Ce travail, mené dans le cadre d’une thèse CIFRE en collaboration avec le fabricant d’outil de coupe ValeniteSafety et le Laboratoire de Mécanique et Rhéologie EA 2640 de l’Université François Rabelais de Tours (Polytech’Tours), a été réalisé au sein du Centre d’Etude et de Recherche sur les Outils Coupants (CEROC). Il s’agit d’étudier le rayon d’arête noté ER et son influence sur l’intégrité de surface lors d’une opération de tournage à sec sur l’acier 27MnCr5. L’usinage par enlèvement de matière résulte du cisaillement de matière par l' arête de coupe, partie active d’une plaquette. C’est l'élément le plus sollicité pendant la coupe. Une plaquette est caractérisée par son substrat, son revêtement, la géométrie de la zone de coupe et sa micro géométrie d’arête qui influence intimement le cisaillement de la matière. Elle conditionne ainsi l’intégrité de surface usinée. Théoriquement une finition d’arête idéale au bon cisaillement de la matière doit être « vive ». En réalité, dans un grand nombre de cas les arêtes ont un mouchage (arrondie). L’objectif de cette étude est d’analyser le comportement des rayons d’arête. La maîtrise de la finition d’arête peut augmenter de façon significative la durée de vie de la plaquette et assurer la reproductibilité de la qualité de surface usinée. Après un rappel des principes généraux de la coupe, nous nous attachons à décrire la micro géométrie d’arête et son influence lors du procédé d’usinage à sec. Nous présentons ensuite la procédure suivie pour la détermination des conditions d’utilisations de l’outil. Puis nous décrivons les protocoles expérimentaux de préparation des pièces à usiner et des arêtes de coupe de la plaquette. Pour caractériser l’intégrité des surfaces usinées et le comportement des rayons d’arête nous employons plusieurs techniques telles que la Microscopie Electronique à Balayage, la Microscopie Interférentielle, la Micro indentation. Des paramètres tels que les efforts de coupe, les phénomènes d’usures développées pendant les tests de durée de vie, la topographie et la métallurgie de surface ont été analysés. Ces analyses permettent de quantifier le comportement des rayons d’arête et l’influence des tolérances de fabrication sur l’intégrité de surface de la pièce. / This work performed at the Research Cutting Tools Centre “CEROC” has been carried out in the framework of a collaboration with the cutting tool manufacturer ValeniteSafety and the Mechanical & Rheology Laboratory EA 2640 of the University François Rabelais of Tours (Polytech’Tours). It’s devoted to investigate the behaviour of the cutting edge radius denoted ER on the surface integrity of worked piece after dry turning of 27MnCr5 steel. Cutting process involving material removal occurs by a large plastic deformation in a zone of concentrated shear due to the cutting edge. Cutting edge radius is the essential working part of the insert during machining process. An insert is a combination of a substrate, a coating, the geometry of a cutting zone and the edge finish geometry. These parameters related to the shearing property of the worked piece are critical for the quality of the surface integrity. Sharp edge is considered as an ideal edge in theory. However, in many cases, the cutting edges are “honed” on purpose during the manufacturing process of the insert. The aim of this research work is to establish correlations between relevant parameters and examine how the surface integrity of machined steel and tool life can be affected by the cutting tool edge preparation. Control of the micro edge radius geometry can considerably increase the tool life and assure the reproducibility of the machined surface quality. After a summary of the metal cutting principles, we describe how the presence of a honed edge affects the performance of machining operation in different ways. We present the procedures followed to determine the cutting conditions adapted to our cutting tool and material during dry turning. The experimental procedure of machined samples and edge radius preparation methods used in this study are illustrated. Scanning Electronic Microscope, White Light Interferometry and Micro Indentation, were the employed techniques to understand the impact of honed insert edges in the surface integrity of the worked piece and to investigate tool life performances. Parameters such as: cutting efforts, wear types generated during life time tests, topographic and metallurgic surface were evaluated and allow to quantify the effect of the variation of the cutting edge radius “manufacturing spread” on the life time of the insert and the surface finish of the worked piece.

