<p>Mechanical oscillating drills and saws are used in orthopaedic surgery to cut bone and develop screw-holes; however, their use causes friction resulting in significant thermal damage. Ultrashort pulsed lasers appear well-suited to replace traditional tools as they have the ability to efficiently remove bone tissue while causing only minimal collateral damage. Laser ablation also has the added advantages of: (i) no mechanical vibration; (ii) minimal invasiveness; and (iii) small focus spot size. In this thesis work, we experimentally investigated a few key aspects of ultrashort laser ablation of bone tissue.</p> <p>The ablation threshold of unaltered bone was measured using the <em>D</em>²technique and found to range from 1.66 J/cm²± 0.87 J/cm² to 2.37 J/cm²± 0.78 J/cm² depending on incident pulse number. The reduction in ablation threshold with pulse number was an indication of an incubation effect. Using a power law model, the incubation coefficient, ζ, was measured to be 0.89 ± 0.03.</p> <p>The effect of specific laser parameters and drilling protocols on ablation efficiency was also characterized. For ultrashort pulses (≤10 ps), the removal rate was found to be inversely related to the pulse duration; however, irradiation with 5-10 ps pulses were also shown to result in significant tissue removal. With a pulse repetition rate of 1 kHz, the removal rate was observed to be highest when ablating with 50-100 pulses per spot.</p> <p>Larger volumes (>1 mm³) of bone tissue were removed using laser scanning procedures. A series of scanned concentric circles produced a structure ~2.4 mm deep; however, ablated side-lobes were present at oblique angles to the incident beam. A two-layer structure subsequently produced no side-lobes. The ablative precision in trabecular bone was observed to be less than cortical bone. Using mimicked Nd:YAG laser parameters, cylindrical drilling produced craters significantly less deep than those achieved with a typical Ti:Sapphire configuration. The ability to drill large-scale holes using low average pulse energies and optimized scanning procedures will alleviate the stringent requirements for optical components in clinical practice.</p> / Master of Science (MSc)

Our motivation for this work is based on the need to monitor the cure and inservice health of composite materials. We describe the continuation of an effort to design a multi-functional fiber optic sensor which can be embedded in polymeric composite laminates for monitoring the degree of cure during its fabrication, as well as internal composite strains occurring post-cure.3 In short, this dual-purpose sensor combines the characteristics of a Fresnel reflectometer with those of the extrinsic Fabry-Perot interferometer. For monitoring cure, a broadband source is used so the output intensity of the sensor is amplitude-modulated as the refractive index of the composite is increased during the polymerization process. Post-cure, a coherent light source is implemented so a. sinusoidal variation of the output signal occurs when strains within the composite cause the sensor output to be phase-modulated. We demonstrate the measurement of refractive index with the Fresnel reflectometer/EFPL and test it as an embedded refractive index monitor. Our experimental results demonstrate that the refractive index of 5-minute epoxy increases by approximately 2 % during the cure process. In addition, the sensor can be used as an interferometer to measure internal composite strains, where the phase difference between consecutive fringe peaks is one-half the wavelength of the source. / Master of Science

The main objective of the present research work is to fabricate three dimensional photonic nanostructures in photo-sensitive polymers using a novel diffractive optical element (DOE) based lithography technique. A diffractive optical element is a promising alternative device for 3D fabrication where one DOE creates multiple laser beams in various diffraction orders that are inherently phase-locked and stable for reproducible creation of 3D near-field diffraction patterns from a single laser beam. These near-field patterns are captured inside a photosensitive material like photoresist to fabricate 3D photonic crystal templates. We have demonstrated fabrication of a wide range of 3D structures having different crystal symmetries and different relative crystal axis ratios. The present work has provided 3D photonic crystal nanostructures with uniform optical and structural properties over large sample area (~3-4 mm diameter) and through large 15-50 micron thickness with large number of layers (> 40) having period 550 nm - 650 nm and feature sizes between 200 nm and 300 nm. The short exposure time and small number of process steps shows promise for scaling to very large volume fabrication, dramatically improving the throughput, quality and structural uniformity of 3D periodic nanostructures, especially over that provided by tedious and costly semiconductor processing technology. The diffractive optics lithography is a parallel processing method that is easily scalable to generate centimeter-scale 3D nanostructures having large number of layers in several seconds. Due to low refractive index contrasts these polymer templates possess partial stopgaps along several crystallographic directions which can be practically used in several device or sensor applications where complete bandgap is not necessary. The potential usefulness of these partial stopbands for refractive index sensing of liquids has been demonstrated. These low refractive index polymer structures have been inverted with amorphous silica to convert a "soft" polymer structure to a robust "hard" structure. Further, few preliminary tests were done in fabricating 3D nanostructures into micro-fluidic channels for potential chromatography applications. The practical merits of this 3D fabrication technique will enable new practical manufacturing methods for optical and MEMS applications of 3D micro and nano structures.

