy were employed to examine the extent of corrosion and identify the corrosion products. Transmission electron microscopy was used to verify the corrosion products identity via electron diffraction patterns. Oxides of iron were found to be the primary corrosion products in the presence of the molten alkali nitrates-nitrite salt mixture because of the dissolution of the protective chromium oxide (Cr2O3) scale formed on AISI 304 stainless steel coupons. The corrosion scale was uniform in thickness and made up of sodium iron oxide (NaFeO2), iron oxide, hematite (Fe2O3), and chromium-iron oxide (Cr,Fe)2O3 solid solution. The latter was iv found near the AISI 304 stainless steel. This indicates that the scale formed, particularly on the upper layers with presence of sodium iron oxide and iron oxide, hematite, is protective, and forms an effective barrier against penetration of fused solar salt. At the alloy interface with the bulk corrosion scale, the corrosion process induced a compositional modification in the grains located at the interface. There are iron rich and iron depleted grains at the interface if compared to the nominal iron content of the alloy. The mode of attack is identified as uniform at the test temperature of 530°C, showing a parabolic behavior with a parabolic rate constant (Kp) equals to (m2 /sec). By extrapolation, annual corrosion rate is estimated to reach 0.784 mils per year. Corrosion behavior of AISI 304 stainless steel is discussed in terms of thermodynamics and reaction paths.

Various nitrides, such as chromium nitride and titanium nitride, find extensive use in cutting tools, micromechanical devices, and medical implants due to their exceptional physical, mechanical, and chemical properties. These coatings exhibit superior hardness compared to high-speed steel and cemented carbide along with notable protective capabilities against corrosion and wear. These coatings have been successfully used to enhance the properties of cemented carbide and steel tools while safeguarding their surfaces. By adjusting deposition parameters like N2 gas pressure, the properties of PVD coatings can be tailored to effectively withstand specific dominant wear modes during machining. The study investigates and demonstrates that CrN coatings can be specifically engineered to have distinct mechanical and tribological properties by adjusting the N2 gas pressure, which enhances machining performance in cases where BUE formation occurs. A comprehensive coating characterization was conducted for each CrN coating studied. Wear performance assessments of the various CrN-coated WC tools were carried out during dry finish turning of SS 304. Additionally, high temperature coating characterization was performed for the best-performing in house deposited coating (nitrogen gas pressure of 4 Pa, bias voltage of -50 V) and a commercial coating, up to 450°C. The results highlighted the influence of N2 gas pressure on the structural, mechanical, and tribological properties of CrN coatings. The findings indicate that coatings with a comparatively low H/E ratio (while maintaining higher elastic modulus values), low roughness, moderate residual stress, high plasticity index, and high toughness exhibited superior performance when machining sticky materials and in high-temperature applications prone to adhesive wear and built-up edge (BUE) formation. Furthermore, high-temperature studies confirmed that the in-house coating retained a low H/E ratio, high plasticity index, high toughness, and low roughness, without compromising the hardness or elastic modulus values. In contrast, the commercial coating failed to retain its properties at higher temperatures. These high-temperature studies provide valuable insights for selecting CrN coatings tailored for machining materials that tend to adhere to the cutting tool and for high-temperature applications. / Dissertation / Master of Applied Science (MASc) / Coating properties such as hardness, residual stress, adhesive behaviour, elastic modulus, and roughness significantly affect tool performance and wear patterns, besides machining parameters and conditions. This research focuses on CrN coatings deposited by PVD cathodic arc deposition, adjusting the N2 gas pressure while keeping bias voltage constant. The research investigates and illustrates that CrN coatings can be specifically tailored (by adjusting the N2 gas pressure) to possess unique mechanical, and tribological properties that ameliorate machining performance in scenarios involving BUE formation. Three CrN coatings were deposited using the PVD technique by varying the N2 gas pressure. A thorough coating characterization was conducted for each of three in house deposited coatings and one commercially available coating. The wear behaviour of different CrN-coated WC tools was evaluated during dry finish turning of SS 304 to identify the best-performing coating. Lastly, high-temperature coating characterization was performed up to 450 ˚C for one in-house deposited coating (nitrogen gas pressure of 4 Pa, bias voltage of -50 V) and one commercial coating. The results showed that a coating that has low H/E ratio (without compromising elastic modulus), high plasticity index, high toughness, moderate residual stress and low roughness effectively minimizes issues related to sticking and BUE formation and retains coating properties at high temperatures.

