Objetivos: avaliar espécimes com as seguintes combinações de materiais/processamentos: a) porcelana feldspática aplicada por meio de técnica tradicional sobre infraestrutura de zircônia; b) porcelana feldspática injetada sobre infraestrutura de zircônia, c) porcelana feldspática usinada em sistema CAD-CAM e cimentada (Rapid Layer Technique) sobre infraestrutura de zircônia; d) vitro-cerâmica à base de dissilicato de lítio processada por meio de sistema CAD-CAM e unida à infraestrutura de zircônia por meio da sinterização de um vidro na interface (técnica CAD-on) com relação a: (1) resistência ao lascamento de aresta do material de recobrimento (a influência do tipo de resfriamento foi analisada para os processamentos a e b) e; (2) níveis de tensão residual superficial mensurados nos materiais de recobrimento, por meio de ensaio de fratura por endentação (a influência do tipo de resfriamento foi analisada para os processamentos a e b). Material e métodos: Barras de duas camadas com dimensões de 25 mm de comprimento por 4 mm de largura e com espessuras de porcelana e infraestrutura combinadas de modo a oferecer a razão de 1 mm de cada material foram confeccionadas seguindo as orientações dos fabricantes. O teste de lascamento de aresta foi realizado em uma máquina universal de ensaios, utilizando um endentador Vickers acoplado a essa máquina. A tensão térmica residual superficial foi calculada a partir de endentações feitas na camada de porcelana. Resultados: A resistência ao lascamento (ReA) foi significativamente maior para os espécimes processados pelo sistema CAD-on (ReA = 612,8±271,8 N/mm). Bilayers confeccionadas pelo sistema Rapid Layer Technique apresentaram valor de ReA intermediário de (417,9±187,2 N/mm) e os grupos nos quais foi utilizada porcelana processada pela técnica de sinterização tradicional ou por injeção foram os que apresentaram os menores valores de resistência ao lascamento, com médias de 349,7±116,8 N/mm (tradicional/resfriamento lento) 285,6±117,5 N/mm (tradicional/resfriamento rápido), 298,4±119,9 N/mm (injetado/resfriamento lento) e 263,5±107,9 N/mm (injetado/resfriamento rápido). Para os grupos com porcelana aplicada sobre a infraestrutura pela técnica tradicional e injetada o teste t de Student mostrou que houve um efeito significativo do protocolo de resfriamento, sendo que os espécimes que passaram por resfriamento lento atingiram maiores valores de ReA. Apenas o grupo Rapid Layer Technique apresentou média de tensão superficial correspondente a tensões de tração. Todos os outros grupos apresentaram tensões de compressão na superfície. Conclusões: há um efeito significativo da associação material/processamento na resistência ao lascamento de aresta das bilayers testadas e com relação ao efeito da velocidade de resfriamento (lento e rápido). Os espécimes que passaram por resfriamento lento atingiram maiores valores de resistência ao lascamento, independentemente do método de processamento (tradicional ou injeção). A combinação material/processamento afetou significativamente as tensões residuais superficiais das bilayers testadas, porém, não houve efeito da velocidade de resfriamento no nível de tensões térmicas residuais superficiais para os espécimes processados tanto pela técnica tradicional como pela técnica de injeção. / Objectives: to evaluate specimens with the following materials/processing combinations: a) feldspathic porcelain applied on zirconia through traditional technique; b) feldspathic porcelain applied on zirconia through press-on technique, c) feldspathic porcelain milled in CAD-CAM system and cemented (Rapid Layer Technique) on zirconia infrastructure; D) lithium disilicate glass-ceramic milled in CAD-CAM system and bonded to the zirconia infrastructure by means of a fusion glass-ceramic applied at the interface (CAD-on technique) relating to: (1) edge chipping resistance of the veneering materials (influence of the cooling rate was analyzed for the processing methods a and b) and; (2) surface residual stress levels measured in the veneering materials through indentation fracture method (influence of the cooling rate was analyzed for the processing methods a and b). Materials and methods: Bilayer bars with 25 mm length, 4 mm width and thicknesses of porcelain and infrastructure combined to provide 1 mm ratio of each material were made following manufacturers\' instructions. The edge chipping test was performed in an universal testing machine, using a Vickers indenter coupled to it. The surface residual thermal stress was calculated from indentations made on the porcelain layer. Results: The chipping resistance (ReA) was significantly higher for the specimens processed by the CAD-on system (ReA = 612.8±271.8 N/mm). Bilayers made by the Rapid Layer Technique system presented an intermediate ReA mean value of 417.9±187.2 N/mm and the groups in which the porcelain layer was processed by traditional or press-on technique presented the lowest values of chipping resistance, with mean values of 349,7±116,8 N/mm (traditional/slow cooling) 