Dissertations / Theses on the topic 'Fractura interlaminar'

Os compósitos de matriz polimérica são actualmente utilizados num vasto campo de sectores de actividade, que vão desde a electrónica de grande consumo até às indústrias aeronáutica e espacial. Apesar dos progressos conseguidos, subsistem alguns obstáculos à generalização das aplicações estruturais de compósitos, associados aos elevados custos dos materiais e à complexidade do comportamento mecânico. Na realidade, devido a lacunas no conhecimento dos mecanismos de dano e de ruína, há um enorme potencial de optimização de estruturas compósitas. Um dos modos de dano mais perigoso dos laminados compósitos de alto desempenho é a delaminagem. Após inúmeros estudos publicados, estão disponíveis normas que permitem caracterizar a resistência à delaminagem de compósitos unidireccionais. Porém, na grande maioria das aplicações estruturais usam-se laminados multidireccionais e as delaminagens tendem a formar-se entre camadas de diferentes orientações. O objectivo principal deste trabalho foi por isso caracterizar a resistência à delaminagem de laminados multidireccionais, nomeadamente avaliar a influência da orientação das camadas adjacentes à delaminagem. Atendendo à importância prática das solicitações e dos materiais, foram realizados ensaios de modo I “double cantilever beam” (DCB), de modo II “end-notched flexure” (ENF) e de modo misto I+II “mixed mode bending” (MMB), em provetes vidro/epóxido e carbono/epóxido. Os provetes escolhidos tinham interfaces de delaminagem dos tipos 0/θ e θ/−θ, sendo θ variável entre 0 e 90 graus. A componente experimental foi amplamente suportada por modelação tridimensional com elementos finitos. Os resultados mostraram ser possível evitar fenómenos espúrios de dano intralaminar em ensaios de modo II. Todavia, em modo I, foi frequentemente possível medir apenas taxas críticas de libertação de energia, GIc, de iniciação. Por outro lado, verificou-se que à interface 0/0 corresponderam geralmente os menores valores de GIc e GIIc, e que a interface de delaminagem afectou mais esta última. Finalmente, em modo misto I+II, Gc variou de forma aproximadamente linear com a fracção de modo II, GII/G, embora se tenha constatado alguma ambiguidade na partição de modos em provetes carbono/epóxido.
Polymer matrix composites are nowadays widely used in a vast range of applications, from consumer electronics to aircraft and aerospace industries. However, in spite of the enormous progress, the spreading of structural applications still faces obstacles associated to high material costs and complex mechanical behaviour. In fact, the present unability to master composite damage mechanics leaves an enormous potential for optimization of composite structures. Delamination is considered one of the most dangerous damage modes of high performance laminated composites. Following numerous published studies, standards are currently available for the measurement of the delamination resistance of unidirectional laminates. However, the vast majority of structural applications involves multidirectional laminates and delaminations are seen to occur between differently oriented plies. The main objective of this work was therefore to characterise the delamination resistance of multidirectional laminates. The emphasis was on evaluating the effect of the orientation of delaminating plies on toughness. In view of the practical importance of the loadings and materials, mode I “double cantilever beam” (DCB), mode II “end-notched flexure” (ENF) and mixed-mode I+II “mixed mode bending” (MMB) tests were performed on glass/epoxy and carbon/epoxy laminates. Selected specimens had delaminations in 0/θ and θ/−θ type interfaces, θ varying between 0 and 90 degrees. The experimental component was supported by extensive threedimensional finite element modelling. The results showed it was possible to avoid spurious intraply damage phenomena in mode II tests. However, it was frequently only possible to measure mode I critical strain energy release rates, GIc, for initiation. On the other hand, it was seen that the 0/0 interface had the lowest GIc and GIIc values. Moreover, the latter was more sensitive to the delamination interface. Finally, under mixed-mode I+II, Gc varied quasi linearly with the mode II ratio, GII/G, although there was some mode partitioning ambiguity in carbon/epoxy specimens.

