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Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-06-29Bitstream added on 2014-06-13T20:58:30Z : No. of bitstreams: 1 siqueira_ej_me_guara.pdf: 1915411 bytes, checksum: f4773809a370af2f9216a9eac68d8816 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O constante desenvolvimento dos materiais aliado à necessidade de se obter componentes estruturais de alto desempenho como materiais alternativos na indústria aeronáutica, bem como considerando a aplicabilidade atual dos compósitos estruturais, previsões de falha da estrutura e análise das cargas máximas que as mesmas podem suportar se tornam tópicos fundamentais de pesquisas com a finalidade de garantia da confiabilidade quanto ao emprego dos mesmos em diversas áreas. Considerando que o compósito termoplástico do tipo PPS/C – Poli(sulfeto de fenileno) reforçado com fibras de carbono está surgindo como uma alternativa a compósitos poliméricos termorrígidos e que ainda há escassez na literatura atual de dados relativos à previsão de falhas, este trabalho se detém na analise bidimensional do comportamento mecânico do compósito PPS/C sob carregamento estático linear em flexão de três pontos e em tração com relação a alguns critérios de previsão de falhas inseridos no aplicativo computacional ANSYS, que são os critérios da máxima tensão, dos índices de forças e das relações inversas dos índices de forças de Tsai-Wu, bem como os critérios de previsão de falhas de Hill e de Hoffman calculados através do EXCEL com base nas tensões fornecidas pelo ANSYS e nas resistências contidas na literatura. Por fim, foram comparados os resultados obtidos através do modelo computacional com os resultados experimentais com o objetivo de analisar, avaliar e validar a simulação numérica como complementação dos ensaios experimentais. / The continuous development of materials associated with the need to obtain structural components of high performance that can serve the purpose of alternate material for the aircraft industry; in addition to the current applicability of the structural composite, structural failure predictions, as well as the maximum loads that such structures may have the capacity to bear, have become the subject-matter to a number of fundamental researches, which purpose is to guarantee the reliability of such materials, so that they can be duly applied in a variety of fields. Taking into account that the thermoplastic composite of PPS/C – Poly(phenylene-sulfide) type, reinforced with carbon fibers, is springing up as an alternate to the thermoset polymers composites, besides the fact that the current literature lacks data regarding failure predictions, the present paper limits itself to the two-dimensional analysis of PPS/C composite type mechanical behavior under a linear static loading at a three point bending and in traction with regards to some predicted failure criteria that have been inserted in ANSYS computer model, namely the maximum stress criteria, the strength ratio, and the reversed relation of strength ratio of Tsai-Wu, as well as the criteria of Hill and Hoffman to predict failure, which in turn were calculated on EXCEL, but based on the stresses supplied by ANSYS, and on the tensile strengths found on the literature. At last, a comparison was made between the results obtained from the computer model against the experimental results. The purpose of such comparison was to analyze, assess and validate the numerical simulation as a supplement to the experimental trials.