285,6±117,5 N/mm (traditional/fast cooling), 298,4±119,9 N/mm (press-on/slow cooling) and 263,5±107,9 N/mm (press-on/fast cooling). For the groups with porcelain applied on the infrastructure by the traditional and press-on technique, Student\'s t test showed that there was a significant effect of the cooling rate, and the specimens that went through slow cooling rate reached higher ReA values. Only the Rapid Layer Technique group presented mean of surface stresses corresponding to tensile stresses. All other groups exhibited surface compression stresses. Conclusions: there is a significant effect of the material/processing association on the edge chipping resistance of the tested bilayers and regarding the cooling rate effect (slow and fast), the specimens that went through slow cooling rate reached higher values of edge chipping resistance, regardless of the processing method (traditional or press-on). The material/processing combination significantly affected the surface residual stresses of the tested bilayers, however, there was no effect of the cooling rate on the superficial residual thermal stresses levels for the specimens processed by both the traditional technique and the press-on technique.

Le broyage de bois de qualité secondaire est un processus en pleine expansion avec l'augmentation de l'utilisation de la biomasse pour la production d'énergie. La transformation du bois en plaquettes facilite l'automatisation des chaudières. Peu de recherches ont traité le mécanisme de la formation des plaquettes et des efforts de coupe durant cette opération. Lors de ce travail de thèse, nous nous sommes focalisés sur le système de déchiquetage à disque. Un banc d'essais de taille réelle a été construit afin de permettre la variation de plusieurs paramètres, tels que la vitesse de coupe, la vitesse d?amenage, les angles de coupe, la direction d'amenage, la hauteur du contre-couteau, le mode de coupe, le nombre des couteaux et leur saillie.Les expérimentations ont montré que la taille des plaquettes augmente avec l'augmentation de l'avance par dent, l'angle de coupe réel et l'angle de taillant, et diminue avec l'augmentation de la vitesse de coupe. Le processus de la formation des plaquettes est composé de deux mécanismes, qui sont le cisaillement et la propagation de fissures. La mesure des efforts de coupe et de la puissance électrique consommée pour une bande passante pouvant atteindre 3 kHz complète ces données granulométriques. Grâce au banc d'essais de déchiquetage, nous avons pu montrer la corrélation ou l'indépendance de facteurs influents intervenant dans l'optimisation des conditions de coupe / Chipping wood of second quality is a rapidly growing process because of the increasing use of the biomass in energy production field. The utilization of wood chips as a combustible, make it easier to automate the wood boilers function. Few studies were carried out in order to understand the mechanism of the chip formation and the evolution of cutting force during the chipping operation. In this thesis, we focused our analysis on the disc chipper. A test bench of real dimensions was built up in order to be able to vary many parameters such as cutting and feeding speed, cutting angles, feeding direction, anvil height, cutting directions, knives number and their height.Experimental study showed that chip size grows when the feeding tooth, the cutting angle and the sharpness angle increase, whereas it decreases when the cutting speed increases. The process of the chip formation is composed of two mechanisms that are shear and cracks propagation. Measurement of cutting force and electric power consumption for a bandwidth up to 3 kHz bring important results to the chip size study. The chipping test bench allowed us to reveal the correlation or the independency between the parameters needed to optimize the chipping operation

En stor andel av restprodukterna från skogen används i kraft- och fjärrvärmeverk. I kraftvärmeverket i Lugnvik används skogsbränslen som grot, bark, spån och rundtimmer vilka omvandlas till värmeenergi eller elektrisk energi. I förhållande till de andra skogsbränslena är rundtimmer energieffektivt att transportera, möjligt att lagra och har högre energidensitet än övriga nämnda skogsbränslen. Dock så finns en begränsad möjlighet till torrhaltsbestämning av rundtimmer och idag görs energibedömningen på inkommande lass med hjälp av ett omräkningstal oberoende av kvalitet, trädslag eller torrhalt. Därmed finns osäkerheter kring energiinnehåll och torrhalt vid beställningar samt lagerhantering. Denna studie syftar därmed till att utveckla och precisera bedömningen av energiinnehåll i rundtimmer för att möjliggöra energieffektivare bränslehantering. En kartläggning av energivärdet i ingående rundtimmer gjordes genom bedömning av relevanta parametrar för energivärdet. Torrhaltsmätning utfördes med motorsåg med spånuppsamlare samt genom flisning och uttag ur flisad stack. Energivärden beräknades därefter med hjälp av torrhalterna. Studien kunde inte visa på rötans inverkan på