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The abrasive mechanism of polymer wear is dominant in the startup, or "breakin", stage of polymer/steel sliding systems. This mechanism controls the polymer wear rate until the voids in the hard metal surface are filled, much like the filling observed with a file when used on soft metals. This regime of polymer wear is modeled on an event-by-event basis. The model utilizes a digitized profile of the metal surface, bulk polymer properties such as flow pressure and elongation at break, and a few system parameters such as load and slider geometry. The predictions of the model are compared with experimental data. The predicted wear rates are within a factor of 3 of the measured wear rates for polymers with glass transition temperatures, Tg, above the interfacial temperature (rigid PVC and PCTFE). The validity of the model is shown to be related to the ductile or brittle behavior of the sliding polymer. / Ph. D. / Bibliography: leaves 78-80

The modification of polymeric materials using plasticizers or elastomers has been investigated in three research programs. The first describes epoxy resins modified with dimethylsiloxane, dimethyl-co-methyltrifluoropropyl siloxane, and dimethyl-co-diphenyl siloxane. The apparent compatibility between the epoxy and the siloxanes was enhanced by increasing methyltrifluoropropyl or diphenyl siloxane content or lowering molecular weight, resulting in profound changes in morphology and the resultant mechanical properties of the modified resins. Fracture toughness was most significantly improved using siloxanes containing at least 40% methyltrifluoropropyl siloxane or 20 and 40% diphenyl siloxane. Comparison of siloxane modifiers with butadiene acrylonitrile modifiers was valuable with regard to both property and morphological effects. The second research project considers the structure-property behavior of polyvinyl chloride (PVC) plasticized with low molecular weight diesters with emphasis on the contrasting effects of different plasticizers on the breadth of PVC's dynamic mechanical spectrum. It was clearly demonstrated that a less soluble plasticizer promoted a greater broadening at intermediate concentrations. Crystallization phenomena and static mechanical properties reflected the greater diluent effect of a more soluble plasticizer. The dynamic mechanical behavior as well as other critical experimental observations were explained using a model which postulates that the network junctions of plasticized PVC consist of "pockets" containing several small crystallites. These pockets are randomly dispersed in a matrix whose homogeneity is governed by the plasticizer's solubility and molar volume. The third research project describes the modification of high 1,4 polybutadiene (PB) with isopropyl azodicarboxylate (IAD) for potential .use as impact modifiers for polar polymers. A method for finding the extent of IAD modification of the PB has been developed using ¹³C nmr and UV spectroscopy. Solution blends of PVC with PB modified with up to 11 mol% IAD were found to be immiscible. Stress-strain testing suggested that IAD modification (11%) enhanced the apparent compatibility between PB and PVC at 25% rubber content. The relatively poor mechanical response of the blends was believed to be related to their somewhat porous morphology. / Ph. D. / incomplete_metadata

The need for sustainable energy use has motivated the exploration of renewable alternative fuels and fuel conversion technology on a global scale. Fuel cells, which convert chemical energy directly into electrical energy with high efficiency and low emissions, provide a promising strategy for achieving energy sustainability. The current progress in fuel cell commercialization is mainly in portable and stationary applications, but fuel cell technology for transportation applications, which make up a substantial portion of the global energy market, have seen little commercial success. Proton exchange membrane fuel cells (PEMFCs) have high potential for addressing the future energy needs of the transportation energy sector. However, one of the prevailing limitations of the PEMFC is the availability of high-performance, cost-effective electrolyte materials. These materials may be realized in the near future by developing multi-functional polymer blends targeted at specific performance capabilities. Due to the near-infinite possibilities of polymer combinations and processing techniques high-throughput polymer characterization techniques are necessary to effectively and systematically screen for optimal materials and relevant structure-property relationships. In this work, a high-throughput mass transport assay (HT-MTA) has been developed to characterize water flux and permeability at multiple sample locations in parallel. The functionality of HT-MTA was evaluated using standard Nafion® films and a model semi-interpenetrated polymer network with commercial polyvinylidine fluoride as the host matrix for a proprietary polyelectrolyte supplied by Arkema, Inc. To further demonstrate the utility of HT-MTA, the instrument was incorporated into the lab's current high-throughput characterization toolset and used to investigate the mechanisms and effects of rapid free radical degradation of Nafion® membranes based on various concentrations of hydrogen peroxide and iron(II) sulfate in solution. The results have been used suggest the effects of these regent components on preferential degradation pathways and will prove to be useful in later simulating the membrane performance during in-situ fuel cell lifetime which is both time-intensive and costly. The high-throughput toolset was also used to develop a novel optimized blend consisting of polyetherimide (PEI), a low-cost high performance resin, and sulfonated PEI (S-PEI) made using a relatively mild post sulfonation reaction with trimethylsilyl chlorosulfonate. The effects of blend composition and thermal annealing on film performance were evaluated and the polymer system was shown to have optimal performance properties that should prove to be useful in other high-performance applications where mechanical strength is critical. In general, this work shows promising results for efficiently developing advanced polymer materials using high-throughput screening techniques.

