In fabrication of nanoparticle-reinforced polymers, two critical factors need to be taken into account to control properties of the final product; nanoparticle dispersion/distribution in the matrix; and interfacial interactions between nanoparticles and their surrounding matrix. The focus of this thesis was to examine the role of these two factors through experimental methodologies and molecular-level simulations. Carbon nanotubes (CNTs) and vinyl ester (VE) resin were used as nanoparticles and matrix, respectively. In a parametric study, a series of CNT/VE nanocomposites with different CNT dispersion conditions were fabricated using the ultrasonication mixing method. Thermomechanical properties of nanocomposites and quality of CNT dispersion were evaluated. By correlation between nanocomposite behavior and CNT dispersion, a thermomechanical model was suggested; at a certain threshold level of sonication energy, CNT dispersion would be optimal and result in maximum enhancement in properties. This threshold energy level is also related to particle concentration. Sonication above this threshold level, leads to destruction of nanotubes and renders a negative effect on the properties of nanocomposites. In an attempt to examine the interface condition, a novel process was developed to modify CNT surface with polyhedral oligomeric silsesquioxane (POSS). In this process, a chemical reaction was allowed to occur between CNTs and POSS in the presence of an effective catalyst. The functionalized CNTs were characterized using TEM, SEM-EDS, AFM, TGA, FTIR and Raman spectroscopy techniques. Formation of amide bonds between POSS and nanotubes was established and verified. Surface modification of CNTs with POSS resulted in significant improvement in nanotube dispersion. In-depth SEM analysis revealed formation of a 3D network of well-dispersed CNTs with POSS connections to the polymer. In parallel, molecular dynamics simulation of CNT-POSS/VE system showed an effective load transfer from polymer chains to the CNT due to POSS linkages at the interface. The rigid and flexible network of CNTs is found to be responsible for enhancement in elastic modulus, strength, fracture toughness and glass transition temperature (Tg) of the final nanocomposites. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Composites have been developed with great success by the use of fiber reinforcements in metallic materials. Fiber reinforced metal matrices possess great potential to be the next generation of advanced composites offering many advantages compared to fiber reinforced polymers. Specific advantages include high temperature capability, superior environmental stability, better transverse modulus, shear and fatigue properties. Although many Metal Matrix Composites (MMCs) are attractive for use in different industrial applications, Aluminium Matrix Composites (AMCs) are the most used in advanced applications because they combine acceptable strength, low density, durability, machinability, availability, effectiveness and cost. The present study focuses on the fabrication of aluminium matrix composite plates by squeeze casting using plain weave carbon fiber preform (AS4 Hexcel) as reinforcement and a matrix of wrought aluminium alloy 1235-H19. The objective is to investigate the process feasibility and resulting materials properties such as hardness at macro- and micro-scale, impact and bend strength. The properties obtained are compared with those of 6061/1235-H19 aluminium plates that were manufactured under the same fabrication conditions. The effect of fiber volume fraction on the properties is also investigated. Furthermore, the characterization of the microstructure is done using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) in order to establish relationships between the quality of the fiber/aluminium interface bond and mechanical properties of the composites. In conclusion, aluminium matrix composite laminate plates were successfully produced. The composites show a good chemical bond between the fiber and the aluminium matrix. This bond resulted from heterogeneous precipitation of aluminium carbides (Al4C3) at the interface between aluminium matrix and carbon fiber. The hardness at macro- and micro-scale of the composites increases by over 50% and the flexural modulus increases by about 55%. The toughness of the composite decreases due to the presence of brittle phases which can be improved by better oxidation prevention. Also, an optimal carbon volume fraction was observed that provides optimal properties including peak hardness, peak stiffness and peak toughness.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 153-159). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 153-159). Also available on the Internet.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2008. / Additional advisors: Gregg M. Janowksi, Tamara Floyd Smith, Gregory B. Thompson, Uday Vaidya. Description based on contents viewed July 7, 2009; title from PDF t.p. Includes bibliographical references.

No description available.

