No description available.

Composite materials have the potential to revolutionize life in the 21st century. They are contributing significantly to developments in aerospace, hydrogen fuel cells, electronics and space exploration today. While a number of composite material processing methods exist, resin transfer molding (RTM) has the potential of becoming the dominant low-cost process for the fabrication of large, high-performance products. RTM has many advantages over alternative processes, including the capability of producing complex 3D shapes with a good surface finish, the incorporation of cores and inserts, a tight control over fiber placement and resin volume fraction and the possibility of embedding sensors into manufactured components for structural health monitoring. Part of the reason RTM has not received widespread use is due to its drawbacks such as its relatively trial and error nature, race tracking, washout, high cycle time and void formation. The basic operation of the process involves loading a fiber reinforcement preform into a mold cavity, closing the mold, injecting resin into the mold and allowing the resin to cure. To study the resin transfer molding process and issues affecting it, a laboratory containing an experimental RTM apparatus has been established. The apparatus has a glass window to observe the mold filling process and can incorporate various mold shapes such as a quasi-2D panel, a 3-D rectangular section and a 3-D semicircular section. To characterize the flow through the molds a commercial CFD software has been used. This thesis describes the establishment of this laboratory and preliminary studies that have been conducted.

- / -

Σκοπός της παρούσας μεταπτυχιακής εργασίας ειδίκευσης είναι η πειραματική μελέτη και η θεωρητική πρόβλεψη των εναπομενουσών μηχανικών ιδιοτήτων, πολυμερών και πολυμερικών σύνθετων υλικών, μετά από χαμηλής ενέργειας επαναλαμβανόμενη κρουστική καταπόνηση. Στα πλαίσια της εργασίας μελετήθηκαν δύο διαφορετικά πολυμερικά υλικά (EP και PMMA) και δύο πολυμερικά σύνθετα υλικά (CFRP και GFRP). Τα δοκίμια από εποξειδική ρητίνη υποβλήθηκαν σε επαναλαμβανόμενη κρούση, με σταθερή ενέργεια κρούσης κάθε φορά, 1.25 Joule, ενώ τα υπόλοιπα δοκίμια σε επαναλαμβανόμενη κρούση, με σταθερή ενέργεια κρούσης 1 Joule. Μετά την κρούση, τα δοκίμια χαρακτηρίστηκαν μηχανικά με στατικά πειράματα κάμψης τριών σημείων, έτσι ώστε να μελετηθεί η υποβάθμιση, τόσο του μέτρου ελαστικότητας σε κάμψη, όσο και η μέγιστη αντοχή τους σε κάμψη, σαν συνάρτηση του αριθμού κρούσεων. Ανάλογα με το υλικό, παρατηρήθηκε και διαφορετικό μέγεθος υποβάθμισης, γεγονός που οφείλεται στη λειτουργία διαφορετικών μηχανισμών αστοχίας. Από θεωρητικής σκοπιάς, εφαρμόστηκαν δύο διαφορετικά μοντέλα πρόβλεψης των εναπομενουσών μηχανικών ιδιοτήτων. Το μοντέλο Παπανικολάου – Σταυρόπουλου και το μοντέλο Πρόβλεψης των Εναπομενουσών Ιδιοτήτων (Residual Property Model – R.P.M.) που εφαρμόστηκαν, έδωσαν αποτελέσματα άκρως ικανοποιητικά, με πολύ καλή σύγκλιση των πειραματικών αποτελεσμάτων με τις θεωρητικές προβλέψεις. / The purpose of the present work was to experimentally investigate the residual strength and stiffness of polymers and polymer-matrix composites and to theoretically predict the observed degradation by means, after low energy repeated impact. Two different types of composites (CFRP and GFRP) and two types of polymers (EP and PMMA), were examined. The plates of epoxy resin were repeatedly impacted with constant amount of impact energy on the order of 1.25 J and the rest of the above materials with constant impact energy on the order of 1.00 J. Afterwards the damaged specimens were tested under three-point bending conditions in order to investigate the degradation of both the bending modulus and strength as a function of the number of impacts. The results showed that there is a characteristic threshold of impact accumulated energy and/or number of repeated impacts, above which an abrupt degradation of the mechanical properties was observed. From theoretical point of view the measured variations were predicted by applying two different models. Namely, the Papanicolaou – Stavropoulos model and second the Residual Property Model (R.P.M.) have been applied in order to predict the observed degradations, using a minimum number of input data (one or two points only). A fair agreement between experimental results and theoretical predictions was found.