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M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / A project investigating the behaviour of an assembled preloaded rotor was performed for an M-Tech qualification in the Mechanical Engineering Department. Pre-Stressing of mechanical structures is widely applied to improve their performance, and in this project the behaviour of an assembled preloaded rotor was investigated. An Impact Test was done on the structure to see if induced stresses originated by a set of bolts which keep the discs system together, would influence the natural dynamic response or the rotor. Tendencies in the natural response were investigated. Analytical models like the Finite Element Beam model and the Solid Finite Element model were studied in order to find a represntative description of this particular structure's dynamic behaviour after pre-tension. From the experimental results it was apparent that the slenderness of the pre-tensioned sector influences the natural frequency. The solid finite element model appears to be the most applicable model to present the assembled rotor-disk system as a continuous shaft. Furthermore, modelling and predictions for a typical rotor and similar assembled structures can be generated from the findings.

Afin de mieux comprendre les interactions entre les modifications des contraintes induites par l'exploitation minière et la génération d'activité sismique, une zone profonde de la mine de Garpenberg (Suède) a été instrumentée par l’Ineris avec de sondes microsismiques et de cellules géotechniques. L’analyse spatio-temporelle des événements microsismiques enregistrés entre 2015 et 2016, ainsi que leurs paramètres à la source, ont mis en évidence deux types de réponses sismiques : une locale et courte dans le temps directement induite par les tirs de production, l’autre plus persistante et distante des excavations étant principalement contrôlée par des hétérogénéités géologiques. L’analyse des données géotechniques a montrée l’occurrence de déformations asismiques, ainsi que de phénomènes de fluage induits par l’exploitation. De plus l'activité sismique décroît proportionnellement au taux de diminution des déformations mesurées. Cette dernière observation implique que le fluage peut être un autre mécanisme menant à la sismicité, s’ajoutant au changement de contrainte immédiat induit par les tirs de production. Dans la dernière partie de cette thèse, un modèle géomécanique élasto-plastique 3D a été réalisé et ses résultats ont été comparés aux données géophysiques. Cette comparaison a montré que les modèles numériques à l'échelle de la mine peuvent être des outils puissants pour étudier la sismicité induite à grande échelle. Cependant, il y a certains aspects de la sismicité induite que le modèle ne peut expliquer entièrement. Cela est le cas pour la sismicité déclenchée à distance des excavations, alors que de meilleures corrélations sont trouvées lorsque l'on considère la sismicité à proximité des zones de production. Les résultats de cette thèse ont démontré qu'une approche combinée associent les données sismiques et géotechniques à la modélisation numérique peut améliorer considérablement notre compréhension de la réponse des massifs rocheux à l'exploitation minière. La combinaison de ces méthodologies dans une approche intégrée peut réduire considérablement leurs limites explicites qui sont évidents lorsque ces instruments sont considérés séparément. / With the aim of better understanding interactions between stress modifications induced by mining and the generation of seismic activity, a deep area of Garpenberg mine (Sweden) was instrumented by Ineris with microseismic probes and geotechnical cells. Spatiotemporal analysis of recorded seismicity between 2015 and 2016, as well as seismic source parameters, have highlighted two types of seismic rock mass responses: one local and temporally short directly induced by production blasts, the other long-lasting over time and remote from excavations being mainly controlled by geological heterogeneities. Geotechnical data analysis showed the occurrence of aseismic deformations, as well as creep phenomena induced by mining exploitation. In addition, seismic activity decays proportional to the decaying rate of measured strains. This latter observation implies that creep may be another mechanism driving seismicity, in addition to the immediate stress change induced by blasting. In the last part of this thesis, a 3D elasto-plastic geomechanical model has been realized and its results have been compared with geophysical data. This comparison showed that mine-wide numerical models can be suitable for the analysis of mining induced seismicity at large-scale. However, there are some aspects of the induced seismicity that the model cannot fully explain. This is particularly true for remote seismicity occurring at a distance from excavations, while better correlations are found when considering seismicity close to production areas. Results of this thesis demonstrated that a combined approach which associates seismic and geotechnical data with numerical modelling can significantly improve our understanding of the rock mass response to mining. The combination of these methodologies in an integrated approach can significantly reduce their straightforward limitations, which appears evident when these instruments are considered separately.