Resumo: O constante desenvolvimento dos materiais aliado à necessidade de se obter componentes estruturais de alto desempenho como materiais alternativos na indústria aeronáutica, bem como considerando a aplicabilidade atual dos compósitos estruturais, previsões de falha da estrutura e análise das cargas máximas que as mesmas podem suportar se tornam tópicos fundamentais de pesquisas com a finalidade de garantia da confiabilidade quanto ao emprego dos mesmos em diversas áreas. Considerando que o compósito termoplástico do tipo PPS/C - Poli(sulfeto de fenileno) reforçado com fibras de carbono está surgindo como uma alternativa a compósitos poliméricos termorrígidos e que ainda há escassez na literatura atual de dados relativos à previsão de falhas, este trabalho se detém na analise bidimensional do comportamento mecânico do compósito PPS/C sob carregamento estático linear em flexão de três pontos e em tração com relação a alguns critérios de previsão de falhas inseridos no aplicativo computacional ANSYS, que são os critérios da máxima tensão, dos índices de forças e das relações inversas dos índices de forças de Tsai-Wu, bem como os critérios de previsão de falhas de Hill e de Hoffman calculados através do EXCEL com base nas tensões fornecidas pelo ANSYS e nas resistências contidas na literatura. Por fim, foram comparados os resultados obtidos através do modelo computacional com os resultados experimentais com o objetivo de analisar, avaliar e validar a simulação numérica como complementação dos ensaios experimentais. / Abstract: The continuous development of materials associated with the need to obtain structural components of high performance that can serve the purpose of alternate material for the aircraft industry; in addition to the current applicability of the structural composite, structural failure predictions, as well as the maximum loads that such structures may have the capacity to bear, have become the subject-matter to a number of fundamental researches, which purpose is to guarantee the reliability of such materials, so that they can be duly applied in a variety of fields. Taking into account that the thermoplastic composite of PPS/C - Poly(phenylene-sulfide) type, reinforced with carbon fibers, is springing up as an alternate to the thermoset polymers composites, besides the fact that the current literature lacks data regarding failure predictions, the present paper limits itself to the two-dimensional analysis of PPS/C composite type mechanical behavior under a linear static loading at a three point bending and in traction with regards to some predicted failure criteria that have been inserted in ANSYS computer model, namely the maximum stress criteria, the strength ratio, and the reversed relation of strength ratio of Tsai-Wu, as well as the criteria of Hill and Hoffman to predict failure, which in turn were calculated on EXCEL, but based on the stresses supplied by ANSYS, and on the tensile strengths found on the literature. At last, a comparison was made between the results obtained from the computer model against the experimental results. The purpose of such comparison was to analyze, assess and validate the numerical simulation as a supplement to the experimental trials. / Orientador: Fernando de Azevedo Silva / Coorientador: Edson Cocchieri Botelho / Banca: Marcos Valério Ribeiro / Banca: Luiz Claudio Pardini / Mestre

RESUMO A tensão de contração desenvolvida durante a polimerização de um compósito aderido às paredes do preparo cavitário pode comprometer a integridade da interface dente/restauração. O objetivo deste trabalho foi verificar a relação entre a tensão de contração e o grau de conversão em compósitos híbridos (Z250 e Tetric Ceram) e microparticulados (A110 e Heliomolar). Para o teste de tensão de contração foram utilizados bastões de vidro de silicato de boro (Pyrex), com 5 mm de diâmetro e 5 cm de altura. Os bastões foram presos às garras de uma máquina de ensaios (modelo 5565, Instron, Canton, MA, EUA) e o compósito foi aplicado às superfícies planas do vidro, as quais passararam por jateamento com óxido de alumínio (250 mm), seguido de silanização e aplicação de adesivo. A distância entre as superfícies dos vidros foi ajustada em 2 mm (Fator C=1,25). O grau de conversão (GC) foi determinado através de espectroscopia