[ES] El presente trabajo de investigación se enmarca dentro del campo de los materiales compuestos o composites de resina viniléster y tejido de alto gramaje (780 g/m2) de fibra de vidrio E. Más concretamente esta resina viniléster es relativamente novedosa y no existe mucha investigación al respecto de ella, su novedad radica en que contiene en su cadena una segmentación uretano que le confiere propiedades más elásticas que sus homónimas de bisfenol-A tradicionales. Cada vez más las resinas viniléster están introduciéndose en mercados donde las resinas epoxi eran las indiscutibles dueñas. El desarrollo de estas nuevas resinas de mejor tixotropía y resistencia a los agentes básicos puede ayudar a incrementar su uso en refuerzos estructurales, así como en elementos que tengan per se su naturaleza alcalina, como puede ser el hormigón. Si bien, los fabricantes de resinas no suelen dar valores de resistencia al agrietamiento interlaminar o de tenacidad a la fractura, es uno de los valores más representativos a la hora de poder evaluar la adherencia entre fibra y matriz. En el caso de fracturas en modo de cizallamiento interlaminar que es como más comúnmente pueden generar el fallo los típicos composites de matriz termoestable, existe literatura científica al respecto, pero no de esta nueva resina. El presente trabajo tiene como objetivos el caracterizar el comportamiento a fractura interlaminar por carga en Modo II de los compuestos de resina viniléster-uretano reforzada con tejido de fibra de vidrio y curados a diferentes ciclos de temperatura para optimizar el proceso productivo de fabricación del composite. Así como estudiar el efecto de la degradación por inmersión prolongada en medios químicos, con carácter básico, de este nuevo material, simulando ambientes habituales de exposición causados por el exudado de hormigón a temperatura ambiente y a alta temperatura de servicio y también embebiendo este material en hormigón autocompactante. Este trabajo nos ha permitido caracterizar y cuantificar la influencia de la etapa de curado realizada para reducir el plazo de procesado del composite, en los indicadores de resistencia y de tenacidad a la deslaminación en un material compuesto de viniléster de segmento uretano. Se ha establecido que para esta resina, entre las propiedades mecánicas estáticas, la resistencia a deslaminación por cortadura o cizalladura, ¿, es la menos sensible al proceso de curado y al tiempo de degradación. También la tasa de relajación de energía por deformación se encuentra dentro de las características menos sensibles a los envejecimientos utilizados, así como al ambiente básico del hormigón. Características muy interesantes pues las tradicionales resinas bisfenol-A son muy sensibles a la basicidad del hormigón.
[CAT] El present treball de recerca s'emmarca dins el camp dels materials compostos o compòsits de resina vinilèster i teixit d'alt gramatge (780 g / m2) de fibra de vidre E. Més concretament aquesta resina vinilèster és relativament nova i sobre la qual no hi ha molta investigació, la seva novetat radica en que conté en la seva cadena una segmentació poliuretà que li confereix propietats més elàstiques que les seves homònimes de bisfenol-a tradicionals. Cada vegada més les resines vinilèster estan introduint-se en mercats on les resines epoxi eren les indiscutibles propietàries. El desenvolupament d'aquestes noves resines de millor tixotropia i resistència als agents bàsics pot ajudar a incrementar el seu ús en reforços estructurals, així com en elements que tinguen per se naturalesa bàsica, com pot ser el formigó. Ara bé, els fabricants de resines no solen donar valors de resistència a l'esquerdament interlaminar o de tenacitat a la fractura, és un dels valors més representatius a l'hora de poder avaluar l'adherència entre fibra i matriu. En el cas de fractures en mode de cisallament interlaminar que és com més comunament poden generar la decisió els típics composites de matriu termoestable, hi ha literatura científica sobre aquest tema, però no d'aquesta nova resina. El present treball té com a objectius caracteritzar el comportament a fractura interlaminar per càrrega en mode II dels compostos de resina vinilèster-uretà reforçada amb teixit de fibra de vidre i curats a diferents cicles de temperatura per optimitzar el procés productiu de fabricació del compòsit. Així com estudiar l'efecte de la degradació per immersió prolongada en mitjans químics, amb caràcter bàsic, d'aquest nou material, simulant ambients habituals d'exposició causats pel exsudat de formigó a temperatura ambient i a alta temperatura de servei i també embevent aquest material en formigó autocompactant. Aquest treball ens ha permès caracteritzar i quantificar la influència de l'etapa de curat realitzada per reduir el termini de processament del composite, en els indicadors de resistència i de tenacitat a la deslaminació en un material compost de vinilèster de segment uretà. S'ha establert que per a aquesta resina, entre les propietats mecàniques estàtiques, la resistència a deslaminació per tall o cisallament, ¿, és la menys sensible al procés de curat i al temps de degradació. També la taxa de relaxació d'energia per deformació es troba dins de les característiques menys sensibles als envelliments utilitzats, així com l'ambient bàsic del formigó. Característiques molt interessants ja que les tradicionals resines bisfenol-A són molt sensibles a la basicitat del formigó.
[EN] This research work is part of the field of vinyl ester resin composites and composites and high grammage (780 g/m2) glass fiber E. More specifically, this vinylester resin is relatively new and there is not much research Regarding it, its novelty lies in that it contains a polyurethane segmentation in its chain that gives it more elastic properties than its traditional bisphenol-A homonymous. More and more vinylester resins are entering markets where epoxi resins were the undisputed owners. The development of these new resins of better thixotropy and resistance to basic agents can help to increase their use in structural reinforcements, as well as elements that have per-se its basic nature, such as concrete. Although, the manufacturers of resins do not usually give values of resistance to the cracking interlaminar or of tenacity to the fracture, it is one of the most representative values when it comes to being able to evaluate the adherence between the fiber and the matrix. In the case of fractures in the interlaminar shear mode, which is the most common form in which the fault can generate the typical thermostable matrix composites, there is scientific literature on this, but not this new resin. The objective of this work is to characterize the behavior to interlaminar fracture toughness in Mode II of vinyl ester-urethane resin composites reinforced with fiberglass fabric and cured at different temperature cycles to optimize the production process of manufacturing of the composite. As well as studying the effect of the degradation by prolonged immersion in chemical means, with basic character, of this new material, simulating habitual atmospheres of exposure caused by the exudate of concrete at room temperature and high temperature of service and also imbibing this material in self-compacting concrete. The present investigation has allowed us to characterize and quantify the influence of the curing stage carried out to reduce the processing time of the composite, in the indicators of resistance and tenacity to delamination in a vinyl ester compound of urethane segment. It has been established that, for this resin between the static mechanical properties: the resistance to delamination by shearing or shearing, ¿, is the least sensitive to the curing process and to the degradation time. Also, the rate of relaxation of energy by deformation is found within the characteristics less sensitive to the aging used, as well as to the basic environment of the concrete. Very interesting characteristics because the traditional bisphenol-A resins are very sensitive to the basicity of concrete.
Navarro Muedra, A. (2020). Durabilidad a fractura interlaminar de composites de viniléster-poliuretano con tejido 2d de alto gramaje en vidrio E [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/138395
TESIS

NSM strengthening technique under the influence of temperature and relative humidity, in which the interaction between materials involved is analyzed, is studied in this PhD. Therefore, this work is aimed at contributing to a better knowledge about short – term bond behaviour of NSM Carbon FRP (CFRP) bars reinforcement Systems. The influence of temperature and relative humidity on the short-term bond behavior is analysed and an analytical model, based on the fracture mechanical apporach to determine bond toughness according to the failure mode, is developed. To achieve the goal, an experimental campaign with two series has been carried out. Single shear pull-out concrete blocs strengthened with NSM CFRP bars have been conducted. The experimental results of experimental test campaign, together with the application of development analytical model, are used to characterize the fracture bond behavior
Aquesta tesi és un estudi del comportament adherent instantani entre el reforç de CFRP (de l’anglès, Carbon fiber reinforced polymer) i el formigó, mitjançant la tècnica de reforç NSM (de l’anglès, Near – Surface Mounted), on s’analitza la interacció entre els tres constituents: barres de CFRP, adhesiu i formigó, sota diferents condicions de temperatura i humitat relativa. Per tant, l’objectiu d’aquest treball és contribuir a la millora del coneixement analitzant la influència de la temperatura i humitat relativa en el comportament de la unió i desenvolupant un model analític basat en la mecànica de fractura per a determinar la tenacitat de la unió en funció del mode de ruptura. Per assolir-lo, s’ha realitzat una campanya experimental formada per dues sèries executant assajos de pull-out directe. Amb els resultats experimentals juntament amb el model analític desenvolupat, s’ha caracteritzat el comportament a fractura de la unió
Programa de Doctorat en Tecnologia