Målen med denna uppsats var att studera två aspekter av temperatur inducerade spänningar med referens till kärnkraftsanläggningen Forsmark F1. Ena aspekten inkluderade den termiska kyleffekten av de ventilerade spännkabelrören i cylinderväggen. Det var av intresse att studera om den termiska kyleffekten av de ventilerade spännkabelrören hade en positiv global effekt som var relevant att beakta i globala tredimensionella modeller. Den andra aspekten inkluderade inverkan av ingjutet stål i den övreringplattan. Med syftet att studera om ingjutet stål var en aspekt som ansågs nödvändigt att beakta i transienta analyser.   Huvudanalyseringsverktyg var finita element metoden (FEM), genom användning av det kommersiellt tillgängliga finita element programmet SOLVIA.   Inverkan av den termiska kyleffekten av de ventilerade spännkabelrören indikerade en spännings reducerande effekt, med reducerade zoner av sprucken betong i cylinderväggen vid förhöjda temperaturer. Inverkan av ingjutet stål indikerade ökade temperaturskillnader mellan det ingjutna stålet och den omgivande betongen, med sprucken betong lokalt mellan stålet och betongen vid förhöjda temperaturer. Den termiska kyleffekten av de ventilerade spännkabelrören ansågs relevant att beakta i globala tredimensionella modeller. Ingjutet stål ansågs vara nödvändigt att inkludera i transienta analyser. / The aims of this thesis were to study two aspects of temperature induced stresses with reference to the nuclear power plant Forsmark F1. One aspect included the thermal cooling effect of the ventilated tendon ducts in the cylinder wall. It was of interest to study if the thermal cooling effect of the ventilated tendon ducts had a positive global effect which was relevant to consider in global three-dimensional models. The other aspect included the influence of embedded steel in the upper ring slab. With the purpose to study if embedded steel was an aspect that was considered necessary to include in transient analyses.   The used main analysis tool was the finite element method (FEM), through the use of the commercially available finite element program SOLVIA.   The influence of the thermal cooling effect of the ventilated tendon ducts indicated a stress reducing effect, with reduced cracked concrete in the cylinder wall at elevated temperatures. The influence of embedded steel indicated increased temperature differences between the embedded steel and the surrounding concrete, with cracked concrete locally between the steel and the concrete at elevated temperatures. The thermal cooling effect of the ventilated tendon ducts was considered relevant to consider in global three-dimensional models. Embedded steel was considered necessary to include in transient analyses.

There is an intense, worldwide effort to develop durable lithium ion batteries with high energy and power densities for a wide range of applications, including electric and hybrid electric vehicles. For improvement of battery technology understanding the capacity fading mechanism in batteries is of utmost importance. Novel electrode material and improved electrode designs are needed for high energy- high power batteries with less capacity fading. Furthermore, for applications such as automotive applications, precise cycle-life prediction of batteries is necessary. One of the critical challenges in advancing lithium ion battery technologies is fracture and decrepitation of the electrodes as a result of lithium diffusion during charging and discharging operations. When lithium is inserted in either the positive or negative electrode, there is a volume change associated with insertion or de-insertion. Diffusion-induced stresses (DISs) can therefore cause the nucleation and growth of cracks, leading to mechanical degradation of the batteries. With different mathematical models we studied the behavior of diffusion induces stresses and effects of electrode shape, size, concentration dependent material properties, pre-existing cracks, phase transformations, operating conditions etc. on the diffusion induced stresses. Thus we develop tools to guide the design of the electrode material with better mechanical stability for durable batteries. Along with mechanical degradation, chemical degradation of batteries also plays an important role in deciding battery cycle life. The instability of commonly employed electrolytes results in solid electrolyte interphase (SEI) formation. Although SEI formation contributes to irreversible capacity loss, the SEI layer is necessary, as it passivates the electrode-electrolyte interface from further solvent decomposition. SEI layer and diffusion induced stresses are inter-dependent and affect each-other. We study coupled chemical-mechanical degradation of electrode materials to understand the capacity fading of the battery with cycling. With the understanding of chemical and mechanical degradation, we develop a simple phenomenological model to predict battery life. On the experimental part we come up with a novel concept of using liquid metal alloy as a self-healing battery electrode. We develop a method to prepare thin film liquid gallium electrode on a conductive substrate. This enabled us to perform a series of electrochemical and characterization experiments which certify that liquid electrode undergo liquid-solid-liquid transition and thus self-heals the cracks formed during de-insertion. Thus the mechanical degradation can be avoided. We also perform ab-initio calculations to understand the equilibrium potential of various lithium-gallium phases.