fotoacústica no infravermelho (PAS-IR) utilizando-se as razões entre as bandas correspondentes às duplas ligações carbônicas alifáticas (1640 cm -1 ) e aromáticas (1610 cm -1 ). Para cada compósito, tanto no teste de tensão como na análise do grau de conversão, foram constituídos cinco grupos variando-se o tempo de irradiação, a fim de se obter diferentes níveis de densidade de energia (4,8; 13,5; 27,0; 54,0 e 108,0 J/cm 2 ). Foram registrados os valores de tensão máxima e de grau de conversão observados no período de 10 minutos, contados a partir do início da fotoativação. A análise de dados foi feita através de ANOVA de fator duplo e teste de Tukey (a=0,05). Para os valores de tensão de contração, a interação compósito x densidade de energia foi significante. Os valores de tensão de contração para o compósito A110 variaram entre 1,2 e 7,0 MPa, para o Heliomolar entre 0,6 e 6,6 MPa, para o compósito Tetric Ceram entre 1,3 e 8,1 MPa e para o Z250 entre 2,0 e 6,6 MPa. Em geral, valores de tensão maiores foram observados nos níveis de densidade de energia mais elevados. Para o compósito A110 4,8<13,5<27,0<54,0=108,0 J/cm 2 . Para o compósito Heliomolar todos os níveis foram diferentes exceto entre 27,0 e 54,0 J/cm 2 . O compósito Tetric Ceram apresentou 4,8<13,5<27,0<54,0=108,0 J/cm 2 enquanto o compósito Z250 obteve 4,8=13,5<27,0=54,0<108,0 J/cm 2 . O GC foi influenciado pelo compósito (A110: 24% = Heliomolar: 28% = Z250: 32% < Tetric: 39%) e pela densidade de energia. As densidades de energia de 27,0 (33%); 54,0 (35%) e 108,0 (36%) J/cm 2 forneceram graus de conversão estatisticamente semelhantes, o mesmo ocorrendo entre 4,8 (23%) e 13,5 (26%) J/cm 2 e entre 13,5 e 27,0 J/cm 2 . Os resultados mostraram ainda que existe uma relação não-linear entre a tensão de contração e o grau de conversão de compósitos restauradores. Pode-se concluir que densidades de energia elevadas não necessariamente contribuem para um aumento significante no GC, mas podem acentuar o desenvolvimento de tensões de contração. / ABSTRACT The contraction stress developed during polymerization of composites bonded to cavity walls cavity is often associated with marginal gaps and interfacial failure. The aim of this study was to verify the relationship between contraction stress and degree of conversion (DC) in four composites (Z250, A110 – 3M ESPE; Tetric Ceram, Heliomolar – Vivadent). For the contraction stress test, composite (2 mm thick) was bonded between sandblasted and silane-treated glass stubs (Pirex: 5 mm diameter), mounted in a testing machine (model 5565, Instron, Canton, MA, EUA) equipped with a tensilometer to monitor the distance between the rods (C-factor=1.25). DC was determined by Infrared Photoacustic spectrometry (PAS-IR). The ratio between the aliphatic (1640 cm -1 ) and the aromatic (1610 cm -1 ) carbon double-bonds was used for calculating the DC. In both tests, each composite was light-cured for different times in order to provide different energy densities (4.8, 13.5, 27.0, 54.0, 108.0 J/cm 2 ). Maximum contraction stress and DC were measured 10 minutes after the beginning of polymerization. Results were analyzed by two-way ANOVA and Tukey’s test (a=0.05). For contraction stress, the interaction between composite and energy density was significant. Contraction stress values for A110 were between 1,2 and 7,0 MPa, Heliomolar between 0,6 and 6,6 MPa, Tetric Ceram between 1,3 and 8,1 Mpa and Z250 between 2,0 and 6,6 MPa. In general, contraction stress increases with higher energy density levels. For A110, 4.8<13.5<27.0<54.0=108.0 J/cm 2 . Heliomolar showed significant differences between all energy densities, except 27.0 and 54.0 J/cm 2 . Tetric was 4.8<13.5<27.0<54.0=108.0 J/cm 2 and Z250 showed 4.8=13.5<27.0=54.0<108.0 J/cm 2 . DC was influenced by composite (A110: 24%;Heliomolar: 28%, Z250: 32%; Tetric: 39%) and by energy density. The 27.0 (33%), 54.0 (35%) and 108.0 (36%) J/cm 2 energy densities showed similar DC, the same occurring with 4.8 (23%) and 13.5 (26%) J/cm 2 and between 13.5 and 27.0 J/cm 2 .The results showed a non-linear relationship between contraction stress and degree of conversion. It can be concluded that higher energy densities will not necessary contribute to increase DC, but may result in increased contraction stress development.

