NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor Company (PBMR), and is used as the preferred material for the internal graphite core structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18 graphite is manufactured using pitch coke, and is vibrationally molded. To assess the structural behaviour of graphite many destructive techniques have been performed in the past. Though the destructive techniques are easy and in some cases relative inexpensive to perform, these methods lead to waste material and require cumbersome time consuming sample preparations. To overcome this problem numerous non–destructive testing techniques are available such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency Eddy current analysis, acoustic emission and impulse excitation techniques. The Hammer Impulse Excitation technique was used as a method in predicting the fatigue life of NBG–18 graphite by focussing on the application of modal frequency analysis of determined natural frequencies. Moreover, the typical fatigue characteristics of NBG–18 graphite were determined across a comprehensive set of load ranges. In order to be able to correlate modal frequency parameters with fatigue life, suitable uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue test specimens were manufactured from two NBG–18 graphite sample blocks. The relationship between natural frequencies of uniaxial test specimens, fatigue life, sample positioning and sample orientation was investigated for different principle stress ratios. Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the Pearson correlation coefficients investigated. However, there was no significant trend found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

NBG–18 graphite is developed by SGL Carbon for the Pebble Bed Modular Reactor Company (PBMR), and is used as the preferred material for the internal graphite core structures of a high–temperature gas–cooled nuclear reactor (HTR). The NBG–18 graphite is manufactured using pitch coke, and is vibrationally molded. To assess the structural behaviour of graphite many destructive techniques have been performed in the past. Though the destructive techniques are easy and in some cases relative inexpensive to perform, these methods lead to waste material and require cumbersome time consuming sample preparations. To overcome this problem numerous non–destructive testing techniques are available such as sonic resonance, resonant inspection, ultrasonic testing, low and multifrequency Eddy current analysis, acoustic emission and impulse excitation techniques. The Hammer Impulse Excitation technique was used as a method in predicting the fatigue life of NBG–18 graphite by focussing on the application of modal frequency analysis of determined natural frequencies. Moreover, the typical fatigue characteristics of NBG–18 graphite were determined across a comprehensive set of load ranges. In order to be able to correlate modal frequency parameters with fatigue life, suitable uniaxial fatigue test specimen geometry needed to be obtained. The uniaxial fatigue test specimens were manufactured from two NBG–18 graphite sample blocks. The relationship between natural frequencies of uniaxial test specimens, fatigue life, sample positioning and sample orientation was investigated for different principle stress ratios. Load ratios R = –oo and R = +2 tested proved to show the highest r–values for the Pearson correlation coefficients investigated. However, there was no significant trend found between the natural frequency and the fatigue life. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

This diploma thesis deals with the determination of the Young’s modulus of coatings using the impulse excitation technique (IET). The theoretical part of the thesis describes Cold and Thermal Spray technology, theoretical foundations of the impulse excitation technique and models of composite materials. The experimental part of the thesis deals with the determination of the tensile modulus of copper coating created by Cold Spray technology. The impulse excitation technique has been used to measure fifteen samples with coating thickness ranging approximately from 0,4 to 2 mm. Results from this measurement were evaluated using five composite models to establish the Young’s modulus of the applied coating. The best results were achieved by using the composite model based on rule of mixtures (ROM).