Na última década, muitas minas a céu aberto têm alcançado alturas de 600 metros ou mais, algumas com perspectiva em projeto de alcançar mais de 1100 m. A literatura especializada revela que os mecanismos de ruptura para taludes altos ainda não são bem entendidos. Existem dúvidas tanto em relação aos mecanismos de ruptura, como quanto à estimativa da resistência do maciço rochoso em tal escala. Recentemente, há uma tendência crescente da aplicação de análises numéricas para estudar a estabilidade de taludes altos, mas ainda não se consegue reproduzir todos os fenômenos envolvidos. Análises reportadas na literatura consideram apenas a configuração final da cava, sem levar em conta o processo evolutivo da escavação, e o dano induzido ao maciço decorrente deste processo. Este trabalho analisa este efeito e suas conseqüências na avaliação da segurança. Realizaram-se análises bidimensionais de tensão-deformação em taludes de rocha. Tais análises foram realizadas com modelos elástico linear e elasto plástico de amolecimento da coesão e de endurecimento do atrito, considerando a mobilização não simultânea das componentes de resistência no critério de Mohr-Coulomb, e a danificação do maciço rochoso. Avaliação preliminar da segurança de um talude hipotético mostrou que estas considerações são muito importantes. Foram considerados a altura do talude, o ângulo do talude e as tensões in situ. 0 histórico de tensões modifica os parâmetros de resistência do maciço ao longo do talude por danificação. A região do pé do talude, em cada estágio de escavação, está sujeita a concentração de tensões induzidas que geram danificação ao maciço nestas áreas. A danificação em regiões do pé do talude pode explicar o inicio do processo de rupturas do tipo progressivo. / Along the last decade, many open pit mines have reached up to 600 meters or more in height, and some of them are planned to reach more than 1100 meters. The specialized literature shows that the failure mechanisms for high rock slopes are not well understood as yet. Doubts exist in relation to failure mechanisms, as well as to rock mass strength estimation in such scale. In recent years, there is a growing trend for the use of numerical analyses in order to study high rock slope stability, but they are not capable to reproduce all the phenomena involved. Analyses reported in the literature consider only the final configuration of the open pit, without taking into consideration the excavation evolution process, and damage induced to the rock mass resulting from this process. This work analyzes this effect and its consequences on the slope safety evaluation. Two dimensional stress strain analyses in rock slopes are described. Such analyses were conducted with linear elastic model and elasto plastic strain cohesion softening - friction hardening model considering the non-simultaneous mobilization of the strength components in the Mohr-Coulomb criterion, by including the rock mass damage. An approximate safety evaluation of a hypothetical slope shows that these considerations are very important. The stress path modifies the rock mass strength parameters close to the slope face by damage. The regions of the slope toe at each excavation stage are subjected to induced stress concentration causing damage to rock. This damage can explain the beginning of the progressive failure mechanism.

O processo de moldagem por injeção de peças de paredes finas apresenta diferenças significativas em relação a processos convencionais de moldagem por injeção de termoplásticos. Processos de paredes finas são caracterizados pelo preenchimento de cavidades com espessuras inferiores a 1 mm utilizando velocidades de preenchimento elevadas. Estes dois fatores afetam o desenvolvimento de tensões induzidas pelo escoamento durante o preenchimento da cavidade, sendo que não foram encontrados na literatura estudos de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas. Neste trabalho são apresentados resultados de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas em comparação com resultados de simulação com cavidades características de processos convencionais. Para o cálculo das tensões induzidas pelo escoamento foi utilizado o modelo incompressível de Leonov. Para isso foi desenvolvida uma metodologia numérica para tratar problemas não isotérmicos utilizando o pacote CFD OpenFOAM. Foi utilizada a abordagem não acoplada, ou seja, o comportamento viscoelástico não é considerado na obtenção dos campos de velocidade, pressão e temperatura. Esta metodologia foi utilizada na simulação do preenchimento de cavidades bidimensionais. Os resultados indicaram que as tensões são influenciadas fortemente pela espessura da cavidade enquanto a velocidade de escoamento causou pequena variação das tensões induzidas pelo escoamento. Este trabalho mostrou que as tensões induzidas pelo escoamento não podem ser desconsideradas na produção de peças moldadas por injeção pelo processo de paredes finas. / Thin wall injection molding process of thermoplastics has significant differences compared to conventional injection molding process. Thin wall processes are characterized by cavities thinner than 1 mm and very high injection velocities. Although these two factors are expected to increase the flow induced stresses development during cavities filling, no previous study on this subject has been found in literature. In the present work, flow induced stresses under thin wall injection molding conditions are calculated using a viscoelastic model and compared to the results obtained under conventional injection conditions. In order to do this, a numerical methodology, based on the solver viscoelasticInterFoam, was developed in the OpenFOAM package to deal with the non-isothermal flow occurring during the mold filling stage. A non-coupled approach was used to calculate the stress field, i.e., the viscoelastic behavior was not considered in the determination of velocity, pressure and temperature fields. This methodology was used in the analysis of the filling stage of two-dimensional cavities. The results indicated that the cavity thickness has more influence on the flow induced stresses than the injection velocity. The obtained results also indicate that the flow induced stresses cannot be neglected in thin wall injection molding processes.

