This thesis is focused on the development of multiple experimental frameworks to characterize the material properties of composite materials for the LS-DYNA MAT213 model. The main objective is to characterize these properties based on the full-field capture of the evolution of strain and stress fields in coupon-level tests at multiple scales (i.e. macroscopic and microscopic). The experimental work characterized the full-field stress-strain curves and subsequently derived the material properties of T700G/LM-PAEK thermoplastic composites. The data was later successfully utilized to generate the deformation and damage sub-models in the LS-DYNA MAT213 model for the material. Additionally, a three-point bending test methodology was created using a size effect study and geometrically scaled coupons to investigate the Mode-II interlaminar fracture toughness of the material. The experimental frameworks developed herein were also extended to characterize other composite materials, such as those produced via additive manufacturing techniques. Future experimental work will investigate fatigue failure methods for three-point bending in T700G/LM-PAEK. The experimental methods described herein will also continue to support analytical efforts that seek to develop a simulation tool based on the LS-DYNA MAT213 model for modeling the temperature and strain rate-dependent impact damages in composites under multi-axial loading.

The future of the aerospace industry in large part relies on two factors: (i) development of advanced damage tolerant materials and (ii) development of advanced smart sensors with the ability to detect and evaluate defects at very early stages of component service life. Laminated composite materials, such as carbon fibre reinforced plastics (CFRP), have emerged as the materials of choice for increasing the performance and reducing the cost and weight of aircrafts, which leads to less fuel consumption and therefore lower CO2 emissions. However, it is well known that these materials exhibit fragile behaviour, poor resistance to impact damage caused by foreign objects and require a relatively slow and labour intensive manufacturing process. These factors prevent the rapid expansion of composite materials in several industrial sectors at the current time. Inspired by the use of rope throughout history and driven by the necessity of creating a lean manufacturing process for composites and enhancing their impact properties, the first part of this work has shown that enhanced damage tolerance and pseudo-ductile behaviour can be achieved with standard CFRP by creatively arranging the fibres into a 3D twisted helical configuration. Through an extensive experimental campaign a new method to arrange fibre reinforcement was presented and its effect investigated. The second part of this PhD work focused on developing a new smart sensor. A spiral passive electromagnetic sensor (SPES) for damage detection on CFRP and glass fibre reinforced plastics (GFRP) is presented in this work. A range of defect types in glass and carbon composite has been considered, such as delamination, perforated holes and cracks. Furthermore, throughout this work, the SPES has been exploited as a multi-sensing device allowing the ability to detect temperature and humidity variation, presence of ice and act as an anti/de-icing device.