energivärdet, däremot visas stor variation i energivärde mellan trädslagen gran och björk beroende på skillnad i torr-rådensitet. Torr-rådensiteten varierade också tydligt inom trädslagen. Torrhaltens variation uppgick till ca 20 % mellan lassen och har generellt en avgörande betydelse för energivärdet. Studien visar också på att motorsågsmetoden främst är representativ för mätningar över större partier och kan fungera bra för exempelvis lagerinventering. Studien belyser vidare att energiomvandling bör göras med hänsyn till tre torrhaltsklasser. Genom visuell bedömning av torrhalten matchas rådensiteten med bedömd torrhaltsklass och lassets energiinnehåll beräknas. / A large proportion of forest residues is used in district heating and combined heat and power plants (CHP). The CHP in Lugnvik, Östersund, uses wood fuels such as bark, chips and roundwood which is converted into heat or electricity. In relation to the other wood fuels, roundwood is energy efficient to transport, possible to store and has higher energy density than the other forest fuels mentioned. There is, however, limited possibilities for dry content determination of roundwood and today the energy assessment of incoming loads is made with one conversion factor regardless of quality, tree type or dry content. Thus, there is uncertainties in ordering and inventory management connected to energy content and dry content. This study aims to develop the assessment of energy content in roundwood to enable more energy efficient fuel management. An analysis of the energy value in incoming roundwood was done by assessing relevant parameters for the energy value. Dry content measurement was carried out both with a chainsaw with chip collector and by chipping and extraction from chipped stack. Dry content was then used to calculate energy values per load. The study could not show the effect of rot on the energy value, however, there is a large variation in energy value between spruce and birch due to difference in dry-raw density. The dry-raw density also clearly varied within the tree species. The dry content variation amounted to about 20% between the loads and is of general importance for the energy value. The study also shows that the chainsaw method is primarily representative of measurements across larger lots and can work well for inventory management. The study further highlights that energy conversion should be done regarding three dry content classes. By visual assessment of the dry content, the raw density is matched with the estimated dry content class and the energy content of the load is calculated. / <p>2020-06-05</p>

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Shuting Lei / This study experimentally and numerically investigates laser assisted milling (LAMill) of silicon nitride ceramics. Experiments are conducted to study the machinability of Si3N4 under LAMill. The effects of temperature on cutting forces, tool wear, surface integrity, edge chipping and material removal mechanisms are investigated. It is shown that when temperature increases, cutting force and tool wear are significantly decreased, surface integrity is improved, chip size is increased and material removal demonstrates more plastic characteristics. The mechanisms of edge chipping at elevated temperature are investigated theoretically and experimentally. When temperature is above the softening point and below the brittle/ductile transition temperature, the mechanism is mainly through softening. When temperature is above the brittle/ductile transition temperature, toughening mechanism contributes significantly to the reduced edge chipping. The coupled effect of softening and toughening mechanisms shows that temperature range between 1200 to 1400°C has the most significant effect to reduce edge chipping. Distinct element method (DEM) is applied to simulate the micro-mechanical behavior of Si3N4. First, quantitative relationships between particle level parameters and macro-properties of the bonded particle specimens are obtained, which builds a foundation for simulation of Si3N4. Then, extensive DEM simulations are conducted to model the material removal of machining Si3N4. The simulation results demonstrate that DEM can reproduce the conceptual material removal model summarized from experimental observations, including the initiation and propagation of cracks, chip formation process and material removal mechanisms. It is shown that material removal is mainly realized by propagation of lateral cracks in machining of silicon nitride. At the elevated temperature under laser assisted machining, lateral cracks are easier to propagate to form larger machined chips, there are fewer and smaller median cracks therefore less surface/subsurface damage, and crushing-type material removal is reduced. The material removal at elevated temperature demonstrates more plastic characteristics. The numerical results agree very well with experimental observations. It shows that DEM is a promising method to model the micro-mechanical process of machining Si3N4.

