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Orientador: João Sinezio de Carvalho Campos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-13T12:36:21Z (GMT). No. of bitstreams: 1 IvanovJunior_Anatoli_M.pdf: 1192015 bytes, checksum: f5927a9e17a52427545658820eae73f8 (MD5) Previous issue date: 2009 / Resumo: A utilização de borracha SIS (copolímero em bloco estireno/isopreno/estireno) em diversas aplicações tais como solados de sapatos, artefatos de vedação, adesivos com baixa resistência térmica (até 40º C). No entanto, neste trabalho apresentam -se os resultados obtidos com a incorporação de PPO (polioxidofenileno) a borracha SIS, o que resulta o aumento de resistência térmica da borracha, ampliando assim suas aplicações. Neste trabalho estudou-se a melhor condição em massa dos materiais SIS e PPO. De acordo com análises físico-químicas encontrou-se a composição de 50% de cada material uma condição onde se tem um incremento na resistência térmica da borracha de até 70° C, o que então era de -51º C. No sentido de apresentar uma aplicação, realizou-se a confecção de um laminado auto-adesivo com resistência térmica até 70º C. / Abstract: The rubber use SIS (block copolymer) in several such applications as shoes, technical engines, stickers with low thermal resistance (up to 40º C). However, in this work they come the results obtained with the incorporation of PPO (polioxide phenilene) on rubber SIS, with results the increase of thermal resistance of the rubber, increase the applications. In this work it was studied the best condition in mass of material SIS and PPO. In agreement with analyses it met the composition of 50% of each material a condition where an increment is had in the thermal resistance of the rubber of up to 70° C, what then was of -50º C. In the sense of presenting an application, it took place the adhesive laminated with thermal resistance up to 70º C. / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

External prestressed carbon fibre reinforced polymer (CFRP) straps can be used to strengthen shear deficient reinforced concrete (RC) structures. The strengthening system is associated with a number of parameters including the number of straps, strap locations, strap stiffness, and strap prestress. The initial goal of this research was to identify the optimum values for these parameters in order to design an efficient and effective shear retrofitting system. The shear friction theory (SFT) and modified compression field theory (MCFT) were identified as potential predictive theories to model the shear behaviour of RC beams retrofitted with CFRP straps. Possible modifications to the theories to reflect CFRP prestressed straps were investigated. Two popular optimisation algorithms namely the genetic algorithm (GA) and particle swarm optimisation (PSO) were coded and tested with six test functions. These algorithms were used to find the optimum shear retrofitting configurations and also to reduce the computational cost associated with the SFT and MCFT evaluations. An experimental investigation was carried out to validate the SFT and MCFT predictions for various CFRP strap configurations. The investigation consisted of an unstrengthened control beam and five CFRP strengthened beams. The shear behaviour of the beams was significantly influenced by the CFRP strap configurations. A critical load level where the beam stiffness started to deteriorate significantly was identified. It was found that there was a correlation between this load level and the yielding of the internal shear links and a rapid increase in crack openmg. The SFT and MCFT were validated using the experimental results. The peak shear capacities predicted using the SFT were more consistent with the stiffness deteriorating loads identified in the experimental investigation than with the ultimate loads of the beams. The reinforcement forces and crack opening values found from the SFT were consistent with the experimental results. The MCFT predicted the total shear response, ultimate shear capacity, crack opening, and internal and external reinforcement forces in the beams. The accuracy of the MCFT predictions reduced slightly when either the strap configuration was highly nonuniforrn or the initial prestress level in the straps was relatively low. The shear link yielding load levels predicted by the MCFT were found to be similar to the SFT predictions. By using the coded optimisation algorithms in combination with the SFT or MCFT, the optimum CFRP strap configurations were found for a selected case study. Both theories predicted an offset for the optimum strap locations from the locations associated with equal spacings along the shear span. A reasonable agreement between the SFT and MCFT predictions for the optimum shear strengths and strap locations was observed. A parametric study demonstrated that the concrete strength, internal shear link locations, beam depth, and shear