Este trabalho apresenta um estudo sobre a utilização de redes de Bragg em fibra ótica (FBG), para a monitoração das deformações mecânicas oriundas do processo de secagem de tintas. No intervalo de tempo referente ao processo de secagem, uma fina camada de tinta sofreu uma mudança de estado físico de líquido para sólido, se transformando em um filme contínuo e mecanicamente estável. As deformações mecânicas presentes neste processo foram mensuradas pelo transdutor, demonstrando a real possibilidade das redes de Bragg serem aplicadas para estes fins. Para o acompanhamento temporal das deformações mecânicas no processo de secagem de uma tinta látex, a FBG foi encapsulada com o objetivo de evitar o contato da tinta com a fibra ótica, devido à ineficaz aderência entre ambas, e consequentemente melhorar a aderência da tinta sobre o dispositivo encapsulado. Este processo de encapsulação da FBG permitiu que as deformações mecânicas oriundas do processo de secagem fossem eficientemente transformadas em perturbações mecânicas mensuradas pelo transdutor. O acompanhamento temporal das deformações mecânicas oriundas do processo de secagem também foi investigado com a utilização de tinta diluída. Finalmente, um estudo sobre as deformações mecânicas de uma segunda camada de tinta (duas demãos) é ainda abordado. As redes de Bragg utilizadas neste trabalho foram produzidas e caracterizadas quanto à deformação mecânica longitudinal e temperatura, no Núcleo de Dispositivos Fotônicos da UTFPR. / This work shows results obtained with the use of fiber Bragg grating (FBG) transducer to monitor the drying process of latex paints. When a thin film of wet paint is dried on the substrate surface, the paint film change from a sticky liquid state to a solid state, transforming to a continuous, transparent and mechanically stable film. The mechanical deformations in this process were measured by the FBG sensor head, showing the real possibility of FBG strain sensor application in this area. To monitor the mechanical deformation in the film during the drying process, the FBG was packaged. The FBG packaging has two main functions: allows a better measurement of the paint mechanical deformation inherent to the drying process and also avoids paint poor adhesion to the bare optical fiber. The packaged FBG, showed that this is a promising device to be used for the measurement of stress evolution in paints during the drying time. The mechanical deformation during drying time of diluted latex paint also was investigated. Finally, a study about the mechanical deformation of a second coating application of latex paint was also carried out. The Bragg gratings used in this work were produced in photosensitive fibers by means of a phase-mask interferometric external fabrication technique at Núcleo de Dispositivos Fotônicos laboratories of UTFPR.

Este trabalho apresenta um estudo sobre a utilização de redes de Bragg em fibra ótica (FBG), para a monitoração das deformações mecânicas oriundas do processo de secagem de tintas. No intervalo de tempo referente ao processo de secagem, uma fina camada de tinta sofreu uma mudança de estado físico de líquido para sólido, se transformando em um filme contínuo e mecanicamente estável. As deformações mecânicas presentes neste processo foram mensuradas pelo transdutor, demonstrando a real possibilidade das redes de Bragg serem aplicadas para estes fins. Para o acompanhamento temporal das deformações mecânicas no processo de secagem de uma tinta látex, a FBG foi encapsulada com o objetivo de evitar o contato da tinta com a fibra ótica, devido à ineficaz aderência entre ambas, e consequentemente melhorar a aderência da tinta sobre o dispositivo encapsulado. Este processo de encapsulação da FBG permitiu que as deformações mecânicas oriundas do processo de secagem fossem eficientemente transformadas em perturbações mecânicas mensuradas pelo transdutor. O acompanhamento temporal das deformações mecânicas oriundas do processo de secagem também foi investigado com a utilização de tinta diluída. Finalmente, um estudo sobre as deformações mecânicas de uma segunda camada de tinta (duas demãos) é ainda abordado. As redes de Bragg utilizadas neste trabalho foram produzidas e caracterizadas quanto à deformação mecânica longitudinal e temperatura, no Núcleo de Dispositivos Fotônicos da UTFPR. / This work shows results obtained with the use of fiber Bragg grating (FBG) transducer to monitor the drying process of latex paints. When a thin film of wet paint is dried on the substrate surface, the paint film change from a sticky liquid state to a solid state, transforming to a continuous, transparent and mechanically stable film. The mechanical deformations in this process were measured by the FBG sensor head, showing the real possibility of FBG strain sensor application in this area. To monitor the mechanical deformation in the film during the drying process, the FBG was packaged. The FBG packaging has two main functions: allows a better measurement of the paint mechanical deformation inherent to the drying process and also avoids paint poor adhesion to the bare optical fiber. The packaged FBG, showed that this is a promising device to be used for the measurement of stress evolution in paints during the drying time. The mechanical deformation during drying time of diluted latex paint also was investigated. Finally, a study about the mechanical deformation of a second coating application of latex paint was also carried out. The Bragg gratings used in this work were produced in photosensitive fibers by means of a phase-mask interferometric external fabrication technique at Núcleo de Dispositivos Fotônicos laboratories of UTFPR.