Capítulo 1. Objetivos: Medir e comparar o perfil de tensão residual da cerâmica de recobrimento aplicada sobre infraestruturas em zircônia tetragonal policristalina estabilizada por ítria (Y-TZP), em um compósito de alumina/zircônia (ZTA) e em uma alumina policristalina (AL). Material e Métodos: Os perfis de tensão residual de cada um dos materiais foi medido por meio do método \"hole-drilling\" em discos de 19 mm de diâmetro e 2,2 mm de espessura (0,7 mm de infraestrutura + 1,5 mm de porcelana de cobertura) .Resultados: Os espécimes de AL exibiram tensões de compressão que aumentaram numericamente com a profundidade, enquanto que as tensões compressivas mudaram para tensões de tração no interior das amostras de Y-TZP. As amostras de ZTA exibiram tensões de compressão na superfície, decrescendo com a profundidade até 0,6 mm, tornando-se compressivas novamente próximo à infraestrutura. Conclusão: O ZTA não apresentou tensões de tração em nenhum ponto ao longo da espessura da cerâmica de recobrimento. A AL apresentou um perfil de tensão residual mais favorável, gerado pelas tensões compressivas. A Y-TZP apresentou o perfil mais desfavorável, por apresentar tensões de tração próximo à infraestrutura. Capítulo 2. Objetivos: 1) Comparar os coeficientes de susceptibilidade ao crescimento subcrítico (n), de uma zircônia tetragonal policristalina estabilizada por ítria, obtidos por meio de dois ensaios de fadiga: cíclica e dinâmica. 2) Verificar o efeito da frequência usada no ensaio de fadiga cíclica no tempo de vida característico. Material e Métodos: Espécimes em forma de barras (25 mm x 4 mm x 3 mm) foram confeccionadas de acordo com as recomendações do fabricante. Os ensaios de fadiga dinâmica (n=70) e de fadiga cíclica (n=75) foram realizados por meio de resistência à flexão em quatro pontos para a obtenção dos parâmetros de crescimento de trincas subcrítico (SCG). O ensaio de fadiga cíclica também foi realizado em duas frequências (2 e 10 Hz), utilizando valores de tensão máxima entre 350 e 600 MPa. Todos os espécimes fraturados foram inspecionados em microscópio eletrônico de varredura para que fosse identificada a origem da fratura. Os dados de fadiga dinâmica foram analisados por meio das fórmulas apresentadas na ASTM C 1368-00. Os dados de fadiga cíclica foram analisados por meio da estatística de Weibull e por meio de análise tipo \"General Log Linear Model\". Resultados: A Y-TZP apresentou valores dos parâmetros de SCG obtidos no ensaio de fadiga dinâmica de ?fo = 667 MPa e n = 54. Os parâmetros de Weibull obtidos a partir dos resultados do mesmo ensaio foram de m = 7,9, ?0 = 968,9 MPa e ?5% = 767 MPa. Os parâmetros de Weibull obtidos no ensaio de fadiga cíclica foram estatisticamente semelhantes para as duas frequências utilizadas, o m* foi de 0,17 para 2Hz e de 0,21 10Hz; os tempos de vida característicos (?, em número de ciclos) foram de 1,93 x 106 e 40.768, respectivamente para 2 e 10 Hz. O valor de n obtido na fadiga cíclica foi de 48 e 40, nas frequências de 2 e 10 Hz, respectivamente. Não foi observado o efeito da frequência da aplicação da tensão, do nível de tensão, nem da interação dos dois no tempo de vida da Y-TZP, quando analisados pelo General Log Linear Model. Conclusão: Os coeficientes de susceptibilidade ao crescimento subcrítico (n) obtidos por meio de fadiga cíclica e dinâmica foram semelhantes para a Y-TZP testada. Os extensos intervalos de confiança obtidos nos ensaios