Dissertations / Theses on the topic 'Hybrid joints'

The use of fibre composites in the design of load carrying aircraft structures has been increasing over the last few decades. At the same time, aluminium alloys are still present in many structural parts, which has led to an increase of the number of hybrid composite-aluminium structures. Often, these materials are joined at their interface by bolted connections. Due to their different response to thermal, mechanical and environmental impact, the composite and the aluminium alloy parts are subject to different design and certification practices and are therefore considered separately.The current methodologies used in the aircraft industry lack well-developed methods to account for the effects of the mismatch of material properties at the interface.One such effect is the thermally induced load which arises at elevated temperature due to the different thermal expansion properties of the constituent materials. With a growing number of hybrid structures, these matters need to be addressed.  The rapid growth of computational power and development of simulation tools in recent years have made it possible to evaluate the material and structural response of hybrid structures without having to entirely rely on complex and expensive testing procedures.However, as the failure process of composite materials is not entirely understood, further research efforts are needed in order to develop reliable material models for the existing simulation tools. The work presented in this dissertation involves modelling and testing of bolted joints in hybrid composite-aluminium structures.The main focus is directed towards understanding the failure behaviour of the composite material under static and fatigue loading, and how to include this behaviour in large scale models of a typical bolted airframe structure in an efficient way. In addition to that, the influence of thermally induced loads on the strength and fatigue life is evaluated in order to establish a design strategy that can be used in the industrial context. The dissertation is divided into two parts. In the first one, the background and the theory are presented while the second one consists of five scientific papers.

Friction Stir Processing (FSP) of aluminium alloys has been used to modify and improve the microstructure and relevant properties of fusion welded aluminium alloys. The effect of FSP on MIG-Laser Hybrid (MLH) welded aluminium alloy 6082-T6 mechanical and microstructural properties has been studied in this research. The FSP process was used on 6mm thick aluminium alloy plates and a tool was designed specifically for FSP, and the effect of varying speeds was analysed before the final FSP welds were made. The effect of FSP was analysed by optical microscopy, tensile, microhardness and fatigue testing. The aim of the study was to determine whether the FSP process has a beneficial influence on the mechanical properties and metallurgical integrity of MIG-Laser Hybrid welded 6082-T6 aluminium alloy with varying gap tolerances. Three welding processes were compared, namely combined Friction Stir Processing on MIG-Laser hybrid process (FSP-MLH), MLH and Friction Stir Welding (FSW) as part of the analysis. (FSP was carried out on MLH components when it was found that FSP is not an entirely complete welding process but rather a finishing process per se.) The aim of this dissertation is to investigate the effects of the FSP process on the weld quality of MLH welded joints and also to compare this to individual processes like FSW and MLH. This investigation was undertaken in order to gain an understanding of the effect of these processes on fatigue performance and microhardness distribution on aluminium alloy 6082-T6 weld joints.

Submitted by Regina Correa (rehecorrea@gmail.com) on 2016-10-03T18:50:36Z No. of bitstreams: 1 DissNZB.pdf: 8463882 bytes, checksum: 493c4ee9ac0735d4fab21c75b50bef13 (MD5)<br>Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-10T14:21:16Z (GMT) No. of bitstreams: 1 DissNZB.pdf: 8463882 bytes, checksum: 493c4ee9ac0735d4fab21c75b50bef13 (MD5)<br>Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-10T14:21:24Z (GMT) No. of bitstreams: 1 DissNZB.pdf: 8463882 bytes, checksum: 493c4ee9ac0735d4fab21c75b50bef13 (MD5)<br>Made available in DSpace on 2016-10-10T14:21:33Z (GMT). No. of bitstreams: 1 DissNZB.pdf: 8463882 bytes, checksum: 493c4ee9ac0735d4fab21c75b50bef13 (MD5) Previous issue date: 2015-12-18<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Friction Riveting is an innovative spot joining technology for metal-polymer hybrid structures. This MSc thesis provided for the first time in the literature, a fundamental understanding on the Friction Riveting process for metal-thermoset composites joints. Joints of Ti-6Al-4V rivet and pultruded glass fiber reinforced thermoset polyester part were produced under three joining conditions with different heat input. Thorough analytical techniques were used to understand the physics of the process and the effect of the energy input on the final microstructure of the joined parts, the physico-chemical changes in the composite and the local and global mechanical properties of the joints. The process temperature reached values up to 761 ± 2°C indicating intrinsic degradation of the composite, formation of a softened/molten glass interlayer between the rivet and the composite and complex metallurgical transformations in the metallic rivet. Through monitoring of the process temperature and torque, an unstable friction regime was observed for FricRiveting of pultruded thermoset composites leading to distinguished extents of composite degradation. The microstructure of the Ti-6Al-4V alloy changed across the length of the rivet, from the equiaxed morphology to acicular structures in the rivet tip, where plastic deformation occurred. Three microstructural zones were proposed for each joint part including two thermo-mechanically affected zones and a heat affected zone. Microhardness mapping was performed in the metallic rivet evidencing an increase from the center to the tip of the rivet, with a hardness increment of over 20% compared to the base material (HVTi6Al4V= 300- 320 HV). The glass interphase consolidated in the metallic surface reached values of up to 974 HV followed by a drastic decrease to 24 HV in the polyester matrix located out of the joint area. The ultimate bearing strength ranged between 60 MPa and 166 MPa. Lesser composite degraded areas led to stronger joints. Two failure modes were observed combining initial composite bearing followed by final failure through shear of the rivet with partial rivet pullout or by full rivet pull-out. Complex failure micro-mechanisms were observed including the combination of cohesive and adhesive failures through the glass layer and the damaged composite interface. Friction-riveted joints achieved an ultimate lap shear strength of up to 80% to that of a similar bolted joint. A case study for a presumptive truss bridge application of friction-riveted joints showed a necessary of 92 rivets per truss node, 43% less than previous studies and with potential for further optimization.<br>Rebitagem por Fricção é uma tecnologia de união pontual inovadora para estruturas híbridas metal-polímero. Esta tese de mestrado apresenta pela primeira vez na literatura um entendimento aprofundado do processo de Rebitagem por Fricção para juntas de metal e compósito termofixo. Juntas de rebite de Ti-6Al-4V e componente pultrudado de poliéster termofixo reforçado com fibra de vidro foram produzidas seguindo três condições de processo com diferentes aportes térmicos. Diversas técnicas analíticas foram utilizadas para entender a física do processo e o efeito do aporte térmico na microestrutura final dos componentes unidos, mudanças físico-químicas no compósito, formação de camada vítrea intermediária entre o compósito e o rebite metálico e transformações metalúrgicas. Através do monitoramento da temperatura processual e do torque, um regime friccional não estável foi observado para a Rebitagem por Fricção de compósito pultrudado termofixo resultando em distintas extensões da degradação do compósito. A microestrutura da liga de Ti-6Al-4V transforma-se ao longo da secção transversal do rebite, de uma morfologia equiaxial no centro do rebite para uma estrutura acicular em sua extremidade, onde ocorre deformação plástica. Três zonas microestruturais foram propostas para cada componente da junta incluindo duas zonas termo mecanicamente afetadas e uma termicamente afetada. Mapa de microdureza foi realizado no rebite metálico evidenciando um aumento do centro para a extremidade do mesmo, próximo a 20% comparado com o material de base (HVTi6Al4V= 300-320 HV). A interfase vítrea consolidada na superfície do rebite metálico apresentou dureza em torno de 974 HV seguido de um drástico decaimento para 24 HV na matriz de poliéster localizada fora da região de união. A tensão máxima de apoio variou entre 60 e 166 MPa. Juntas com menor área degradada apresentaram os melhores desempenhos mecânicos em ensaio quase estático de cisalhamento. Dois modos de falha foram observados combinando um modo de falha inicial por deformação plástica severa no compósito seguida de falha final por cisalhamento no rebite metálico com parcial remoção do mesmo ou por remoção completa do rebite. Complexos micro mecanismos de falha foram observados incluindo a combinação de falha adesiva e coesiva através da interface entre interfase vítrea e compósito degradado. Juntas rebitadas por fricção atingiram resistência ao cisalhamento de 80% da obtida para juntas parafusadas. O estudo de caso para uma ponte hipotética treliçada revelou um número necessário de rebites de até 92 rebites por nó da ponte, 43% a menos que o encontrado em trabalhos anteriores, com potencial para futuras optimizações.

Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.<br>"May 2007." Title from PDF title page (viewed on Dec. 20, 2007). Thesis adviser: Hamid M. Lankarani. Includes bibliographic references (leaves 62-64).

Reliable line production processes and simulation tools play a central role for the structural integration of thermoplastic composites in advanced lightweight constructions. Provided that material- adapted joining technologies are available, they can be applied in heavy-duty multi-material designs (MMD). A load-adapted approach was implemented into the new fully automatic and faulttolerant thermo mechanical flow drill joining (FDJ) concept. With this method it is possible to manufacture reproducible high strength FRP/metal-joints within short cycle times and without use of extra joining elements for the first time. The analysis of FDJ joints requires a simplified model of the joint to enable efficient numerical simulations. The present work introduces a strategy in modeling a finite-element based analogous-approach for FDJ-joints with glass fiber reinforced polypropylene and high-strength steel. Combined with a newly developed section-force related failure criterion, it is possible to predict the fundamental failure behavior in multi-axial stress states. The functionality of the holistic approach is illustrated by a demonstrator that represents a part of a car body-in-white structure. The comparison of simulated and experimentally determined failure loads proves the applicability for several combined load cases.