span to depth ratio of the beam do not significantly influence the optimum strengthening configurations for the CFRP strap system. External prestressed carbon fibre reinforced polymer (CFRP) straps can be used to strengthen shear deficient reinforced concrete (RC) structures. The strengthening system is associated with a number of parameters including the number of straps, strap locations, strap stiffness, and strap prestress. The initial goal of this research was to identify the optimum values for these parameters in order to design an efficient and effective shear retrofitting system. The shear friction theory (SFT) and modified compression field theory (MCFT) were identified as potential predictive theories to model the shear behaviour ofRC beams retrofitted with CFRP straps. Possible modifications to the theories to reflect CFRP prestressed straps were investigated. Two popular optimisation algorithms namely the genetic algorithm (GA) and particle swarm optimisation (PSO) were coded and tested with six test functions. These algorithms were used to find the optimum shear retrofitting configurations and also to reduce the computational cost associated with the SFT and MCFT evaluations. An experimental investigation was ca1Tied out to validate the SFT and MCFT predictions for various CFRP strap configurations. The investigation consisted of an unstrengthened control beam and five CFRP strengthened beams. The shear behaviour of the beams was significantly influenced by the CFRP strap configurations. A critical load level where the beam stiffness started to deteriorate significantly was identified. It was found that there was a correlation between this load level and the yielding of the internal shear links and a rapid increase in crack opening. The SFT and MCFT were validated using the experimental results. The peak shear capacities predicted using the SFT were more consistent with the stiffness deteriorating loads identified in the experimental investigation than with the ultimate loads of the beams. The reinforcement forces and crack opening values found from the SFT were consistent with the experimental results. The MCFT predicted the total shear response, ultimate shear capacity, crack opening, and internal and external reinforcement forces in the beams. The accuracy of the MCFT predictions reduced slightly when either the strap configuration was highly nonuniform or the initial prestress level in the straps was relatively low. The shear link yielding load levels predicted by the MCFT were found to be similar to the SFT predictions. By using the coded optimisation algorithms in combination with the SFT or MCFT, the optimum CFRP strap configurations were found for a selected case study. Both theories predicted an offset for the optimum strap locations from the locations associated with equal spacings along the shear span. A reasonable agreement between the SFT and MCFT predictions for the optimum shear strengths and strap locations was observed. A parametric study demonstrated that the concrete strength, internal shear link locations, beam depth, and shear span to depth ratio of the beam do not significantly influence the optimum strengthening configurations for the CFRP strap system.

A variety of retrofitting methods are used to upgrade existing structures. For example, steel plates and Fiber Reinforced Polymer (FRP) jackets are externally bonded to members to increase their capacity in flexure and shear. However, due to the issue of corrosion these strengthening systems may lose their efficiency with time. FRP materials have been used to strengthen many structural components of different shapes and types. FRP jackets, FRP Strips, and FRP rods have commonly been used to rehabilitate existing structural components. The many advantages of using FRP as strengthening materials have made this material an attractive alternative: advantages such as lightweight, high strength, and ease of setting up. Among the many applications using FRP, Near Surface Mounted -- Fiber Reinforced polymer (NSM-FRP) is a promising technique used to strengthen concrete members. However, de-bonding issues have to be overcome to make this technique efficient and reliable. The NSM-FRP technique consists of making a groove along the surface of the concrete member to be retrofitted with depth less than the cover of the member. After cleaning the groove, epoxy paste is used to fill two-thirds of the groove's depth. The FRP element is then mounted in the groove. Finally, the groove is filled with epoxy and the excessive epoxy is leveled with surface of the concrete. This technique makes the FRP material completely covered by epoxy in the cover of the concrete. This method can be used for strengthening both the positive and negative moment regions of girders and slabs. Groove size, paste, concrete, and rods properties are the main variables that control the efficiency of the NSM-FRP rods. The main objective of this research project is to determine the behavior of reinforced concrete beams that are strengthened with NSM-CFRP reinforcement bars. In this research project, the bond characteristics of NSM-CFRP reinforcement bars are first determined from pullout tests. Then, NSM-CFRP rods are installed in reinforced concrete beams and the beams are tested. Loads, strains, and deflections are measured and theoretical and measured capacities are compared. Finally, the reliability and efficiency of using NSM-CFRP rods technique in retrofitting existing structures is observed.