[EN] The research represented by this thesis deals with bisphenol-A epoxy vinyl ester resin (VEBA) composite materials reinforced with E-fiberglass fabric of medium weight (450 g/m2) and quasi-orthotropic 0-90°/±45° configuration. The increasing use of vinyl ester resin is due to the advantageous combination of their physical, chemical and mechanical characteristics, which makes it economic and competitive in certain technological applications traditionally reserved for epoxy resins. The use of glass fiber reinforcements extends its applicability as structural material not only in the fields of chemical, industrial and marine engineering but also in civil construction. Manufacturers of VE resin do not provide the following information: interlaminar crack strength of composites, properties of reinforcements different from mat, durability of the material until structural failure and collapse due to delamination. On the other hand, low cost manufacturing and not amortizable production infrastructure, or producing a material in situ to repair any infrastructure damages where it is not feasible to supply sufficient energy for curing composite, which is another aspect not widely established by research publications concerning the influence on the mechanical properties achieved by the composite. The given thesis aims: to characterize the interlaminar mode II fracture behavior of the composite (VEBA/0-90º±45º)4 cured at low temperature; quantify the influence of curing temperature on interlaminar mechanical characteristics; determine the mechanism of influence of curing temperature on the toughness in Mode II; establish durability of the composite during Mode II delamination in severe conditions of prolonged exposure to high temperature (95 °C) and also connections between durability and the temperature of curing. The mechanical characterization: flexural, interlaminar shear and Mode II interlaminar fracture strengths and fractographic, calorimetric and thermogravimetric studies indicate that the composites cured at low temperatures (20 to 50 °C) have better mechanical properties than composites with mat, and very close to the 0-90º taffeta ones. The curing temperature influences the resistance against delamination and the loss of those mechanical properties by prolonged exposure to high temperature. Shear strength and interlaminar fracture toughness properties are the most sensitive mechanical characteristics. Even with low curing temperature, the resin VEBA maintains good resistance to prolonged thermal degradation. Curing at 50 ° C makes possible low cost manufacturing and reparation in situ.
[ES] El trabajo de investigación que conforma esta publicación se inscribe en el campo de los materiales compuestos de resina viniléster de segmento epoxy-bisfenol A (VEBA), reforzada con tejido de medio gramaje (450 g/m2) en fibra de vidrio E, y configuración cuasi ortotrópica 0-90º±45º. El uso creciente de la resina viniléster viene dado por la combinación ventajosa de sus características mecánicas, químico-físicas, y económicas que la hace competitiva en algunas aplicaciones tecnológicas tradicionalmente reservadas para las resinas epoxy. La introducción de refuerzos de fibra de vidrio incrementa su aplicabilidad estructural a sectores no solamente de la ingeniería química, industrial, naval sino también de la construcción civil. Los fabricantes de resinas VE no aportan información sobre propiedades resistentes al agrietamiento interlaminar de compuestos, ni sobre otras tipologías de refuerzo diferentes a mat, ni de la durabilidad del material frente al fallo y colapso estructural por delaminación. Por otro lado, la fabricación en condiciones de bajo coste e infraestructura de producción no amortizable, o elaboración in situ con fines de reparación de desperfectos en instalaciones, donde no es factible un aporte energético suficiente para curado del compuesto, es otro aspecto no tratado por publicaciones de investigación en cuanto a la influencia sobre las propiedades mecánicas alcanzadas por el compuesto. La presente publicación tiene como objetivos para el compuesto (VEBA/0-90º±45º)4 caracterizar su comportamiento a fractura interlaminar por carga en Modo II, cuantificar la influencia de la temperatura de curado en las características de tenacidad a fractura del material compuesto, determinar el mecanismo de influencia de la temperatura de curado en la tenacidad del material en Modo II, y establecer la durabilidad del compuesto a la delaminación en Modo II para condiciones severas de exposición prolongada a alta temperatura (95 ºC) y relación de la misma con respecto a la temperatura de la etapa de curado. La caracterización mecánica a flexión, cizalladura interlaminar, fractura interlaminar en modo II, y el estudio fractográfico, calorimétrico y termogravimétrico indican que el compuesto curado a bajas temperaturas (20 y 50 ºC) tiene buenas características mecánicas, superiores a los compuestos con mat, y muy cercanas a los tafetán 0-90º. La temperatura de curado tiene influencia en el comportamiento contra la delaminación, y frente a la merma de éstas por exposición prolongada a alta temperatura. Resistencia a cizalladura y tenacidad a fractura interlaminar son las propiedades más sensibles. En estas condiciones de curado, la resina VEBA mantiene una buena resistencia a la degradación térmica. Curar a 50 ºC hace factible la reparación o elaboración in situ.
[CAT] El treball d'investigació que conforma esta tesi doctoral s'inscriu en el camp dels materials compostos de resina viniléster de segment epoxy-bisfenol A (VEBA) , reforçada amb teixit de mig gramatge (450 g/m2) en fibra de vidre E, i configuració quasi ortotrópica 0-90º±45º. L'ús creixent de la resina viniléster ve donat per la combinació avantatjosa de les seues característiques mecàniques, quimicofísiques, i econòmiques que la fa competitiva en algunes aplicacions tecnològiques tradicionalment reservades per a les resines epoxy. La introducció de reforços de fibra de vidre incrementa la seua aplicabilitat estructural a sectors no sols de l'enginyeria química, industrial, naval sinó també de la construcció civil. Els fabricants de resines VEU no aporten informació sobre propietats resistents al clavillament interlaminar de compostos, ni sobre altres tipologies de reforç diferents de mat, ni de la durabilitat del material enfront de la fallada i col·lapse estructural per delaminación. D'altra banda, la fabricació en condicions de baix cost i infraestructura de producció no amortitzable, o elaboració in situ amb fins de reparació de desperfectes en instal·lacions, on no és factible una aportació energètica suficient per a curat del compost, és un altre aspecte no tractat per publicacions d'investigació quant a la influència sobre les propietats mecàniques aconseguides per el compost (VEBA/0-90º±45º)4 caracteritzar el seu comportament a fractura interlaminar per càrrega en Mode II, quantificar la influència de la temperatura de curat en les característiques de tenacitat a fractura del material compost, determinar el mecanisme d'influència de la temperatura de curat en la tenacitat del material en Mode II, i establir la durabilitat del compost a la delaminación en Mode II per a condicions severes d'exposició prolongada a alta temperatura (95 ºC) i relació de la mateixa respecte a la temperatura de l'etapa de curat. La caracterització mecànica a flexió, cizalladura interlaminar, fractura interlaminar en mode II, i l'estudi fractográfico, calorimètric i termogravimétrico indiquen que el compost curat a baixes temperatures (20 i 50 ºC) té bones característiques mecàniques, superiors als compostos amb mat, i molt pròximes als tafetà 0-90º. La temperatura de curat té influència en el comportament contra la delaminación, i enfront de la minva d'estes per exposició prolongada a alta temperatura. Resistència a cizalladura i tenacitat a fractura interlaminar són les propietats més sensibles. En estes condicions de curat, la resina VEBA manté una bona resistència a la degradació tèrmica. Curar a 50 ºC fa factible la reparació o elaboració.
Sánchez Bolinches, A. (2016). INFLUENCIA DE LA ETAPA DE CURADO A BAJA TEMPERATURA EN EL COMPORTAMIENTO A FRACTURA EN MODO II DE COMPOSITES VINILESTER-BPA Y SU DURABILIDAD EN CONDICIONES EXTREMAS DE TEMPERATURA [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63665
TESIS