La conception des turbomachines à haute densité énergétique nécessite de plus en plus la maîtrise d'un plus grand nombre de paramètres fonctionnels. La moindre défaillance d'un composant conduit quasi immédiatement la machine à la rupture. C'est en particulier le cas pour le comportement des composants à films minces.L'appellation "film mince" correspond à tout espace de très faible épaisseur situé entre le rotor et le stator de la turbomachine. Leur but est soit de limiter les fuites de manière à optimiser les performances intrinsèques de la machine, soit alors à supporter et stabiliser le rotor. Ces derniers cas sont plus appelés communément "joints lisses ou annulaires" et "paliers fluides".Lorsqu'un fluide circule dans un espace de très faible épaisseur, typiquement quelques centièmes de millimètres sur une distance très longue, son champ de vitesses, donc de pression, dépend fortement des phénomènes visqueux aux parois dont l'une est mise en rotation et l'autre est immobile. Les efforts fluides sur ces parois peuvent être alors importants et doivent être pris en compte dans le dimensionnement de la machine.La connaissance précise de ces écoulements très complexes est indispensable pour déterminer les efforts statiques et dynamiques appliqués au rotor de manière à pouvoir dimensionner un fonctionnement calme<br>The design of high performance aerospace turbo pumps requires more control of an increasing number of functional parameters. Any component failure led almost immediately to a machine failure. This is particularly the case for the behavior of thin film lubricated components.The term "thin film" means any thin space between the rotor and the stator of the engine. Their goal is either to limit leakage to maximize the machine intrinsic performance, or to support and stabilize the rotor. These cases are more commonly called "smooth or annular seals" and "fluid film bearings".When a fluid flows in a space of very small thickness, typically a few hundredths of a millimeter, the velocity field, hence the pressure, are highly dependent on the walls viscous forces. Fluid forces on the walls (which one is rotated and the other is stationary) can then be important and should be taken into account in the design of the machine.The precise knowledge of these complex flows is essential to determine the static and dynamic forces applied to the rotor to ensure a quite functioning of the turbo pump

This diploma thesis deals with bonded hybrid joints which are used for connecting parts of modern coachwork. Firstly, the thesis describes in general the process of production of the whole coachwork, from cutting of the blanks to the surface treatment including the analysis of the used materials. Subsequently, the problem of joining body parts through adhesives, but also by welding, soldering or other methods is discussed. Another part of this thesis is dedicated to an experiment in which the qualities of bonded hybrid joints were determined. Different ways of realizing the joint have been made which differed in the size of the glued surface, in the welding methods and in the process of their creation. The produced joints were tested for their strength and quality.

O presente trabalho consiste basicamente num estudo experimental de juntas híbridas metal-compósito unidas mecanicamente por fixadores. Foram analisadas juntas fabricadas através de uma chapa metálica de titânio unida a uma placa em compósito de fibra de carbono e resina epóxi por fixadores de monel. As juntas avaliadas são juntas simples (\"single lap joint\"), ou seja, as mesmas foram submetidas ao simples cisalhamento. Antes, porém, dos ensaios das juntas, foram fabricados corpos-de-prova (CDPs) do compósito seguindo as especificações das normas ASTM D3039 e ASTM D3518. Os ensaios de tração e cisalhamento dos CDPs de compósito possibilitaram a determinação de propriedades mecânicas, bem como de valores de resistência. Sob posse das propriedades e resistência média, foram executadas simulações computacionais via Método dos Elementos Finitos com o intuito de prever o comportamento mecânico das juntas a serem ensaiadas seguindo a norma ASTM D5961 e, assim, delinear estratégias para os ensaios. Os ensaios das juntas foram realizados, possibilitando assim a avaliação do comportamento mecânico de juntas híbridas e de seus mecanismos de falha. Por fim, as conclusões e as perspectivas para trabalhos futuros foram apresentadas.<br>This work consists on an experimental investigation of hybrid joints (metal-composite) joined by fasteners. For this work, hybrid joints of titanium joined to composite (carbon fiber with epoxy resin) by monel fasteners were manufactured. Only single lap joints were investigated. However, before manufacturing specimens of joints, composite specimens were tested following the ASTM D3039 e ASTM D3518. The tensile and shear tests provided the mechanical properties and strength values of the composite. Finite element analyses of the hybrid joints were carried out, using average mechanical properties and strength values. These simulations followed the specifications of ASTM D5961 in order to predict the mechanical behavior of the joints during the experimental tests, as well as, provide a good strategy for the test setup. The experimental tests were carried out, observing the mechanical behavior and failure mechanisms of the hybrid joints. Finally, the conclusions and perspective of future works were showed.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>An advanced electro-optic hybrid rotary joint (EOHRJ) has been developed in Phase II of an AF SBIR effort with Physical Optics Corporation (POC) to replace cable wrap structure for multi-channel rotation-to-fixed (RTF) signal transmission. The EOHRJ meets AFFTC and other range special needs with a generic, high performance, rotary joint solution. At the moment, we have successfully installed and tested the EOHRJ on our KTM tracker system with the following capabilities: 1) able to accommodate hundreds of transmission channels, including electrical power, control, feedback, and low-speed signals; 2) able to accommodate multiple channel, high data rate (over gigabits per second), and bi-directional signal transmission; 3) able to be reliable for harsh environmental operation, adaptive to stringent sized requirement, and accommodating existing electrical and mechanical interfaces. The completed EOHRJ contains three uniquely integrated functional rings. The first and the outmost one is power ring, which provides RTF transmission channels for over 50 high voltage and high current channels. The second and the middle one is low speed electrical signal ring, which provides RTF transmission for over hundred control, feedback, and low speed data signals. The third and the inmost one is optical fiber slip ring, which, incorporating with current advanced signal multiplexing technologies (either time division or wavelength division multiplexing ) is able to provide multiple channel, high data rate, and bi-directional signal transmission. At the moment, the prototype module of the tree-layer EOHRJ has been successfully assembled in Air Force’s tracker system, and is providing a satisfactory performance. This paper presents our joint work on this project.

Die motorischen Fähigkeiten humanoider Roboter werden häufig von antriebsbedingten Nichtlinearitäten und Reibungseffekten negativ beeinflusst. Zur deren Kompensation werden üblicherweise modellbasierte Regelkreise genutzt, die i.d.R. von einer hochfrequenten Signalverarbeitung und mehreren Sensorqualitäten abhängen. Entgegen solch modellbasierten Techniken werden in der vorliegenden Arbeit modellfreie Steuerungsmethoden auf Basis parallel gekoppelter Antriebe entwickelt. Zur Entwicklung und Untersuchung dieser Steuerungsmethoden wird nach der von Pfeifer in seinem Werk “How the body shapes the way we think” beschriebenen synthetischen Methodik vorgegangen. Entgegen modellbasierten Untersuchungen auf Basis von Simulationen stehen bei der synthetischen Methodik empirische Untersuchungen am realen System im Vordergrund. Als Ausgangspunkt dienen konventionelle elektromechanische Antriebe mit deren bekannten leistungseinschränkenden Nichtlinearitäten und Reibungseffekten. Durch die parallele Kopplung mehrerer Antriebe an einem einzelnen Gelenk wird das Spektrum der Steuerungsmöglichkeiten deutlich erweitert. Es zeigt sich, dass (1) durch eine konstante antagonistische Vorspannung das Arbeitsverhalten von konventionellen Proportionalreglern optimiert werden kann, (2) durch dynamische asymmetrische Änderung der Vorspannung Nichtlinearitäten bei niedrigen Geschwindigkeiten ausgeglichen werden können und (3) getriebebedingte Reibungseffekte mit einer phasenverschobenen Pulsmodulation der Steuersignale kompensiert werden können. Weiterhin wird gezeigt, wie die erarbeiteten Steuerungsmethoden auf beliebig viele parallel gekoppelte Antriebe übertragen werden können. Für den praktischen Einsatz der Steuerungsmethoden werden diese in einer hybriden Steuerung zusammengeführt. Diese wird durch eine weitere Funktion, den Energiesparmodus beim Halten statischer Positionen, ergänzt und am humanoiden Roboter Myon implementiert und experimentell evaluiert.<br>Motor functions of humanoid robots are often negatively influenced by nonlinearities and friction effects of the actuators. The popular means of compensation are control circuits based on modelling, which rely on powerful HF Signal processing and various sensor qualities. In contrast, this thesis develops non-modelling control methods based on parallel coupled actuators. Development and exploration of these control methods follow Pfeifer’s synthetic methodology as described in his work “How the body shapes the way we think”. In contrast to the analysis based on emulation as used in modelling, the synthetic methodology focuses rather on empirical tests within the real system. The present work explores control methods for parallel coupled actuators for use in robot points. It starts from conventional electromechanical actuators with their known power limiting nonlinearities and frictional effects. Linking several parallel coupled actuators to a single joint significantly expands the spectrum of control capabilities. Using two parallel coupled actuators as an example, it is examined to which extent undesirable properties of single actuators can be compensated. The results show that (1) the Performance of conventional proportional controllers can be optimized by a constant antagonistic bias voltage, (2) nonlinearities at low velocities can be balanced out by a dynamic asymmetrical adjustment of the bias, and that (3) gear related frictional effects can be compensated by a phase shifted pulse modulation of the control signals. In addition, it is shown how the developed control methods can be applied to a random number of parallel coupled actuators. For practical use, the various control methods are combined in a hybrid control, which is supplemented by an energy saving mode when maintaining static positions. The hybrid control is being implemented into the humanoid robot Myon and evaluated by experiment.