Fabricating and 3D printing gamepads is challenging not only in terms of appearance of them but also in terms of their physical validity and user experience that they might provide. This thesis addresses the issue of providing users the ability to hold in their hand a fabricated gamepad, which is an object similar to that the virtual character keeps in his/her hand inside the virtual world. Thus, this thesis presents a basic approach for converting 3D objects found in a variety of online datasets to functional gamepads by retargeting the structure of the gamepad’s buttons to the 3D model. The fabricated gamepads can then be used by gamers to enjoy their favorite game. The authors assumed that gamepads that have a relationship with the game enhance the game experience of users. This assumption is mainly based on a variety of previous work that investigates the use of “natural” interfaces. Therefore, in addition to the proposed approach, a two-part user study was also conducted to firstly understand whether the fabricated gamepads can be considered as valid physical objects and also to understand the way that participants experienced a game. First, the results indicated that the fabricated gamepads can be considered as valid physical objects and secondly, that they enhance the gaming experience of the users.

With life expectancy on the rise, age-related ailments are a significant strain on the welfare of individuals and the economy. Progress is being made towards combating the leading cause of unavoidable blindness, age-related macular degeneration (AMD). AMD affects ten million Americans and costs the world economy $343 billion annually. Retinal implants promise to restore sight by replacing the eye's damaged photoreceptors with electronic photodiodes. Clinical trials succeed at restoring some vision, but are limited by the stimulating electrodes. We study the electrode-neuron interface with a focus on the geometrical dependence of the electrode. The functionality of neurons is intimately connected to their branching and curving shape, described by fractal geometry. We examine the morphology of neurons using fractal analysis. The results inform our electrode designs, which are fabricated using top-down lithographic and bottom-up self-assembly techniques. A novel technique for fabricating a fractal electrode is presented. Heating and cooling a film of poly(methyl methacrylate) on a SiO2 substrate causes fractal structures to form on the surface. The geometry of the structures is temperature dependent, producing crystalline branches at lower temperatures and diffusion-limited aggregates at higher temperatures. Subsequent deposition of antimony nanoclusters shows preferred diffusion to the fractal surface features. The dependence of a photodiode's performance on its top contact geometry is explored using modified nodal analysis. The results reinforce the need to balance a low mean semiconductor-metal separation distance with an adequate contact width for low resistance, all while maximizing light input. Future designs will benefit from the spatial voltage maps produced by the simulation. The electric field emanating from an electrode is also dependent on the geometry of the electrode. The Faraday cage effect is exploited to achieve similar electric field responses to traditional electrode shapes. A preliminary study of neural adhesion to SU-8 fractal electrodes is promising. The neuron grows along the electrode even at 90° turns. The role the fractal geometry plays in neuron and electrode functionality is shown to be significant. Continued study of, and experimentation with, new electrode designs is sure to produce exciting possibilities in the future. This dissertation includes previously unpublished co-authored material.

La miniaturisation des transistors ayant atteint ses limites, des technologies alternatives capables de traiter les données sont aujourd’hui beaucoup étudiées. Dans ce contexte, nous développons une architecture de réseau de neurones mécaniques, capable de résoudre effi- cacement des problèmes non-triviaux comme la classification ou la prédiction de fonctions chaotiques. Cette architecture est inspirée des travaux sur les réseaux de neurones récur- rents (RNN), et plus particulièrement du reservoir computing. Le dispositif est un réseau d’oscillateurs MEMS anharmoniques, lui permettant ainsi d’être compact et de consom- mer peu d’énergie. Les poutres en silicium bi-encastrées ont été choisies pour réaliser le dispositif, sachant qu’elles ont été largement étudiées et sont simples à implémenter. Nous présentons ici le travail expérimental sur les MEMS non linéaires qui seront utilisés par la suite pour réaliser le dispositif. Des simulations numériques du réseau ont permis, dans un premier temps, d’identifier les requis sur la dynamique des résonateurs. Ceux-ci ont été par la suite conçus de manière à répondre le mieux possible à ces requis. Un couplage méca- nique efficace a été élaboré pour relier chacun des oscillateurs. Afin de prédire précisément le comportement des résonateurs couplés dans le régime linéaire et non linéaire, des ana- lyses par éléments finis ont été réalisées. Un procédé de micro fabrication rapide et simple a été développé. Enfin, les structures ont été caractérisées optiquement et électriquement. Les résultats expérimentaux sont en accord avec les simulations ce qui suggère que notre approche convient à la conception et à la fabrication d’un dispositif neuromorphique.

