This project was funded by Automotive Partnership Canada (APC), an initiative created by the Government of Canada in an attempt to support significant, collaborative R&D activities in order to benefit the entire Canadian automotive industry. / High strength Al-Zn-Mg-Cu alloys have been increasingly employed in the transportation industry due to the increased demands for light structural components. However, their applications have been limited to relatively expensive wrought products. Application of the shape cast Al-Zn-Mg-Cu parts has never been the focus of attention due to their poor castability and mechanical properties. Improving the casting quality is expected to increase their utilization within the automotive industry. The poor castability and mechanical properties of some alloys in this family may be effectively improved through optimized chemistry control and melt treatment including grain refinement. The primary objective of this project is to optimize the chemistry and heat treatment of the Al-Zn-Mg-Cu alloy family that results in improved strength with acceptable level of ductility and casting quality relative to other shape cast Al alloys. The Taguchi experimental design method was used to narrow down the number of required casting experiments required to meet the research objective. Three levels across four elements yielded a total of 9 Al-Zn-Mg-Cu alloys, which were cast using a tilt pour permanent mold process. The effect of each major alloying element on the microstructure, and mechanical properties was investigated. Tensile measurements were made on the 9 alloys subjected to two steps solution treatments. Mechanical properties such as yield strength (YS), ultimate tensile strength (UTS), and elongation at fracture (El.%) were experimentally measured and statistically analyzed. An ANOVA analysis was employed to quantify the percentage contribution of the alloying elements on the material properties. Grain refinement was found to play a significant role in improving the hot tearing resistance and, thereby ameliorating quality. The alloying element that affected the YS and UTS to the greatest extent was Cu, followed by Zn. In contrast, the effect of Mg and Ti on YS and UTS was insignificant. Moreover, a decrease in Mg content had the greatest effect in enhancing the El.%. A regression analysis was used to obtain statistical relationships (models) correlating the material properties with the variations in the content of the major alloying elements. The R-square values of YS, UTS, and El.% were 99.7 %, 98 %, and 90 %, respectively, showing that the models replicated the experimental results. Verification measurements made on shape cast Al-6Zn-2Mg-2Cu alloy revealed that the material property model predictions were in agreement with the experimentally measured values. The results show that secondary and over ageing treatments of the shape cast Al-Zn-Mg-Cu alloys lead to superior combination of YS and El.%. The ongoing advances in shape casting of Al-Zn-Mg-Cu alloys with high will make them suitable choices for commercial load-bearing automotive components, when it comes to the selection of a material meeting the minimum requirements for strength, damage tolerance, cost and weight. / Thesis / Master of Applied Science (MASc)