De nos jours, la construction mixte est en plein essor pour des raisons architecturales et environnementales. Dans ce contexte, les structures mixtes bois-métal sont de plus en plus utilisées car elles permettent d'allier légèreté et élancement des structures. Cependant, l'alliance d'un matériau sensible à l'environnement -le bois, et d'un autre peu déformable - le métal, pose des problèmes de fissuration dans les assemblages. En effet, un nombre important d'assembleurs entraine des blocages limitant la libre déformation du bois par retrait/gonflement. Pour limiter l'impact de ces blocages, l'emploi de trous oblongs dans les platines métalliques des assemblages bois-métal est une solution qui est envisagée dans ces travaux. Face au manque de documentation sur les couvre-joints avec trou oblong, un ensemble d'analyses reposant sur des études expérimentales a été mené en utilisant la corrélation d'images numériques. Une première partie de l'étude a permis de mieux comprendre le comportement des assemblages en étudiant les déformations à la surface des éprouvettes. Cette analyse a montré que deux modes de ruines sont possibles dans la pince longitudinale : un par flexion et l’autre par pression diamétrale. Par la suite, un modèle analytique permettant de prédire la raideur initiale des trous oblongs sur la base d'un modèle numérique et d’essais en laboratoire a été proposé. Enfin, la dernière partie de la thèse est consacrée à évaluer l'impact de la présence des trous oblongs dans des assemblages bois-métal soumis à un moment fléchissant sur la base d'une campagne expérimentale. Les résultats de cette étude ont montré que l'emploi des trous oblongs ne perturbe pas le comportement des assemblages bois-métal boulonnés soumis à un moment fléchissant et permet, dans certaines conditions, d'augmenter leur résistance<br>Nowadays, hybrid structures are common because of architectural and environmental reasons. In that context, timber steel structures are very relevant because they combine lightness with large slenderness. However, combining both timber that presents a hydroscopic behavior and steel material that is not, raises a problem of cracking in connection zone. Indeed, the large number of connectors in this part of the structure prevents timber from swelling and shrinkage deformations and then creates cracks. In order to limit the effect of the connection on the cracking of the timber, the present work proposes to release degrees of freedom using slotted holes in steel plates in bolted timber-steel connections. Due to the lack of studies on bolted cover plate with slotted holes, a large part of this work proposes to analyze the behavior of such connections based an experimental study using full field measurement technique. The first part of the present work allows to better understanding the behavior of bolted cover plate with slotted holes using load-displacement curves, failure modes and strain analyses obtained with Digital Image Correlation (DIC) technique. This analysis highlights the presence of two types of behaviors. The first one is mostly due to the bending of the end distance area whereas the second is due to bearing. Thereafter, an analytical model predicting the initial stiffness of such connections is proposed. This model is based on numerical and experimental results obtained by DIC. In the last part of the study, an experimental campaign is dedicated to the evaluation of the effect of the presence of slotted holes in steel plate of bolted timber-steel connection under bending moment. The result of the study shows that using slotted holes has no negative impact on the short-time behavior of bolted timber steel connections and, in certain circumstance, an increase of the resistance is observed

O presente trabalho correlacionou diversas funções de respostas em frequência (FRF) de juntas do tipo simples, coladas e fabricadas em titânio-compósito (resina epóxi reforçada por fibra de carbono). As FRFs produzidas foram investigadas (experimental e numericamente) tanto para juntas intactas como para juntas com falha, estas provenientes, por exemplo, do uso em serviço ou então, com resultado do processamento inadequado de um reparo. Com base nessas análises buscou-se, portanto, subsidiar o desenvolvimento de um sistema de monitoramento estrutural a partir da avaliação de seu comportamento dinâmico, medido pelo uso de pastilhas piezelétricas integradas à estrutura. Para que o respectivo objetivo fosse alcançado. Num primeiro momento, a fim de compreender os fenômenos envolvidos, conduziu-se a atividade de revisão bibliográfica, que baseada na consulta dos trabalhos mais recentes publicados sobre a análise de juntas coladas empregando abordagem numérica, analítica e/ou experimental. Em seguida, foram desenvolvidos modelos computacionais preliminares com solução via Método dos Elementos Finitos (MEF), a fim de se obter as diretrizes mínimas para uma proposta de fabricação das juntas híbridas (metal-compósito). Tal estratégia permitiu reduzir efeitos indesejados, que pudessem comprometer os resultados experimentais. Em posse dos resultados computacionais fabricou-se amostras de juntas metal-compósito com e sem dano. Num primeiro momento, foram realizadas análises numéricas através do desenvolvimento de modelos computacionais (com solução via MEF) das juntas, metal-compósito, monitoradas por transdutores piezelétricos. Em seguida, as juntas híbridas foram submetidas a ensaios experimentais dinâmicos, empregando técnicas de monitoramento com auxílio de transdutores piezelétricos e acelerômetros. Por fim, avaliaram-se potencialidades e limitações dos modelos computacionais desenvolvidos, através de estudos de caso, comparando os resultados experimentais com os resultados numéricos.<br>The herein proposed research has correlates Frequency Response Functions (FRF) of several hybrid titanium-composite (epoxy resin reinforced with carbon fiber) single lap bonded joints. The FRFs were investigated (numerically and experimentally) for joints with and without failures which may arise as the result of in service events or bad maintenance practices. The result of the dynamic analyses provided by the FRFs has substantiated the proposal of a damage detection method using piezoelectric elements capable which are capable to detect minor alterations on the dynamic behavior of the joint. In order to reach the proposed objective, the first action towards the given objective was study the problem through a bibliographic revision of the research subject, for this purpose the most recent published works related to numerical, analytical and experimental analyses of bonded joints were thoroughly evaluated and segregated. Afterwards, models of the joints were proposed using Finite Element Models (FEM) to obtain a preliminary result of the joints behavior to eventually substantiate the manufacturing processes, reducing the amount of material, time and cost of the experiments. Based upon the results of the FEM the coupons were manufactured with and without damages, using the methods and techniques available on the maintenance field for restoration of composite elements. Before proceed to the comparison between the modeled and experimental results, additional models were proposed using previous work\'s results to get results from the piezoelectric monitored joints. Afterwards, all experimental tests were conducted using accelerometers and piezoelectric elements to provide the means through it the advantages and drawbacks of the proposed monitoring method could be checked, by comparison between the experimental and modeled results.

The first part of the diploma thesis with name „Hybrid adhesive bonded joints of metals and composite materials“ comprise surface pretreatment review. There is also mentioned current review of adhesives for composite and aluminium adherends. The second part of the thesis is dedicated to lap hybrid joint shear strength tests. The effects of adherend thickness, overlap lenght and surface pretreatment on shear strength were investigated. Measured parameters of hybrid joints are proved with a FE analysis with enough accuracy. Conclusions could be used for optimum design of hybrid joint with aluminium and composite adherends.

A hybrid cloud radio access network (H-CRAN) architecture has been proposed to alleviate the midhaul capacity limitation in C-RAN. In this architecture, functional splitting is utilized to distribute the processing functions between a central cloud and edge clouds. The flexibility of selecting specific split point enables the H-CRAN designer to reduce midhaul bandwidth, or reduce latency, or save energy, or distribute the computation task depending on equipment availability. Meanwhile, techniques for caching are proposed to reduce the content delivery latency and the required bandwidth. However, caching imposes new constraints on the functional splitting. In this study, considering H-CRAN, a constraint programming problem is formulated to minimize the overall power consumption by selecting the optimal functional split point and content placement, taking into account the content access delay constraint. We also investigate the trade-off between the overall power consumption and occupied midhaul bandwidth in the network. Our results demonstrate that functional splitting together with enabling caching at edge clouds reduces not only content access delays but also fronthaul bandwidth consumption but at the expense of higher power consumption.<br>En hybrid-grönåtkomstnätverk (H-CRAN) -arkitektur har föreslagits för att lindra kapacitetsbegränsningen i C-RAN. I denna arkitektur används funktionell uppdelning för att distribuera bearbetningsfunktionerna mellan en central moln och kantmoln. Flexibiliteten att välja specifika delningspunkter gör det möjligt för H-CRANkonstruktören att minska bandbredden för midhaul eller minska latens eller spara energi eller distribuera beräkningsuppgiften beroende på tillgången till utrustning. Samtidigt föreslås tekniker för cachning för att minska innehållsfördröjningslatet och den nödvändiga bandbredden. Emellertid ställer caching nya hinder på funktionell uppdelning. I den här studien, med tanke på H-CRAN, formuleras ett begränsningsprogrammeringsproblem för att minimera den totala effektförbrukningen genom att välja den optimala funktionella splitpunkten och innehållsplaceringen, med hänsyn till begränsningen av innehållsfördröjningsbegränsningen. Vi undersöker också avvägningen mellan den totala strömförbrukningen och den upptagna midhaulbandbredden i nätverket. Våra resultat visar att funktionell splittring tillsammans med att möjliggöra cachning vid kantmoln minskar inte bara innehållsåtgångsfördröjningar utan även förbrukning av bandbredd, men på bekostnad av högre strömförbrukning.

Submitted by Caroline Periotto (carol@ufscar.br) on 2016-09-26T18:13:21Z No. of bitstreams: 1 DissMS.pdf: 7587278 bytes, checksum: b78af0b72b6cb2a9f5e605c25bfac1d1 (MD5)<br>Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-27T20:12:11Z (GMT) No. of bitstreams: 1 DissMS.pdf: 7587278 bytes, checksum: b78af0b72b6cb2a9f5e605c25bfac1d1 (MD5)<br>Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-27T20:12:18Z (GMT) No. of bitstreams: 1 DissMS.pdf: 7587278 bytes, checksum: b78af0b72b6cb2a9f5e605c25bfac1d1 (MD5)<br>Made available in DSpace on 2016-09-27T20:12:23Z (GMT). No. of bitstreams: 1 DissMS.pdf: 7587278 bytes, checksum: b78af0b72b6cb2a9f5e605c25bfac1d1 (MD5) Previous issue date: 2016-02-29<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Conselho Nacional de Pesquisa (CNPq)<br>This master thesis aims to study hybrid joints of polyetherimide (PEI) and aluminum 6082-T6 produced by Friction-based Injection Clinching Joining (FICJ). The influences of the process parameters in the frictional heat and polymer degradation were analyzed through a half factorial design. The degradation of PEI was evaluated by size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and infrared spectroscopy (FTIR). The effect of degradation in the joint microstructure and mechanical properties was also analyzed. The macro and microstructural characteristics were evaluated by optical microscopy and Vickers hardness. The static mechanical properties were determined by lap shear testing and cross tensile testing. It has been shown that the F-ICJ causes degradation through multiple chains scissions. Additionally, a thermomechanically affected zone, with lower hardness, and defects such as pores and weld lines are formed. The mechanical performance, mainly in cross tensile testing, is negatively affected by degradation and presence of defects. These results contribute to the optimization and application of F-ICJ to join hybrid structures.<br>Nesta dissertação de mestrado fabricou-se juntas híbridas de polieterimida (PEI) e alumínio 6082-T6 por rebitagem por injeção baseada em energia friccional (Friction-based Injection Clinching Joining - F-ICJ). Foi analisada a influência dos parâmetros de processo na geração de calor por fricção e na degradação polimérica através de planejamento de experimentos fatorial fracionário. O nível de degradação do PEI foi avaliado por cromatografia de exclusão por tamanho (SEC), calorimetria exploratória diferencial (DSC) e espectroscopia de infravermelho (FTIR). Estudou-se o efeito da degradação em características macro e microestruturais e nas propriedades mecânicas estáticas das juntas. As características macro e microestruturais foram avaliadas por meio de microscopia ótica e microdureza Vickers. A propriedade mecânica estática foi determinada por ensaio de cisalhamento de juntas sobrepostas e de tração da cabeça do rebite. Mostrou-se que o processo F-ICJ causou degradação por cisão de cadeias múltiplas. Adicionalmente, há criação de uma zona termomecanicamente afetada com menor microdureza e formação de defeitos, como poros e linhas de solda. O desempenho mecânico principalmente, em ensaio de tração da cabeça do rebite é negativamente afetado pela degradação e presença de defeitos. Estes resultados contribuem para a otimização e aplicação da técnica F-ICJ, na união de estruturas híbridas.

