O titânio é amplamente empregado em indústrias químicas, geração de energia, aeroespaciais e biomédicas, pois além de suas boas propriedades mecânicas e resistência à corrosão, apresenta também boa biocompatibilidade. Porém, quando usado, por exemplo, em turbinas a vapor é necessário aumentar ainda mais sua resistência à corrosão em altas temperaturas. Ou quando usado em odontologia a cor acinzentada do metal compromete as reabilitações orais. Sendo assim, torna-se interessante o recobrimento do titânio com uma camada cerâmica, sendo a 3YTZP (zircônia tetragonal policristalina) adequada a tal aplicação, pois além de apresentar resistência mecânica, boa resistência a ciclos térmicos, apresenta boa biocompatibilidade. Neste trabalho foi feito o estudo do recobrimento do titânio com 3YTZP utilizando a técnica da deposição eletroforética além de realizar a irradiação do filme cerâmico utilizando o laser contínuo Nd:YAG com a finalidade de sinterização. O pó de 3YTZP foi obtido pela rota de coprecipitação de óxidos em meio amoniacal e caracterizada por DRX e MEV-FEG. Os resultados de DRX do pó mostraram a presença das fases tetragonal e monoclínica, e pelas micrografias observa-se que as partículas têm estruturas alongadas em formas de bastonetes. Por meio da densificação dos corpos cerâmicos foi possível observar boa sinterabilidade do pó. Como substrato para EPD foram utilizadas chapas de titânio (15 mm x 15 mm) e foram caracterizadas por DRX, que confirmou apenas a presença da fase α do Ti, indicando assim que são de titânio comercialmente puro. As chapas foram atacadas quimicamente com ácido sulfúrico 50% em volume por 10s. A deposição eletroforética foi realizada com as suspensões de 75%vol.acetona:25%.vol.etanol a 30 V por 20, 45 e 60 segundos; 50%vol.acetona:50%vol.etanol a 20 V por 30, 45 e 60 segundos; 25%vol.acetilacetona:75%vol.etanol a 60 V por 20, 40 e 60 segundos e a 40 V por 20 segundos; e com acetilacetona pura a 60 V por 20, 40 e 60 segundos e a 40 V por 20 e 40 segundos. Por meio das microscopias ópticas dos filmes depositados pode-se observar que a melhor condição de deposição foi utilizando a suspensão de acetilacetona a 40 V por 20 segundos, gerando filmes homogêneos e sem trincas. Foram realizados cinco ensaios de irradiação com lazer a fim de alcançar uma condição ideal de sinterização. As condições fixas para todos os ensaios foram energia de 0,5 J, coeficiente de duração de pulso (Tp) de 10 ms e coeficiente de repetição de pulso de 10 Hz. No decorrer dos ensaios foi variada a fluência do laser e o número de incidência. As amostras irradiadas foram caracterizadas por microscopia óptica e eletrônica, DRX e Scratch, e verificou-se que a melhor condição de irradiação foi utilizando a fluência de 120 J/cm2 para o número de incidência do laser de igual a 27. / Titanium is widely used in chemical, power generatin, aerospace and biomedical industries because of you good mechanical properties, corrosion resistance and good biocompatibility. However, when is used, for example, in steam turbines is necessary increase the corrosion resistance at high temperature. Or when is used in dentistry, when the gray color compromisse the aesthetics rehab. In this case, it becomes interesting to coat the titanium with a ceramic layers, and 3YTZP (Yttria-stabilized tetragonal zirconia) is suitable for this application, because it has good mechanical properties, good resistance to thermal cycles and good biocompatibility. In this work it was studied the coating of titanium with 3YTZP using electrophoretic deposition technique in addition irradiation of films using the Nd:YAG continuous laser. The 3YTZP powder was obtained by hydroxide coprecipitation route in ammoniacal medium and characterized by XDR and SEM. The XDR results shower presence os monoclinic and tetragonal phases, and micrographs it can be observed the the particles agglomerates. These particles have elongated structure. Through the densification of the ceramic bodies it was possible to observe good sinterability of the powder. Was used as the substrate to EPD titanium plates (dimension 15 mm x 15 mm), and was characterized by XRD, that show presence of α-fase, thus indicating that they are commercially pure titanium. The plates were chemically etched with 50% vol. Sulfuric acid for 10 s. Electrophoretic deposition was performed with suspensions of 75%vol.acetone: 25%.vol.ethanol at 30 V for 20, 45 e 60 seconds; 50%vol.acetone:50%vol.ethanol at 20 V for 30, 45 e 60 seconds; 25%vol.acetylacetone:75%vol.ethanol at 60 V for 20, 40 e 60 seconds and at 40 V for 20 seconds; and with pure acetylacetone at 60 V for 20, 40 e 60 seconds and at 40 V for 20 e 40 seconds. From observation in an optical microscope of the deposited films, we concluded that the best deposition condition was the acetylacetone suspension at 40 V for 20 seconds, being homogeneous films and free of cracks. Five laser irradiation tests were performed in order to achieve an optimum sintering condition. The fixed conditions for all the tests were energy of 0.5 J, pulse duration coefficient (Tp) of 10 ms and pulse repetition coefficient of 10 Hz. In the course of the tests, the laser fluency and the laser incidence number were varied. The irradiated samples were characterized by optical and electron microscopy, XRD and Scratch, and it was found that the best irradiation condition was using fluency of 120 J/cm2 and laser incidence number of 27.

