Zr-2.5 Nb pressure tubes in CANDU reactors are susceptible to delayed hydride cracking (DHC), which is a sub-critical cracking process requiring hydrogen diffusion to a stress concentrator, precipitation, growth and fracture of hydrides. Service-induced and manufacturing flaws are present in some pressure tubes and these flaws may act as crack initiators. An engineering approach has been developed to assess the susceptibility of flaws to DHC. In this methodology, DHC is separated into the initiation and growth stages, and in terms of initiation, flaws are classified as blunt, sharp or crack-like. The experiments performed in this thesis are related to crack-like flaws, which are assessed in terms of the threshold stress intensity factor, K1H, below which DHC cannot occur. There is a large scatter in the overall KIH data base and a lower bound value is conservatively used for flaw assessment. Systematic studies on un irradiated Zr-2.5 Nb pressure tube material have shown that KIH increases with decreasing hydrogen in solution, increasing deviation from the radial-axial plane of the tube, and increasing temperature, while thermal cycling has no significant effect on K1H. Therefore, it may be justifiable to use higher KIH values for assessing flaws with known orientation, hydrogen concentration at the flaw location and operating thermal history. If crack initiation is postulated, as part of a defence-in-depth approach, crack growth is assessed under two scenarios. (1) When the hydrogen concentration is sufficient for cracking to continue under sustained hot conditions, a leak-before-break assessment is performed. DHC velocity is required to determine the time for a crack to grow to the critical crack length for unstable fracture. This thesis shows that crack velocities at different temperatures depend strongly on the thermal history, which affects the hydrogen concentration in solution. Crack velocity increases with increasing hydrogen in solution. In addition, hydrogen supersaturation is required for cracking to occur at the reactor operating temperatures of 2S0-31O°C. (2) When the hydrogen concentration is insufficient for cracking to occur at normal operating temperatures, cracking can only occur during reactor cool-down when hydrides can precipitate as a result of the lowering of temperature. The amount of postulated crack growth per cool-down cycle depends on the crack initiation temperature during cooling. This thesis shows that the crack initiation temperature decreases with increasing cooling rate, and by applying a load-reduction of 20% prior to cooling. Cracking during cooling can be suppressed altogether by allowing the crack tip stress to relax by creep, followed by a load reduction of 15-20%. Recommendations are made regarding reactor loading and thermal history which can reduce the propensity for DHC. From the observations on hydride morphologies and fracture surface features of the DHC cracks under different test conditions, evidence is presented which supports the hydride/stress interaction diffusion model. The observations also demonstrate the inadequacies of the critical length criterion for fracture of a hydrided region.