RESUMO A tensão de contração desenvolvida durante a polimerização de um compósito aderido às paredes do preparo cavitário pode comprometer a integridade da interface dente/restauração. O objetivo deste trabalho foi verificar a relação entre a tensão de contração e o grau de conversão em compósitos híbridos (Z250 e Tetric Ceram) e microparticulados (A110 e Heliomolar). Para o teste de tensão de contração foram utilizados bastões de vidro de silicato de boro (Pyrex), com 5 mm de diâmetro e 5 cm de altura. Os bastões foram presos às garras de uma máquina de ensaios (modelo 5565, Instron, Canton, MA, EUA) e o compósito foi aplicado às superfícies planas do vidro, as quais passararam por jateamento com óxido de alumínio (250 mm), seguido de silanização e aplicação de adesivo. A distância entre as superfícies dos vidros foi ajustada em 2 mm (Fator C=1,25). O grau de conversão (GC) foi determinado através de espectroscopia fotoacústica no infravermelho (PAS-IR) utilizando-se as razões entre as bandas correspondentes às duplas ligações carbônicas alifáticas (1640 cm -1 ) e aromáticas (1610 cm -1 ). Para cada compósito, tanto no teste de tensão como na análise do grau de conversão, foram constituídos cinco grupos variando-se o tempo de irradiação, a fim de se obter diferentes níveis de densidade de energia (4,8; 13,5; 27,0; 54,0 e 108,0 J/cm 2 ). Foram registrados os valores de tensão máxima e de grau de conversão observados no período de 10 minutos, contados a partir do início da fotoativação. A análise de dados foi feita através de ANOVA de fator duplo e teste de Tukey (a=0,05). Para os valores de tensão de contração, a interação compósito x densidade de energia foi significante. Os valores de tensão de contração para o compósito A110 variaram entre 1,2 e 7,0 MPa, para o Heliomolar entre 0,6 e 6,6 MPa, para o compósito Tetric Ceram entre 1,3 e 8,1 MPa e para o Z250 entre 2,0 e 6,6 MPa. Em geral, valores de tensão maiores foram observados nos níveis de densidade de energia mais elevados. Para o compósito A110 4,8<13,5<27,0<54,0=108,0 J/cm 2 . Para o compósito Heliomolar todos os níveis foram diferentes exceto entre 27,0 e 54,0 J/cm 2 . O compósito Tetric Ceram apresentou 4,8<13,5<27,0<54,0=108,0 J/cm 2 enquanto o compósito Z250 obteve 4,8=13,5<27,0=54,0<108,0 J/cm 2 . O GC foi influenciado pelo compósito (A110: 24% = Heliomolar: 28% = Z250: 32% < Tetric: 39%) e pela densidade de energia. As densidades de energia de 27,0 (33%); 54,0 (35%) e 108,0 (36%) J/cm 2 forneceram graus de conversão estatisticamente semelhantes, o mesmo ocorrendo entre 4,8 (23%) e 13,5 (26%) J/cm 2 e entre 13,5 e 27,0 J/cm 2 . Os resultados mostraram ainda que existe uma relação não-linear entre a tensão de contração e o grau de conversão de compósitos restauradores. Pode-se concluir que densidades de energia elevadas não necessariamente contribuem para um aumento significante no GC, mas podem acentuar o desenvolvimento de tensões de contração. / ABSTRACT The contraction stress developed during polymerization of composites bonded to cavity walls cavity is often associated with marginal gaps and interfacial failure. The aim of this study was to verify the relationship between contraction stress and degree of conversion (DC) in four composites (Z250, A110 – 3M ESPE; Tetric Ceram, Heliomolar – Vivadent). For the contraction stress test, composite (2 mm thick) was bonded between sandblasted and silane-treated glass stubs (Pirex: 5 mm diameter), mounted in a testing machine (model 5565, Instron, Canton, MA, EUA) equipped with a tensilometer to monitor the distance between the rods (C-factor=1.25). DC was determined by Infrared Photoacustic spectrometry (PAS-IR). The ratio between the aliphatic (1640 cm -1 ) and the aromatic (1610 cm -1 ) carbon double-bonds was used for calculating the DC. In both tests, each composite was light-cured for different times in order to provide different energy densities (4.8, 13.5, 27.0, 54.0, 108.0 J/cm 2 ). Maximum contraction stress and DC were measured 10 minutes after the beginning of polymerization. Results were analyzed by two-way ANOVA and Tukey’s test (a=0.05). For contraction stress, the interaction between composite and energy density was significant. Contraction stress values for A110 were between 1,2 and 7,0 MPa, Heliomolar between 0,6 and 6,6 MPa, Tetric Ceram between 1,3 and 8,1 Mpa and Z250 between 2,0 and 6,6 MPa. In general, contraction stress increases with higher energy density levels. For A110, 4.8<13.5<27.0<54.0=108.0 J/cm 2 . Heliomolar showed significant differences between all energy densities, except 27.0 and 54.0 J/cm 2 . Tetric was 4.8<13.5<27.0<54.0=108.0 J/cm 2 and Z250 showed 4.8=13.5<27.0=54.0<108.0 J/cm 2 . DC was influenced by composite (A110: 24%;Heliomolar: 28%, Z250: 32%; Tetric: 39%) and by energy density. The 27.0 (33%), 54.0 (35%) and 108.0 (36%) J/cm 2 energy densities showed similar DC, the same occurring with 4.8 (23%) and 13.5 (26%) J/cm 2 and between 13.5 and 27.0 J/cm 2 .The results showed a non-linear relationship between contraction stress and degree of conversion. It can be concluded that higher energy densities will not necessary contribute to increase DC, but may result in increased contraction stress development.