The main objective of the present research work is to fabricate three dimensional photonic nanostructures in photo-sensitive polymers using a novel diffractive optical element (DOE) based lithography technique. A diffractive optical element is a promising alternative device for 3D fabrication where one DOE creates multiple laser beams in various diffraction orders that are inherently phase-locked and stable for reproducible creation of 3D near-field diffraction patterns from a single laser beam. These near-field patterns are captured inside a photosensitive material like photoresist to fabricate 3D photonic crystal templates. We have demonstrated fabrication of a wide range of 3D structures having different crystal symmetries and different relative crystal axis ratios. The present work has provided 3D photonic crystal nanostructures with uniform optical and structural properties over large sample area (~3-4 mm diameter) and through large 15-50 micron thickness with large number of layers (> 40) having period 550 nm - 650 nm and feature sizes between 200 nm and 300 nm. The short exposure time and small number of process steps shows promise for scaling to very large volume fabrication, dramatically improving the throughput, quality and structural uniformity of 3D periodic nanostructures, especially over that provided by tedious and costly semiconductor processing technology. The diffractive optics lithography is a parallel processing method that is easily scalable to generate centimeter-scale 3D nanostructures having large number of layers in several seconds. Due to low refractive index contrasts these polymer templates possess partial stopgaps along several crystallographic directions which can be practically used in several device or sensor applications where complete bandgap is not necessary. The potential usefulness of these partial stopbands for refractive index sensing of liquids has been demonstrated. These low refractive index polymer structures have been inverted with amorphous silica to convert a "soft" polymer structure to a robust "hard" structure. Further, few preliminary tests were done in fabricating 3D nanostructures into micro-fluidic channels for potential chromatography applications. The practical merits of this 3D fabrication technique will enable new practical manufacturing methods for optical and MEMS applications of 3D micro and nano structures.

A new concept of a "fiber sorbent" has been investigated. The fiber sorbent is produced as a pseudo-monolithic material comprising polymer (cellulose acetate, CA) and zeolite (NaY) by applying hollow fiber spinning technology. Phase separation of the polymer solution provides an appropriately porous structure throughout the fiber matrix. In addition, the zeolite crystals are homogeneously dispersed in the polymer matrix with high loading. The zeolite is the main contributor to sorption capacity of the fiber sorbent. Mass transfer processes in the fiber sorbent module are analyzed for hydrogen recovery and compared with results for an equivalent size packed bed with identical diameter and length. The model indicates advantageous cases for application of fiber sorbent module over packed bed technology that allows system downsizing and energy saving by changing the outer and bore diameters to maintain or even reduce the pressure drop. The CA-NaY fiber sorbent was spun successfully with highly porous structure and high CO2 sorption capacity. The fiber sorbent enables the shell-side void space for thermal moderation to heat of adsorption, while this cannot be applied to the packed bed. The poly(vinyl alcohol) coated CA-NaY demonstrated the thermal moderation with paraffin wax, which was carefully selected and melt at slightly above operating temperature, in the shell-side in a rapidly cycled pressure swing adsorption. So this new approach is attractive for some hydrogen recovery applications as an alternative to traditional zeolite pellets.

No description available.

Scania Ferruform AB is an independent affiliate of the truck- and bus manufacturer Scania AB which produces rear axle housings among other chassis components for said vehicles. The banjo part, i.e. the base of the rear axle housings undergoes processes which have issues both in terms of exceeded technical life span and insufficient production capacity. These three processes consist of both milling and welding operations. In order to resolve these issues the discussion of future investments arise. As this is discussed, the question whether alternative technologies could be of interest, specifically the performance of welding- and cutting operations with the use of laser technologies. By reviewing state-of-the-art literature, studying the present production conditions and interviewing experts within academia as well as parties active in developing and supplying industrial laser systems it has been shown that a laser arc hybrid welding technique would be the most suitable replacement, while laser nitrogen cutting would be the most suitable cutting technique. This project presents the theoretical outcome of implementing laser arc hybrid welding as a replacement to the present and conventional gas metal arc welding, as well as the possibility of using laser nitrogen cutting as a replacement to a set of milling processes. The study has shown that by implementing these technologies in a manner which also alters the balance in performed operations achieves a cycle time below the future goal for each production section. Cycle time values, quantities and costs are expressed with an indexed value of t, n and k respectively due to confidentiality. The first investment scenario results in an annual saving of consumption costs by 4 738k SEK, with a total investment cost of 112 743k SEK and 6,9 years pay-off time. The second scenario results in an annual saving of consumption costs by 5 018k SEK, with a total investment cost of 114 843k SEK and 5,2 years pay-off time. The third scenario is similar to the second in terms of the manufacturing processes, but it is the alternative of the lowest investment cost. This scenario would result in the same sum of annual savings as the second scenario, but with an investment cost of 89 843k SEK and 0,2 years pay-off time.