Made available in DSpace on 2019-03-29T23:59:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-05-22 / Although the use of crack have spread among the different social classes, the association between being poor or even more so to be on the streets and being user is still hegemonic, mainly because of its use have been spreading first among these groups , contributing to exacerbate stigma associated with these social groups. They live in conditions of restrictions of possibilities for (re) integration into society, and that the actions that would aim to get them out of this condition end up reinforcing the stigma attached to crack user, further restricting the possibilities and opportunities of them. Be crack users can be the fuel for the social construction of humiliation, disrespect, marginalization and stigma, and keeping them bound in the chains of a life with few opportunities. We seek to understand the situation experienced by crack users men on the streets, know the moral world where you give the rituals of use, forms of interaction, the symbols and codes that emerge and are built by these men; as well as check for health care and socio-cultural construction of illness. We chose a qualitative approach, which is efficiently applied to this study. The ethnographic method was chosen to allow the understanding of crack culture. The complexities surrounding the use, abuse and crack addiction showed that any attempt to understand not glimpse the socio-cultural environment in which the subject using the crack is located, can be reductionist and incur misinterpretations of the existing reality in streets and in their lives. The study permitted to understand that the beginning and the continuation of crack use are beyond its active chemical-physical potential, far beyond the effect that this substance produces the human body. Social values and idiosyncratic meanings attributed by the user are added to the construction of crack use experience. I could see that there is an awareness on the part of users in general, that the crack is a drug that destroys people in various occupations, which destroys family ties, stigmatize, segregate and cause heavy dependence. However, despite knowing their misdeeds users continue making use of the substance, confirming its potential for addiction, drug addiction. Aside from the physical problems caused in the body, the mental part is always strongly affected, and even if the user through the treatment can succeed in order to get rid of addiction, carry brands brought by crack use, indelible marks - the stigma. Observing and experiencing the context in which the crack user is inserted, better understood the representation of health and illness and that each person has different ways of dealing with it; enabling the understanding of it as a participant in the sociocultural context and glimpsing it holistically, by his life story and the perception of its work to what ails you. I conclude by insisting on the concept that there are many gains when it comes to observing the world from within and near, it allows us to observe interactions and connections among crack users. Especially because it helps us to expand the vision of this scenario and to stop stigmatizing the user and their local moral world, that is, failing to see them in a "world apart" inlaid in the streets and squares of the city of Fortaleza. / Apesar de o uso do crack ter se propagado entre as distintas classes sociais, a associação entre ser pobre ou, mais ainda, estar em situação de rua e ser usuário é ainda hegemônica, principalmente pelo fato de seu uso ter se difundido inicialmente entre estes grupos, colaborando para exacerbar estigmas associados a esses grupos sociais. Vivem em condições de restrições de possibilidades de (re)inserção na sociedade, e que as ações que teriam como objetivo tirá-los dessa condição acabam por reforçar o estigma ligado ao usuário de crack, restringindo ainda mais as possibilidades e oportunidades deles. Ser usuário de crack pode ser o combustível para a construção social da humilhação, do desrespeito, marginalização e estigma, e mantendo-os presos às correntes de uma vida com poucas oportunidades. Buscamos compreender a situação vivenciada pelos homens usuários de crack em situação de rua, conhecer o mundo moral local onde se dão os rituais de uso, as formas de interação, os símbolos e os códigos que emergem e são construídos por estes homens; bem como, verificar a existência de cuidados com a saúde e a construção sociocultural do adoecimento. Optamos pela abordagem qualitativa, que é eficientemente aplicada a este estudo. O método etnográfico foi escolhido por permitir a compreensão da cultura de crack. A complexidade em torno do uso, abuso e dependência do crack evidenciou que toda e qualquer tentativa de compreensão que não vislumbre a conjuntura sociocultural em que o sujeito que utiliza o crack está inserido, pode ser reducionista e incorrer em erros de interpretação da realidade existente nas ruas e na vida dessas pessoas. O estudo permitiu entender que o início e a continuidade do uso do crack, estão para além do seu potencial físico-químico ativo, muito além do efeito que esta substância produz no organismo humano. Os valores sociais e os sentidos idiossincráticos atribuídos pelo usuário somam-se na construção da experiência do uso do crack. Pude constatar que existe uma consciência, por parte dos usuários de modo geral, que o crack é uma droga que destrói a pessoa em várias esferas da vida, que destrói vínculos familiares, estigmatiza, segrega e que causa grande dependência. No entanto, apesar de conhecer os seus malefícios os usuários continuam fazendo uso dessa substância, confirmando seu potencial de dependência, a dependência química. Afora os problemas físicos causados no organismo, a parte psíquica é sempre fortemente afetada, e mesmo que o usuário, por meio do tratamento consiga êxito no sentido de livrar-se da dependência, carregará as marcas trazidas pelo uso do crack, marcas indeléveis o estigma. Observando e vivenciando o contexto no qual está inserido o usuário de crack, se compreendeu melhor a representação de saúde e adoecimento que cada indivíduo apresenta e as diferentes maneiras de lidar com ela; possibilitando o entendimento dele como participante do contexto sociocultural e vislumbrando-o holisticamente, por meio da sua história de vida e da percepção da sua experiência diante do que lhe aflige. Finalizo insistindo na concepção que há muitos ganhos quando se passa a observar o mundo de dentro e de perto, isso nos permite observar interações e conexões entre os usuários de crack. Especialmente porque nos ajuda a expandir a visão sobre esse cenário e a deixar de estigmatizar o usuário e o seu mundo moral local, ou seja, deixando de vê-los em um mundo à parte incrustado nas ruas e praças da cidade de Fortaleza.