Das Forschungsvorhaben liefert einen Beitrag zum Schweißen von Gleich- und Mischmaterialverbindungen aus Naturfaserverstärkten Kunststoffen (NFK) sowie deren Verarbeitung im Compoundieren und Spritzguss. Es wurde holzfasergefülltes (WPC) und flachsfasergefülltes (FFC) Polypropylen (PP) mit unterschiedlichen Füllgraden verwendet. Der Einsatz synthetisch-organsicher Fasern (PET-Fasern) im Compound zielte darauf ab, besonders die Schlagzähigkeit zu verbessern. Im Bereich des Urformens wurden Aussagen zur Verarbeitbarkeit, zu rezepturabhängigen Kurz- und Langzeiteigenschaften sowie Aussagen zur Dauergebrauchsfähigkeit erarbeitet. Die Anwendbarkeit der Fügeverfahren Heizelement- (HE-Schweißen) und Vibrationsschweißen (VIB-Schweißen) konnte für Gleich- und Mischmaterialverbindungen sowohl ohne als auch mit angepasster Energieeinbringung nachgewiesen werden. In diesem Zusammenhang können Aussagen zur Rezepturabhängigkeit, Verfahrensführung, Parameterauswahl, Prüfkriterien sowie den technischen Grenzen der Schweißverbindung unter kurzzeitmechanischer Beanspruchung getroffen werden. Weiterhin wird ein Beitrag zur Dauergebrauchsfähigkeit unter UV-Globalbewitterung und thermischer Alterung sowie zu langzeitmechanischen Eigenschaften von NFK-Schweißverbindungen geliefert.

The continuous research of lightening mechanical and aeronautical structures is leading to the adoption of innovative materials and structure designs. and this development has to be necessarily followed by research in optimising structural health monitoring techniques. The set up of a reliable and quick monitoring technique. together with the enhancement of the mechanical performances of structures, is the tUl1ung point to the usage of even lighter and longer-lifed structures. Being impossible to build up a monolithic structure, it is common sense to understand that the most critical part of a structure is the joint between two or more different parts. For this reason, research is being focused on both the improvement of existing joint configuration, and the development of automatic systems which are able to monitor the health state of these joints when the structure is in service. The main reason urging to improve the current composite fastening joint and to develop innovative in situ monitoring techniques is linked to the continuous pursuit of cost reduction. In fact, a stronger and longer lifed fastening configuration, together with a reliable. quick and real-time non-destructive monitoring system applied on in service structures, would allow a considerable cut in maintenance time, with a consequent drop of costs. The objectives of this PhD work are manifold. On one side it focuses on the development of an innovative structural coupling configuration which is able to improve the mechanical properties of the joint; on the other hand, it aims to define reliable indexes able to assess the state of health of a joint structure. More precisely. the entire part concerning the monitoring side of the problem, it focuses on the definition of different possible method capable of determining the loosening state of a bolted connection. These methods are all based on the vibration and ultrasonic based techniques. The first step consists in the development of indexes able to predict the healthy state of a joint by studying some properties related to acoustic signals passing through the part's connection. After theoretically defining the parameters involved, experimental campaigns aimed to validate the models have been carried-out. Once the indexes were found, and confirmed to work on a small simplified structure, the most reliable and accurate IS chosen to be applied for the monitoring procedure on larger and more complicated structures. Both theoretical and experimental approaches were adopted to justify the reliability of the used method. Ultimately it was proved that with the adoption of few sensors and natural frequencies based vibration, with the developed method, it is possible to assess the location of a loosening bolt also on a multibolted structure. Additional research has to be done on real larger scale structures, hut promising results based on solid theoretical principles have been achieved. With regards to the necessity of enhancing existing fastening coupling configuration, all the efforts concentrate on the adoption and optimization of hybrid joints. Hybridization joint process takes advantages of positive aspects of both composite materials and fastening joints. Most important, the rising use of composite parts contributes to the reduction of structures' weight, with all the advantages involved, such as for instance, fuel consumption reduction with a consequent decrease of running costs. For this reason the second part of the thesis will discuss possible solution able to get out the best from coupling together composite materials and fastening configuration. More precisely all the attentions will focus on how to reduce problems generated by fastening composite parts, such as low bearing and shear strength, notch sensitivity and high dependency of joint strength from the lay-up configuration. The proposed solution will be as strong as the hybrid solutions developed so far, but also lighter at the same time

This thesis presents systematic numerical study of stresses in the adhesive of a single-lap joint subjected to various loading scenarios (mechanical and thermal loading). The main objective of this work is to improve understanding of the main material and geometrical parameters determining performance of adhesive joint for the future analysis of failure initiation and development in these structures. The first part of the thesis deals with development of a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates). The model takes into account the nonlinearity of materials (adherend and adhesive) with geometrical nonlinearity also accounted for. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criteria and it allows separation of edge and end effects. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters is carefully examined by analyzing peel and shear stress distributions in the adhesive layer. Discussion and conclusions with respect to the magnitude of the stress concentration at the ends of the joint overlap as well as overall level of stresses within overlap are presented. Recommendations concerning use of nonlinear material model are given. The rest of the work is related to the various methods of manufacturing of joint (curing) and application of thermo-mechanical loading suitable to these scenarios. The appropriate sequences of application of thermal and mechanical loads for the analysis of the residual thermal stresses developed due to manufacturing of joints at elevated temperature required to cure polymer (adhesive/composite) are proposed. It is shown that the most common approach used in many studies of simple superposition of thermal and mechanical stresses works well only for linear materials and produces wrong results if material is non-linear. The model and simulation technique presented in the current thesis rectifies this issue and accurate stress distributions are obtained. Based on the analysis of these stress distributions the following conclusions can be made: joint processing at elevated temperature causes high stresses inside the adhesive layer; the residual thermal stresses will reduce the peel stress concentration at the ends of overlap joint and the shear stress within the overlap, moreover, this effect is more pronounced for the case of the one-step joint manufacturing in comparison with two-step processing technique. This study has generated a lot of results for better understand of behavior of adhesive joints and it will help in design of stronger, more durable adhesive single-lap joints in the future.

Das ultraschallunterstützte Rührreibschweißen (USE-FSW) als innovatives Hybrid-Pressschweißverfahren zeichnet sich durch eine Reihe von Vorteilen aus, welche es für die Kombination artfremder metallischer Werkstoffe mit deutlich unterschiedlichem Schmelzpunkt ermöglichen, qualitativ hochwertigere Verbunde zu realisieren. Die vorliegende Arbeit thematisiert experimentelle Untersuchungen der Auswirkungen des zusätzlich eingekoppelten Leistungsultraschalls auf das Prozessverhalten und die Bindungsmechanismen sowie daraus resultierender mechanischer Verbundeigenschaften beim ultraschallunterstützten Rührreibschweißen von Aluminium/Stahl-Verbunden. Im Anschluss an die Ermittlung geeigneter Parameter für das konventionelle Rührreibschweißen erfolgen grundlegende Betrachtungen des Einflusses des Leistungsultraschalls auf das Schwingungsverhalten, das thermische Verhalten und das insitu- Prozesskraftverhalten, aus denen bestmögliche Ultraschallparameter abgeleitet werden. Nachfolgende detaillierte, vergleichende Untersuchungen des konventionellen und des ultraschallunterstützten Rührreibschweißprozesses belegen unter anderem eine Reduktion der Dicke spröder, aluminiumreicher intermetallischer Phasen am Verbund-Interface des USE-FSW-Verbundes, was in einer Erhöhung der Zugfestigkeit und der Duktilität resultiert.<br>The ultrasound enhanced friction stir welding (USE-FSW) as an innovative hybrid solid state joining process is characterized by a number of advantages that enable the realization of higher quality joints for the combination of dissimilar, metallic material combinations with strongly differing melting points. The present work addresses the impact of the additional power ultra- sound transmission on the process behavior and the bonding mechanisms as well as resulting mechanical joint properties for the ultrasound enhanced friction stir welding of aluminum/steel joints via experimental investigations. Subsequent to the determination of suitable parameters for the conventional friction stir welding basic considerations of the power ultrasound influence on the oscillation behavior, the thermal behavior and the in-situ process force behavior take place for deriving a best possible set of ultrasound parameters. Moreover, the conventional and the ultrasound enhanced friction stir welding process are investigated comparatively in detail, proving a reduction in thickness for brittle, aluminum-rich intermetallic phases at the USE-FSW joint interface among other things, resulting in an improved tensile strength and ductility.