The increasingly personal and ubiquitous capabilities of computing—everything from smartphones to virtual reality—are enabling us to build a brave new world in the digital realm. Despite these advances in the virtual world, our ability as end-users to transform the physical world still remains limited. The emergence of low-cost fabrication technology (most notably 3D printing) has brought us a dawn of making, promising to empower everyday users with the ability to fabricate physical objects of their own design. However, the technology itself is oblivious of the physical world—things are, in most cases, assumed to be printed from scratch in isolation from the real world objects they will be attached to and work with. To bridge this ‘gulf of fabrication’, my thesis research focuses on developing fabrication techniques with design tool integration to enable users to expressively create designs that can be attached to and function with existing real-world objects. Specifically, my work explores techniques that leverage the 3D printing process to create attachments directly over, onto and around existing objects; a design tool further enables people to specify and generate adaptations that can be attached to and mechanically transform existing objects in user-customized ways; a user-driven approach allows people to express and iterate structures that are optimized to support existing objects; finally, a library of ‘embeddables’ demonstrate that existing objects can also augment 3D printed designs by embedding a large variety of material to realize different properties and functionalities. Overall my thesis aspires to make fabrication real—enabling people to express, iterate and fabricate their designs that closely work with real-world objects to augment one another.

Femtosecond laser interaction with dielectrics has unique characteristics for micromachining, notably non-thermal interaction with materials, precision and flexibility. The nature of this interaction is highly nonlinear due to multiphoton ionization, so the laser energy can be nonlinearly absorbed by the material, leading to permanent change in the material properties in a localized region of Mu-m3. This dissertation demonstrated the potential of these nonlinear interactions induced changes (index modification and ablation for machining) in the dielectrics and explored several practical applications. We studied femtosecond laser ablation of Poly-methayl methacrylate (PMMA) under single and multiple pulse irradiation regimes. We demonstrated that the onset of surface ablation in dielectric surface is associated with surface swelling, followed by material removal. Also, the shape of the ablation craters becomes polarization dependent with increasing fluence, except for circular polarization. The morphology of the damaged/ablated material was examined by optical and scanning electron microscopy. The dynamics of laser ablation of PMMA was simulated using a 2 dimensional Molecular Dynamics model and a 3 dimensional Finite Difference Time Domain model. The results from numerical simulations agreed well with experimental results presented in this thesis. We also demonstrated the formation of nano-pillar within the ablation crater when the surface of bulk-PMMA was irradiated by two femtosecond pulses at a certain delay with energies below single shot ablation threshold. With increasing fluence, the nano-pillar vanished and the structure within the ablation crater resembled volcanic eruption. At higher fluences we demonstrated nanoscale porosity in PMMA. For application, a novel in-line fiber micro-cantilever was fabricated in bend insensitive fiber, that provides details of in-line measurement of frequency and amplitude of vibration, and can be further extended to be used as chemical/bio and temperature sensors. By modifying the refractive index at random spacing within the single mode fiber core, a unique quasi-random micro-cavities fiber laser was fabricated, which exhibits comparable characteristics with a commercial fiber laser in terms of narrow linewidth and frequency stability.