In the oil and gas industry, threaded pipe connection is frequently used to connect the casing string, drill pipe strings or production and transportation risers and pipelines. The connection is normally preloaded in order to maintain a sealed and secure connection while in service and avoid leakage. Tapered thread are a common connection and in order to introduce preload to the threaded connection when they are assembled a certain make-up torque is going to be applied. The make-up torque plus external loads result in a multiaxial stress distribution over the connection, where the threaded connections act as stress risers. Environment such as waves and currents cause dynamic loads acting on the pipe line and offshore structures. The weakest point in offshore structure is the pipe connection because of fatigue crack initiated in the connection's threads. Researchers and engineers developed a variety of patented threaded pipe connection which all claiming to improve a connection's fatigue life. The experimental data for patented designs, available in literature, is limited. Most published studies usually comprise experiments on a single connection type. For detailed fatigue analysis those published studies cannot be used since there is no uniformity in testing setup, loading conditions and damage detection technique exist. Moreover, current design curves in codes and standards lead to overly conservative or inaccurate results. The aim of this work is to provide a better understanding of the fatigue mechanisms of threaded pipe connections and to study the effect of different design features on a connection's fatigue life. The final goal is to formulate guidelines for new fatigue resistant connection designs. API connection is used as a reference in this study. Several modifications and design features are applied to the connection type. To simulate the effect of these modifications, a parametric 2D axisymmetric finite element model, ABAQUS is used. 2D finite element result are compared with a 3D model to prove its validity for both make-up. In addition, the results of the 2D axisymmetric simulation are validated by static strain gauge measurements during a make-up test and an axial tension test. The validated model is then used to evaluated the influence of the connection properties and design features on the threaded connection's behaviour. Test rigs were designed to perform axial fatigue experiment on two scales: the small-scale experiments on 1" (33.4 mm outer diameter) connections are performed in axial fatigue testing, the medium scale tests on 4.5" (114.3 mm) connections are carried out under axial tension for which a setup is developed. The majority of the performed fatigue tests are small scale experiments. Several modified configurations are tested. The S-N curve is constructed, so that the effect of certain configuration on the connection's fatigue life can be quantified. The local modification of the threaded connection's geometry as well as the connection's contact condition's contact conditions can have an important influence on the fatigue life of the connection. A beach marking technique is used to visualized the crack fronts at different moments during the tests so that exact crack shape can be seen during post-mortem analysis. The result shown that a crack initiates at the root of the last engaged thread of the male part of the connection, and propagates slowly over a large segment of the circumference, forming a long shallow crack. When the crack penetrates the pipe wall, it rapidly increases in size along two crack fronts. The shape of crack observed in beach mark analysis do not have a semi-elliptical shape as commonly used in fracture mechanics. A fatigue crack growth analysis that considers the crack as an annular flaw, is effective in describing the crack growth behaviour. The experimentally obtained S-N curves and the result from the finite element simulations are combined in multiaxial damage evolution law. The observed trend in fatigue lives of the configuration are explained by using the fatigue analysis. Using a connection's thread load distribution as a measure for its fatigue life is proven to be inaccurate. The main reason for this is that the load distribution is related to axial stresses over the connection. The fatigue life of a threaded connection is determined by the local multiaxial stress distribution and strain range around the root of the last engaged thread. These local conditions are not only the result of the load distribution, but they are also affected by the hoop stress introduced during make-up, which can additionally be affected by a changed connection stiffness. The multiaxial damage evolution law is used to analyse the influence of several features on a connection's fatigue life. It is not for all patented modifications that an increased fatigue life is predicted when applied to the API connection. The final conclusion reached is that, in order to optimize a fatigue resistant connection, several design features must be combined together. The thread shape can be optimized to obtained a low stress concentration factor and reduce the local strains at the thread root. The connection's global geometry and make-up conditions can be optimized to improve the load distribution over the threads and reduce local stresses and strains at the threads.

Aerospace structures are optimally designed and analyzed to specifically-defined engineering parameters. Thus, there is a strong drive to understand fatigue properties of materials, enabling an engineer determine their influence on these constraints. Space structures are usually designed to minimize weight and volume; hence thin designs utilizing strong, lightweight materials are ultimately desired. The goal of this research is to address an innovative testing technique of material properties not readily obtained from current test methods. The properties studied in this research include crack growth rates of small diameter rods in both the radial and transverse grain directions under a constant-amplitude tensile load at room temperature. This approach is illustrated on I-beam specimen manufactured from Aluminum 7075-T7351 Bar. The crack growth rates from the experimental data are then compared with literature results for plates, sheets, and extrusions of the same material. The research completed reveals the test results have comparable [Paris relationship] exponential m-values. The significance of quantifying small diameter metallic material properties have potential for great impact on the future of space structures, but are not limited to one part of the industry.