The rate sensitivities of mode-I and mode-II fracture toughness, in the form of GIc and GIIc of Toray T800S/3900 carbon unitape/epoxy, T700G/3900 Plain weave carbon fabric/epoxy, and Newport NB321/7781 fiberglass/epoxy materials were investigated experimentally. Static and dynamic tests, with stroke rates ranging from 8.33×10-4in/s to 100in/s, were conducted on double cantilever beam and end notch flexure specimens. Both [0°] N and [±45°] N laminates were studied in this investigation. The rate sensitivities were characterized in terms of the initiation fracture toughness and crack growth resistance. The average mode-I initiation fracture toughness, GIc of NB321/7781 [0°] laminate was observed to decrease with stroke rate from 6.5lbf-in/in2 to 4lbf-in/in2 and further increased to 6lbf-in/in2 over a range of 5 decades of crack opening displacement rates. The resistance tended to be constant with crack length for the low rate tests. At higher rates, the resistance decreased gradually. The tests data indicated ductile stable and brittle unstable behavior with a transition stick-slip behavior. The average mode-II fracture toughness of the NB321/7781 [0°] laminate was observed to increase from 12lbf-in/in2 to 17lbf-in/in2 over the entire range of 5 decades of shear displacement rates. The fracture behavior was observed to be brittle stable at all rates. The NB321/7781 [±45°] laminate’s opening mode initiation toughness was observed to decrease from 9lbf-in/in2 to 3lbf-in/in2 and further increased to 4lbf-in/in2 over a range of 5 decades of crack opening displacement rates. The delamination resistance increased with crack length for the low rate tests. At higher rates, the resistance decreased gradually. The fracture behavior transitioned from ductile stable to brittle unstable. The opening mode initiation toughness of T700G/3900 [0°] laminate decreased from 3.5lbf-in/in2 to 2lbf-in/in2 and further increased to 3.2lbf-in/in2 over a range of 5 decades of viii crack opening displacement rates. The delamination resistance indicated constant pattern irrespective of the stroke rates. The fracture behavior at low rates indicated transition stick-slip behavior, whereas brittle unstable behavior was evident at higher rates. The mode-II fracture toughness tended to be constant at 4.5lbf-in/in2 over a range of 5 decades of shear displacement rates. Brittle stable fracture behavior was observed at all rates. The opening mode initiation toughness of T700G/3900 [±45°] laminate was observed to decrease from 2.75lbf-in/in2 to 1.8lbf-in/in2 and further increased to 2.8lbf-in/in2 over a range of 5 decades of crack opening displacement rates. The delamination resistance tended to increase with crack length at lower rates, whereas it tended to decrease at higher rates. The fracture behavior indicated transition stick-slip behavior at lower rates, whereas brittle unstable behavior was evident at the highest rate tested. The T800S/3900 [0°] laminate’s opening mode initiation toughness was observed to steadily decrease from 5lbf-in/in2 to 2.5lbf-in/in2 over a range of 5 decades of crack opening displacement rates. The delamination resistance was observed to increase with crack length at lower rates, whereas it tended to decrease gradually at higher rates. Brittle stable fracture behavior was observed at all rates. Fiber bridging was prominent with an increase in test rates. The mode-II fracture toughness increased steadily from 9lbf-in/in2 to 20lbf-in/in2 over a range of 5 decades of shear displacement rates. Brittle stable fracture behavior was observed at all rates.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.

The main objective of this research is to understand the mechanisms of interlaminar toughness using non-woven veils as the interleaf materials. The vacuum assisted resin transfer moulding (VaRTM) method was chosen for making specimens. Several types of non-woven veils were used as the toughening materials, because the non-woven veil was expected for good resin permeability. Three types of carbon fabrics, (plain, 5-harness satin, and unidirectional) and two types of resins (epoxy and vinyl ester) were selected for base materials. Firstly, the Mode-I and Mode-II interlaminar toughness tests, which are double cantilever beam (DCB) and four-point end notched flexure (4ENF) tests, were carried out to evaluate the effect of toughening by the interleaf veils. The mechanisms of the improvement by the interleaf veils were evaluated by microscopy. The adhesion between veil fibres and matrix is an important factor of the improvement of the interlaminar toughness. If veil fibres have poor adhesion to resin, these fibres would be pulled out from the matrix and work as fibre-bridging. In contrast, good adhesion of veil fibres is not necessary improvement of the interlaminar fracture toughness. Because these fibres are embedded in the matrix and interleaf veil cannot contribute to suppression of the crack propagation. The second stage of experiments was impact and compression after impact (CAI) tests. In this stage, the base materials were plain weave fabric only. Impact damage was evaluated using ultrasonic C-scan. The polyamide veils interleaved samples had superior impact and CAI resistance properties in all interleaved materials. In the final stage, correlation between each mechanical property was analysed and discussed. It was found that the relationship between each fracture toughness is affected by fabric and resin. Moreover, this work and previous literature data were compared. It can be found that the non-woven veils are effective toughening materials.