No description available.

Sheet Molding Compounds (SMC) present a promising alternative for sheet metal in automotive exterior body panel applications. They offer excellent specific mechanical properties, improved design freedom and a cost-efficient manufacturing process. However, the paintability of SMCs is challenging and this issue has kept the material from a more widespread application, in spite all inherent advantages. This work investigates the underlying reasons of paint defect occurrence and proposes novel solutions to improve upon state-of-the-art technology. Through the modification of conventional SMC an improved surface compound is proposed. This can be combined with a novel manufacturing process, denoted Co-Compression-Molding, which enables the molding of two individual compounds in a single step. The work offers insight into appropriate molding parameter selection to ensure a flawless compression molding process. Additional processing steps are proposed to further improve manufacturing, such as thermography for the early detection of sub-surface voids, and post-processing via electron beam curing.:1 Introduction 1.1 Motivation and Objectives 1.2 Solution Approach 2 State of the Art 2.1 Automotive Production 2.1.1 Paint Processes 2.1.2 Quality Assessment Techniques 2.2 Sheet Molding Compounds 2.2.1 Manufacturing and Composition 2.2.2 Mechanical Properties 2.2.3 Conventional Methods of Surface Improvement 2.2.4 Recycling Methods 2.3 Compression Molding 2.3.1 Mold Flow of Sheet Molding Compounds 2.3.2 Compound Rheology 2.3.3 Inherent Porosity 2.3.4 Co-Molding Process 2.3.5 Alternative Approaches and Auxiliary Processes 3 Reduced Fiber Weight Fraction Compounds 3.1 Porosity as the Source of Defects 3.2 Compounding and Compression Molding 3.3 Compound Characterization 3.3.1 Fiber Network Permeability 3.3.2 Rheology and Flowability 3.3.3 Physical Properties 3.3.4 Pore Content and Porosity Elimination 3.4 Effect on Paintability 4 Co-Compression Molding 4.1 Hybrid Material Flow 4.2 Materials 4.3 Molding Trials and Testing 4.3.1 Flat Plaque Testing 5 Auxiliary Processes 5.1 Thermography 5.1.1 Materials 5.1.2 Experiments 5.2 Electron Beam Curing 5.2.1 Residual Reactivity 5.2.2 Irradiation and Post-Curing 6 Full-Scale Trials 6.1 Class-A Panel 6.2 Semi-Structural Component 6.3 Technology Demonstrator 6.3.1 Cost Comparison 6.4 Application Guidance 6.4.1 Reduced Fiber Fraction Compounds 6.4.2 Co-Compression Molding 6.4.3 Application of Auxiliary Processes 7 Summary Bibliography Appendix A Evolution of Vehicle Curb Weight B Porosity Structure of Normal Density Compound C Surface Veil Distortion During Compression Molding

The objective of this study is to synthesize nematic-thermotropic liquid crystalline polymers (LCP) and determine their possible application areas. In this context, thirty different LCP&rsquo / s were synthesized and categorized with respect to their fiber formation capacity, melting temperature and mechanical properties. The basic chemical structure of synthesized LCP&rsquo / s were composed of p-acetoxybenzoic acid (p-ABA), m-acetoxybenzoic acid (m-ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA) and isophthalic acid (IPA) and alkyl-diacids monomers. In addition to mentioned monomers, polymers and oligomers were included in the backbone such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) polymers, and polybutylene naphthalate (PBN), polyhexylene naphthalate (PHN) and poly butylene terephthalate (PBT) oligomers that contain different kinds of alkyl-diols. We adjusted the LCP content to have low melting point (180oC-280oC) that is processable with thermoplastics. This was achieved by balancing the amount of linear (para) and angular (meta) groups on the aromatic backbones together with the use of linear hydrocarbon linkages in the random copolymerization (esterification) reaction. LCP species were characterized by the following techniques / Polarized Light Microscopy, Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Analysis (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), X-ray Scattering (WAXS, Fiber diffraction), surface free energy, end group analysis (CEG), intrinsic viscosity (IV) and tensile test. According to