In aerospace applications, use of laminates made of composite materials as face sheets in sandwich panels are on the rise. These composite laminates have low transverse shear and transverse normal moduli compared to the in-plane moduli. It is also seen that the corresponding transverse strength values are very low compared to the in-plane strength leading to delaminations. Further, in sandwich structures, the core is subjected to significant transverse shear stresses. Therefore the interlaminar stresses (i.e., transverse shear and normal) can govern the design of sandwich structures. As a consequence, the first step in achieving efficient designs is to develop the ability to reliably estimate interlaminar stresses. Stress analysis of the composite sandwich structures can be carried out using 3-D finite elements for each layer. Owing to the enormous computational time and resource requirements for such a model, this process of analysis is rendered inefficient. On the other hand, existing plate/shell finite elements, when appropriately chosen, can help quickly predict the 2-D displacements with reasonable accuracy. However, their ability to calculate the thickness-wise distributions of interlaminar shear and normal stresses and 3-D displacements remains as a research goal. Frequently, incremental refinements are offered over existing solutions. In this scenario, an asymptotically correct dimensional reduction from 3-D to 2-D, if possible, would serve to benchmark any ongoing research. The employment of a mathematical technique called the Variational Asymptotic Method (VAM) ensures the asymptotical correctness for this purpose. In plates and sandwich structures, it is typically possible to identify (purely from the defined material distributions and geometry) certain parameters as small compared to others. These characteristics are invoked by VAM to derive an asymptotically correct theory. Hence, the 3-D problem of plates is automatically decomposed into two separate problems (namely 1-D+2-D), which then exchange relevant information between each other in both ways. The through-the-thickness analysis of the plate, which is a 1-D analysis, provides asymptotic closed form solutions for the 2-D stiffness as well as the recovery relations (3-D warping field and displacements in terms of standard plate variables). This is followed by a 2-D plate analysis using the results of the 1-D analysis. Finally, the recovery relations regenerate all the required 3-D results. Thus, this method of developing reduced models involves neither ad hoc kinematic assumptions nor any need for shear correction factors as post-processing or curve-fitting measures. The results are most general and can be made as accurate as desired, while the procedure is computationally efficient. In the present work, an asymptotically correct plate theory is formulated for composite sandwich structures. In developing this theory, in addition to the small parameters (such as small strains, small thickness-to-wavelength ratios etc.,) pertaining to the general plate theory, additional small parameters characterizing (and specific to) sandwich structures (viz., smallness of the thickness of facial layers com-pared to that of the core and smallness of elastic material stiffness of the core in relation to that of the facesheets) are used in the formulation. The present approach also satisfies the interlaminar displacement continuity and transverse equilibrium requirements as demanded by the exact 3-D formulation. Based on the derived theory, numerical codes are developed in-house. The results are obtained for a typical sandwich panel subjected to mechanical loading. The 3-D displacements, inter-laminar normal and shear stress distributions are obtained. The results are compared with 3-D elasticity solutions as well as with the results obtained using 3-D finite elements in MSC NASTRAN®. The results show good agreement in spite of the major reduction in computational effort. The formulation is then extended for thermo-elastic deformations of a sandwich panel. This thesis is organized chronologically in terms of the objectives accomplished during the current research. The thesis is organized into six chapters. A brief organization of the thesis is presented below. Chapter-1 briefly reviews the motivation for the stress analysis of sandwich structures with composite facesheets. It provides a literature survey on the stress analysis of composite laminates and sandwich plate structures. The drawbacks of the existing anlaytical approaches as opposed to that of the VAM are brought out. Finally, it concludes by listing the main contributions of this research. Chapter-2 is dedicated to an overview of the 3-D elasticity formulation of composite sandwich structures. It starts with the 3-D description of a material point on a structural plate in the undeformed and deformed configurations. Further, the development of the associated 3-D strain field is also described. It ends with the formulation of the potential energy of the sandwich plate structure. Chapter-3 develops the asymptotically correct theory for composite sandwich plate structure. The mathematical description of VAM and the procedure involved in developing the dimensionally reduciable structural models from 3-D elasticity functional is first described. The 1-D through-the-thickness analysis procedure followed in developing the 2-D plate model of the composite sandwich structure is then presented. Finally, the recovery relations (which are one of the important results from 1-D through-the-thickness analysis) to extract 3-D responses of the structure are obtained. The developed formulation is applied to various problems listed in chapter 4. The first section of this chapter presents the validation study of the present formulation with available 3-D elasticity solutions. Here, composite sandwich plates for various length to depth ratios are correlated with available 3-D elasticity solutions as given in [23]. Lastly, the distributions of 3-D strains, stresses and displacements along the thickness for various loadings of a typical sandwich plate structure are correlated with corresponding solutions using well established 3-D finite elements of MSC NASTRAN® commerical FE software. The developed and validated formulation of composite sandwich structure for mechanical loading is extended for thermo-elastic deformations. The first sections of this chapter describes the seamless inclusion of thermo-elastic strains into the 3-D elasticity formulation. This is followed by the 1-D through-the-thickness analysis in developing the 2-D plate model. Finally, it concludes with the validation of the present formulation for a very general thermal loading (having variation in all the three co-ordinate axes) by correlating the results from the present theory with that of the corresponding solutions of 3-D finite elements of MSC NASTRAN® FE commercial software. Chapter-6 summarises the conclusions of this thesis and recommendations for future work.

[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

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.

Cieľom diplomovej práce je príprava polymerných kompozitov vyztužených sklenenými vláknami s riadenou medzifázou za použitia metódy plazmochemickej depozície z plynnej fáze a monomeru tetravinylsilanu. Teoretická časť je zameraná na literárnu rešerš o plazme, plazmovej polymerácií, tenkých vrstvách a kompozitoch. Experimentálna časť popisuje použité materiály a aparaturu použitú na povrchovú modifikáciu sklenených vlákien a prípravu vláknom vyztužených kompozitov. Povrchová úprava sklenených vlákien prebiehala za rôznych depozičných podmienok. Chemické a mechanické analýzy vytvorenej medzivrstvy prebiehali za použitia FTIR spektrometrie a vrypového testu. Vliv povrchovej úpravy bol zistený pomocou získanej interlaminárnej šmykovej sily použítím testu krátkych trámečkov.