Composites have been developed with great success by the use of fiber reinforcements in metallic materials. Fiber reinforced metal matrices possess great potential to be the next generation of advanced composites offering many advantages compared to fiber reinforced polymers. Specific advantages include high temperature capability, superior environmental stability, better transverse modulus, shear and fatigue properties. Although many Metal Matrix Composites (MMCs) are attractive for use in different industrial applications, Aluminium Matrix Composites (AMCs) are the most used in advanced applications because they combine acceptable strength, low density, durability, machinability, availability, effectiveness and cost. The present study focuses on the fabrication of aluminium matrix composite plates by squeeze casting using plain weave carbon fiber preform (AS4 Hexcel) as reinforcement and a matrix of wrought aluminium alloy 1235-H19. The objective is to investigate the process feasibility and resulting materials properties such as hardness at macro- and micro-scale, impact and bend strength. The properties obtained are compared with those of 6061/1235-H19 aluminium plates that were manufactured under the same fabrication conditions. The effect of fiber volume fraction on the properties is also investigated. Furthermore, the characterization of the microstructure is done using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) in order to establish relationships between the quality of the fiber/aluminium interface bond and mechanical properties of the composites. In conclusion, aluminium matrix composite laminate plates were successfully produced. The composites show a good chemical bond between the fiber and the aluminium matrix. This bond resulted from heterogeneous precipitation of aluminium carbides (Al4C3) at the interface between aluminium matrix and carbon fiber. The hardness at macro- and micro-scale of the composites increases by over 50% and the flexural modulus increases by about 55%. The toughness of the composite decreases due to the presence of brittle phases which can be improved by better oxidation prevention. Also, an optimal carbon volume fraction was observed that provides optimal properties including peak hardness, peak stiffness and peak toughness.

No description available.

Yes / Composites have clinical application for their ability to mimic the hierarchical structure of human tissues. In tissue engineering applications the use of degradable biopolymer matrices reinforced by bioactive ceramics is seen as a viable process to increase osteoconductivity and accelerate tissue regeneration, and technologies such as additive manufacturing provide the design freedom needed to create patient-specific implants with complex shapes and controlled porous structures. In this study a medical grade poly(l-lactide) (PLLA) was used as matrix while apatite-wollastonite (AW) was used as reinforcement (5 wt% loading). Premade rods of composite were pelletized and processed to create a filament with an average diameter of 1.6 mm, using a twin-screw extruder. The resultant filament was 3D printed into three types of porous woodpile samples: PLLA, PLLA reinforced with AW particles, and PLLA with short AW fibres. None of the samples degraded in phosphate buffered solution over a period of 8 weeks, and an average effective modulus of 0.8 GPa, 1 GPa and 1.5 GPa was obtained for the polymer, particle and fibre composites, respectively. Composite samples immersed in simulated body fluid exhibited bioactivity, producing a surface apatite layer. Furthermore, cell viability and differentiation were demonstrated for human mesenchymal stromal cells for all sample types, with mineralisation detected solely for biocomposites. It is concluded that both composites have potential for use in critical size bone defects, with the AW fibre composite showing greater levels of ion release, stimulating more rapid cell proliferation and greater levels of mineralisation. / The research was funded in part by the UK EPSRC Centre for Doctoral Training in Additive Manufacturing and 3D Printing (EP/L01534X/1), the UK EPSRC Centre for Innovative Manufacture in Medical Devices (EP/K029592/1), and Glass Technology Services Ltd., Sheffield, UK.

As fiber reinforced polymer (FRP) structures find application in highway bridge structures, methodologies for describing their long-term performance under service loading will be a necessity for designers. The designer of FRP bridge structures is faced with out-of-plane damage and delamination at ply interfaces. The damage most often occurs between hybrid plys and dominates the life time response of a thick section FRP structure. The focus of this work is on the performance of the 20.3 cm (8 in) pultruded, hybrid double web I-beam structural shape. Experimental four-point bend fatigue results indicate that overall stiffness reduction of the structure is controlled by the degradation of the tensile flange. The loss of stiffness in the tensile flange results in the redistribution of the stresses and strains, until the initiation of failure by delamination in the compression flange. These observations become the basis of the assumptions used to develop an analytical life prediction model. In the model, the tensile flange stiffness is reduced based on coupon test data, and is used to determine the overall strength reduction of the beam in accordance the residual strength life prediction methodology. Delamination initiation is based on the out-of-plane stress sz at the free edge. The stresses are calculated using two different approximations, the Primitive Delamination Model and the Minimization of Complementary Energy. The model successfully describes the onset of delamination prior to fiber failure and suggests that out-of-plane failure controls the life of the structure. / Master of Science