these analysis LCPs were classified into five main categories / (I) fully aromatics, (II) aromatics+ PET/PEN, (III) aromatics + oligomers (IV) aromatics + short aliphatic diacids, (V) aromatics + long aliphatic diacids. The foremost results of the analysis can be given as below. DSC analysis shows that some LCPs are materials that have stable LC mesogens under polarized light microscopy. In TGA analysis LCPs that have film formation capacity passed the thermal stability test up to 390oC. NMR results proved that predicted structures of LCPs from feed charged to the reactor are correct. In FTIR due to the inclusion of new moieties, several peaks were labeled in the finger-print range that belongs to reactants. In X-ray analysis, LCP24 (containing PET) was found to be more crystalline than LCP25 (containing PEN) which is due to the symmetrical configuration. Block segments were more pronounced in wholly aromatic LCP2 than LCP24 that has flexible spacers. Another important finding is that, as the amount of the charge to the reactor increases CEG value increases and molecular weight of the product decreases. Selected group V species were employed as reinforcing agent and mixed with the thermoplastics / acrylonitrile butadiene styrene (ABS), nylon6 (PA6), polyethylene terephthalate (PET), polypropylene (PP) and appropriate compatibilizers in micro compounder and twin screw extruder. The blends of them were tested in dog-bone and/or fiber form. In general LCPs do not improve the mechanical properties except in composite application with polypropylene. A significant increase in tensile properties is observed by LCP24 and LCP25 usage. Capillary rheometer studies show that the viscosity of ABS decreases with the inclusion PA6 and LCP2 together. In addition to the composite applications, some LCPs are promising with new usage areas. Such as nano fibers with 200nm diameter were obtained from LCP27 by electrospinning method. The high dielectric constant of LCP29 has shown that it may have application areas in capacitors.

The research presented in this dissertation presents a methodology to experimentally predict and simulate the mechanical behavior of polymers under high strain rate deformation. Specifically, the interplay between the effects of temperature and strain rate on polymer behavior is examined and then used as a tool to help recreate the high rate mechanical response of several different polymers: ranging from rubbers to amorphous polymers to composites. Multiple literature reviews are conducted and presented in this thesis, e.g. experimental mechanics test methods, high rate behavior, time-temperature equivalence, constitutive modeling, and temperature measurement methods. In accordance with mechanical theory, an experimental and analytical protocol in rate- and temperature- dependence was applied to a range of PVC materials ranging in plasticizer contents. Further to this, these PVC materials were modeled with a rubbery model describing the network stress seen in polymer behavior, and an amorphous polymer model to describe PVC low to high rate responses to deformation. This modeling develops insights in the adiabatic nature of high rate response. Time-temperature equivalence, and the temperature rise during adiabatic deformation, are studied and exploited in order to implement a proposed experimental method which simulates the high rate deformation of polymeric materials. The development of an experimental methodology to simulate and predict high rate behavior is presented, applied, and expanded to a range of materials: amorphous polymers (e.g. PVC 20wt% plasticizer, PMMA, PC) and composites (e.g. polymer bonded explosive simulant). The work also presents and highlights the fact that micro to nano-scale imaging may be used in parallel with the simulation method in order to better understand high rate behavior. Furthermore, in result of the studies conducted in this body of work, several novel techniques were developed, or improved upon, and applied to the current research (e.g. additions to time-temperature equivalence, temperature measurement methods at high, moderate, and low strain rates, and a method for measuring the high rate behavior of soft materials).