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, May 2016 / In this study, hybrid multiscale epoxy composites were developed from woven glass fabrics and PAN nanofibers embedded with short ECNFs (diameters of ~200nm) produced via electrospinning. Unlike VGCNFs or CNTs which are prepared through bottom-up methods, ECNFs were produced through a top-down approach; hence, ECNFs are much more cost-effective than VGCNFs or CNTs. Impact absorption energy, tensile strength, and flexural strength of the hybrid multiscale reinforced GFRP composites were investigated. The control sample was the conventional GFRP composite prepared from the neat epoxy resin. With the increase of ECNFs fiber volume fraction up to 1.0%, the impact absorption energy, tensile strength, and flexural strength increased. The incorporation of ECNFs embedded in the PAN nanofibers resulted in improvements on impact absorption energy, tensile strength, and flexural properties (strength and modulus) of the GFPC. Compared to the PAN reinforced GRPC, the incorporation of 1.0% ECNFs resulted in the improvements of impact absorption energy by roughly 9%, tensile strength by 37% and flexural strength by 29%, respectively. Interfacial debonding of matrix from the fiber was shown to be the dominant mechanism for shear failure of composites without ECNFs. PAN/ECNFs networks acted as microcrack arresters enhancing the composites toughness through the bridging mechanism in matrix rich zones. More energy absorption of the laminate specimens subjected to shear failure was attributed to the fracture and fiber pull out of more ECNFs from the epoxy matrix. This study suggests that, the developed hybrid multiscale ECNF/PAN epoxy composite could replace conventional GRPC as low-cost and high-performance structural composites with improved out of plane as well as in plane mechanical properties. The strengthening/ toughening strategy formulated in this study indicates the feasibility of using the nano-scale reinforcements to further improve the mechanical properties of currently structured high-performance composites in the coming years. In addition, the present study will significantly stimulate the long-term development of high-strength high-toughness bulk structural nanocomposites for broad applications. / MT2016

To meet the need of lightweight chassis in the near future, a technological step of introducing anisotropic materials like Carbon Fibre Reinforced Plastics (CFRP) in structural parts of cars is a possible way ahead. Though there are commercially available tools to find suitability of Fibre Reinforced Plastics (FRPs) and their orientations, they depend on numerical optimization and complexity increases with the size of the model. Nevertheless, the user has a very limited control of intermediate steps. To understand the type of material system that can be used in different regions for a lightweight chassis, especially during the initial concept phase, a more simplified, yet reliable tool is desirable.The thesis aims to provide a framework for determining fibre orientations according to the most-ideal loading path to achieve maximum advantage from FRP-materials. This has been achieved by developing algorithms to find best-fit material orientations analytically, which uses principal stresses and their orientations in a finite element originating from multiple load cases. This thesis takes inspiration from the Durst criteria (2008) which upon implementation provides information on how individual elements must be modelled in a component subjected to multiple load cases. This analysis pre-evaluates the potential of FRP-suitable parts. Few modifications have been made to the existing formulations by the authors which have been explained in relevant sections.The study has been extended to develop additional MATLAB subroutines which finds the type of laminate design (uni-directional, bi-axial or quasi-isotropic) that is suitable for individual elements.Several test cases have been run to check the validity of the developed algorithm. Finally, the algorithm has been implemented on a Body-In-White subjected to two load cases. The thesis gives an idea of how to divide the structure into sub-components along with the local fibre directions based on the fibre orientations and an appropriate laminate design based on classical laminate theory.