This thesis addresses the influence of veil architecture on interlaminar fracture toughness (IFT) of interleaved unidirectional (UD) carbon fibre-epoxy composites with the aim to provide insights. Two nonwoven veils sets formed from polyphenylene sulfide (PPS) fibres with different diameters, with a range of increasing areal density, and a sample of polyetheretherketone (PEEK) fibres, with comparable fibre diameter, are characterised gravimetrically and by tensile tests (long and zero span). Consequently, the anisotropy and maximum stress transfer efficiency (MSTE) parameters are shown by these veils. Subsequently, the veils are interleaved within UD composites and assessed for mode I and mode II IFT. In both modes the veils show a strong dependence on areal density before a plateau at high areal densities, although the lower diameter fibres showed higher IFT values. Interpretation of the results reveal that the difference is attributable to the coverage of veils and thus, to the fraction of fibres in the propagation of crack. However, the effect of fibres is quite evident through the fibre bridging mechanism in the propagation of cracks, more significantly in mode I than in mode II. Moreover, in mode I and mode II a linkage of MSTE of veils with low data variability in IFT is observed. With regard to the anisotropy, this is notably significant only for the PEEK sample, though a statistical analysis supports that the IFT values from both types of fibres are consistent. A comparison of data revealed a slight dependence of the ratio mode II/mode I on areal density only for the larger diameter PPS fibre and the anisotropy of PEEK sample has a strong influence on this ratio. In both modes, however, data presented by this study are consistent with data provided by previous work. Subsequently, mass distribution of veil handsheets is assessed for both modes of IFT into UD composites, revealing no significant dependence of mass distribution on mode I IFT, whereas for mode II this dependence is significant due to the effect a variety of fractional open area size and the floculatted fibres. Fractographic observations via SEM (Scanning Electro Microscope) from representative interleaved composites are analysed and discussed.

Natural fibre reinforced composites have been extensively used in non-structural components, mainly in automotive industry. For these composites to be used in structural applications, an understanding of fracture toughness behaviour is important. In this study, the influence of water absorption and hybridisation of flax and flax/basalt hybrid laminates are presented with the aim to investigating the Mode I and Mode II interlaminar fracture toughness characteristics. Four types of composite laminates namely, neat vinyl ester (neat VE), flax fibre reinforced vinyl ester (FVE), flax fibre hybridised basalt unstitched (FBVEu) and flax hybridised basalt stitched (FBVEs), were fabricated by vacuum assisted resin infusion technique. Double cantilever beam (DCB) and Three-point-end-notched flexure (3ENF) tests were performed to evaluate the critical strain energy release rates, GIC and GIIC (initiation and propagation) as well as the crack length (R-curve) in dry and wet conditions by using different data reduction methods. The morphology of delamination and the fracture shear failure of composite laminates were evaluated using scanning electron microscopy (SEM) and X-ray micro computed tomography (μCT). From the experimental results, it was found that the Mode I fracture toughness initiation GIIC init. and propagation GIIC prop. of water immersed FVE composites were decreased by an average of 27% and 10% respectively, compared to the dry specimens, whereas the fracture toughness propagation of water immersed FBVEu and FBVEs composites were increased by approximately 15% and 17% compared to dry specimens. The results of Mode II fracture toughness obtained experimentally exhibited that the fracture energy of FBVEu composites, GIIC init. and GIIC prop. were improved by 58% and 21%, respectively compared to that of FVE dry specimens. Moisture absorption behaviour caused an increase in the ductility of matrix which resultantly improved the resistance to crack initiation. However, there was a reduction in the fibre/matrix interfacial strength of FBVEu wet composites and a deterioration in the delamination resistance to crack propagation. The critical strain energy release rate of neat VE increased about 52% with reinforcement of flax fibre composites. The fracture mechanisms showed energy dissipation through matrix deformation, fibre pull-out, fibre debonding, and fibre breakage. The experimental results confirmed that basalt fibre hybridisation enhanced the durability and water repellence behaviour of flax fibre reinforced composites. Finally, this thesis provides a unique manufacturing technique to improve the interlaminar fracture toughness of flax fibre and flax/basalt hybrid composite laminates to be used in load bearing applications as an alternative to E-glass fibre reinforced composites. The outcomes of this study will be beneficial to automotive, marine and construction industries. In addition, the findings of this study will be useful for academic and researchers who are involved in the research and development of sustainable composites for light-weight structural applications.