Micro-electro-mechanical systems (MEMS) became possible thanks to the silicon based technology used to fabricate integrated circuits. Originally, MEMS fabrication was limited to silicon based techniques and materials, but the expansion of MEMS applications brought the need of a wider catalog of materials, including polymers, now being used to fabricate MEMS. Polyimide is a very attractive polymer for MEMS fabrication due to its high temperature stability compared to other polymers, low coefficient of thermal expansion, low film stress and low cost. The goal of this thesis is to expand the Polyimide usage as structural material for MEMS by the development of a multi-user fabrication process for the integration of this polymer along with multiple metal layers on a silicon substrate. The process also integrates amorphous silicon as sacrificial layer to create free-standing structures. Dry etching is used to release the devices and avoid stiction phenomena. The developed process is used to fabricate platforms for micro-hotplate gas sensors. The fabrication steps for the platforms are described in detail, explaining the process specifics and capabilities. An initial testing of the micro-hotplate is presented. As the process was also used as educational tool, some designs made by students and fabricated with the Polyimide-MEMS process are also presented.

No description available.

“Building processes seem best evoked in terms of various forms of endemic uncertainty which, in turn, define an essentially turbulent industrial environment. The pursuit of stability is re-interpreted as ‘unstable equilibrium’ in building processes, requiring constant feedback to maintain control.” (Groak, 1992) The process of addressing a troubled spatial legacy within the context of South Africa has presented a challenging atmosphere regarding the preservation or reprogramming of urban and architectural space. This becomes a prevalent issue when considering critical urban regions such as Westbury in Johannesburg, where the social and built environment remain in a constant struggle for identity and defensibility. The need to address this reformation of urban space as well as urban programme has lead this dissertation to question the manifestation of social processes in spatial form. This dissertation hopes to propose a system of architecture and supporting infrastructure that will address existing spatial legacy, through responding to social and contextual issues; leading to a new platform for the sustainable progression of social activity and identity in the form of urban densification. / Mini Dissertation (MArch(Prof)) --University of Pretoria, 2018. / Architecture / MArch(Prof) / Unrestricted

The environmental challenges are increasing, and so is the need for renewable energy. For photovoltaic applications, thin film Cu(In,Ga)(S,Se)2 (CIGS) and CuIn(S,Se)2 (CIS) solar cells are attractive with conversion efficiencies of more than 20%. However, the high-efficiency cells are fabricated using vacuum technologies such as sputtering or thermal co-evaporation, which are very costly and unfeasible at industrial level. The fabrication involves the uses of highly toxic gases such as H2Se, adding complexity to the fabrication process. The work described here focused on non-vacuum deposition methods such as printing. Special attention has been given to printing designed in a moving Roll-to-Roll (R2R) fashion. The results show potential of such technology to replace the vacuum processes. Conversion efficiencies for such non-vacuum deposition of Cu(In,Ga)(S,Se)2 solar cells have exceeded 15% using hazardous chemicals such as hydrazine, which is unsuitable for industrial scale up. In an effort to simplify the process, non-toxic suspensions of Cu(In,Ga)S2 molecular-based precursors achieved efficiencies of ~7-15%. Attempts to further simplify the selenization step, deposition of CuIn(S,Se)2 particulate solutions without the Ga doping and non-toxic suspensions of Cu(In,Ga)Se2 quaternary precursors achieved efficiencies (~1-8%). The contribution of this research was to provide a new method to monitor printed structures through spectral-domain optical coherence tomography SD-OCT in a moving fashion simulating R2R process design at speeds up to 1.05 m/min. The research clarified morphological and compositional impacts of Nd:YAG laser heat-treatment on Cu(In,Ga)Se2 absorber layer to simplify the annealing step in non-vacuum environment compatible to R2R. Finally, the research further simplified development methods for CIGS solar cells based on suspensions of quaternary Cu(In,Ga)Se2 precursors and ternary CuInS2 precursors. The methods consisted of post deposition reactive annealing for performance enhancement up to 2.0% solar cell conversion efficiency. Chemical treatment using metal salt solutions and Na2Se4 for Na and Se incorporation provided efficiencies up to 1.1%.