O processo de moldagem por injeção de peças de paredes finas apresenta diferenças significativas em relação a processos convencionais de moldagem por injeção de termoplásticos. Processos de paredes finas são caracterizados pelo preenchimento de cavidades com espessuras inferiores a 1 mm utilizando velocidades de preenchimento elevadas. Estes dois fatores afetam o desenvolvimento de tensões induzidas pelo escoamento durante o preenchimento da cavidade, sendo que não foram encontrados na literatura estudos de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas. Neste trabalho são apresentados resultados de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas em comparação com resultados de simulação com cavidades características de processos convencionais. Para o cálculo das tensões induzidas pelo escoamento foi utilizado o modelo incompressível de Leonov. Para isso foi desenvolvida uma metodologia numérica para tratar problemas não isotérmicos utilizando o pacote CFD OpenFOAM. Foi utilizada a abordagem não acoplada, ou seja, o comportamento viscoelástico não é considerado na obtenção dos campos de velocidade, pressão e temperatura. Esta metodologia foi utilizada na simulação do preenchimento de cavidades bidimensionais. Os resultados indicaram que as tensões são influenciadas fortemente pela espessura da cavidade enquanto a velocidade de escoamento causou pequena variação das tensões induzidas pelo escoamento. Este trabalho mostrou que as tensões induzidas pelo escoamento não podem ser desconsideradas na produção de peças moldadas por injeção pelo processo de paredes finas. / Thin wall injection molding process of thermoplastics has significant differences compared to conventional injection molding process. Thin wall processes are characterized by cavities thinner than 1 mm and very high injection velocities. Although these two factors are expected to increase the flow induced stresses development during cavities filling, no previous study on this subject has been found in literature. In the present work, flow induced stresses under thin wall injection molding conditions are calculated using a viscoelastic model and compared to the results obtained under conventional injection conditions. In order to do this, a numerical methodology, based on the solver viscoelasticInterFoam, was developed in the OpenFOAM package to deal with the non-isothermal flow occurring during the mold filling stage. A non-coupled approach was used to calculate the stress field, i.e., the viscoelastic behavior was not considered in the determination of velocity, pressure and temperature fields. This methodology was used in the analysis of the filling stage of two-dimensional cavities. The results indicated that the cavity thickness has more influence on the flow induced stresses than the injection velocity. The obtained results also indicate that the flow induced stresses cannot be neglected in thin wall injection molding processes.