Analyse et determination des differents constituants utilises dans les assemblages de circuits integres hybrides de puissance. Caracterisation thermomecanique des joints realises. Evaluation de l'endurance thermique

Analyse et determination des differents constituants utilises dans les assemblages de circuits integres hybrides de puissance. Caracterisation thermomecanique des joints realises. Evaluation de l'endurance thermique

Dans cette thèse, nous nous adressons le problème du contrôle de systèmes multi-agents connectés via des modèles réalistes de systèmes de communication. Nous traitons principalement les systèmes de véhicules connectés et automatisés (CAVs) communiquant via des systèmes de communication 5G qui permettent deux types de communication : la communication directe entre les nœuds, connue sous le nom de communication véhicule-à-véhicule (V2V), et la communication à travers l'infrastructure réseau, qui est la manière traditionnelle de communiquer dans les réseaux cellulaires.La thèse traite de trois problèmes : premièrement, nous analysons les propriétés de stabilité et de convergence de l'algorithme du consensus pour agents d'intégrateurs du premier ordre en utilisant un schéma d'accès multiple par répartition temporelle (TDMA) pour partager les ressources du réseau d'un canal de communication partagé. La stabilité exponentielle du système considéré est démontrée, et une borne explicite dépendant des paramètres du système de communication est fournie pour estimer la vitesse de convergence. Ensuite, nous abordons le problème du contrôle de formation d'un groupe de véhicules connectés dans un contexte de communication 5G. Nous proposons un algorithme d'allocation de ressources pour sélectionner les utilisateurs émetteurs afin d'atteindre la formation souhaitée tout en respectant les contraintes imposées par le couche de communication. Enfin, nous étudions les propriétés de stabilité des filtres de Kalman pour les systèmes hybrides, précisément, des systèmes avec une dynamique en temps continu observée à travers des mesures en temps discret. La stabilité d'entrée-à-état (ISS) est démontrée pour de tels systèmes en utilisant une fonction de Lyapunov appropriée. Ce résultat peut être considéré comme une première étape dans l'analyse de la robustesse du système global, car il permet de prendre en compte les effets des erreurs de communication sur la stabilité du système contrôlé<br>In this thesis, we address the problem of control of multi-agent systems connected over realistic models of communication systems. We mainly focus on systems of connected and automated vehicles (CAVs) that communicate through a 5G communication system, which allows two types of communication: direct communication between nodes, known as Vehicle-to-Vehicle (V2V) communications, and communication through the network infrastructure, which is the traditional way of communication in cellular networks.The thesis discusses three problems: first, we analyze the stability and convergence properties of the consensus algorithm of first-order integrator agents using a time-division multiple access (TDMA) scheme to share the network resources of a broadcast shared communication channel. Exponential stability of the considered system is proved, and an explicit bound depending on the communication system parameters is provided to estimate the convergence rate. Second, we treat the problem of formation control of a float of connected vehicles in a 5G communication context. We propose a resource allocation algorithm to select the transmitting users to achieve the desired formation while satisfying the constraints imposed by the communication system. Finally, we study the stability properties of Kalman filters for hybrid systems, i.e., systems with continuous-time dynamics observed through discrete-time measurements. Input-to-state stability (ISS) is proved for such systems relying on an appropriate Lyapunov function. This result can be considered as a first step in the robustness analysis of the overall system since it allows to treat the effects of communication errors on the controlled system stability

<p>This dissertation considers packet-switched wireless networks for transmission of variable-rate layered hybrid video streams. Target applications are video streaming and broadcasting services. The work can be divided into two main parts.</p><p>In the first part, a novel quality-scalable scheme based on coefficient refinement and encoder quality constraints is developed as a possible extension to the video coding standard H.264. After a technical introduction to the coding tools of H.264 with the main focus on error resilience features, various quality scalability schemes in previous research are reviewed. Based on this discussion, an encoder decoder framework is designed for an arbitrary number of quality layers, hereby also enabling region-of-interest coding. After that, the performance of the new system is exhaustively tested, showing that the bit rate increase typically encountered with scalable hybrid coding schemes is, for certain coding parameters, only small to moderate. The double- and triple-layer constellations of the framework are shown to perform superior to other systems.</p><p>The second part considers layered code streams as generated by the scheme of the first part. Various error propagation issues in hybrid streams are discussed, which leads to the definition of a decoder quality constraint and a segmentation of the code stream to transmit. A packetization scheme based on successive source rate consumption is drafted, followed by the formulation of the channel code rate optimization problem for an optimum assignment of available codes to the channel packets. Proper MSE-based error metrics are derived, incorporating the properties of the source signal, a terminate-on-error decoding strategy, error concealment, inter-packet dependencies, and the channel conditions. The Viterbi algorithm is presented as a low-complexity solution to the optimization problem, showing a great adaptivity of the joint source channel coding scheme to the channel conditions. An almost constant image qualiity is achieved, also in mismatch situations, while the overall channel code rate decreases only as little as necessary as the channel quality deteriorates. It is further shown that the variance of code distributions is only small, and that the codes are assigned irregularly to all channel packets.</p><p>A double-layer constellation of the framework clearly outperforms other schemes with a substantial margin. </p><p>Keywords — Digital lossy video compression, visual communication, variable bit rate (VBR), SNR scalability, layered image processing, quality layer, hybrid code stream, predictive coding, progressive bit stream, joint source channel coding, fidelity constraint, channel error robustness, resilience, concealment, packet-switched, mobile and wireless ATM, noisy transmission, packet loss, binary symmetric channel, streaming, broadcasting, satellite and radio links, H.264, MPEG-4 AVC, Viterbi, trellis, unequal error protection</p>

Evolution had played a significant role in structuring on how humans stand, walk or run. The nervous system plays a major role in the control of locomotion and injuries to the system can lead to gait abnormalities or disabilities. A Spinal Cord Injury (SCI) causes lack of signal communication between the central nervous system and the muscle fibers leading to deprived or no activation of the muscles thus resulting in paraplegia or quadriplegia. Over the past decade wearable robotics and exoskeletons have been gaining outstanding recognition in the field of medical, assistive and augmentative robotics and have led to numerous new innovative mechanisms in the mechanical engineering field. Due to fast paced research activities, the critical importance and performance of mechanisms such as wrap spring clutch/brake,Wafer Disc brakes are overlooked or used ineffectively. So, researchers tend to create new actuators from scratch and have limited their use of previously available resources, which has prevented us to explore the potential of these devices.The research presented focuses on developing a mechanism (“A Wrap Spring Clutch/Brake Mechanism”) from scratch using a trade study approach. This thesis addresses the fundamental relationship between coefficient of friction, interference, spring diameter and the holding torque of the mechanism using analytical, testing and simulation results. The human biomechanical data during ground level walking was used as design targets to develop the mathematical model of the system. Data from the testing stated that these targeted goals have been achieved by the design. This mechanism is used as a Knee Joint for the Hybrid EXoskeleton (HEX) GEN-1 project which is developed at the Automation and Interventional Medicine (AIM) Robotics Research Laboratory to rehabilitate the SCI.

