A common problem whit Polyvinyl chloride (PVC) is that plasticisers tend to migrate during use. When the plasticisers migrate the material gets stiffer, this can for example cause cracks in the PVC material. Some PVC tends to crack more easily than other; finding out what is causing this problem would bring answers to a number of questions.We have done a study in cooperation with VCC. Former studies, by VCC, with variable results have been executed trying to solve the problem with cracks. We wanted to design a new test method to see if we were able to provoke cracks. If we were able to provoke these cracks, we could see when and why cracks appear in the current PVC item.During our work, we evaluated two different PVC coated materials; PVC1 and PVC2. Both materials had two different structures - with foam backing and without foam backing. We performed mechanical, thermal and chemical treatments on the materials and with help from those experiment we were able to provoke cracks in one of our PVC coated materials.According to our results, PVC1 shows a higher tendency to crack in comparison with PVC2, which only developed wrinkles. In PVC1 we could see cracks in an early stage during our mechanical testing. We evaluated our result by using a microscope and we observed a pattern in the tendency to develop cracks. PVC1 with foam backing had a higher tendency to crack in comparison with PVC1 without foam. Materials that have been abraded before flexing also tend to crack more easily.In order to see if the plasticisers migrated into the foam during our experimental work we performed an extraction of PVC1, according to the results the plasticisers might have migrated to the foam.The major conclusion from this study of PVC1 and PVC2 is that PVC1 tends to crack more easily than PVC2. The foam seems to have a negative effect on the PVC. The abrasion before ageing also have a negative effect on the PVC coated material. We could not see that the chemicals affected the materials.One of the main purposes with this study was to find a new test method for PVC coated items. We think that our test method with the ageing of the material in combination with the mechanical tests as Martindale and Ballyflex is a suitable test method while testing PVC coated materials. / Program: Textilingenjörsutbildningen

In this work, two innovations were demonstrated for in-situ 3D study of fatigue cracks and their closure as a function of applied load. The first related to improvements in how absorption microtomography is used to study fatigue cracks. The second is a new approach to 3D crack mapping relying on X-ray phase imaging and stereometric approaches. Absorption microtomography was used to determine crack surface positions. Crack opening was measured from absorption microtomography data both before and after crack extension and patterns of opening at several loads were analyzed for both cases. X-ray phase contrast imaging, an alternative approach to absorption microtomography, whose sensitivity to cracks is not strongly affected by the shape of the specimen, was also investigated. Increased sensitivity of phase imaging to cracks, compared to that of the absorption X-ray methods, allowed detecting crack positions up to the crack tip with no load applied to the sample. Stereometry reconstruction based on the phase microradiographs was carried out, and the results were compared with those of absorption microtomography on the same specimen. This study demonstrated that it is possible to reconstruct accurate 3D positions of features inside optically opaque sample by recording several X-ray phase microradiographs.

This thesis focuses on the growth of cracks which are small in relation to the material microstructure especially the situation of clusters of small cracks grown from smooth surfaces, termed micro-multi-site cracking, as is frequently the case for components in service. A proper understanding of this regime of crack growth will allow for less conservative maintenance schedules as well as the application of more sensitive health monitoring systems which are currently under development. To address the problem a significant experimental investigation of micro-multi-site cracking was conducted on 7075-T7351 aluminum alloy. Using the resulting data a micro-structurally based transition crack length is defined to determine the point which separates small and long crack growth. This definition is based upon the observed evolution of scatter in the growth rates of growing small cracks. It is shown that this scatter falls with growth until the transition point is reached where it assumes a constant value for the growth of long cracks. It is then shown that the total population of cracks within the clusters can be considered as bi-modal. One distribution consists of primary cracks which can grow and ultimately cause specimen failure. The second distribution consists of secondary cracks, the growth of which ultimately arrests. Several methods for experimentally separating the two distributions have been developed. The first method relies upon the defined transition point between small and long crack behavior. A second method based upon the second derivative of the crack length versus cycle count data has also been developed. Since the secondary cracks cannot lead to failure their data must be discarded prior to any analysis. It is then shown that failure to do so will lead to erroneous non-conservative predictions of crack growth.