de fadiga cíclica indicaram não haver efeito da frequência usado nesse método de fadiga nos tempos de vida característicos da Y-TZP testada. / Chapter 1. Objective: was: to measure and compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic frame-work materials: Y-TZP, alumina polycrystalline (AL) and zirconia toughened alumina (ZTA).Materials and Methods. The stress profile was measured with the hole-drilling method in bilayered disk samples of 19 mm diameter with a 0.7 mm thick Y-TZP, AL or ZTA framework and a 1.5 mm thick layer of the corresponding veneering ceramic. Results: The AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6 mm from the surface, and then becoming compressive again near the framework. Conclusions: Y-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Chapter 2. Objectives: 1) To compare the stress corrosion coefficient (n) of a Y-TZP, obtained by two fatigue tests: cyclic and dynamic and 2) Evaluate the effect of frequency used in the cyclic fatigue test in the characteristic lifetime. Methods: Bar shaped specimens (4 mm x 25 mm x 3 mm) were prepared according to the manufacturer\'s recommendations. The dynamic fatigue test (n = 70) and cyclic fatigue (n = 75) were performed by four-point bending to obtain the slow crack growth parameters (n) .The cyclic fatigue test was also conducted in two frequencies (2 and 10Hz), using stress levels between 350 and 600 MPa. All fractured specimens were inspected by SEM so that the origin of the fracture were identified. The dynamic fatigue data were analyzed using the formulas given in ASTM C 1368-00. Cyclic fatigue data were analyzed using Weibull statistics and by the Log General Linear Model. Results: The material showed values of parameters obtained in the SCG assay dynamic fatigue ?fo = 667 and n = 54. The Weibull parameters obtained from the same test results were m = 7.9, ?0 = 968, 9 and ?5% = 767. The Weibull parameters obtained by cyclic fatigue were statistically similar for the two frequencies used, the m* was 0.17 (2 Hz) and 0.21 (10 Hz); characteristic lifetimes (?) were 1.93 x 106 and 40768, respectively. The n value obtained by cyclic fatigue was 48 and 40 at frequencies of 2 and 10 Hz, respectively. There was no effect of the frequency, the stress level or the interaction of the two in the Y-TZP lifetime, when analyzed by General Log Linear Model. Conclusion: The n values obtained by cyclic and dynamic fatigue tests were similar to Y-TZP tested. The extensive confidence intervals obtained in cyclic fatigue tests showed no effect of frequency used this method in fatigue characteristic lifetimes of the Y-TZP tested.

Aufbauend auf einer Analyse ausgewählter methodentheoretischer Ansätze der Produktionsstättenplanung und des Umweltmanagements wird eine Methode des planungsintegrierten Umweltschutzes bei der Produktionsstättenplanung entwickelt. Sie besteht zum Einen aus einer umweltbezogenen Analyse und Bewertung, basierend auf der Ökobilanzierung, die an die Belange der Produktionsstättenplanung angepasst und integriert wird. Zum Anderen erfolgt das Entwerfen umweltverträglicher Lösungen. Hierzu wird das Konzept des planungsintegrierten Umwelschutzes zu heuristischen Regeln operationalisiert und den Planungsaktivitäten Funktionsbestimmung/Dimensionierung/Strukturierung/Gestaltung zugeordnet. Es erfolgt abschließend der beispielhafte Einsatz der Methode in einer Branchenstudie zur spanenden Metallbearbeitung.