The complexity of the fiber-matrix interphase in a composite is largely due to the myriad of variables (material, processing, and design) that affect its formation. The interphase, thus formed, has to be characterized at several levels (micro-structural, chemical, and mechanical) in order for one to fully understand the nature of the bond between the fiber and matrix and in order to perform a stress analysis of the fiber-interphase-matrix assemblage. A thorough thermo-mechanical characterization of the interphase is difficult, at present, due to the necessity of studying the interphase in situ, its small dimension (usually on the order of a micrometer), and its general complexity. However, a cursory glance at the literature shows that great progress has been made in all of the three levels of characterization mentioned above for various composite systems. Several recent attempts have focused on the physical characterization (evaluation of volume fraction, thickness, Young's modulus, shear modulus and coefficient of thermal expansion) of the interphase. Models of physical properties (thickness, Young's modulus, Poisson's ratio and coefficient of thermal expansion) of the interphase have been considered by several researchers in an effort to study the influence of the interphase on overall composite properties and behavior. Hypotheses on interphase formation and properties have been proposed and tested by some researchers. Both experimental characterization as well as modeling studies are necessary to achieve a more profound understanding of the interphase and its behavior. The interphase, in a composite, is usually modeled as a homogeneous region, despite the fact that it may have spatial property variations.However, it is important to the understanding of composite behavior to incorporate a realistic interphasial region into the analysis and testing of composite material systems. A new thermo-elastic model for the interphase properties in fiber-reinforced thermosets is proposed. The Young’s modulus and coefficient of thermal expansion of the interphase are assumed to be functions of distance from the fiber in this model. The Poisson’s ratio of the interphase is assumed to be the same as that of the matrix. The new model is used in a concentric cylinder assemblage analysis for the determination of the residual thermal stresses in unidirectional fiber-reinforced epoxies. The governing field equations in terms of displacements are solved in “closed form”. It is found that, although the solution is dilute, the property variations in the interphase have a distinct effect on the residual thermal stresses. This is significant, considering the fact that residual thermal stresses play an important role in controlling the structural performance of a composite. The new model is used in Mori-Tanaka analyses for the determination of non-dilute local stress fields in unidirectional fiber-reinforced epoxies under thermo-mechanical loading situations. The governing field equations in terms of displacements are solved in “closed form”. It is found that property variations in the interphase have a distinct effect on the local stresses. This is also significant, considering the fact that local stresses play an important role in controlling the structural performance of a composite. A model composite system consisting of a coated glass rod embedded in Epon 828 is considered; coatings are applied to the glass rod in succession to simulate two different interphase types. The model composite specimens are loaded in transverse compression and transverse shear, and the resulting in-plane displacements are measured by the use of the Moire interferometry technique. Differences in displacement fields between the various specimens, due to the presence of interphasial regions, are found to be minimal. More sensitive measurements are needed to measure pointwise displacements in the interphasial (coatings) region. / Ph. D.

The friction and wear of injection molded Poly(ether ether ketone) (PEEK) and Poly(ether imide) (PEI), PEEK/PEI blends with the weight compositions of 50/50 %, 70/30 %, and 85/15 %, with and without short carbon fibers were measured in a pin(52100 steel ball)-on-disk(polymer blend) configuration under dry friction. 50/50, 70/30, and 85/15 compositions were annealed to study the effect of crystallinity on wear test. The test variables were sliding speed and normal load. The wear mechanism of pure PEEK matrix was plowing and as the weight percentage of PEI in the blend was increased the wear mechanism changed to the generation of small particles. The wear rates of the unfilled PEEK/PEI blends were found to be a function of not only the blend composition, but also of the normal load, sliding speed and crystallinity in complex manner. However, the coefficient of friction of the unfilled blends did not seem to significantly depend on those testing parameters. When no wear debris was produced, it was below 0.15 otherwise it was ranged from 0.2 to 0.3. The 30 weight % carbon fiber reinforced (CFR) PEEK did produced wear particles but 70/30 and 100 % PEI composites showed reduced wear rates compared to those of unfilled blends. The coefficients of friction of CFR did not seem to be changed from those of the untreated blends except for 100% PEI. Presence of the incubation time before wear particles were produced indicated that the predominant wear mechanism was fatigue. An increase in friction correlated with the generation of wear particles and the formation of a wear groove. / Master of Science