Non-destructive monitoring of residual elastic stress in silicon wafers is a matter of strong concern for modern photovoltaic industry. The excess stress can generate cracks within the crystalline structure, which further may lead to wafer breakage. Cracks diagnostics and reduction in multicrystalline silicon, for example, are ones of the most important issues in photovoltaics now. The industry is intent to improve the yield of solar cells fabrication. There is a number of techniques to measure residual stress in semiconductor materials today. They include Raman spectroscopy, X-ray diffraction and infrared polariscopy. None of these methods are applicable for in-line diagnostics of residual elastic stress in silicon wafers for solar cells. Moreover, the method has to be fast enough to fit in solar cell sequential production line.

High mast illumination poles (HMIPs) are tall cantilevered structures used to efficiently illuminate large portions of highways and interchanges. Great interest in the performance of HMIPS has arisen from the discovery of extensive premature cracking at the toes of base plate to pole shaft welds of poles currently in service. These cracks, in some cases, have become so severe that HMIPs have actually collapsed, and therefore present a great threat to public safety. Previous research at the University of Texas at Austin sought to solve the design problems posed by these pole failures by conducting both full-scale and analytical tests on optimized designs of HMIPs for fatigue loads. These studies indicated that using full penetration welds to connect 3" thick base plates to relatively thin shaft walls minimized warping of the base plate during fatigue loading, and maximized fatigue performance. Toward the end of these studies when researchers sought to test an uncoated optimized HMIP back-to-back against a galvanized HMIP of the same design and material, researchers discovered the galvanized specimen had cracked during the galvanizing process. This finding prompted an in-depth study to determine the cause of these cracks, and to determine if practices could be implemented to prevent crack formation. Initially, bend radius, chemistry, and shaft to base plate thickness studies were conducted to find how these parameters affect HMIPs during galvanizing. These parameters were found to play a minor role in the cracking of HMIPs relative to the thermal effects induced during the galvanizing process. Full-scale and analytical tests verified the impact of thermal straining within HMIPs during galvanizing. Instrumenting HMIPs and smaller HMIP stub sections with thermocouples and strain gages provided temperature and initial strain gradients resulting from exposure to the molten zinc bath. This data, as well as observations of cracks in the tested HMIP sections, aided the development of a finite element parametric study comparing HMIPs of the same 150' length and 80 mph design but varying shaft thicknesses. This research concludes that reducing the pole shaft diameter to thickness ratio reduces the likelihood of galvanizing crack formation. / text

Levees are earth structures used for flood protection. Due to their easy availability and low permeability, clays are the most common material used for the construction of levees. Clays are susceptible to desiccation cracks when subjected to long dry spells during summers. There has been an increased interest in studying the occurrence of cracks in soil mass. In particular, many experimental investigations for soils have been undertaken to learn about the crack pattern in earth embankment. However, there is a dearth of work that focuses on the numerical modeling of desiccation cracks effects on levees. This study has been undertaken to analyze the effect of desiccation cracking on the hydraulic behavior of an earth embankment under flooding conditions. A numerical model was developed using the finite element package CODE_BRIGHT. The model was validated from the data obtained from a small scale embankment experiment under controlled environmental conditions. As the phenomenon of desiccation cracking is highly random, a simple random model was developed to capture the variability in crack geometry. The random crack geometry was then passed on to the finite element mesh, so that a probabilistic analysis can be carried out using a Monte Carlo approach, for assessing the embankment’s integrity. The results obtained from the analysis such as time to steady state saturation and steady state flow rate at the outward slope were very interesting to study and provided an insight on the effect of desiccation cracks on unsaturated earth embankments.