Experimentation exploring the movement of voids within carbon fiber reinforced plastics was performed using fluorescent dye infused into the laminates observed through a transparent mold under ultraviolet light. In situ photography was used as an inspection method for void content during Resin Transfer Molding for these laminates. This in situ inspection method for determining the void content of composite laminates was compared to more common ex-situ quality inspection methods i.e. ultrasonic inspection and cross-section microscopy. Results for localized and total void count in each of these methods were directly compared to test samples and linear correlations between the three test methods were sought. Test coupons were then cut from these laminates and were used to calculate the interlaminar shear strength at certain locations throughout the laminates. Although this research did not adequately observe correlations between results obtained from ultrasonic C-scans, cross-sectional microscopy and in situ photography of the surface, it was seen that the fluid dynamics of the thermosetting epoxy used in this experimentation correlated to results obtained from previous experimentation performed by students at Brigham Young University using vegetable oil as a substitute for resin.

Composite materials and hybrid materials such as fiber-metal laminates, and functionally graded materials are increasingly common in application in aerospace structures. However, adhesive bonding of dissimilar materials makes these materials susceptible to delamination. The use of integrated Sinc methods for predicting interlaminar failure in laminated composites and hybrid material systems was examined. Because the Sinc methods first approximate the highest-order derivative in the governing equation, the in-plane derivatives of in-plane strain needed to obtain interlaminar stresses by integration of the equilibrium equations of 3D elasticity are known without post-processing. Interlaminar stresses obtained with the Sinc method based on Interpolation of Highest derivative were compared for the first-order and third-order shear deformable theories, the refined zigzag beam theory and the higher-order shear and normal deformable beam theory. The results indicate that the interlaminar stresses by the zigzag theory compare well with those obtained by a 3D finite element analysis, while the traditional equivalent single layer theories perform well for some laminates. The philosophy of the Sinc method based on Interpolation of Highest Derivative was extended to create a novel weak form based approach called the Integrated Local Petrov-Galerkin Sinc Method. The Integrated Local Petrov-Galerkin Sinc Method is easily utilized for boundary-value problem on non-rectangular domains as demonstrated for analysis of elastic and elastic-plastic plane-stress panels with elliptical notches. The numerical results showed excellent accuracy compared to similar results obtained with the finite element method. The Integrated Local Petrov-Galerkin Sinc Method was used to analyze interlaminar debonding of composite and fiber-metal laminated beams. A double-cantilever beam and a fixed-ratio mixed mode beam were analyzed using the Integrated Local Petrov-Galerkin Sinc Method and the results were shown to correlate well with those by the finite element method. An adaptive Sinc point distribution technique was implemented for the delamination analysis which significantly improved the methods accuracy for the present problem. Delamination of a GLARE, plane-strain specimen was also analyzed using the Integrated Local Petrov-Galerkin Sinc Method. The results correlate well with 2D, plane-strain analysis by the finite element method, including interlaminar stresses obtained by through-the-thickness integration of the equilibrium equations of 3D elasticity. / Ph. D.

Six poly(ether ketone ketone)/carbon composite panels were manufactured from powder coated towpreg. All six panels were initially processed using a hot press equipped with controlled cooling. Four of the panels were used to investigate the effect of cooling rate on crystallinity. A fifth panel was used to investigate the effect of annealing the composite after completion of the standard fabrication process. The sixth panel was used to investigate changes in toughness due to manufacturing towpreg with polymer that had been reclaimed from the towpreg fabrication system’s air cleaner. Cooling rates of 2°C/min, 4°C/min, 6°C/min, and 8°C/min resulted in composites with crystallinities of 33%, 27%, 24%, and 23%, respectively. The principal investigation of the effect of cooling rate on crystallinity and mode I and mode II strain energy release rates, G_Ic and G_IIc, respectively, showed that G_Ic and G_IIc values increase with increasing cooling rate. Comparison of the toughness values as a function of crystallinity showed that the dependence of toughness on crystallinity is approximately equivalent to the dependence of toughness on cooling rate. Comparison of the data from the annealed panel to that from the analogous principal panel showed that annealing increased the crystallinity and decreased the mode I strain energy release rate. There was no effect, however, on the mode II strain energy release rate. Comparison of the data from the panel made with reclaimed polymer to that from its analogous principal panel showed that the reclaimed polymer panel had equivalent crystallinity and G_Ic values. On the other hand, the G_IIc values in this panel were lower than in the analogous principal panel. / Master of Science

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.