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της συμπεριφοράς συνθέτων υλικών με τροποποιημένη πολυμερή μήτρα σε υγροθερμικές συνθήκες κόπωσης. Συγκεκριμένα τα υλικά που χρησιμοποιήθηκαν είναι CFRP (Carbon Fiber Reinforced Polymers), δηλαδή σύνθετα υλικά πολυμερικής μήτρας, τα οποία είναι ενισχυμένα με ίνες άνθρακα. Πρέπει να σημειωθεί ότι χρησιμοποιήθηκαν δυο τύποι πολυμερικών συστημάτων. Το πρώτο σύστημα αποτελείται από την εποξειδική ρητίνη LY 564 και τον σκληρυντή Aradur 2954, ενώ το δεύτερο σύστημα αποτελείται από την κυανεστερική ρητίνη Primaset και το σκληρυντή DT-4000. Επίσης και στα δυο συστήματα τα υλικά που κατασκευάστηκαν ήταν μονο-διεύθυντα (UD προς μία διεύθυνση 00), με εξαίρεση ότι στο εποξειδικό σύστημα κατασκευάστηκαν και Quasi υλικά, στο οποίο οι ίνες έχουν προσανατολισμό σε τέσσερις διαφορετικές διεθύνσεις [(0/+45/-45/90)2]s. Όλα τα υλικά περιέχουν συνολικά 16 στρώσεις ινών. Ακόμη η μήτρα των υλικών μας είναι τροποποιημένη, καθώς περιέχει CNTs (Carbon Nano Tubes) νανοσωληνίσκους, σε διαφορετικά ποσοστά. Τα ποσοστά που μελετήθηκαν ήταν 0%, 0,1%, 0,5% και 1% CNTs για τα εποξειδικά UD υλικά, 0% CNTs για τα Quasi και τέλος 0%,0,5% και 1% CNTs για το κυανεστερικό σύστημα. Τα συγκεκριμένα υλικά τοποθετήθηκαν σε ειδικό μπάνιο για 60 ημέρες, που ήταν γεμάτο με απιονισμένο νερό και σε θερμοκρασία 800C. Μελετήθηκε συστηματικά η απορρόφηση υγρασίας μέχρι και τον κορεσμό τους, καθώς και η μεταβολή της ηλεκτρικής αντίστασης των υλικών αυτών. Ακόμη μετά από 60 ημέρες και αφού τα υλικά βγήκαν από το μπάνιο τοποθετήθηκαν σε φούρνο θερμοκρασίας 800C. Σκοπός της διαδικασίας αυτής ήταν η ξήρανση τους, καθώς και η μέτρηση του χρόνου που απαιτείται για την διαδικασία αυτή. Έγιναν επίσης πειράματα δυναμικής-μηχανικής ανάλυσης (DMA), για την μέλετη της μεταβολής της θερμοκρασίας υαλώδους μετάβασης (Tg) για όλα τα στάδια. Αρχικά έγιναν πειράματα DMA σε όλα τα δοκίμια πρίν τοποθετηθούν στο μπάνιο, στην συνέχεια μετά το στάδιο του κορεσμού τους (περίπου στις 20 ημέρες παραμονής τους στο μπανιο), στις 60 ημέρες παραμονής των δοκιμίων στο νερό και τελικά μετά την διασικασία της ξήρανσης. Τέλος έγιναν πειράματα διηλεκτρικής φασματοσκοπίας για να καθοριστεί η ηλεκτρική αγωγιμότητα σε δοκίμια πριν τοποθετηθούν στο μπάνιο, κατά την διάρκεια του κορεσμού τους και τέλος μετά την ξήρανσή τους. / --

The scope of this project is the realization of composite and hybrid sub-aerostructures which exhibit superior blast performance compared to reference composite and hybrid substructures. The scope will be fulfilled with minimum weight penalty. Within the scope of this work is to provide a roadmap for the integration of explicit hardening measures for blast in future aerospace structural components. In the case of blast loading, the proposed methodology for achieving these aims involves vulnerability analysis of the composite and the hybrid substructures (scaled fuselage substructure). The vulnerability analysis will be based on numerical results, obtained by the systematic, analysis of the coupled blast / structural problem. The aims and objectives of the present project can be summarized as follows: • Development of numerical models and their correlation against experimental results. • Development of numerical tools for blast vulnerability analysis of composite and hybrid aeronautic structures • Blast vulnerability map of composite and hybrid scaled fuselage substructure for different charge locations • Explicit blast hardening strategies of composite and hybrid aerostructures by design and by novel materials / Σκοπός της εργασίας αυτής είναι η μελέτη αεροπορικών κατασκευών από σύνθετα υλικά όπου θα παρουσιάζουν βελτιωμένες ιδιότητες υπό συνθήκες έκρηξης σε σύγκριση με υπάρχουσες αντίστοιχες κατασκευές.Ο στόχος αυτός επετεύχθη με ελάχιστη προσθήκη βάρους. Μέσα στους στόχους της παρούσας διατριβής είναι να παρέχει μια μεθοδολογία για την προσθήκη μέσων προστασίας για τις μελλοντικές αεροπορικές κατασκευές.