Ce travail a porté sur l'étude des mécanismes d'oxydation de l'acier AISI 304 sur une gamme de température allant de 800 à 1000°C. Nous avons examiné plus particulièrement l'influence des dépôts sol-gel de lanthane et de cérium sur les processus d'oxydation. L' apport de la spectroscopie IR a permis de mieux identifier les oxydes mixtes de type spinelle FeCrO4 et Mn1,5Cr1,5O4 et corindon Fe2O3. L'association des différentes techniques d'analyse telles que la DRX in situ, la spectroscopie IR, le MEB, l'EDS et la microscopie électronique à transmission (MET) ont permis de proposer un nouveau mécanisme d'oxydation de l'acier AISI 304 au cours de son oxydation à 1000°C. Les dépôts sol-gel de lanthane et de cérium conduisent à une diminution importante des constantes de vitesse d'oxydation. Dans le cas de l'AISI 304 recouvert d'un dépôt sol-gel d'oxyde de lanthane, la DRX in situ montre que la croissance de l'oxyde mixte LaCrO3 intervient dès le début de l'oxydation. Cet oxyde est localisé à l'interface interne et bloque la diffusion externe du fer tout en retardant la diffusion externe du manganèse. Ceci peut être dû au fait que le lanthane agit de façon synergique avec le silicium afin de bloquer la diffusion externe du fer et favoriser la formation de la chromine. Le lanthane peut aussi agir en bloquant la diffusion externe des cations métalliques au travers de la couche de chromine selon un processus de ségrégation dynamique au joint de grains. Dans le cas du dépôt sol-gel d'oxyde de cérium le régime linéaire que nous avons observé à toute température est le témoin d'un processus de croissance de la couche d'oxyde limité par la diffusion à travers une couche de CeO2 d'épaisseur constante située à l'interface externe. Dans ce cas l'absence des oxydes contenant du fer dans la couche d'oxyde permet de conclure à un effet synergique avec le silicium qui bloque la diffusion externe du fer. Les essais de cycles thermiques montrent que l'adhérence des couches d'oxyde formées en présence de dépôts sol gel ne s'en trouve pas améliorée

The "incorporation" of the GDR into FRG's existing system of institutions after 1989 has led to a dynamic process of change in the living situation of East Germans. In the following paper stability and change of various dimensions of individual coping strategies are to be examined. To do this, I analytically distinguish four elements: frames, habits, utilisation of available resources, and framing.

Der Aufsatz rekonstruiert die Dialektik von Individualisierung und moderner Sozialpolitik und führt zu diesem Zweck die Diskussionsstränge um die Entstehungsbedingungen von staatlicher Sozialpolitik und um die Weiterentwicklung von Sozialpolitik zusammen. Die Analyse befaßt sich zunächst mit Individualisierung als Voraussetzung für die Entstehung moderner Sozialpolitik, um dann, ebenfalls noch in historischer Perspektive, die Bedeutung von Sozialpolitik für die Vollendung der modernen Individuen als Staatsbürger zu betrachten. Anschließend wird die sozialpolitische Strukturierung von Lebensläufen in der Gegenwart diskutiert und dargelegt, daß Sozialpolitik nicht nur reguliert, sondern auch Handlungsspielräume eröffnet und deren individuelle Nutzung möglich macht. Zuletzt wird nach aktuellen staatlichen Reaktionen auf individuelles Handeln gefragt. Die Beobachtung der historischen Kontinuität, mit der Individuum und Sozialpolitik von den Anfängen der gesellschaftlichen Moderne bis in die Gegenwart aufeinander einwirken und in ihrer Entwicklung miteinander verwoben sind, soll dazu anregen, die Analyse moderner Sozialpolitik in eine umfassende gesellschaftstheoretische Perspektive zu stellen.

In a norm game, under certain conditions, there exist Nash equilibria of mutual cooperation. Experimental work demonstrates that even in one-shot situations the level and proportion of cooperative behavior increases if an punishment option is available to the players of a public goods game. It is therefore important to analyze conditions such that this is consistent with a rational choice approach. The paper is meant as a first step toward this task. The main result will be that nonstandard assumptions about human motivations or preferences can explain norms with sanctions even in one-shot situations. This is shown by an analysis of the norm game with two well-known recent models of fairness from behavioral game theory.

Empirically, self-employed persons often operate with the support of their partners or other household members as co-workers in the firm. The formal or informal employment of the marriage partner in particular seems to have a lot of advantages, such as fiscal benefits and low wage costs. But from a theoretical point of view, these advantages are jeopardized by serious cooperation problems: If the spouse of the self-employed decides to work in the jointly-run business, former qualifications are lost. Hence a one-sided dependence on the part of the co-working spouse arises, which increases with the amount of relation-specific investments. Hence the actors are confronted with a cooperation problem, because the decision for co-working requires trust concerning the future action of the self-employed. Within this framework, this paper is focused on the determinants which influence the decisions concerning collaborating in the business of a self employed life’s companion as well as the extent of labor provided in the case of co-working. It can be assumed that the three types of determinants investigated in this paper affect the assignment of a spouse or cohabitation partner in the business of a self-employment person: (1) economic determinants which are individual productivity and human capital of the life’s companion, (2) the situation of the family and the household, and (3) characteristics of the entrepreneur and the firm. Based on a sample of self-employed empirical analysis indicates that trust and specialization play a crucial role in explaining co-working of the life’s companions of self-employed persons. However, economic determinants like productivity and human capital do not show the expected effects on collaboration.