The Hybrid Warfare phenomena, which is the subject of the current research, has been framed by the work of Professor Agostino Bruzzone (University of Genoa) and Professor Erdal Cayirci (University of Stavanger), that in June 2016 created in order to inquiry the subject a dedicated Exploratory Team, which was endorsed by NATO Modelling &amp; Simulation Group (a panel of the NATO Science &amp; Technology organization) and established with the participation as well of the author. The author brought his personal contribution within the ET43 by introducing meaningful insights coming from the lecture of “Fight by the minutes: Time and the Art of War (1994)”, written by Lieutenant Colonel US Army (Rtd.) Robert Leonhard; in such work, Leonhard extensively developed the concept that “Time”, rather than geometry of the battlefield and/or firepower, is the critical factor to tackle in military operations and by extension in Hybrid Warfare. The critical reflection about the time - both in its quantitative and qualitative dimension - in a hybrid confrontation it is addressed and studied inside SIMCJOH, a software built around challenges that imposes literally to “Fight by the minutes”, echoing the core concept expressed in the eponymous work. Hybrid Warfare – which, by definition and purpose, aims to keep the military commitment of both aggressor and defender at the lowest - can gain enormous profit by employing a wide variety of non-military tools, turning them into a weapon, as in the case of the phenomena of “weaponization of mass migrations”, as it is examined in the “Dies Irae” simulation architecture. Currently, since migration it is a very sensitive and divisive issue among the public opinions of many European countries, cynically leveraging on a humanitarian emergency caused by an exogenous, inducted migration, could result in a high level of political and social destabilization, which indeed favours the concurrent actions carried on by other hybrid tools. Other kind of disruption however, are already available in the arsenal of Hybrid Warfare, such cyber threats, information campaigns lead by troll factories for the diffusion of fake/altered news, etc. From this perspective the author examines how the TREX (Threat network simulation for REactive eXperience) simulator is able to offer insights about a hybrid scenario characterized by an intense level of social disruption, brought by cyber-attacks and systemic faking of news. Furthermore, the rising discipline of “Strategic Engineering”, as envisaged by Professor Agostino Bruzzone, when matched with the operational requirements to fulfil in order to counter Hybrid Threats, it brings another innovative, as much as powerful tool, into the professional luggage of the military and the civilian employed in Defence and Homeland security sectors. Hybrid is not the New War. What is new is brought by globalization paired with the transition to the information age and rising geopolitical tensions, which have put new emphasis on hybrid hostilities that manifest themselves in a contemporary way. Hybrid Warfare is a deliberate choice of an aggressor. While militarily weak nations can resort to it in order to re-balance the odds, instead military strong nations appreciate its inherent effectiveness coupled with the denial of direct responsibility, thus circumventing the rules of the International Community (IC). In order to be successful, Hybrid Warfare should consist of a highly coordinated, sapient mix of diverse and dynamic combination of regular forces, irregular forces (even criminal elements), cyber disruption etc. all in order to achieve effects across the entire DIMEFIL/PMESII_PT spectrum. However, the owner of the strategy, i.e. the aggressor, by keeping the threshold of impunity as high as possible and decreasing the willingness of the defender, can maintain his Hybrid Warfare at a diplomatically feasible level; so the model of the capacity, willingness and threshold, as proposed by Cayirci, Bruzzone and Gunneriusson (2016), remains critical to comprehend Hybrid Warfare. Its dynamicity is able to capture the evanescent, blurring line between Hybrid Warfare and Conventional Warfare. In such contest time is the critical factor: this because it is hard to foreseen for the aggressor how long he can keep up with such strategy without risking either the retaliation from the International Community or the depletion of resources across its own DIMEFIL/PMESII_PT spectrum. Similar discourse affects the defender: if he isn’t able to cope with Hybrid Threats (i.e. taking no action), time works against him; if he is, he can start to develop counter narrative and address physical countermeasures. However, this can lead, in the medium long period, to an unforeseen (both for the attacker and the defender) escalation into a large, conventional, armed conflict. The performance of operations that required more than kinetic effects drove the development of DIMEFIL/PMESII_PT models and in turn this drive the development of Human Social Culture Behavior Modelling (HCSB), which should stand at the core of the Hybrid Warfare modelling and simulation efforts. Multi Layers models are fundamental to evaluate Strategies and Support Decisions: currently there are favourable conditions to implement models of Hybrid Warfare, such as Dies Irae, SIMCJOH and TREX, in order to further develop tools and war-games for studying new tactics, execute collective training and to support decisions making and analysis planning. The proposed approach is based on the idea to create a mosaic made by HLA interoperable simulators able to be combined as tiles to cover an extensive part of the Hybrid Warfare, giving the users an interactive and intuitive environment based on the “Modelling interoperable Simulation and Serious Game” (MS2G) approach. From this point of view, the impressive capabilities achieved by IA-CGF in human behavior modeling to support population simulation as well as their native HLA structure, suggests to adopt them as core engine in this application field. However, it necessary to highlight that, when modelling DIMEFIL/PMESII_PT domains, the researcher has to be aware of the bias introduced by the fact that especially Political and Social “science” are accompanied and built around value judgement. From this perspective, the models proposed by Cayirci, Bruzzone, Guinnarson (2016) and by Balaban &amp; Mileniczek (2018) are indeed a courageous tentative to import, into the domain of particularly poorly understood phenomena (social, politics, and to a lesser degree economics - Hartley, 2016), the mathematical and statistical instruments and the methodologies employed by the pure, hard sciences. Nevertheless, just using the instruments and the methodology of the hard sciences it is not enough to obtain the objectivity, and is such aspect the representations of Hybrid Warfare mechanics could meet their limit: this is posed by the fact that they use, as input for the equations that represents Hybrid Warfare, not physical data observed during a scientific experiment, but rather observation of the reality that assumes implicitly and explicitly a value judgment, which could lead to a biased output. Such value judgement it is subjective, and not objective like the mathematical and physical sciences; when this is not well understood and managed by the academic and the researcher, it can introduce distortions - which are unacceptable for the purpose of the Science - which could be used as well to enforce a narrative mainstream that contains a so called “truth”, which lies inside the boundary of politics rather than Science. Those observations around subjectivity of social sciences vs objectivity of pure sciences, being nothing new, suggest however the need to examine the problem under a new perspective, less philosophical and more leaned toward the practical application. The suggestion that the author want make here is that the Verification and Validation process, in particular the methodology used by Professor Bruzzone in doing V&amp;V for SIMCJOH (2016) and the one described in the Modelling &amp; Simulation User Risk Methodology (MURM) developed by Pandolfini, Youngblood et all (2018), could be applied to evaluate if there is a bias and the extent of the it, or at least making clear the value judgment adopted in developing the DIMEFIL/PMESII_PT models. Such V&amp;V research is however outside the scope of the present work, even though it is an offspring of it, and for such reason the author would like to make further inquiries on this particular subject in the future. Then, the theoretical discourse around Hybrid Warfare has been completed addressing the need to establish a new discipline, Strategic Engineering, very much necessary because of the current a political and economic environment which allocates diminishing resources to Defense and Homeland Security (at least in Europe). However, Strategic Engineering can successfully address its challenges when coupled with the understanding and the management of the fourth dimension of military and hybrid operations, Time. For the reasons above, and as elaborated by Leonhard and extensively discussed in the present work, addressing the concern posed by Time dimension is necessary for the success of any military or Hybrid confrontation. The SIMCJOH project, examined under the above perspective, proved that the simulator has the ability to address the fourth dimension of military and non-military confrontation. In operations, Time is the most critical factor during execution, and this was successfully transferred inside the simulator; as such, SIMCJOH can be viewed as a training tool and as well a dynamic generator of events for the MEL/MIL execution during any exercise. In conclusion, SIMCJOH Project successfully faces new challenging aspects, allowed to study and develop new simulation models in order to support decision makers, Commanders and their Staff. Finally, the question posed by Leonhard in terms of recognition of the importance of time management of military operations - nowadays Hybrid Conflict - has not been answered yet; however, the author believes that Modelling and Simulation tools and techniques can represent the safe “tank” where innovative and advanced scientific solutions can be tested, exploiting the advantage of doing it in a synthetic environment.

Hybrid entrepreneurial is phenomenal but remains under-studied in the management literature. This paper investigated the joint influence of hybrid entrepreneurs’ trait regulatory focus and wage work to entrepreneurial work enrichment (WE enrichment) on their entrepreneurial engagement and the subsequent proficient, adaptive, and proactive performance in entrepreneurial work. I first interviewed 16 hybrid entrepreneurs to obtain the understanding of their reasons for being in hybrid entrepreneurship, their regulatory focus tendencies, and the resources they transfer from wage work to entrepreneurial work. To validate the measurement scales of promotion and prevention focus, I conducted a pilot study among 66 hybrid entrepreneurs. Then, I conducted a multi-source questionnaire survey among 329 hybrid entrepreneurs and their entrepreneurial partners in Ghana. The final sample included 272 completed and matched responses. I used structural equation modeling of Mplus 7.4 to test the hypothesized model. Results of the questionnaire survey provided strong support to my hypothesized model. Promotion focus and prevention focus had positive and negative relationships with these three types of entrepreneurial performance, respectively. I also found that the opposite relationships of promotion focus and prevention focus with these three types of entrepreneurial performance were mediated by entrepreneurial engagement. Furthermore, hybrid entrepreneurs work across the wage-work and entrepreneurial roles, and I found that WE enrichment played a moderating role. Specifically, WE enrichment strengthened the positive relationship between promotion focus and entrepreneurial engagement as well as the positive indirect relationships between promotion focus and the three types of entrepreneurial performance through entrepreneurial engagement. In contrast, WE enrichment weakened the negative relationship between prevention focus and entrepreneurial engagement as well as the negative indirect relationships between prevention focus and the three types of entrepreneurial performance through entrepreneurial engagement. This research sheds light on how personality traits and dual-work context affect hybrid entrepreneurs’ entrepreneurial processes and performance outcomes. Thus, I provide theoretical implications for the literature of hybrid entrepreneurial and dual work roles. Further, this research offers important practical implications for hybrid entrepreneurs and their entrepreneurial partners, as well as investors.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>Trace metal cycling is one of many processes that influence ocean ecosystem dynamics. Cobalt, iron, and manganese are redox active trace metal micro-nutrients with oceanic distributions that are influenced by both biological and abiotic sources and sinks. Their open ocean concentrations range from picomolar to nanomolar, and their bioavailabilities can impact primary production. Understanding the biogeochemical cycling of these hybrid-type metals with an emphasis on cobalt was the focus of this thesis. This was accomplished by determining the dissolved distributions of these metals in oceanic regions that were characterized by different dominant biogeochemistries. A large subsurface plume of dissolved cobalt, iron, and manganese was found in the Eastern South Atlantic. The cause of this plume is a combination of reductive dissolution in coastal sediments, wind-driven upwelling, advection, biological uptake, and remineralization. Additional processes that are discussed as sources of metals to the regions studied during this thesis include isopycnal uplift within cold-core eddies (Hawaii), ice melt (McMurdo Sound, Antarctica), riverine input (Arctic Ocean), and winter mixing (McMurdo Sound). The biological influence on surface ocean distributions of cobalt was apparent by the observation of linear relationships between cobalt and phosphate in mid to low latitudes. The cobalt:phosphate ratios derived from these correlations changed over orders of magnitude, revealing dynamic variability in the utilization, demand, and sources of this micronutrient. Speciation studies suggest that there may be two classes of cobalt binding ligands, and that organic complexation plays an important role in preventing scavenging of cobalt in the ocean. These datasets provided a basis for comparing the biogeochemical cycles of cobalt, iron, and manganese in three oceanic regimes (Hawaii, South Atlantic, McMurdo Sound). The relative rates of scavenging for these metals show environmental variability: in the South Atlantic, cobalt, iron, and manganese were scavenged at very different rates, but in the Ross Sea, mixing and circulation over the shallow sea was fast, scavenging played a minor role, and the cycles of all three metals were coupled. Studying the distributions of these metals in biogeochemically distinct regions is a step toward a better understanding of their oceanic cycles.<br>by Abigail Emery Noble.<br>Ph.D.