There are presently many solutions to dealing with aging or deteriorated structures. Depending on the state of the structure, it may need to be completely over-hauled, demolished and replaced, or only specific components may need rehabilitation. In the case of bridges, rehabilitation and maintenance of the decks are critical needs for infrastructure management. Viable rehabilitation options include replacement of decks with aluminum extrusions, hybrid composite and sandwich systems, precast reinforced concrete systems, or the use of pultruded fiber-reinforced polymer (FRP) shapes. Previous research using pultruded glass fiber-reinforced polymer (GFRP) decks, focused on behaviour under various strength and serviceability loading conditions. Failure modes observed were specific to delamination of the flexural cross sections, local crushing under loading pads, web buckling and lip separation. However certain failure mechanisms observed from in-situ installations differ from these laboratory results, including behaviour of the connectors or system of connection, as well as the effect of cyclic and torsional loads on the connection. This thesis investigates the role of mechanical and non-mechanical connectors in the composite action and failure mechanisms in a pultruded GFRP deck system. There are many interfaces including top panel to I-beam, deck panel to girder, and panel to panel, but this work focuses on investigating the top panel connection. This is achieved through comparative component level shear, uplift, and flexure testing to characterize failure and determine connector capacity. Additionally, a connection of this GFRP deck system to a concrete girder is investigated during the system-level test. Results show that an epoxy non-mechanical connection may be better than mechanical options in ensuring composite behaviour of the system.

Bioabsorbable orthopedic fixation devices are conceptually more attractive than metallic devices in repairing damaged tissues or in fastening implants. Our study focuses on investigating bioabsorbable composites for potential use as materials for orthopedic appliances. The study focuses on Poly(l-lactic acid) (PLLA), Polyglycolic acid (PGA), Poly-e-caprolactone (PCL), matrices with Carbon fibers (AS4), Nylon fibers and PLLA fibers. Fiber coating effects have also been investigated, with compliant polymers (1%, 50% and 100% of matrix properties) and with hydroxyapatite (HA). Unidirectional, continuous fiber plies, and multi-directional, random and quasi-random short-fiber composites were considered in our study. NDSANDS a concentric cylinder model computer software, was used to evaluate the stiffness and strength of the bioabsorbable composites with unidirectional fiber orientation. To achieve a better physical understanding, the NDSANDS predictions were also compared with those given by a simple, mechanics of materials approach. The theory for multidirectional short fiber composites, recently developed by Giurgiutiu and Reifsnider was employed with three fiber-orientation distribution functions and three failure mechanisms. Stiffness and strength of bioabsorbable composites were predicted over a range of fiber volume fraction. It was found that AS4/PLLA with 16% fiber volume fraction can have properties close to the bone when used in short fiber composite. Similar results are obtained using AS4/PLLA with hydroxyapatite coating. PLLA/PGA and PLLA/PLLA also demonstrated properties close to those of the bone in the range of 25% and 64%. / Master of Science

The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation.

In a fiber spinning process molten polymer is extruded into a fiber. The resulting fiber known as as-spun fiber is relatively weak and shows a large plastic central zone in its constitutive behavior. As a result the fiber deforms substantially without a significant change in load thus making it unsuitable for stress bearing applications. The range of plastic deformation is related to the natural draw ratio. In order to improve the mechanical properties of as spun fibers, fiber spinning is followed by a fiber draw process. With multi stage draw the as-spun fiber is drawn beyond the plastic region in various drawing zones which produces greater orientation of the polymer chains in the axial direction of the fiber thus enhancing mechanical strength characteristics of the fiber. The multistage draw process consists of several rollers each rotating at a speed greater than the one prior to it. The objective of this work is to develop a first approximation to model fiber draw in the multistage drawing process, with and without a draw pin. As the first step the slippage of fibers on rollers was analysed by including centrifugal acceleration and acceleration due to stretching. The draw in a free span is also modelled. Several representative draw processes were examined. It was found draw pin localizes the draw significantly although the resulting mechanical unloading complicates the analysis. Draw in the free span is impossible for isothermal draw processes, and anisothermal draw induces thermal unloading in the system. A comprehensive analysis of various draw processes will be examined.