Around 80% of women experience vaginal tears during labor when the diameter of the vagina must increase from ~2.5 cm to ~9.5 cm to allow the passage of a full-term baby. Vaginal tears vary from superficial cuts of the mucosal lining to tears propagating through the entire vaginal wall and into the surrounding tissues and organs. Complications associated with vaginal tears include postpartum hemorrhaging, fecal incontinence, urinary incontinence, and dyspareunia. Beyond the agonizing pain, these complications are emotionally and psychologically traumatic for women. Prevention, evaluation, and treatment of vaginal tears and subsequent conditions are limited due to the lack of studies examining the mechanical behavior of the pelvic floor tissues. Therefore, the mechanical response of healthy and torn vaginal tissue is investigated here to establish quantitative metrics for maternal healthcare. Toward this end, swine and rat vaginal tissue is subjected to biaxial loads until tearing to reveal its mechanical properties. The resulting large inhomogeneous deformations are measured by the digital image correlation optical method to calculate material strain. The influence of these strains near to and far from the immediate vicinity of the tears on the tearing behavior is studied. Coupling mechanisms of the mechanical properties in the circumferential and axial directions as well as their effect on the nature of tear resistance is studied. Collagen fibers, the component within tissue responsible for its strength under tension, are imaged using a multiphoton microscopy technique known as second-harmonic generation imaging to investigate the change in organization with mechanical loading. Furthermore, imaging is performed in the near-regions of tears to reveal the relationship between collagen fibers and tearing resistance. The data collected through these studies provide new knowledge on the nonlinear elastic behavior of vaginal tissue, the geometrical and micro-structural characteristics of tears, and the mechanisms that contribute to the formation and propagation of tears. The mechanical properties and tearing mechanisms of vaginal tissue will be crucial in developing new prevention and treatment methods for maternal trauma following childbirth. Episiotomy, late-term stretching, surgical treatment with graft materials and other protocols will all benefit from a mechanically-informed perspective. It is our hope that this work will raise awareness to the serious complexities of pelvic floor trauma and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery. This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech. / Doctor of Philosophy / Every year nearly three million women give birth vaginally with 80% experiencing vaginal tears. These injuries sustained during delivery vary with severity and are associated with several conditions, including pelvic floor disorders. These disorders are a set of long-term conditions of the pelvic region presently affecting one-fourth of adult women in the United States. Pelvic floor disorders are: pelvic organ prolapse - a pelvic organ such as the uterus "falls" from its natural position, urinary incontinence - difficulty controlling urination, and fecal incontinence - difficulty controlling bowel movements. Pelvic floor disorders lower the quality of life for women not only physically due to pain and daily discomfort, but also mentally as the disorders are generally perceived as an embarassing and private matter. The pelvic floor represents a complex system of muscles, organs, and support structures that work together to ensure everything stays in place and is functioning properly. Injury to any of these structures poses the risk of developing a disorder. As a central supporting organ, injuries to the vagina may be particularly worrisome. Surprisingly, little is known about the magnitude of forces and/or stretching that is placed on the pelvic floor during delivery, how much force and/or stretching is required for an injury, or how various injuries relate to future complications. The goal of this research is to describe how much the normal, healthy vagina stretches to various forces including forces that will result in injuries. The research further examines the stretching of injured vaginas to quantify any observable differences due to this injury. Finally, the relationships between the biological components of the vagina, such as collagen, and the forces placed on the vagina are examined. The result of this work will provide doctors and engineers with guidelines for understanding the conditions that produce vaginal injuries. The relationships examined between the tissue makeup and forces exerted onto the tissue may also aid in identifying any irregularities that would place a woman at risk for injury. Many of the medical procedures surrounding childbirth as well as surgical treatment for pelvic floor disorders will benefit from knowing how far the vagina can stretch before being injured. It is our hope that this work will raise awareness to the serious complexities of pelvic floor injuries and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery. This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / The finite element tearing and interconnect(FETI) domain decomposition(DD) method is investigated in terms of the 2D transverse electric(TEz) finite element method(FEM). The FETI is for the first time rigorously derived using the weighted residual framework from which important insights are gained. The FETI is used in a novel way to implement a total-/scattered field decomposition and is shown to give excellent results. The FETI is newly formulated for the time domain(FETI-TD), its feasibility is tested and it is further formulated and tested for implementation on a distributed computer architecture.

It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration. One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device. The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges. <b>Keywords</b>Nuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX

<p>It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration.</p><p>One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device.</p><p>The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges.</p><p><b>Keywords</b>Nuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX</p>