L'objectif de cette recherche est d'établir des mécanismes de formation de la structure des systèmes hybrides organique-inorganique à base des oligomères uréthane et silicates en fonction de la réactivité de la composant organique, d'identifier l'impact de l'organisation structurelle du OIS obtenue sur leurs propriétés électriques et thermomécaniques, de sorption et de l'activité du capteur. La signification pratique des résultats est la détermination de l'impact de la réactivité composant organique sur la structure des systèmes hybrides polymère organique-inorganique avec la possibilité d'obtenir des matériaux avec des propriétés spéciales prévisibles. Les résultats peuvent être utilisés comme base scientifique pour comprendre l'interconnexion de la structure, les propriétés et les moyens de leur régulation en direction de systèmes hybrides polymère organique-inorganique. La sensibilité très élevée pour les différents types de solvants, qui, combiné avec une haute sélectivité, a été révélé pour les systèmes de synthèse, la possibilité de leur utilisation pratique en tant que matières capteur existe.

Dans le secteur des soins de santé, les données d'images médicales toujours croissantes, le développement de technologies d'imagerie, la conservation à long terme des données médicales et l'augmentation de la résolution des images entraînent une croissance considérable du volume de données. En outre, la variété des dispositifs d'acquisition et la différence de préférences des médecins ou d'autres professionnels de la santé ont conduit à une grande variété de données. Bien que la norme DICOM (Digital Imaging et Communication in Medicine) soit aujourd'hui largement adoptée pour stocker et transférer les données médicales, les données DICOM ont toujours les caractéristiques 3V du Big Data: volume élevé, grande variété et grande vélocité. En outre, il existe une variété de charges de travail, notamment le traitement transactionnel en ligne (en anglais Online Transaction Processing, abrégé en OLTP), le traitement analytique en ligne (anglais Online Analytical Processing, abrégé en OLAP) et les charges de travail mixtes. Les systèmes existants ont des limites concernant ces caractéristiques des données et des charges de travail. Dans cette thèse, nous proposons de nouvelles méthodes efficaces pour stocker et interroger des données DICOM. Nous proposons un modèle de stockage hybride des magasins de lignes et de colonnes, appelé HYTORMO, ainsi que des stratégies de stockage de données et de traitement des requêtes. Tout d'abord, HYTORMO est conçu et mis en œuvre pour être déployé sur un environnement à grande échelle afin de permettre la gestion de grandes données médicales. Deuxièmement, la stratégie de stockage de données combine l'utilisation du partitionnement vertical et un stockage hybride pour créer des configurations de stockage de données qui peuvent réduire la demande d'espace de stockage et augmenter les performances de la charge de travail. Pour réaliser une telle configuration de stockage de données, l'une des deux approches de conception de stockage de données peut être appliquée: (1) conception basée sur des experts et (2) conception automatisée. Dans la première approche, les experts créent manuellement des configurations de stockage de données en regroupant les attributs des données DICOM et en sélectionnant une disposition de stockage de données appropriée pour chaque groupe de colonnes. Dans la dernière approche, nous proposons un cadre de conception automatisé hybride, appelé HADF. HADF dépend des mesures de similarité (entre attributs) qui prennent en compte les impacts des informations spécifiques à la charge de travail et aux données pour générer automatiquement les configurations de stockage de données: Hybrid Similarity (combinaison pondérée de similarité d'accès d'attribut et de similarité de densité d'attribut) les attributs dans les groupes de colonnes; Inter-Cluster Access Similarity est utilisé pour déterminer si deux groupes de colonnes seront fusionnés ou non (pour réduire le nombre de jointures supplémentaires); et Intra-Cluster Access La similarité est appliquée pour décider si un groupe de colonnes sera stocké dans une ligne ou un magasin de colonnes. Enfin, nous proposons une stratégie de traitement des requêtes adaptée et efficace construite sur HYTORMO. Il considère l'utilisation des jointures internes et des jointures externes gauche pour empêcher la perte de données si vous utilisez uniquement des jointures internes entre des tables partitionnées verticalement. De plus, une intersection de filtres Bloom (intersection of Bloom filters, abrégé en ) est appliqué pour supprimer les données non pertinentes des tables d'entrée des opérations de jointure; cela permet de réduire les coûts d'E / S réseau. (...)<br>In the health care industry, the ever-increasing medical image data, the development of imaging technologies, the long-term retention of medical data and the increase of image resolution are causing a tremendous growth in data volume. In addition, the variety of acquisition devices and the difference in preferences of physicians or other health-care professionals have led to a high variety in data. Although today DICOM (Digital Imaging and Communication in Medicine) standard has been widely adopted to store and transfer the medical data, DICOM data still has the 3Vs characteristics of Big Data: high volume, high variety and high velocity. Besides, there is a variety of workloads including Online Transaction Processing (OLTP), Online Analytical Processing (OLAP) and mixed workloads. Existing systems have limitations dealing with these characteristics of data and workloads. In this thesis, we propose new efficient methods for storing and querying DICOM data. We propose a hybrid storage model of row and column stores, called HYTORMO, together with data storage and query processing strategies. First, HYTORMO is designed and implemented to be deployed on large-scale environment to make it possible to manage big medical data. Second, the data storage strategy combines the use of vertical partitioning and a hybrid store to create data storage configurations that can reduce storage space demand and increase workload performance. To achieve such a data storage configuration, one of two data storage design approaches can be applied: (1) expert-based design and (2) automated design. In the former approach, experts manually create data storage configurations by grouping attributes and selecting a suitable data layout for each column group. In the latter approach, we propose a hybrid automated design framework, called HADF. HADF depends on similarity measures (between attributes) that can take into consideration the combined impact of both workload- and data-specific information to generate data storage configurations: Hybrid Similarity (a weighted combination of Attribute Access and Density Similarity measures) is used to group the attributes into column groups; Inter-Cluster Access Similarity is used to determine whether two column groups will be merged together or not (to reduce the number of joins); and Intra-Cluster Access Similarity is applied to decide whether a column group will be stored in a row or a column store. Finally, we propose a suitable and efficient query processing strategy built on top of HYTORMO. It considers the use of both inner joins and left-outer joins. Furthermore, an Intersection Bloom filter () is applied to reduce network I/O cost.We provide experimental evaluations to validate the benefits of the proposed methods over real DICOM datasets. Experimental results show that the mixed use of both row and column stores outperforms a pure row store and a pure column store. The combined impact of both workload-and data-specific information is helpful for HADF to be able to produce good data storage configurations. Moreover, the query processing strategy with the use of the can improve the execution time of an experimental query up to 50% when compared to the case where no is applied

Cette thèse explore le comportement mécanique des joints et des poutres en composite bois-béton (TCC) collés par adhésif à travers des investigations expérimentales et numériques.Le comportement mécanique des joints collés par adhésif entre le bois (GL24h) et le béton auto-plaçant (SCC) formés par un processus de collage à sec ou humide est étudié. À cette fin, des essais de cisaillement double push-out ont été réalisés sur des joints TCC collés par de la résine époxy. Les résultats ont montré que le collage semble être une alternative réalisable aux moyens mécaniques pour produire des joints TCC secs et humides. Dans des conditions de bois sec, la résistance au cisaillement peut être considérée comme très satisfaisante, avec une plage de valeurs moyennes de 6 à 8 MPa. Le mode de rupture est principalement influencé par la rupture du béton et du bois.Une investigation expérimentale des caractéristiques de rupture, du glissement de l'interface, de la distribution des contraintes et de la réponse charge-déformation des poutres en composite bois-béton collées par adhésif, fabriquées selon des procédés humides ou secs, a été menée. Six poutres en composite bois-béton collées par adhésif à échelle réelle ont été produites avec une portée de 3,2 mètres et soumises à des essais de flexion à quatre points. Les poutres en composite bois-béton fabriquées par voie humide ou sèche ont révélé des modes de rupture distincts. Les résultats ont souligné le rôle critique de l'intégrité du collage pour garantir une action composite efficace et un mécanisme de contribution partagée. Les poutres en composite bois-béton fabriquées par voie humide ont présenté un collage rigide caractérisé par un alignement neutre et une distribution de charge uniformes le long de la portée de la poutre, tandis que les poutres fabriquées par voie sèche ont connu une séparation d'interface et une contribution de charge compromise, entraînant une réduction significative de la capacité de flexion ultime des poutres en composite bois-béton. Les résultats ont montré que les poutres en composite bois-béton fabriquées par voie humide et sèche présentaient des réponses de déflexion charge-mi-portée comparables avant la rupture, mettant en évidence un comportement uniforme et un alignement avec des caractéristiques totalement composites sous les charges imposées.De plus, un modèle analytique pour le calcul des poutres en composite bois-béton est présenté et validé. La base du modèle analytique est établie sur la méthode γ dérivée de l'Eurocode 5. Le modèle analytique est comparé aux résultats expérimentaux, mettant en évidence sa fiabilité et sa précision. Les réponses charge-déflexion, les distributions des contraintes de flexion et les charges de rupture ultimes sont capturées avec précision, affirmant la capacité du modèle à anticiper le comportement des poutres en composite bois-béton.En outre, un modèle d'éléments finis non linéaire tridimensionnel (FE) pour les poutres en composite bois-béton collées par adhésif est présenté. Le modèle analyse le comportement de déformation, la distribution des contraintes de flexion, la capacité ultime et les caractéristiques de rupture des poutres en composite bois-béton. Le modèle FE a prédit avec précision le degré d'action composite. Notamment, le modèle FE et le modèle analytique basé sur la méthode γ présentent une performance prédictive comparable en termes de déformation. Les résultats de la distribution des contraintes de flexion ont mis en évidence une correspondance étroite entre les simulations FE et les données expérimentales. De plus, le modèle FE a démontré son efficacité dans la prédiction de la capacité ultime des poutres en composite bois-béton et a capturé de manière cohérente les modes de rupture, indiquant sa fiabilité dans la simulation du comportement complexe des poutres en composite bois-béton<br>This thesis explores the mechanical behaviour of adhesively bonded TCC joints and beams Through experimental and numerical investigations.The mechanical behaviour of the adhesive bonded joints between timber (GL24h) and self-compacting concrete (SCC) set by the dry or wet bonding process is investigated. For this purpose, double push-out shear tests on TCC joints bonded by epoxy resin of adhesives were performed. The role of several variables was considered for both fabrication processes. These parameters were: variation of moisture content (m.c.) of timber, adhesive type, adhesive thickness, sand addition, concrete surface treatment, and scale of bonding length. The results showed that glueing seems to be a feasible alternative instead of mechanical means for producing dry and wet TCC joints. Under dry conditions of timber elements, the shear strength can be considered highly satisfactory, with a mean value range of 6-8MPa. The failure mode is primarily affected by concrete and timber failure. However, the findings confirm the hypothesis that increasing the moisture content of the timber before the glueing process significantly reduces the shear strength of adhesively bonded TCC joints by approximately 30% in certain instances.An experimental investigation of the failure characteristics, interface slip, strain distribution, and load-deflection response of adhesively bonded timber-concrete composite (TCC) beams fabricated using wet or dry processes was conducted. A total of six full-scale adhesively bonded TCC beams were produced with a span of 3.2 m and subjected to four-point bending tests. Wet and dry fabricated TCC beams revealed distinct failure modes. The results emphasized the critical role of bonding integrity in ensuring effective composite action and shared contribution mechanism. Wet-fabricated TCC beams exhibited a rigid bonding characterized by a consistent neutral axis alignment and load distribution along the beam span, while dry-fabricated beams experienced interface separation and compromised load-shared contribution, resulting in a significant reduction of the ultimate bending capacity of TCC beams. The outcomes showed that wet and dry TCC beams exhibited comparable load-to-mid-span deflection responses before failure, highlighting uniform behaviour and alignment with fully composite characteristics under the imposed loads.Furthermore, an analytical model for calculating TCC beams is presented and validated. The foundation of the analytical model is established upon the γ-method derived from Eurocode 5. The analytical model is compared with experimental results, highlighting its reliability and precision. Load-deflection responses, bending strain distributions, and ultimate failure loads are accurately captured, affirming the model's capability to anticipate the TCC beam behaviour.Additionally, a 3D non-linear Finite Element (FE) model for adhesively bonded Timber-Concrete Composite (TCC) beams is presented. The model analyzes the deformation behaviour, bending stress distribution, ultimate capacity, and failure characteristics of TCC beams. Despite the challenges that arose in cases of bonding failure, leading to exceptional deviations in behaviour, the results revealed a remarkable agreement between the predictions of the FE model and the outcomes of experimental tests. The FE model accurately predicted the degree of composite action. Notably, the FE model and analytical model based on the γ-method exhibit comparable predictive performance in terms of deformation. Bending stress distribution findings highlighted a strong correspondence between FE simulations and experimental data. Furthermore, the FE model demonstrated efficacy in predicting the ultimate capacity of TCC beams and consistently captured failure modes, indicating its reliability in simulating the complex behaviour of TCC beams