[pt] Nos últimos anos surgiram algumas alternativas para as tubulações de aço carbono que são a grande maioria no transporte de petróleo e gás, com grande destaque para os materiais poliméricos, principalmente por apresentarem baixa densidade em relação aos metais, boa resistência à corrosão e boa processabilidade. Além disso, os polímeros apresentam maior facilidade de manutenção e instalação, tornando-os economicamente viáveis. No entanto, esses materiais podem sofrer degradação quando expostos a produtos químicos e ao calor. O objetivo desse trabalho e avaliar a variação das propriedades mecânicas das poliamidas 12 e dos polietilenos de alta densidade quando envelhecidos em água durante 6 meses a temperatura ambiente e a 70 graus Celsius, tendo em vista que a temperatura de serviço desses materiais varia entre 70 a 80 graus Celsius. Para a caracterização do material foram realizados, ensaio mecânicos de tração, impacto de excitação por impulso sonoro, como a caracterização por microscopia eletrônica. Os resultados das caracterizações das amostras após envelhecimento foram comparados com os resultados obtidos dos materiais originais, de forma a percebermos que todas as amostras sofreram variações em suas propriedades mecânicas. A temperatura ambiente as amostras de PEAD sofreram um aumento em sua rigidez, aumentando sua resiliência, reduzindo sua resistência ao impacto, reduzindo também a tensão de escoamento e reduzindo seu amortecimento. Já para as amostras de PEAD envelhecidas a 70 graus Celsius houve uma redução na sua rigidez e tensão de escoamento, no entanto houve um aumento em sua resistência ao impacto e na resiliência do material. Para as poliamidas 12 envelhecidas a temperatura ambiente houve uma significativa redução na sua rigidez, na sua tensão de escoamento e tensão máxima, houve um aumento na resiliência do material coerente com um aumento da resistência ao impacto e um aumento no amolecimento. A 70 graus Celsius a poliamida 12 mostrou uma redução na sua rigidez, tensão de escoamento e tensão máxima, houve um aumento na resiliência e na resistência ao impacto, seguido de uma redução no amolecimento. Em todas as situações de envelhecimento as PEAD sofreram uma degradação na cor do material, o que não ficou tão visível para as poliamidas 12 principalmente para o envelhecimento a temperatura ambiente. Sendo assim o comportamento mecânico dos polímeros foi influenciado pela temperatura, sempre acarretando variações em suas propriedades mecânicas e dependendo da situação podendo ser mais ou menos relevante. / [en] In recent years, some alternatives have emerged for carbon steel pipelines, which are the majority in the transport of oil and gas, with a great prominence for polymeric materials, mainly due to their low metal density, good corrosion resistance and good processability. In addition, the polymers present greater ease of maintenance and installation, making them economically viable. However, such materials may be degraded when exposed to chemicals and heat. The objective of this work is to evaluate the variation of the mechanical properties of polyamides 12 and high density polyethylenes when aged in water for 6 months at ambient temperature and at 70 degrees Celsius, considering that the service temperature of these materials ranges from 70 to 80 degrees Celsius. For the characterization of the material, mechanical tests of traction, impact and excitation by sonorous impulse were carried out, such as the characterization by electron microscopy. The results of the characterization of the samples after aging were compared with the results obtained from the original materials, in order to realize that all the samples suffered variations in their mechanical properties. At ambient temperature samples of HDPE increased their stiffness, increasing their resilience, reducing their impact resistance, also reducing the yield stress and reducing their damping. However, for HDPE samples aged 70 degrees Celsius, there was a reduction in their stiffness and yield stress, however, there was an increase in their impact strength and material resilience. For polyamides 12 aged at ambient temperature there was a significant reduction in stiffness, flow stress and maximum stress, there was an increase in the resilience of the material consistent with an increase in impact strength and an increase in softening. At 70 degrees Celsius polyamide 12 showed a reduction in stiffness, yield stress and maximum stress, there was an increase in resilience and impact strength, followed by a reduction in softening. In all aging situations the HDPE suffered a degradation in the color of the material, which was not so visible for the polyamides 12 mainly for aging at ambient temperature. Thus, the mechanical behavior of the polymers was influenced by temperature, always leading to variations in their mechanical properties and depending on the situation, being more or less relevant.

Thesis deals with determination of layerwise mechanical properties of composite ceramics by indirect method, namely Youngs modulus. Based on literature review, it was found that a method to determine elastic properties of one or more components of multi layered composites based on experimental modal analysis and finite element modal analysis, or analytical approach exists. Method based on FE modal analysis was applied to ceramic laminate, where it was attempt to determine youngs modulus of one component. Beyond that, it was attempt to determine Youngs moduli of both components using first two bending resonant frequencies. Results were unsatisfying. Sensitivity analysis showed that layers with unknown Youngs modulus were overly sensitive to small changes in input parameters due to their small relative thickness with respect to thickness of laminate and due to location in laminate. Based on this conclusion, recommendations were made with respect to suitable geometry of test specimens.