Devido à crescente demanda por perfis formados a frio destinados à fabricação de estruturas de aço no Brasil, aliada a desatualização da norma brasileira NB-143:1967, fez-se necessário a publicação de uma nova norma brasileira de \'Dimensionamento de Estruturas de Aço Constituídas por Perfis Formados a Frio\' a NBR14762:2001. Essa apresenta, para o dimensionamento das ligações, expressões adaptadas da norma norte-americana AISI:1996. As adaptações foram inseridas com o intuito de simplificar o cálculo e foram determinadas apenas por ajustes teóricos, faltando, portanto uma investigação mais criteriosa. Deste modo tornou-se prioritário o estudo das ligações em chapas e perfis com pequena espessura, para avaliação destas expressões propostas. Neste âmbito analisou-se neste trabalho o comportamento estrutural de ligações parafusadas em chapas e perfis formados a frio de pequena espessura, mediante análise teórica e experimental de corpos-de-prova, os quais foram definidos de maneira a se obter os diversos modos de falha, em especial a ruptura da seção líquida. Com os resultados experimentais pôde-se sugerir modificações nas expressões do coeficiente redutor da área líquida Ct, aplicado na avaliação da resistência ao estado limite de ruptura da seção líquida efetiva. Com os resultados desta pesquisa, espera-se colaborar com futuras edições da norma brasileira, fornecendo subsídios em suas futuras revisões. / The growing demand for cold-formed steel members of steel structures in Brazil, allied to the obsolescence of the brazilian NB-143:1967 standard, led to the need for a new brazilian code for the \'Design of Cold-formed Steel Structural Members\', the NBR14762:2001 standard. This new standard contains expressions adapted from the american AISI:1996 code for the design of connections. The adaptations were included with the purpose of simplifying the calculation and were determined merely for theoretical adjustments; hence, they lack a more careful investigation. It has thus become a matter of priority to study the connections in thin sheets and cold-formed members to evaluate the proposed expressions. The work reported on here therefore analyzed the structural behavior of bolted connections in thin sheets and cold-formed members based on theoretical and experimental analyses of test specimens, which were defined in order to obtain the various failure modes, particularly on sheet tearing in the net section. Based on the experimental results, suggestions are made for modifications in the expressions of the reduction coefficient of the net area Ct, applied in evaluations of the tensile strength of the effective net section. It is expected that the results of this research will contribute to future editions of the new brazilian code, supplying inputs for use in future revisions.

La Nébuleuse du Crabe, contenant en son centre une étoile à neutrons très magnétisée – le pulsar du Crabe, était essentiellement considérée comme une chandelle standard stable dans les rayons-gamma. Récemment, ce point de vue a été contredit par des éruptions en rayons-gamma observées par les satellites spatiaux AGILE/Fermi-LAT. Même si le vent magnétique relativiste du pulsar est considéré comme la source d’énergie, le mécanisme physique à la base de ces événements éruptifs est encore un mystère. Nous avons, dans cette thèse, amélioré la compréhension d’un mécanisme basé sur la reconnexion magnétique rapide, partant du modèle du vent magnétique généré par le pulsar central qui perd son énergie rotationnelle. En effet, la structure du vent magnétique implique la présence des stries à lignes de champ magnétique de polarités alternées (d’où le nom "vent strié") à travers le plan équatorial du pulsar. Dans un modèle simplifié local, nous supposons l’initiation de la dynamique à partir d’une configuration à double nappe de courant (induite par la structure magnétique) dans le repère du vent strié. / The Crab Nebula, containing in its center a highly magnetized neutron star - the Crab pulsar, was essentially considered as a standard steady-state candle in gamma rays. Recently, this point of view has been challenged by gamma-ray flares observed by space satellites AGILE/Fermi-LAT. Even if the relativistic magnetic wind of the pulsar is considered to be the source of energy, the physical mechanism underlying these eruptive events is still a mystery. In this thesis, we improved the understanding of a mechanism based on fast magnetic reconnection, starting from the model of the magnetic wind generated by the central pulsar which loses its rotational kinetic energy. Indeed, the structure of the magnetic wind implies the presence of stripes with magmatic field lines of alternating polarities (hence the name "striped wind") through the equatorial plane of the pulsar. In a simplified local model, we assume the initiation of the dynamics from a double-current sheet configuration (induced by the magnetic structure) in the striped wind reference.