Milling is a common unit operation in industry for the purpose of intentional size reduction. Considerable amount of energy is consumed during a grinding process and much of the energy is dissipated as heat and sound, which often makes grinding into an energy-intensive and highly inefficient operation. Despite many attempts to interpret particle breakage during a milling process, the grindability of a material in a milling operation remains aloof and the mechanisms of particle breakage are still poorly understood. Hence the optimisation and refinement in the design and operation of milling are in great need of an improved scientific understanding of the complex failure mechanisms. This thesis aims to provide an in-depth understanding of particle breakage associated with stressing events that occur during milling. A hybrid of experimental, theoretical and numerical methods has been adopted to elucidate the particle breakage mechanics. This study covers from single particle damage at micro-scale to bulk comminution during the whole milling process. The mechanical properties of two selected materials, i.e. alumina and zeolite were measured by indentation techniques. The breakage test of zeolite granules subjected to impact loading was carried out and it was found that tangential component velocity plays an increasingly important role in particle breakage with increasing impact velocity. Besides, single particle breakage via in-situ loading was conducted under X-ray microcomputed tomography (μCT) to study the microstructure of selected particles, visualize the progressive failure process and evaluate the progressive failure using the technique of digital image correlation (DIC). A new particle breakage model was proposed deploying a mechanical approach assuming that the subsurface lateral crack accounts for chipping mechanism. Considering the limitation of existing models in predicting breakage under oblique impact and the significance of tangential component velocity identified from experiment, the effect of impact angle is considered in the developed breakage model, which enables the contribution of the normal and tangential velocity component to be rationalized. The assessment of breakage models including chipping and fragmentation under oblique impact suggests that the equivalent normal velocity proposed in the new model is able to give close prediction with experimental results sourced from the public literature. Milling experiments were performed using the UPZ100 impact pin mill (courtesy by Hosokawa Micron Ltd. UK) to measure the comminution characteristics of the test solids. Several parameters were used to evaluate the milling performance including product size distribution, relative size span, grinding energy and size reduction ratio etc. The collective data from impact pin mill provides the basis for the validation of numerical simulation results. The Discrete Element Method (DEM) is first used to model single particle breakage subject to normal impact loading using a bonded contact model. A validation of the bonded contact model was conducted where the disparity with the experimental results is discussed. A parametric study of the most significant parameters e.g. bond Young’s modulus, the mean tensile bond strength, the coefficient of variation of the strength and particle & particle restitution coefficient in the DEM contact model was carried out to gain a further understanding of the effect of input parameters on the single particle breakage behavior. The upscaling from laboratory scale (single particle impact test) to industrial process scale (impact pin mill) is achieved using Population Balance Modelling (PBM). Two important functions in PBM, the selection function and breakage function are discussed based on the single particle impact from both experimental and numerical methods. An example of predicting product size reduction via PBM was given and compared to the milling results from impact pin mill. Finally, the DEM simulation of particle dynamics with emphasis on the impact energy distribution was presented and discussed, which sheds further insights into the coupling of PBM and DEM.

Capítulo 1. Objetivos: Medir e comparar o perfil de tensão residual da cerâmica de recobrimento aplicada sobre infraestruturas em zircônia tetragonal policristalina estabilizada por ítria (Y-TZP), em um compósito de alumina/zircônia (ZTA) e em uma alumina policristalina (AL). Material e Métodos: Os perfis de tensão residual de cada um dos materiais foi medido por meio do método \"hole-drilling\" em discos de 19 mm de diâmetro e 2,2 mm de espessura (0,7 mm de infraestrutura + 1,5 mm de porcelana de cobertura) .Resultados: Os espécimes de AL exibiram tensões de compressão que aumentaram numericamente com a profundidade, enquanto que as tensões compressivas mudaram para tensões de tração no interior das amostras de Y-TZP. As amostras de ZTA exibiram tensões de compressão na superfície, decrescendo com a profundidade até 0,6 mm, tornando-se compressivas novamente próximo à infraestrutura. Conclusão: O ZTA não apresentou tensões de tração em nenhum ponto ao longo da espessura da cerâmica de recobrimento. A AL apresentou um perfil de tensão residual mais favorável, gerado pelas tensões compressivas. A Y-TZP apresentou o perfil mais desfavorável, por apresentar tensões de tração próximo à infraestrutura. Capítulo 2. Objetivos: 1) Comparar os coeficientes de susceptibilidade ao crescimento subcrítico (n), de uma zircônia tetragonal policristalina estabilizada por ítria, obtidos por meio de dois ensaios de fadiga: cíclica e dinâmica. 