O processo de moldagem por injeção de peças de paredes finas apresenta diferenças significativas em relação a processos convencionais de moldagem por injeção de termoplásticos. Processos de paredes finas são caracterizados pelo preenchimento de cavidades com espessuras inferiores a 1 mm utilizando velocidades de preenchimento elevadas. Estes dois fatores afetam o desenvolvimento de tensões induzidas pelo escoamento durante o preenchimento da cavidade, sendo que não foram encontrados na literatura estudos de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas. Neste trabalho são apresentados resultados de determinação de tensões induzidas pelo escoamento em cavidades de paredes finas em comparação com resultados de simulação com cavidades características de processos convencionais. Para o cálculo das tensões induzidas pelo escoamento foi utilizado o modelo incompressível de Leonov. Para isso foi desenvolvida uma metodologia numérica para tratar problemas não isotérmicos utilizando o pacote CFD OpenFOAM. Foi utilizada a abordagem não acoplada, ou seja, o comportamento viscoelástico não é considerado na obtenção dos campos de velocidade, pressão e temperatura. Esta metodologia foi utilizada na simulação do preenchimento de cavidades bidimensionais. Os resultados indicaram que as tensões são influenciadas fortemente pela espessura da cavidade enquanto a velocidade de escoamento causou pequena variação das tensões induzidas pelo escoamento. Este trabalho mostrou que as tensões induzidas pelo escoamento não podem ser desconsideradas na produção de peças moldadas por injeção pelo processo de paredes finas. / Thin wall injection molding process of thermoplastics has significant differences compared to conventional injection molding process. Thin wall processes are characterized by cavities thinner than 1 mm and very high injection velocities. Although these two factors are expected to increase the flow induced stresses development during cavities filling, no previous study on this subject has been found in literature. In the present work, flow induced stresses under thin wall injection molding conditions are calculated using a viscoelastic model and compared to the results obtained under conventional injection conditions. In order to do this, a numerical methodology, based on the solver viscoelasticInterFoam, was developed in the OpenFOAM package to deal with the non-isothermal flow occurring during the mold filling stage. A non-coupled approach was used to calculate the stress field, i.e., the viscoelastic behavior was not considered in the determination of velocity, pressure and temperature fields. This methodology was used in the analysis of the filling stage of two-dimensional cavities. The results indicated that the cavity thickness has more influence on the flow induced stresses than the injection velocity. The obtained results also indicate that the flow induced stresses cannot be neglected in thin wall injection molding processes.

Na última década, muitas minas a céu aberto têm alcançado alturas de 600 metros ou mais, algumas com perspectiva em projeto de alcançar mais de 1100 m. A literatura especializada revela que os mecanismos de ruptura para taludes altos ainda não são bem entendidos. Existem dúvidas tanto em relação aos mecanismos de ruptura, como quanto à estimativa da resistência do maciço rochoso em tal escala. Recentemente, há uma tendência crescente da aplicação de análises numéricas para estudar a estabilidade de taludes altos, mas ainda não se consegue reproduzir todos os fenômenos envolvidos. Análises reportadas na literatura consideram apenas a configuração final da cava, sem levar em conta o processo evolutivo da escavação, e o dano induzido ao maciço decorrente deste processo. Este trabalho analisa este efeito e suas conseqüências na avaliação da segurança. Realizaram-se análises bidimensionais de tensão-deformação em taludes de rocha. Tais análises foram realizadas com modelos elástico linear e elasto plástico de amolecimento da coesão e de endurecimento do atrito, considerando a mobilização não simultânea das componentes de resistência no critério de Mohr-Coulomb, e a danificação do maciço rochoso. Avaliação preliminar da segurança de um talude hipotético mostrou que estas considerações são muito importantes. Foram considerados a altura do talude, o ângulo do talude e as tensões in situ. 0 histórico de tensões modifica os parâmetros de resistência do maciço ao longo do talude por danificação. A região do pé do talude, em cada estágio de escavação, está sujeita a concentração de tensões induzidas que geram danificação ao maciço nestas áreas. A danificação em regiões do pé do talude pode explicar o inicio do processo de rupturas do tipo progressivo. / Along the last decade, many open pit mines have reached up to 600 meters or more in height, and some of them are planned to reach more than 1100 meters. The specialized literature shows that the failure mechanisms for high rock slopes are not well understood as yet. Doubts exist in relation to failure mechanisms, as well as to rock mass strength estimation in such scale. In recent years, there is a growing trend for the use of numerical analyses in order to study high rock slope stability, but they are not capable to reproduce all the phenomena involved. Analyses reported in the literature consider only the final configuration of the open pit, without taking into consideration the excavation evolution process, and damage induced to the rock mass resulting from this process. This work analyzes this effect and its consequences on the slope safety evaluation. Two dimensional stress strain analyses in rock slopes are described. Such analyses were conducted with linear elastic model and elasto plastic strain cohesion softening - friction hardening model considering the non-simultaneous mobilization of the strength components in the Mohr-Coulomb criterion, by including the rock mass damage. An approximate safety evaluation of a hypothetical slope shows that these considerations are very important. The stress path modifies the rock mass strength parameters close to the slope face by damage. The regions of the slope toe at each excavation stage are subjected to induced stress concentration causing damage to rock. This damage can explain the beginning of the progressive failure mechanism.