Made available in DSpace on 2014-06-11T19:27:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-06-18Bitstream added on 2014-06-13T19:34:56Z : No. of bitstreams: 1 souza_sdb_me_guara.pdf: 1970649 bytes, checksum: a6625de42e009df77ca5bff840498408 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O desenvolvimento da tecnologia dos compósitos poliméricos avançados tem como uma de suas funções a união de materiais que combinem características como: elevada resistência mecânica e rigidez aliadas à baixa massa específica. Um dos problemas principais de utilização de compósitos poliméricos em aplicações estruturais consiste em sua união efetiva para a integração de componentes. Neste sentido, estudos recentes mostram que a técnica de soldagem por resistência elétrica é um dos processos mais promissores para união de compósitos, por ser um método rápido e por necessitar de pouca preparação de superfície. Este trabalho tem como objetivo avaliar os melhores parâmetros de soldagem por resistência elétrica para laminados de PPS (poli(sulfeto de fenileno)) reforçados com fibras contínuas (vidro e carbono) e híbrido com aplicações aeronáuticas. Para esta finalidade, são avaliados os parâmetros mais adequados quanto ao tempo, corrente elétrica e pressão a serem utilizados no processo de soldagem. A caracterização dos materiais soldados é realizada por meio de ensaios mecânicos (lap shear), análises térmicas (DMA e TMA) e análise morfológica (microscopias óptica e eletrônica de varredura). Com a utilização do planejamento de experimentos, foi encontrado o melhor valor da variável resposta para cada laminado estudado, e desse modo a melhor combinação dos parâmetros de soldagem, sendo para o PPS/fibras de carbono (37,0A, 3,0MPa, 50,0s), para o PPS/fibras de vidro (32,0A, 1,85MPa, 175,0s) e para o laminado híbrido (38,5ª, 3,0MPa, 50,0s). Com relação à temperatura de transição vítrea dos compósitos, esta não foi afetada significativamente pelo processo de soldagem, viabilizando o método de soldagem estudado para a integração de componentes aeronáuticos / The technology improvement of advanced polymeric composites has as one of its functions the junction of materials that present unique properties such as high strength and stiffness allied with low density. One of the major problems of using polymer composites in structural application consists in the effective joint for integrating components. In this behalf, recent studies demonstrate that the technique of electrical resistance welding is one of the most promising for bonding composites, as a rapid method because it does not require much surface preparation. This work aims to evaluate the more appropriate parameters of electrical resistance welding for PPS (poly (phenylene sulfide)) laminates reinforced with fabric continuous fibers (glass and carbon) designed for aeronautical applications. For this purpose, the parameters will be evaluated leading into account time, electric current and pressure to be used in the welding process. The welded material characterization will be accomplished through mechanical testing (lap shear), thermal (DMA and TMA) and morphological analysis (using optical and scanning electron microscopes). Through the procedure of design of experiments, it was found the best value of the response variable for each laminate studied here, and thus the best combination of welding parameters, being for the PPS/carbon fibers (37.0 A, 3.0 MPa, 50.0s) for the PPS/glass fibers (32.0 A, 1.85 MPa, 175.0 s) and the hybrid laminate (38.5 A, 3.0 MPa, 50.0 s). In relation to the glass transition temperature of these composites, this was not significantly affected by the welding process, enabling the welding method for studying the integration of aeronautical components

Orientador: Vicente Lopes Junior / Resumo: Materiais compósitos têm sido cada vez mais utilizados na indústria aeronáutica, devido a inúmeras vantagens que serão apresentadas nesse trabalho. Entretanto, impactos podem comprometer significativamente a estrutura. Tais impactos podem ocorrer a “baixa velocidade”, através de ferramentas derrubadas e contato com veículos/equipe de manutenção, e também a “alta velocidade”, como colisões com aves, raios elétricos, detritos de pneus ou pequenas pedras na pista. Conhecer a ocorrência e localização dos mesmos, assim como o progresso de danos subsequentes, permite realizar inspeções mais focadas e otimizar o custo e eficiência de manutenção. Este trabalho propõe a utilização de transdutores piezelétricos em formato de rosetas piezelétricas para localização de impacto em estruturas de materiais compósitos. As rosetas são compostas de transdutores retangulares de Macro-Fiber Composite (MFC), que apresentam uma resposta altamente diretiva para ondas ultrassonoras, o que foi explorado para determinar a localização da onda emitida, independente da velocidade de propagação da onda na estrutura. A acuracidade do mé- todo foi demonstrada experimentalmente em uma placa de fibra de carbono/ resina epóxi de dimensões 1060 ×1100×2mm, formada de 13 camadas plain-weave com duas rosetas piezelétricas coladas à superfície via adesivo cianoacrilato. Os impactos foram conduzidos utilizando um pequeno martelo com ponta metálica, simulando impactos realísticos sofridos por uma estrutu... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The usage of composite materials has been experiencing a continuous growth in aeronautic industry, due to countless advantages. However, impacts can significantly compromise the structure. These impacts can occur at "low velocity", by tools dropped, contact with maintenance vehicles or personnel and also at "high velocity", by bird/hail strikes, runaway debris from tires os lightnings. Knowing the occurrence and location of the impacts, as well as the progression of any subsequent damage, allows performing focused follow-up inspections, which can optimize maintenance cost and effectiveness. This work proposes using piezoelectric transducers arranged as rosettes to locate impacts on composite materials structures. The rosettes are comprised of rectangular transducers of Macro-Fiber Composite (MFC), which exhibit an highly directive response to ultrasonic waves that will were explored to determine the source of the incoming wave, regardless of the wave velocity. The accuracy of this method is experimentally demonstrated on a 1060x1100x2mm carbon/epoxy plate, formed by 13 plain-weave layers with two piezoelectric rosettes bounded to the surface via cyanoacrylate. The impacts were carried out using a small hammer with hardened steel tip, simulating realistic impacts suffered by an in-service structure. The impact point is determined by the proposed method and compared with the actual location of impact. / Mestre

Orientadora: Maria Odila Hilário Cioffi / Coorientador: Sérgio Roberto Montoro / Banca: Herman Jacobus Cornelis Voorwald / Banca: Carlos Yujiro Shigue / Resumo: O compósito híbrido surgiu com o objetivo de reduzir a quantidade de materiais de elevado custo e, ao mesmo tempo, manter as elevadas propriedades mecânicas. Além disso, viu-se a possibilidade de, em se usando reforços diferentes, obter um novo material que evidenciasse as vantagens dos reforços e diminuísse as desvantagens simultaneamente. Um importante fator durante o processamento de compósitos poliméricos para aplicação estrutural é o controle da formação de vazios, pois estes atuam como concentradores de tensão. O objetivo deste trabalho foi produzir compósitos híbridos utilizando diferentes disposições de tecidos de fibra de vidro e carbono, sem perda significativa de propriedades mecânicas. Para a produção do compósito, a pré-forma foi inicialmente caracterizada quanto à impregnação, sendo, para isto desenvolvido um modelo analítico geral que determina o parâmetro de permeabilidade dos compósitos híbridos. O modelo foi validado através de teste de permeabilidade e a qualidade dos laminados (híbridos, e não híbridos) foi certificada pelo processamento dos compósitos e pela quantificação da fração volumétrica de vazios. Este projeto propôs, ainda, a melhoria da análise de vazios pela técnica de porosimetria de Hg com auxílio do planejamento de experimentos. Assim foi possível determinar a fração volumétrica de poros abertos e fechados, a distribuição do diâmetro dos poros e a distância entre os poros dos compósitos, em uma análise conjunta com as técnicas de digestão ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Hybrid composite arose with the aim of reducing high cost materials and, at the same time, maintaining mechanical properties suitable for use. In addition, using different reinforcements, a new material could be obtained which would evidence the advantages of the reinforcements and decrease the disadvantages simultaneously. An important factor, during the processing of polymeric composites for structural application, is the voids formation control, since they act as stress concentrators. The aim of this work was to produce hybrid composites using different stacking of glass and carbon fabrics without significant loss of mechanical properties. For the composite manuftacturing, the preform was initially characterized as the impregnation, for which a general analytical model was developed that determines the permeability parameter of the hybrid composites. In addition, the model was validated by conducting permeability test and the quality of several laminates (hybrid, and non-hybrid) was certified by processing them, and voids were quantified thereof. This project also proposed the improvement of voids analysis by the Hg porosimetry technique with the support of design of experimental. Therefore, it was possible to determine the volumetric fraction of open and closed voids, pore diameter distribution and the distance between voids, in an ensemble analysis with acid digestion and optical microscopy. Carbon preform presented high flow resistance; on the other hand, an opposite behavior was observed for the glass preform. The hybrid architecture presented a positive hybrid effect, which means a synergy that provided a higher permeability value. Therefore, optimization in injection time can be achieved, considering a combination of balanced glass and carbon fabrics. The analytical model was enabled to predict the flow front behavior by showing ...(Complete abstract click electronic access below) / Mestre