Orthodontic brackets undergo resistance during sliding that includes classical friction, binding, and notching. Current bracket systems are hampered by these challenging forces. As a result, the clinician usually needs to apply additional forces to overcome the resistance which increases the risk of root resorption and discomfort for the patient. This study evaluated frictional properties of a novel bracket that had polytetrafluoroethylene (Teflon™) coated rollers in its design. Five types of brackets (n = 10, each), including a passive self-ligating bracket, a traditional ligated bracket, a three-dimensionally printed direct metal laser sintering (DMLS) bracket with and without Teflon™ rollers, and computer numeric controlled (CNC) machine milled bracket with Teflon™ rollers were tested. The peak resistance values were assessed at 0°, 4°, and 8° of tip on a 0.019 x 0.025” arch wire. At 8° of tip, the DMLS and the CNC milled bracket systems, both with Teflon™ rollers, exhibited less friction as compared to the other brackets tested (p

An algorithm was developed to enable efficient segmentation of dimensionally-large objects into smaller components that can be fabricated within the given Rapid Prototyping (RP) machine workspace. The algorithm uses vertical and horizontal flat plane cuts, as well as feature-based volume decomposition. Due considerations were given to the optimisation of the surface accuracy, the build time, the strength and the number of segments generated by the segmentation process. A computer-aided design (CAD) application programme that interfaces with Unigraphics (UG) was also developed to allow import of objects in Standard Triangulated Language (STL) files into UG without loss of accuracy. In addition, the application software provides the functions that facilitate the implementation of the segmentation algorithm in UG. Two case studies were carried out using the algorithm in a Selective Laser Sintering (SLS) RP system. The resulting objects had properties that matched the research objectives with which the proposed algorithm was validated. / Singapore-MIT Alliance (SMA)

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Rapid prototyping methods embrace a family of manufacturing methods that are developed to speed up the prototyping stage of product design. The sole needed input for production being the solid model of the part, mold/tool-free production characteristics and the geometric part complexity that can be achieved due to layer-by-layer production have extended the applicability/research areas of these methods beyond prototyping. Local pore formation in part that occurs as a result of the discrete manufacturing nature of rapid prototyping methods can be viewed as an opportunity for material development. In this thesis, the manufacturing-internal (porous) structure-mechanical property relations of porous materials are investigated. These porous parts are produced via Selective Laser Sintering (SLS) which is a rapid prototyping method. The elastic modulus, tensile strength, rupture strength and Poisson&rsquo / s ratio of uniform porous specimens with known porosities are determined through standardized mechanical tests for polymeric materials. The mechanical property variation profiles in graded materials are determined using the mechanical properties of uniform parts. The mechanical behavior of uniform and graded materials under applied loads are modeled using finite element method and simulation results are compared to the results of mechanical tests performed on graded materials. In addition, feasibility of producing resin filled composite parts from these uniform and graded porous parts are sought. Porous parts (both uniformly and graded) that are infiltrated with epoxy resin have been characterized mechanically and the results have been compared with the uninfiltrated porous parts.