Le sujet de cette étude est le développement de séquences d’empilement pour la conception d'éprouvettes multidirectionnelles en matériaux composite à matrice polymère destinées à des essais de délaminage.Ces séquences permettent d’obtenir des éprouvettes multidirectionnelles qui, dans le cadre de la théorie classique des stratifiés, montrent un comportement thermoélastique qui reproduit celui des composites unidirectionnels : elles sont complètement libres de tout type de couplage élastique et ils ne développent pas des déformations résiduelles dues au cycle de cuisson.Par ailleurs, ces empilements permettent de tester n’importe quelle interface de délaminage.La conception de ces empilements est basée sur les solutions Quasi-Triviales (QT).Un algorithme pour la création d’une base de données de ces solutions a été conçu et implémenté.Grace à cela, un nombre plus grand de solutions QT et des solutions QT avec un nombre plus grand de plis que dans des études précédentes ont été trouvées.Ensuite, des critères analytiques permettant d’obtenir de nouvelles solutions à partir de la superposition des solutions connues ont été établis.Ces critères permettent d’obtenir des séquences QT avec n’importe quel nombre de couches.En combinant les solutions QT, les principes usuels de conception des stratifiés et les critères de superposition, les séquences d’empilement Fully-Uncoupled Multi-Directional (FUMD) ont été obtenues.Pour évaluer les propriétés des éprouvettes de délaminage obtenues avec ces séquences, un modèle Éléments Finis d’une éprouvette Double Cantilever Beam (DCB) a été développé pour comparer le comportement d’une séquence FUMD à celui d’autres séquences proposées dans la littérature pour les essais de délaminage.En utilisant la méthode de refermeture (Virtual Crack Closure) dans ses formulations originale et révisée, les distributions du taux de restitution d’énergie (Energy Release Rate) et ses partitions modales ont été évaluées.La séquence FUMD démontre les meilleurs résultats.Finalement, une campagne expérimentale de caractérisation du délaminage en mode I a été menée.Des éprouvettes DCB avec des séquences FUMD ont été conçues et fabriquées.Des plis tissés déséquilibrés ont été utilisés pour réduire la probabilité de changement de plan de délaminage.Les rotations des bras des éprouvettes et la forme du front du délaminage ont été étudiés pour évaluer la capacité des éprouvettes à garantir un comportement mécanique optimal lors du test de délaminage en mode I.Les résultats obtenus avec les éprouvettes FUMD sont proches de ceux obtenus avec les éprouvettes unidirectionnelles.En ce qui concerne l'énergie de rupture, les éprouvettes ayant la même interface de délaminage ont montré des valeurs très proches, même si leur rigidité était sensiblement différente.Par ailleurs, la caractérisation d'interfaces différentes a abouti à des énergies de rupture différentes, résultants des modes de ruptures non identiques.Ce travail ne représente qu'une étude préliminaire et des recherches complémentaires sont nécessaires.Néanmoins les éprouvettes de délaminage FUMD ont démontré un bon potentiel, et sont intéressantes pour les essais de délaminage
The object of this study is the development of a novel class of stacking sequencesfor the design of multidirectional polymer matrix laminated composite specimens for interlaminar fracture toughness (or delamination) tests. These sequences allow to obtain multidirectional specimens that, in the framework of Classic Laminated Plate Theory, have a thermo-elastic behaviour that closely matches that of unidirectional specimens: they are completely free from elastic couplings and they do not develop laminate-level thermally-induced deformations due to the curing process. Furthermore, they allow to test delamination interfaces between plies of any desired orientation. Because of their properties, they were labelled Fully-Uncoupled Multi-Directional (FUMD).In order to design these layups, Quasi-Trivial (QT) solutions were exploited.Firstly, an algorithm for the creation of a database of such solutions was conceived and implemented.Thanks to it, more and longer QT solutions were found than in previous studies.Then, analytical rules were established allowing to obtain new QT solutions from the superposition of known ones.These criteria allow to obtain QT sequences of any desired length, thus overcoming existing computational limitations arising when searching for QT solutions using the algorithm.Combining QT solutions with a few basic laminate design principles and the superposition criteria, FUMD stacking sequences are designed.In order to assess the properties of delamination specimens obtained with FUMD layups, a Finite Element model of a Double Cantilever Beam specimen was developed and used to compare the behaviour of a FUMD layup with that of other sequences proposed in relevant literature on the topic of delamination in multidirectional laminates.By means of the standard and of a revised Virtual Crack Closure Technique formulations, Energy Release Rate distributions and modal partitions of the specimens were evaluated.It emerged that the FUMD layup resulted in an optimal behaviour of the specimen.Eventually, a mode I interlaminar fracture toughness experimental campaign was performed.FUMD Double Cantilever Beam specimens were fabricated, along with with unidirectional ones.A UD-fabric material was used to reduce the likelihood of delamination migration.Rotations of the specimens arms and the shape of the delamination fronts were studied in order to assess the capability of the specimens to yield the correct mechanical behaviour for mode I delamination testing.For both aspects, FUMD specimens yielded results similar to those obtained with unidirectional specimens.With respect to interlaminar fracture toughness, specimens with identical delamination interface yielded similar values, even if their global stiffness was different.On the other hand, different interfaces led to different interlaminar fracture toughness, related to different fracture behaviours.While this work represents a preliminary study and further research is clearly required, FUMD delamination specimens have shown a good potential, and they may stand out as a viable solution for interlaminar fracture toughness tests.Possibly, they could be considered for an extension of the scopes of existing standard test methods to multidirectional laminates and interfaces

This thesis reports a study of the effects on processing and properties of incorporating nano-scale reinforcements (multiwall carbon nanotubes, MWCNTs) in the matrix of epoxy- carbon fibre (CF) laminate composites to produce multi-scale composites (M-SC). The main aim of this research was to study the effects of MWCNTs on matrix toughening and the through-thickness properties of M-SCs based on a commonly used aerospace grade epoxy resin — triglycidyl-p-aminophenol (TGPAP) cured with diaminodiphenyl sulphone (DDS). In order to improve resin processing, diglycidyl ether of bisphenol F (DGEBF) was added into the TGPAP/DDS system as a reactive diluent. Factorial experimental design (FED) was used to optimize the composition of this tri-component system to obtain high Tg and low resin viscosity, which gave a TGPAP/DGEBF/DDS system with 30.56 wt.% of DGEBF and a chemical stoichiometry of 0.5. Three types of MWCNTs were used; as-received (AR-), base-washed (BW-) and amine functionalized (NH2-). These were shear-mixed with both the bi- and tri-component systems using a 3-roll mill to produce nanocomposite matrices (NCM). The curing behaviour, dispersion state of MWCNTs in the resin and processability of NCMs were studied to decide upon the preparation method for the final M-SC. The fracture toughness (KIC) and the flexural properties of NCM were affected by both MWCNTs and the matrix type; thus KIC increased by up to 8 % in TGPAP/DDS NCM but decreased by 23% in TGPAP/DGEBF/DDS NCM with 0.5 wt.% AR-CNTs. The addition of both non-functionalized and functionalized MWCNTs increased the flexural modulus. The failure mechanism of NCMs was found to be dominated by the size and distribution of CNT aggregates and the behaviour of MWCNTs, both those dispersed in the matrix and in aggregates. The addition of functionalized MWCNTs increased the interfacial bonding between MWCNT and epoxy resin and thus improved the mechanical properties. All the NCM systems were taken forward to manufacture M-SC using a hybrid resin film infusion (RFI)/hot press process. The fibre volume fraction and the void content could be controlled at 43 ± 5 % for M-SC with TGPAP/DDS NCM and 60 ± 6 % for M-SC with TGPAP/DGEBF/DDS NCM. M-SCs were characterised using a range of tests, including flexural, interlaminar shear strength (ILSS), mode-II interlaminar fracture toughness (GIIC), low velocity impact and compression after impact (CAI). The most obvious improvement occurred for the M-SC with tri-component system with 0.5 wt.% CNTs, whereILSS increased by 16 % upon adding NH2-CNTs and GIIC increased significantly on addition of 0.5 wt.% AR-CNTs and NH2-CNTs, by 85% and 184% respectively. However the effect of MWCNTs on other properties was at best marginal. For example, for the M-SC with TGPAP/DDS, the flexural modulus and ILSS only increased by 4.1 % and 2.3 % with 0.5 wt.% AR-CNT.