Any composite material is made up from two or more materials and therefore contains interfaces, which usually represent planes of weakness. Interfacial fractures are effectively constrained to propagate along these interfaces as mixed-mode fractures with all three opening, shearing and tearing actions (i.e. mode I, mode II and mode III), instead of kinking to maintain pure-mode-I conditions at the advancing crack front, as would typically happen in an isotropic material. This is significant because mixed-mode fracture toughness is load-dependent and not a purely intrinsic material property (although clearly the pure mode fracture toughnesses are indeed intrinsic material properties that can be determined experimentally). Therefore, in order to know the fracture toughness under general loading conditions, it is necessary to know both the interface failure criterion (that describes the fracture toughness as a function of the mode mixity), and the mode mixity of the crack under the specified loading conditions. This is a complex problem that has occupied researchers in the fracture mechanics community for decades. Consequently, the literature contains a large number of different mixed-mode partition theories. This work appears to show that, of all the partition theories assessed, Wang and Harvey s (2012a) Euler beam partition theory is able to most accurately predict the fracture toughness of a mixed-mode delamination in a fibre-reinforced polymer composite laminate. This statement is based on the outcomes of three separate studies: The first study uses data reported in the literature from a thorough programme of mixed-mode fracture testing of unidirectional and multi-directional laminates. The Euler beam partition theory is able to accurately predict the fracture toughness in all cases. Furthermore, the Euler beam partition theory, which is completely analytical, closely agrees over a large domain with Davidson et al. s (2000) independently-derived non-singular field partition theory, which was derived with the aid of experimental test results. In general, the singular-field approach based on 2D elasticity and the finite element method give poor predictions. In the second study, an original programme of mixed-mode fracture testing is carried out, which incorporates several novel aspects including new test apparatus and a methodology for testing with a wide range of applied pure bending moments. Eighty five fracture tests are performed on unidirectional glass/epoxy laminates to determine the initiation and propagation fracture toughnesses. Although the second study was inconclusive with respect to the correctness of any particular partition theory, the development of the test apparatus and test methodology are considered to be major contributions that will be useful for both design engineers and academic researchers, not only working with fibre-reinforced polymer composite laminates, but also working with other composite materials containing interfacial cracks. The third study uses digital image correlation to investigate the near-crack tip strain fields of mixed-mode delaminations to try to discover the underlying mechanics that govern the selection of a mixed-mode partition theory. The new testing apparatus is used again, and another novel testing methodology is developed. The work appears to confirm (with some caveats) that two sets of pure modes exist, that is, two pure mode I modes, and two pure mode II modes, with their numerical values roughly corresponding to those from Wang and Harvey s (2012a) Euler beam partition theory. It should be noted that, as far as the author s knowledge is concerned, Euler beam partition theory is the only one in the literature to predict the existence of two sets of pure modes. Although this work set out to conclusively determine which mixed-mode partition theory is able to most accurately predict the fracture toughness of a mixed-mode delamination in a fibre-reinforced polymer composite laminate, and also, to discover why, the outcomes cannot truly be called conclusions . Rather, they only offer strong support for Wang and Harvey s (2012a) Euler beam partition theory for predicting the fracture toughness fibre-reinforced polymer composite laminates against delamination. Despite this, the work makes major contributions that will be useful for both design engineers and academic researchers in the field, as described in the above.