Selective laser sintering is a rapid prototyping method (RP), which was originally developed, along with other RP methods, to speed up the prototyping stage of product design. The sole needed input for production being the solid model of the part, the mold/tool-free production characteristics and the geometric part complexity that can be achieved due to layer-by-layer production have extended the applicability/research areas of these methods beyond prototyping towards new applications and material development. Local pore formation in a part that occurs as a result of the discrete manufacturing nature of selective laser sintering is normally considered a defect. In the current research, this is viewed as an opportunity for material development: Exploitation of rapid prototyping methods to produce composites/functionally graded materials with controlled porous structures. That the material interior structure (porous structure) and exterior shape are formed during the same course renders selective laser sintering process as an attractive manufacturing alternative for producing complex-geometry composite/porous materials, which may be difficult or impossible to manufacture with other techniques. In this thesis, the use of selective laser sintering (a rapid prototyping method) in producing uniformly porous and graded polymeric graded porous structures is studied. The material used was polyamide powder (PA 2200) and the selective laser sintering machine used was the EOSINT P 380 system. In this research, three process parameters of the SLS system, the hatching distance, the laser power and the laser scanning speed were varied to produce parts that have different porosities. Porous parts with a homogenous porous microstructure (uniformly porous parts) could be produced, as well as graded porous parts. The results of uniformly porous structure production were utilized to build graded porous structures by imparting different porosities along a certain direction within a single part. Both, uniformly porous and graded structures were characterized physically and mechanically. The porous parts (both uniformly porous and graded porous) were infiltrated with epoxy resin to produce epoxy-PA composites and graded materials. The physical and mechanical properties of these parts were compared with those of the uninfiltrated (porous PA) structures

Applications involving high electrical conduction require complex components that are difficult to be manufactured by conventional processes. Laser sintering (LS) is an additive manufacturing technique that overcomes these drawbacks by offering design flexibility. This study focuses upon optimizing the process of laser sintering to manufacture functional prototypes of components used in high electrical conduction applications. Specifically, components for two systems – high current sliding electrical contacts and fuel cells – were designed, manufactured and tested. C-asperity rails were made by LS and tested in a high current sliding electrical setup. Corrugated flow field plates were created by LS and their performance in a direct methanol fuel cell (DMFC) was tested. This is the first experimental attempt at using laser sintering for manufacturing such complex components for use in high electrical conduction applications. The second part of this study involves optimization the laser sintering process. Towards this, efforts were made to improve the green strength of parts made by LS. Particle size of graphite/ phenolic resin and addition of nylon/11 and wax were tested for their effect upon green strength. Of these, significant improvement of green strength was observed by altering the particle size of the graphite/ phenolic resin system. New methods of improving green strength by employing fast cure phenolic resins with carbon fiber additions were successfully demonstrated. This study also identified a binder system and process parameters for indirect LS of stainless steel –for bipolar plate compression/ injection mold tooling. All the experimental results of this study lead us to believe that laser sintering can be developed as a robust and efficient process for the manufacture of specialized components used in advanced electrical conduction systems. / text