IF Steel to be used in this thesis which only have 50ppm carbon is approach Iron. It to be part of BCC. Because BCC material have much slip system when increase the cycle will induce to create multiple slip system. The dislocation structure often to become cell. We observation the same result of SEM and TEM in low cycle fatigue. The cell size is small in high plastic strain amplitude. The cell size is big in low strain amplitude. The difference of dislocation structures in front of crack tip which obtained under propagation rates o f 10-4, 10-5, 10-6 and 10-7 mm/cycle is the volume percentage occupied by the dislocation structures viz. misorientation cell, cell, wall, PSBs.

In this thesis, we use IF Steel to be the matrix which composition of carbon is 50ppm approaches Iron and belongs to the part of BCC structure. After we use the load 350kgf precrack, while the propagation rate approaching 2x10-5~3x10-5mm/cycle, we immediately drop the stress intensity factor(£Gk) to a level which is determined by the propagation rate of 9x10-7mm/cycle. Then we record the cycle number as P1, and after the crack tip continues to propagate, we record the cycle number again as P2, and between the period of (P2 ¡V P1), we take 4 sample which marks are 0.25(P2 ¡VP1), 0.5(P2 ¡VP1), 0.75(P2 ¡VP1), (P2 ¡VP1). By this way, we can find out the difference of microstructure of the crack tip from a high load level to a low one. On this experiment, we observation the vein structure, dislocation walls, and so on. It proves that the same phenomenon could also be happened on BCC material, just like FCC material. As time goes by, after drop load, the stored energy is more and more strong. And the vein structure of reverse evolution would become the structure of dislocation cells of normal evolution. Then the crack would continue to propagate on the circumstances.

Over the past years, there are many studies discusses different modes of die cracking and improvement. Die cracking is one of the crucial issues that influence the reliability of flip chip assemblies. Die cracking depends on a combination of several factors, such as residual bending stresses generated in the package due to mismatches in the coefficients of thermal expansion(CTE) of the various materials in the assembly or wafer dicing process . In this study, the stresses in the chip of a FCBGA (Flip-Chip Ball Grid Array) induced by the temperature raising and by the mechanical load of different pressures on an automatic test handler are investigated by using commercial finite element software ANSYS, while the FCBGA is subjected to the high temperature electrically test. The causes and precautions corresponding to the die cracking are studied in order to improve the reliability of products.

Crack Attenuating Mix (CAM) is relatively a new asphalt mixture type used by the Texas Department of Transportation (TxDOT). These mixtures are fine graded, designed using relatively small stone sized aggregates and screenings with a high asphalt content, specifically for retarding the reflective cracking in thin asphalt overlays without sacrificing rutting resistance. The main goal of this study is to promote the use of local aggregates in CAM design. In order to achieve the goal, the development of a mix design procedure and aggregate quality guidelines for CAM design with local aggregates are essential. Several aggregate sources were identified and characterized in terms of their frictional, strength, and durability properties. A refined mix design procedure is recommended using a Superpave gyratory compactor with the capability to measure shear stress during compaction. The emphasis was on preventing rutting and flushing resulting from overfilling of binder in these mixtures, which was observed during compaction by consistent shear failures. The Hamburg Wheel Tracking Device (HWTD) was used for performance evaluation of rutting, whereas the Overlay Tester (OT) was used for cracking evaluation. It is hypothesized that current performance criteria in terms of HWTD and OT are too severe for being applicable to CAM mixes with local aggregates. A modification in HWTD failure criterion is recommended and is used in developing new aggregate guidelines. A correlation analysis was conducted relating aggregate properties and CAM performance in rutting and cracking. Finally, aggregate quality guidelines were developed for CAM using local aggregates based on the correlation study. The mix design recommendations as well as aggregate guidelines and quality criteria provided in the report are based on laboratory investigations and field validation of these is strongly recommended before implementation. / text

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