Micro/Nanostructuring of polymers by femtosecond pulses is of extreme importance because it drives applications in photonics and biomedicine. A femtosecond pulse, with an intensity of ∼ 10^13 W/cm^2, is capable of causing an optical breakdown and inducing permanent modification in the material. With such high intensity, and considering the fact that polymers possess high band gaps, the interaction nature is completely nonlinear, and the material can be modified locally on the surface and in bulk. The irradiated regions exhibit fluorescence, and they display new wetting properties as a consequence of the optical breakdown of a material. The optical breakdown can be investigated by studying the nonlinear absorption. In this thesis, we discuss the nonlinear absorption of fs-laser pulses inside polymers using transmission measurements. We show a step– function–like behaviour of the transmission, dropping abruptly to ∼ 20% at the optical breakdown threshold with a ∼ 40 % reduction in the band gap. Utilizing spectroscopy, we show that the laser-modified regions contain randomly distributed nanoclusters. The presence of localized nanoclusters is responsible for exhibiting fluorescence, within ∼ 10 µm3 for a single pulse. This feature was exploited to demonstrate high-density data storage in Polymethyl methacrylate (PMMA) without any special material preparation. We demonstrate up to 20 layers of embedded data that can be stored in a standard 120 mm disc. Storage capacity of 0.2 TBytes/disc can be achieved by adjusting read laser parameters. Besides the fluorescence capability induced in the bulk of polymers, the hydrophilicity shown by the fs–laser modified surface is utilized to study selective cell growth on the micro-structured Polydimethylsiloxane (PDMS) surface. We show that the C2C12 cells and rabbit anti-mouse protein attach preferentially to the modified regions when the surface is modified with low pulse energies. However, in the high pulse energy regime, the laser-modified regions exhibit superhydrophobicity inhibiting cell adhesion.

Afin de réduire les déchets et les émissions de CO2, la demande des constructeurs automobiles a évolué vers l'utilisation de nouveaux matériaux biosourcés permettant d'alléger les véhicules et diminuer leur consommation en carburant. Dans ce contexte, la thèse a eu pour objectif de réaliser un panneau sandwich léger et résistant renforcé par des fibres longues de lin pour des applications semistructurelles automobiles. Outre la recherche bibliographique, le travail est réparti en trois volets : la mise en œuvre, la caractérisation et la modélisation du comportement mécanique du panneau sandwich. Les peaux composites sont renforcées par un nouveau renfort « Flaxtape », qui est un voile de fibres longues de lin unidirectionnelles et ne contenant aucune filature en trame. La matrice est une résine thermodurcissable aqueuse permettant un temps de réticulation très court et une bonne processabilité. Les peaux composites et les panneaux sandwichs dérivés sont élaborés à l'aide d'un procédé de thermocompression respectant des cycles de fabrication industriels. La compréhension et l'optimisation des paramètres entrant en jeu dans leur élaboration et leur mise en œuvre (cycle de cuisson, température, séchage, densification, fraction volumique de fibres, taux de réticulation et séquence d'empilement) passent par une série de caractérisations thermomécaniques et physicochimiques. Les résultats obtenus montrent les bonnes propriétés mécaniques spécifiques du panneau sandwich à différentes températures. D'autre part, le panneau sandwich en Flaxpreg est destiné à la réalisation d'un plancher de coffre de véhicule. La modélisation numérique du comportement mécanique du panneau sandwich a permis de prédire sa réponse mécanique lorsqu'il est mis en service à différentes positions dans le coffre. Afin de simplifier la géométrie du panneau sandwich et de réduire le temps de calcul, un modèle d'homogénéisation analytique de l'âme en nid d'abeille a été utilisé pour réaliser cette étude. / To reduce waste and CO2 emissions, car manufacturers use more and more new bio-sourced materials to lighten vehicles and reduce fuel consumption. In this context, this thesis aimed at processing a lightweight sandwich panel reinforced by long flax fibers for automotive semi-structural applications.In addition to the literature state of the art, the work is divided into three parts: the material processing, characterization and modeling of the mechanical behavior of the sandwich panel. The composite skins are reinforced by a new reinforcing material "Flaxtape", which is a veil of long unidirectional flaxfibers withouth any weft spinning. The matrix is an aqueous thermosetting resin with a very short cure time and good processability. The composite skins and derived sandwich panels are processed by a thermocompression technique respecting industrial production cycles. Thermomechanical and physicochemical characterizations are used to understand and optimize the parameters involved in their development (cooking cycle, temperature, drying, densification, fiber volume fraction, degree of crosslinking and stacking sequence). Our results highlight good specific mechanical properties of the sandwich panels at different temperatures.Furthermore, the Flaxpreg sandwich panel has been used for the achievement of a vehicle compartment floor. Numerical modeling of the mechanical behavior of the sandwich panel was used to predict the sandwich panel mechanical response at different positions in the trunk. To simplify the geometry of the sandwich panel and reduce the computation time, an analytical model of the homogenized honeycomb was used in this study.

No description available.