2) Verificar o efeito da frequência usada no ensaio de fadiga cíclica no tempo de vida característico. Material e Métodos: Espécimes em forma de barras (25 mm x 4 mm x 3 mm) foram confeccionadas de acordo com as recomendações do fabricante. Os ensaios de fadiga dinâmica (n=70) e de fadiga cíclica (n=75) foram realizados por meio de resistência à flexão em quatro pontos para a obtenção dos parâmetros de crescimento de trincas subcrítico (SCG). O ensaio de fadiga cíclica também foi realizado em duas frequências (2 e 10 Hz), utilizando valores de tensão máxima entre 350 e 600 MPa. Todos os espécimes fraturados foram inspecionados em microscópio eletrônico de varredura para que fosse identificada a origem da fratura. Os dados de fadiga dinâmica foram analisados por meio das fórmulas apresentadas na ASTM C 1368-00. Os dados de fadiga cíclica foram analisados por meio da estatística de Weibull e por meio de análise tipo \"General Log Linear Model\". Resultados: A Y-TZP apresentou valores dos parâmetros de SCG obtidos no ensaio de fadiga dinâmica de ?fo = 667 MPa e n = 54. Os parâmetros de Weibull obtidos a partir dos resultados do mesmo ensaio foram de m = 7,9, ?0 = 968,9 MPa e ?5% = 767 MPa. Os parâmetros de Weibull obtidos no ensaio de fadiga cíclica foram estatisticamente semelhantes para as duas frequências utilizadas, o m* foi de 0,17 para 2Hz e de 0,21 10Hz; os tempos de vida característicos (?, em número de ciclos) foram de 1,93 x 106 e 40.768, respectivamente para 2 e 10 Hz. O valor de n obtido na fadiga cíclica foi de 48 e 40, nas frequências de 2 e 10 Hz, respectivamente. Não foi observado o efeito da frequência da aplicação da tensão, do nível de tensão, nem da interação dos dois no tempo de vida da Y-TZP, quando analisados pelo General Log Linear Model. Conclusão: Os coeficientes de susceptibilidade ao crescimento subcrítico (n) obtidos por meio de fadiga cíclica e dinâmica foram semelhantes para a Y-TZP testada. Os extensos intervalos de confiança obtidos nos ensaios de fadiga cíclica indicaram não haver efeito da frequência usado nesse método de fadiga nos tempos de vida característicos da Y-TZP testada. / Chapter 1. Objective: was: to measure and compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic frame-work materials: Y-TZP, alumina polycrystalline (AL) and zirconia toughened alumina (ZTA).Materials and Methods. The stress profile was measured with the hole-drilling method in bilayered disk samples of 19 mm diameter with a 0.7 mm thick Y-TZP, AL or ZTA framework and a 1.5 mm thick layer of the corresponding veneering ceramic. Results: The AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6 mm from the surface, and then becoming compressive again near the framework. Conclusions: Y-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Chapter 2. Objectives: 1) To compare the stress corrosion coefficient (n) of a Y-TZP, obtained by two fatigue tests: cyclic and dynamic and 2) Evaluate the effect of frequency used in the cyclic fatigue test in the characteristic lifetime. Methods: Bar shaped specimens (4 mm x 25 mm x 3 mm) were prepared according to the manufacturer\'s recommendations. The dynamic fatigue test (n = 70) and cyclic fatigue (n = 75) were performed by four-point bending to obtain the slow crack growth parameters (n) .The cyclic fatigue test was also conducted in two frequencies (2 and 10Hz), using stress levels between 350 and 600 MPa. All fractured specimens were inspected by SEM so that the origin of the fracture were identified. The dynamic fatigue data were analyzed using the formulas given in ASTM C 1368-00. Cyclic fatigue data were analyzed using Weibull statistics and by the Log General Linear Model. Results: The material showed values of parameters obtained in the SCG assay dynamic fatigue ?fo = 667 and n = 54. The Weibull parameters obtained from the same test results were m = 7.9, ?0 = 968, 9 and ?5% = 767. The Weibull parameters obtained by cyclic fatigue were statistically similar for the two frequencies used, the m* was 0.17 (2 Hz) and 0.21 (10 Hz); characteristic lifetimes (?) were 1.93 x 106 and 40768, respectively. The n value obtained by cyclic fatigue was 48 and 40 at frequencies of 2 and 10 Hz, respectively. There was no effect of the frequency, the stress level or the interaction of the two in the Y-TZP lifetime, when analyzed by General Log Linear Model. Conclusion: The n values obtained by cyclic and dynamic fatigue tests were similar to Y-TZP tested. The extensive confidence intervals obtained in cyclic fatigue tests showed no effect of frequency used this method in fatigue characteristic lifetimes of the Y-TZP tested.