Packages are the means of preservation, distribution and convenience of use for food, medicine and other consumer products. Package opening is becoming complicated in many cases because of cutting cost in design and production of opening techniques. Introduction of new package opening technique, material or geometry for better opening experience, forces new design measurements which require a large number of prototype developments and physical testing. In order to achieve more rapid and accurate design, Finite Element Method (FEM) Simulations are widely used in packaging industries to compliment and reduce the number of physical testing. The goal of this work is to develop the building blocks towards complete package opening simulation. The study focuses on testing and simulation of shear fracture and shear delamination of packaging materials. A modified shear test specimen was developed and optimized by finite element simulation. Test method was validated for High-density polyethylene (HDPE) and Polypropylene (PP). The developed method has been accepted by international standards organization ASTM. Based on linear elastic fracture mechanics, a geometry correction factor of shear fracture toughness for the proposed specimen was derived. The study concluded that, for ease of opening, HDPE is a more favorable material for screw caps than PP. When performing the experiment with the shear specimen to find essential work of fracture, the ligament length should be varied between twice of the thickness and half of the width of the specimen ligament. Multi-layered thin laminate of Low-density polyethylene (LDPE) and aluminum (Al), also known as Al/LDPE laminate, is another key object addressed in this study. Continuum and fracture testing of individual layers provided the base information and input for numerical modeling. The propagation of an interfacial pre-crack in lamination in Al-LDPE laminate was simulated using several numerical techniques available in the commercial FEM solver ABAQUS, and it was concluded that using the combination of VCCT technique to model the interfacial delamination and coupled elasto-plastic damage constitutive for Al and LDPE substrates can describe interfacial delamination and failure due to necking. It was also concluded that the delamination mode in a pre-crack tip is influenced by the ratio of fracture energy release rate of mode I and II. To address the challenge in quantifying shear energy release rate of laminate with very thin substrate, a convenient test technique is proposed. Additionally, scanning electron microscopic study provided useful information on fractured and delaminated surfaces and provided evidence that strengthened the conclusions of this work. The proposed test methods in this work will be crucial to measure the shear mechanical properties in bulk material and thin substrates. Laminates of Al and LDPE or similar material can be studied using the developed simulation technique which can be effectively used for decision support in early package development.

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2004.
Dr. Zureick, Abdul-Hamid, Committee Member; Dr. White, Donald, Committee Member; Dr. Saxena, Ashok, Committee Member; Dr. Jacobs, Laurence, Committee Member; Dr. Haj-Ali, Rami, Committee Chair; Dr. Armanios, Erian, Committee Member. Vita. Includes bibliographical references (leaves 164-172).

Cílem této diplomové práce je lépe porozumět konceptu únavového poškození damage tolerance zmapováním všech možných vlivů na lomovou houževnatost vláknového kompozitu s polymerní matricí. Toho je dosaženo provedením zkoušek za různých podmínek (např. změna parametrů měření, mód zatížení, pořadí vrstev a materiál) a monitorováním odlišností v šíření trhliny. Na základě dat získaných během těchto testů je určena lomová houževnatost. Potenciální rozdíly jsou zkonzultovány a porovnány s ostatními vzorky.

Design and manufacture of a variable thickness composite laminate such as a helicopter yoke involves tapering the laminate by dropping individual plies at discrete internal locations, in order to tailor the stiffness of the laminate. The ply drop in the laminate creates large interlaminar stresses and initiates delamination. Therefore, there is a necessity to investigate the fundamental failure mechanisms and controlling parameters that account for the delamination mode of failure in tapered laminates. In this thesis, a numerical and experimental study on interlaminar stresses and delamination in tapered laminates is presented, including a critical and comprehensive review on earlier works on this type of structure. Numerical analyses performed involved development of partial hybrid stress finite elements needed to enhance computational efficiency, and development of a physical concept-based modified shear-lag model that is based on the essential assumptions that both plies and resin layers are treated as carriers of tensile stress and also to act as stress-transfer media. Experimental analysis was attempted to assess the accuracy of the numerical predictions. For this purpose, tapered NCT-301 Graphite/Epoxy specimens were manufactured using a ply in-fill technique for the cured consolidation and tested under quasi-static uniaxial tension. To perform strength and delamination analyses of the tapered laminate, the laminate was modeled as a generalized plane deformation problem, where all the variables involved in the model are independent of the coordinate system. Also quasi-three dimensional partial hybrid finite elements were used to quantify the analysis. In addition to the plies, the inter-ply resin at the critical ply interface was also modeled in order to have direct and realistic interlaminar responses. Stress-based criteria that have proved to be effective in determination of critical location and load of delamination onset were utilized in this study to predict the delamination strength of the laminate. A good correlation between the predictions and experimental results were observed. Evaluation of strain energy release rates of delaminations occurring at the critical interfaces of the tapered laminate was carried out by using the J -integral approach. This was possible because of the path-independence of the J -integral that results in avoiding the need for analyzing the singular stress field near the delamination tip and reducing the computing effort required. Effects of various design parameters on the structural performance of the tapered laminate were studied so as to gain an insight into design considerations for tapered composite structures.

碩士
國立雲林科技大學
機械工程技術研究所
86
The purpose of this research is to obtain the tearing mode interlaminar fracture toughness of composite Materials. the SCB specimen and its revised version are used to measure Gc values. In order to reduce unsymmetry in the specimen of composite materials,three kinds of stacking sequences will be adopted. Finite element analysis is also applied to separate the different components of strain energy release rate in the SCB specimen, to conform the dominate mode, and to access the suitable stacking design. Futhermore, the influence of initial crack length, specimen width and thickness, test speed and comparative methods to calculate energy release rate for interlaminar fracture toughness will be discussed. Experiment results indicate that the total fracture toughness is most of mode III fracture toughness in the three kinds of stacking sequences. The average values of Gc for the laminate stacking sequence 6G was approximately 40% greater than [0]c measured using a unidirectional laminate.