<p>The introduction of carbon-fibre reinforced plastics in loadbearing automotive structures provides a great potential toreduce vehicle weight and fuel consumption. To enable themanufacture and assembly of composite structural parts,reliable and cost-effective joining technologies must bedeveloped. This thesis addresses several aspects of joining andload introduction in carbon-fibre reinforced plastics based onnon-crimp fabric reinforcement.</p><p>The bearing strength of carbon fibre/epoxy laminates wasinvestigated considering the effects of bolt-hole clearance.The laminate failure modes and ultimate bearing strength werefound to be significantly dependent upon the laminate stackingsequence, geometry and lateral clamping load. Significantreduction in bearing strength at 4% hole deformation was foundfor both pin-loaded and clamped laminates. The ultimatestrength of the joints was found to be independent of theinitial bolt-hole clearance.</p><p>The behaviour of hybrid (bolted/bonded) joints wasinvestigated both numerically and experimentally. Athree-dimensional non-linear finite element model was developedto predict the load transfer distribution in the joints. Theeffect of the joint geometry and adhesive material propertieson the load transfer was determined through a parameter study.An experimental investigation was undertaken to determine thestrength, failure mechanisms and fatigue life of hybrid joints.The joints were shown to have greater strength, stiffness andfatigue life in comparison to adhesive bonded joints. However,the benefits were only observed in joint designs which allowedfor load sharing between the adhesive and the bolt.</p><p>The effect of the environment on the durability of bondedand hybrid joints was investigated. The strength and fatiguelife of the joints was found to decrease significantly withincreased ageing time. Hybrid joints demonstrated increasedfatigue life in comparison to adhesive bonded joints afterageing in a cyclic freeze/thaw environment.</p><p>The strength and failure mechanisms of composite laminatessubject to localised transverse loading were investigatedconsidering the effect of the specimen size, stacking sequenceand material system. Damage was found to initiate in thelaminates at low load levels, typically 20-30% of the ultimatefailure load. The dominant initial failure mode wasintralaminar shear failure, which occurred in sub-surfaceplies. Two different macromechanical failure modes wereidentified, fastener pull-through failure and global collapseof the laminate. The damage patterns and ultimate failure modewere found to depend upon the laminate stacking sequence andresin system. Finite element analysis was used to analyse thestress distribution within the laminates and predict first-plyfailure.</p><p><b>Keywords:</b>Composite, laminate, bearing strength,joining, load introduction, hybrid joint, finite elementanalysis, mechanical testing.</p>

The objective of this thesis research is to develop an adhesive bonding solution in order to remove the classic welding technology exploited nowadays in the automotive steel wheel system. The examined solution is an hybrid joint, based on adhesive boding combined with the presence of an interference fit. This hybrid joining technology consists in coupling two cylindrical components together by force-fitting one into the other after having placed an adhesive on the mating surfaces. This technique would allow the joining of dissimilar material to enable the design of hybrid lightweight wheels. Moreover, it would provide a better stress distribution in the joint area that could induce fatigue life improvement. The contributions of the adhesive and the interference on the performance of the final hybrid joint is still not completely clear. In particular, the effect of the adhesive nature and of its mechanical and adhesive responses on the performance of the hybrid joint is under concern in this research. A study of the phenomena acting at the interference level is conducted at the laboratory level before industrial case application. An experimental method is set up in order to test the adhesives in a press fit joint. Static and dynamic tests are carried out examining the behavior of different adhesives, including rigid epoxies and flexible polyurethanes, and fractographic analysis are then performed. The second part of the study is focused on the feasibility of the hybrid technology on the wheel system. Exploiting the outcomes of the laboratory analysis, bonded wheel prototypes are assembled and tested statically and dynamically, according to component validation in MW. From the laboratory scale analyses it is found that the adhesive type mainly affects the static resistance of the hybrid joint. In particular the curing technology affects the decoupling behavior and the rheology influences the quantity of adhesive that remains inside the joint despites the interference levels. On the other hand, the interference rules the stiffness of the assembly and strongly affects the fatigue behavior of the cylindrical joint. The study conducted on the wheel component confirms the laboratory scale outcomes. For what concern the feasibility study, the bonded wheel shows similar performances compared to the welded wheel without design modifications of the components. However, the joint geometry has to be redesigned to exploit all the advantages of the adhesive bonding.

In the present study, the applicability of the hybrid plasma arc welding, in which a keyhole is responsible of deep penetration and a filler wire electrode supplies a high deposition rate, was examined. The microstructural evolutions in grade 2205 duplex stainless steel plates joined by keyhole and melt-in techniques were investigated. The specimens obtained from welded plates having thickness of 8 mm were examined via optical and scanning electron microscopy. Metallographic investigations were supported by X-ray diffraction and energy dispersed spectra analyses by characterizing the phases formed after welding. Impact toughness properties, hardness profiles, and crack propagation behavior of welding zones were quantitatively and qualitatively compared for mechanical characterization. Fracture characteristics were determined via scanning electron microscopy examinations. It was observed that single-pass HPA weldment seemed to be free of secondary austenite precipitation in acicular form, which is inevitable in multi-pass conventional arc welding methods. Besides &delta<br>-ferrite was successfully kept under 70%, which is presented as a limit to not to deteriorate the mechanical properties of DSS. High linear welding speed and high power density supplied by HPAW presented narrower weld metal and heat affected zone with not only lower hardness but also higher impact toughness energies. Synergic effect of the keyhole formed by a plasma arc and the metal transfer supplied by gas metal arc gave reasonable dilution in the weld metal. Furthermore, fatigue crack growth tests revealed that crack propagation rates in HPAW joints were comparable to GMAW joints.

Une solution d'assemblage par collage des modules de puissance utilisés dans le ferroviaire à basse et haute température est développée dans ce travail. Nous proposons l'utilisation d'un Joint Multi-Adhésifs (JMA) qui se compose de deux types d'adhésifs, un adhésif résistant à haute température et un adhésif résistant à basse température. Ces deux adhésifs sont disposés sous forme de trois joints séparés et mis côte à côte. Afin de valider ce concept pour notre application, nous avons formulé des adhésifs hybrides époxyde/silicone de différentes nuances. Puis, une caractérisation thermomécanique globale a justifié la sélection de deux nuances à utiliser au sein du JMA. L'étude de leur tenue au vieillissement thermo-oxydatif isotherme a permis de déduire les mécanismes de dégradation les plus probables. De plus, lors du vieillissement isotherme des adhésifs, la prédiction de la perte de masse est réalisée par la technique de la courbe maîtresse, et le comportement en fluage par la méthode de la superposition temps/temps de vieillissement. Des simulations numériques ont permis de dresser une cartographie des contraintes lors dune sollicitation dynamique telle que le fluage<br>This work is dealing with a bonding solution associating two adhesives in a same joint without interdiffusion for railways transport application. This concept, called Multi-Adhesive Joint, is a combination of an adhesive for high temperatures use (High Temperature Adhesive (HTA)) and another for low temperatures (LTA) because of a large temperature range in use. We have formulated and thermo-mechanically tested epoxy/silicone "hybrid" adhesive by changing the silicone content. From ageing studies in several thermal conditions, degradation behaviours are investigated and predictive laws are established. In addition, numerical simulations modelize the mixed-joints behaviour subjected to creep solicitations