There is currently a global increase in Eucalyptus pulpwood plantations. Harvesting systems traditionally utilised in the northern hemisphere are being used in Eucalyptus pulpwood plantations worldwide. However, the small tree size and complexity of debarking Eucalyptus have provided harvesting with productivity and cost challenges not previously experienced in northern-hemisphere conditions. Much research has been invested in these two harvesting methods in northern-hemisphere species and conditions. There is little research available on mechanised processing-machine productivity and costs in Eucalyptus. This investigation aimed to quantify the effect that tree and bundle size has on the productivity of different processing machines in Eucalyptus plantation pulpwood. This was done through regression analysis, whereby productivity models that included tree size and bundle size were constructed. The research also aimed to determine whether or not the multi-stem systems were more cost-effective in smaller tree sizes. The research investigated five mechanised harvesting options that forestry managers could use in Eucalyptus pulpwood plantations. These systems consisted of one CTL system, one full-tree system with single-stem processing and three full-tree systems with multi-stem processing. The CTL system used a harvester to process the trees into logs and to extract them. The full-tree system with single-stem processing used a dangle-head processor (DHP) to process trees into logs. The first full-tree system with multi-stem processing used a chain-flail debrancher debarker (CFDD) to produce debarked and debranched tree lengths, which were slashed into logs. The remaining full-tree, multi-stem systems both produced chips. The first used a chain-flail debrancher debarker chipper (CFDDC) and the second, a CFDD feeding into a stand-alone disc chipper (CFDD&C). The productivity data, measured as m3 per productive machine hour (PMH), was then statistically analysed using regression techniques. Productivity equations were formulated, considering tree size and bundle size, as well as the quadratic functions of these two variables and the interaction between them. Bundle size was only applicable to the multi-stem processing machines. The productivity equations successfully predicted processing-machine productivity, using tree size and bundle size as input variables. Apart from the 0.075 m3 tree size class, the CFDD had the highest overall productivity. The costs of the five systems were then calculated for different tree sizes. No single system was more cost-effective than the others across all tree sizes. In 0.075 m3 trees, the CFDDC system proved the most cost-effective. All systems evidenced high costs in the 0.075 m3 trees, ranging between $19.43 per m3 for the CFDDC system to $28.84 for the harvester system. In 0.40 m3 trees, the cost differences between systems were lower, ranging from $6.91 per m3 for the DHP system to $11.84 per m3 for the CFDD&C. This study confirms that the CTL system was very expensive to operate in the small tree sizes (0.075 m3). There is a cross-over point at 0.25 m3 per tree, where the CTL system costs become lower than those of the full-tree system. At the 0.40 m3 tree size, the full-tree system is slightly more expensive than the CTL system. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Plant Production and Soil Science / unrestricted

Aufbauend auf einer Analyse ausgewählter methodentheoretischer Ansätze der Produktionsstättenplanung und des Umweltmanagements wird eine Methode des planungsintegrierten Umweltschutzes bei der Produktionsstättenplanung entwickelt. Sie besteht zum Einen aus einer umweltbezogenen Analyse und Bewertung, basierend auf der Ökobilanzierung, die an die Belange der Produktionsstättenplanung angepasst und integriert wird. Zum Anderen erfolgt das Entwerfen umweltverträglicher Lösungen. Hierzu wird das Konzept des planungsintegrierten Umwelschutzes zu heuristischen Regeln operationalisiert und den Planungsaktivitäten Funktionsbestimmung/Dimensionierung/Strukturierung/Gestaltung zugeordnet. Es erfolgt abschließend der beispielhafte Einsatz der Methode in einer Branchenstudie zur spanenden Metallbearbeitung.