La découpe virtuelle d'objets déformables est au coeur de nombreuses applications pour la simulation interactive. Nous présentons un nouvel algorithme de remaillage permettant la simulation de découpes avec la méthode des éléments finis. Nous avons combiné notre algorithme avec la méthode du «snapping» déplaçant les noeuds la surface de coupe, pour des tétradres linéaires. Notre approche permet de maîtriser le nombre de noeuds et de la qualité numérique du maillage durant les coupes. Elle donne des résultats similaires pour les fonctions de forme quadratiques. Dans ce cadre, nous avons évalué le «snapping» pour simuler la fracture de surfaces triangulées. Nous avons appliqué nos résultats en 3D pour l'assistance aux gestes chirurgicaux, en étant les premiers présenter des résultats sur la détection de déchirures dans un flux vidéo monoculaire. La robustesse de notre algorithme et l'augmentation des structures internes des organes. / Virtual cutting of deformable objects is at the core of many applications in interactive simulation for computational medicine. We present a new remeshing algorithm simulating cuts based on the finite element method. For tetrahedral elements with linear shape tunctions, we combined our algorithm with the movement of the nodes on the cutting surface, called snapping. Our approach shows benefits when evaluating the impact of cuts on the number of nodes and the numerical quality of the mesh. The remeshing algorithm yields similar results for quadratic elements. However, the snapping of nodes entails higher challenges and has been evaluated on triangular elements, simulating fractures. For augmented reality applications, we are the first to present results on the detection of fractures, tearing and cutting from a monocular video stream. Examples in different contexts show the robustness of our algorithm and the augmentation of internai organ structures highlights the clinical interest.

Ces travaux portent sur la déformation des aciers au cours de leur solidification, au moyen d'une expérience instrumentée et de sa simulation numérique. L'étude est focalisée sur deux phénomènes induits par la déformation : la fissuration à chaud et la macroségrégation. L'expérience consiste à poinçonner latéralement un lingot de 450 kg, alors que son cœur est encore partiellement liquide.L'expérience est instrumentée thermiquement et mécaniquement. Les lingots sont analysés, visuellement en termes de lieu et de fréquence d'apparition de fissures, et par microsonde pour les ségrégations chimiques.Pour la fissuration à chaud, une simulation numérique 3D par éléments finis est mise en œuvre avec le logiciel Thercast®, dans lequel a été implanté un critère d'amorçage de fissure basé sur la déformation plastique cumulée en fin de solidification, entre deux valeurs critiques de fraction de liquide. La comparaison entre simulations et observations montre le caractère prédictif du critère.La simulation numérique de la macroségré-gation est réalisée avec le logiciel R2sol qui résout simultanément la déformation du solide et l'écoulement du liquide. La simulation montre la redistribution des solutés dans le cœur du lingot sous l'effet de la compression du squelette solide et de l'écoulement du liquide, induits par le poinçonnement. Elle reproduit qualitativement les mesures expéri-mentales mais sous-estime l'amplitude des hétérogénéités de composition chimique. Une discussion des résultats permet de dégager des pistes permettant d'espérer une prédiction quantitative dans le futur.Les deux thématiques étudiées ont mis en relief la nécessité d'une bonne modélisation des phénomènes de microségrégation des alliages multiconstitués. Un modèle a été spécifiquement développé à cet effet. / Experimental and numerical studies of hot tearing and macrosegregation formation during steel solidification are reported. On one hand, an ingot punching test is considered. It consists of the application of a deformation at the surface of a solidifying 450 kg steel ingot. On the other hand, finite element thermo-mechanical modelling of the test is used.For hot tearing analysis, 3D finite element modeling is applied by use of Thercast® software. The time evolution of the strain tensor serves to evaluate the possibility for hot tear formation with a Hot Tearing Criterion (HTC). The HTC compares the local accumulation of strain over a certain solidification interval with the expression of a critical value proposed in the literature. Detailed comparisons reveal an excellent capability of the HTC to predict the formation of hot tears.For macrosegregation analysis, a two-phase formulation has been implemented (R2sol software), in which the velocities of the liquid and solid phases are concurrently solved for. The simulation shows how solutes are redistributed through the central mushy zone of the ingot under the effect of the com-pression of the solid phase resulting from the punching of the solid shell. The simulation proves its capability to reproduce the main experimental trends. However the predicted intensity of macrosegregation is lower than measured. Through discussion and analysis of different numerical sensitivity tests, critical material parameters and model improvements are identified in view of achieving better quantitative predictions in the future.The two topics studied have clearly shown the need for a good modelling of microsegregation phenomena in multicomponent alloys. A numerical model has especially been developed and implemented in the two software packages.

The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode. In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity. In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science. / <p>QC 20171122</p>