碩士
國立雲林科技大學
機械工程系碩士班
93
In this work, a cantilever beam of thin film is tested by a MTS Tytron 250 microforce testing machine with a probe. By using the theory of mechanics of materials, the Young’s modulus of the thin film can be determined. Also by using the theory of fracture mechanics, the mode I interlaminar fracture toughness between the thin film and the substrate can be measured. To manufacture the cantilever beam of SU-8 photoresrist, silicon oxide, or silicon nitride, the techniques of MEMS fabrication and bulk micro-machining are applied. In addition, the etching rate of silicon by etching liquid that is mixed with TMAH and IPA is measured and it is about 0.65~0.67um/min. Since the silicon nitride is produced by sputtering, the induced residual stresses cause the fracture of the cantilever beam after manufacturing. Hence, only the cantilever beams of SU-8 photoresist or silicon oxide are successfully made. The results indicate that the Young’s modulus of SU-8 photoresist is increased with the increasing of the width of the SU-8 beams, but no significant effect is observed from their lengths. The measured Young’s modulus of SU-8 photoresist is about 1.95~2.70GPa. Because the thickness of silicon oxide beam (~1um) is too small, the test load data is random and it may be out of the range of the testing machine. Hence, the results of silicon oxide beam are not used. In the study of interlaminar fracture toughness (Gc), Gilman theory, Berry theory (compliance calibration method), and finite element method (crack closure integral method) are used and compared. The results indicated that the Gc calculated by finite element method is always larger than those by the others. The Gc is increased with the increasing of the width of the SU-8 beam, but the crack length of the SU-8 beam has no effect on the Gc . Furthermore, the results from the finite element method show that mode I is dominant during the fracture. The Gc was about 100~180 J/m2 for the SU-8 photoresist and silicon wafer.

碩士
國立雲林科技大學
機械工程系碩士班
94
This study fabricated micro-cantilever beam of SU-8 photoresrist on the mirror surface or the rough surface of silicon wafer, and the techniques of MEMS fabrication are involved. In addition, bulk micro-machining techniques were applied to this experiment, and the etching solution is mixed with TMAH and IPA was used. The micro-cantilever beam of thin film is tested by a MTS Tytron 250 microforce testing machine with a probe and CCD camera to observe crack growth condition by CCD camera. By adopting the theory of mechanics of materials, the Young’s modulus of the thin film can be determined. Also by adopting the theory of fracture mechanics, the mode I interlaminar fracture toughness between the thin film and the substrate can be measured. When the beam was fabricated on the mirror surface, the measured Young’s modulus is about 1.6~3.8GPa. When it was fabricated on the rough surface, the measured Young’s modulus is about 1.5~3.22GPa. The results indicate that the Young’s modulus of SU-8 photoresist is increased with the increasing of the width of the beams, but no significant effect is seen with their lengths. The final result of the measured Young’s modulus of SU-8 photoresist is about 1.5~3.8GPa. In the study of interlaminar fracture toughness (GIC), Gilman theory and Berry theory (compliance calibration method) are used. The GIC on silicon mirror surface was about 17~43 J/m2. The GIC on silicon rough surface was about 11~30 J/m2. The results indicated that the GIC on silicon mirror surface is larger than that of rough surface. Furthermore, the GIC is increased with the increasing of the width of the SU-8 beam, but the crack length of the SU-8 beam has no effect on the GIC.

碩士
國立交通大學
機械工程系所
94
This study aims to investigate the organoclay effect on the mechanical behaviors of epoxy resin as well as glass fiber/epoxy composites. To understand organoclay effect on the epoxy phase, three different amounts of organoclay, 2.5, 5 and 7.5 % wt, were dispersed into the epoxy with the mechanical blender followed by the sonication. Both tensile tests and fracture tests were carried on these specimens for characterizing their stiffness, tensile strength and fracture behaviors. The experimental results obtained from tensile tests indicated that with the inclusion of 5% wt organoclay, the stiffness of the epoxy increase up to 16%; however, the corresponding failure strain decreases. Moreover, by utilizing the single-edge-notch bending specimens for fracture tests, the results depicted that the organoclay may dramatically reduce the fracture toughness of the epoxy resin. SEM micrographics demonstrate that the brittle fracture occurs in the nanocomposites. For the examination of organoclay effect on glass/epoxy composites, 5 wt% organoclay were dispersed into the epoxy at the beginning and then the compound were in corporation with dry glass fiber through hand lay-up process to form glass fiber/epoxy/organoclay nanocomposites. Off-axis tensile tests as well as Mode I interlaminar fracture tests were conducted on the fiber nanocomposites to understand the tensile strength and the fracture behavior of the sample with organoclay. From off-axis tests, it is indicated that the nanocomposites exhibit high tensile strength then the conventional fiber composites. On the other hand, the interlaminar fracture toughness decreases in the nanocomposite specimens. The decreasing tendency is similar to that in the pure epoxy case. with glass fiber and epoxy resin. The fracture tests will be performed on the hydraulic MTS machine with 10-1 mm/min loading rate.

碩士
國立成功大學
化學工程研究所
83
Composite materials often fail by delamination. In this study, two thermoplastic polymers, poly(ether imide) (PEI) and poly( hydroxy ether of bisphenol A) (PHENOXY) were used as particulate interlaminar toughening agents in graphite/epoxy system. Mode-I and Mode-II delamination toughness was characterized using the Mode-I double-cantilever beam (DCB) and the Mode-II end-notched flexure (ENF) test specimens. The delamination surface was examined by a scanning electron microscope (SEM) to investigate the morphology and fracture mechanism. The results revealed that as the PEI contents were increased, GIC and GIIC increased. GIC was improved from 167 to 527J/m2 at 1mm/min crosshead rate and GIC was improved from 146 to 493J/m2 at a higher crosshead rate of 10mm/min. GIIC improved from 293 to 1297J/m2. In PHENOXY interlaminar toughened system, GIC was almost the same as PEI toughened system, but GIIC was much lower. The fracture surfaces of PEI toughened system showed phase-inversed morphology, and the toughening mechanism was ductile yielding of PEI.