119f. / Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-04-04T11:43:01Z No. of bitstreams: 1 michelle%20moreira.pdf: 2342001 bytes, checksum: 944e84d72b8631c02a7df196044f3634 (MD5) / Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-04-09T17:38:51Z (GMT) No. of bitstreams: 1 michelle%20moreira.pdf: 2342001 bytes, checksum: 944e84d72b8631c02a7df196044f3634 (MD5) / Made available in DSpace on 2013-04-09T17:38:51Z (GMT). No. of bitstreams: 1 michelle%20moreira.pdf: 2342001 bytes, checksum: 944e84d72b8631c02a7df196044f3634 (MD5) Previous issue date: 2006 / A amamentação é um processo complexo que incorpora valores sociais, culturais, econômicos e políticos, mas se faz necessário considerar o ser-mulher-primípara como ser decisório, valorizando sua vivência. Os programas de Incentivo à Amamentação, no Brasil, enfatizam aspectos biologicistas, apesar das novas estratégias criadas, a exemplo do aconselhamento em amamentação, favorecendo a assistência humanizada, valorizando a mulher como núcleo do processo e, portanto, capaz de optar pela permanência ou substituição da amamentação, na vivência das fissuras. Minha experiência profissional, atrelada à vivência pessoal e singular, no processo do amamentar com fissuras, deu origem a este estudo fenomenológico, momento em que defini como objeto o significado da amamentação para primíparas que vivenciaram fissuras mamárias e que amamentaram, tendo como objetivo compreender o significado que primíparas atribuem à manutenção da amamentação, tendo vivenciado fissuras mamárias. O referencial teórico-filosófico teve como pilar as idéias do filósofo Martin Heidegger, expressas na obra Ser e Tempo. A entrevista fenomenológica, ocorrida em janeiro de 2006, foi realizada no domicílio de oito primíparas, que vivenciaram fissuras e que amamentaram. As questões norteadoras foram as seguintes: Como foi para você amamentar, tendo fissuras mamárias? Como você se sentiu amamentando nessa situação? À luz dos conceitos heideggerianos, caminhei para a interpretação compreensiva, momento em que percebi que o significado da amamentação, atribuído pelas primíparas, na vivência das fissuras mamárias, baseado no modo existencial de ser-com, foi desvelado pelos modos de ser da pre-sença, do ser-aí. Assim sendo, surgiram: a facticidade, a ocupação, a transcendência, a de-cadência, o temor, o cuidado, a existência inautêntica, a fuga, a angústia, o falatório, a curiosidade, a ambigüidade, a solicitude e a temporalidade. Percebi a tristeza diante do aparecimento da fissura, demonstrando impotência por parte da mulher em resolver tal patologia, a felicidade pela continuidade na prática do amamentar, apesar da vivência de dor, desconforto, perpetuando o mito do amor materno, a manutenção da amamentação em benefício da (o) filha (o), o apoio ambíguo por parte da família, cônjuge, outras nutrizes e equipe multidisciplinar, o desejo velado pela suspensão de amamentar, decorrente da pressão social, o valor nutricional do leite materno e, conseqüentemente, o adequado desenvolvimento nutricional da (o) filha (o), atuando como compensadores pela manutenção da amamentação, a tentativa de suspensão justificada pela ausência de leite materno e/ ou rejeição do seio pela criança, o desconhecimento dos cuidados com a mama, posição e pega corretas no momento do amamentar. O estudo contribuirá para que familiares e profissionais assistam o ser-mulherprimípara na vivência das fissuras, compreendendo-a como ser único, refletindo sobre as ações executadas, entendendo a mulher no seu possível. O processo do amamentar com fissuras mamárias, vivenciado pelo ser-primípara, constitui-se numa prática que envolve um componente biológico e que ultrapassa as dimensões do físico, em busca do significado atribuído pelo seu ser, baseado no modo existencial do cotidiano. / Salvador

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