While amputee gait has been studied in great detail, the influence of prosthetic foot sagittal and coronal plane stiffness on amputee walking biomechanics is not well understood. In order to investigate the effects of sagittal and coronal plane foot stiffness on amputee walking, a framework for manipulating the stiffness of a prosthetic foot needs to be developed. The sagittal and coronal plane stiffness of a low profile carbon fiber prosthetic foot was manipulated through coupling with selective-laser-sintered prosthetic ankles. The carbon fiber foot provided an underlying non-linear stiffness profile while the ankle modified the overall stiffness of the ankle-foot combination. A design of experiments was performed to determine the effect of four prosthetic ankle dimensions (keel thickness, keel width, space between the ankle top and bottom faces, and the location of the pyramid connection) on ankle-foot sagittal and coronal plane stiffness. Ankles were manufactured using selective laser sintering and statically tested to determine stiffness. Two of the dimensions, space between the ankle top and bottom faces and the location of the pyramid connection, were found to have the largest influence on both sagittal and coronal plane stiffness. A third dimension, keel thickness, influenced only coronal plane stiffness. A number of prosthetic ankle-foot combinations were created that encompassed a range of sagittal and coronal plane stiffness levels that were lower than that of the low profile carbon fiber foot alone. To further test the effectiveness of the framework to manipulate sagittal and coronal plane stiffness, two ankle-foot combinations, one stiffer than the other in the sagittal and coronal planes, were used in a case study analyzing amputee walking biomechanics. Differences in stiffness were large enough to cause noticeable changes in amputee kinematics and kinetics during turning and straight-line walking. Future work will expand the range of ankle-foot stiffness levels that can be created using this framework. The framework will then be used to create ankle-foot combinations to investigate the effect of sagittal and coronal plane stiffness on gait mechanics in a large sample of unilateral transtibial amputees. / text

Individuals with various lower-limb neuromuscular and musculoskeletal impairments are often prescribed passive-dynamic ankle-foot orthoses (PD-AFOs) to compensate for impaired ankle muscle weakness. Several studies have demonstrated the beneficial effects of PD-AFOs on pathological gait, but few studies have examined the influence of the AFO stiffness characteristics on gait performance. One challenge to performing such studies is the difficulty of manufacturing custom AFOs with a wide range of controlled stiffness levels. However, selective laser sintering (SLS) is a well-suited additive manufacturing technique for generating subject-specific PD-AFOs of varied stiffness. Therefore, the overall goal of this study was to use SLS manufactured PD-AFOs to identify the relationships between AFO stiffness and gait performance in patients with various lower-limb neuromuscular and musculoskeletal impairments. Six subjects with unilateral impairments were enrolled in this study. For each subject, one subject-specific PD-AFO equivalent to the subject’s clinically prescribed carbon fiber PD-AFO (nominal), one 20% more compliant and one 20% more stiff were manufactured using SLS. Three-dimensional kinematic and kinetic data were collected from each subject while ambulating with each PD-AFO at two different speeds to allow a comprehensive biomechanical analysis to assess the influence of PD-AFO stiffness on gait performance. The results showed that in the compliant AFO condition, the AFO limb vertical ground reaction force (GRF) impulse during loading and the non-AFO limb medial GRF impulse during push-off decreased. In addition, the AFO limb braking GRF impulse during loading and the non-AFO limb braking GRF impulse in early single-limb stance decreased. Furthermore, in the compliant AFO condition, negative knee work during early single-limb stance increased while positive hip work in early swing decreased in the AFO limb. Overall, as AFO stiffness decreased, the AFO limb contributed less to body support and braking. In addition, a decreased medial GRF impulse coupled with an increased vertical GRF impulse during non-AFO single-limb stance suggests that walking stability may be compromised as AFO stiffness decreases. Thus, a tradeoff may exist between preserving stability and increasing net propulsion, which should be considered when assessing the mobility needs of individuals prescribed PD-AFOs as a result of various neuromuscular and musculoskeletal impairments. / text

This thesis provides investigation into the interaction between quartz lamp emitters and polyether ether ketone (PEEK) powder. Calculations and experiments concerning the conductivity and emissivity of the powder at various temperatures are performed. The thermal profile of the emitter on a flat powder bed is captured using thermal imaging. The effect of exposing a pile of powder to the emitter and the subsequent thermal gradient through the pile is measured and analyzed. Based on these results, ramifications for the application of these emitters to selective laser sintering (SLS) machines for processing high temperature polymers such as PEEK are discussed. / text