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This study presents characterization of thermo-mechanical viscoelastic and long-term behaviors of thick-section multi-layered fiber reinforced polymer composite materials. The studied multi-layered systems belong to a class of thermo-rheologically complex materials, in which both stress and temperature affect the time-dependent material response. The multi-layered composites consist of alternating layers of unidirectional fiber (roving) and randomly oriented continuous filament mat. Isothermal creep-recovery tests at various stresses and temperatures are performed on E-glass/vinylester and Eglass/ polyester off-axis specimens. Analytical representation of a nonlinear single integral equation is applied to model the thermo-mechanical viscoelastic responses for each off-axis specimen. Long-term material behaviors are then obtained through vertical and horizontal time shifting using analytical and graphical shifting procedures. Linear extrapolation of transient creep compliance is used to extend the material responses for longer times. The extended long-term creep strains of the uniaxial E-glass/vinylester specimens are verified with the long-term experimental data of Scott and Zureick (1998). A sensitivity analyses is then conducted to examine the impact of error in material parameter characterizations to the overall long-term material behaviors. Finally, the calibrated long-term material parameters are used to study the long-term behavior of multi-layered composite structures. For this purpose, an integrated micromechanical material and finite element structural analyses is employed. Previously developed viscoelastic micromodels of multi-layered composites are used to generate the effective nonlinear viscoelastic responses of the studied composite systems and then implemented as a material subroutine in Abaqus finite element code. Several long-term composite structures are analyzed, that is; I-shaped columns and flat panels under axial compression, and a sandwich beam under the point bending and transmission tower under lateral forces. It is shown that the integrated micromechanical-finite element model is capable of predicting the long-term behavior of the multilayered composite structures.

This thesis presents a continuum model for asphalt concrete incorporating non- linear viscoelasticity, viscoplasticity, mechanically-induced damage and moisture- induced damage. The Schapery single-integral viscoelastic model describes the nonlinear viscoelastic response. The viscoplastic model of Perzyna models the time- dependent permanent deformations, using a Drucker-Prager yield surface which is modified to depend on the third deviatoric stress invariant to include more complex dependence on state of stress. Mechanically-induced damage is modeled using continuum damage mechanics, using the same modified Drucker-Prager law to determine damage onset and growth. A novel moisture damage model is proposed, modeling moisture-induced damage using continuum damage mechanics; adhesive moisture- induced damage to the asphalt mastic-aggregate bond and moisture-induced cohesive damage to the asphalt mastic itself are treated separately. The analytical model is implemented numerically for three-dimensional and plane strain finite element analyses, and a series of simulations is presented to show the performance of the model and its implementation. Sensitivity studies are conducted for all model parameters and results due to various simulations corresponding to laboratory tests are presented. In addition to the continuum model, results are presented for a micromechanical model using the nonlinear-viscoelastic-viscoplastic-damage model for asphalt mastic and a linear elastic model for aggregates. Initial results are encouraging, showing the strength and stiffness of the mix as well as the failure mode varying with moisture loading. These initial results are provided as a an example of the model's robustness and suitability for modeling asphalt concrete at the mix scale.

Renewable energy is a serious alternative to deliver the energy needs of an increasing world population and improve economic activity. Wind energy provides better environmental and economic benefits in comparison with the other renewable energy sources. Wind energy is capable of providing 72 TW (TW = 10^12 W) of electric power, which is approximately four and half times the world energy consumption of 15.8 TW as reported in 2006. Since power output extracted from wind turbines is proportional to the square of the blade length and the cube of the wind speed, wind turbine size has grown rapidly in the last two decades to match the increase in power output. As the blade length increases, so does its weight opening up design possibilities to introduce hybrid glass and carbon fiber composite materials as lightweight structural load bearing alternatives. Herein, we investigate the feasibility of introducing modular composite tubulars as well as hybrid sandwich composite skins in the next generation blades. After selecting a target energy output, 8 MW with 80 m blade, airfoil geometry and the layup for the skin as well as internal reinforcements are proposed. They are incorporated into the computational blade via linear shell elements for the skin, and linear beam elements for the composite tubulars to assess the relationship between weight reduction and structural performance. Computational simulations are undertaken to understand the static and dynamic regimes; specifically, displacements, stresses, and vibration modes. The results showed that the composite layers did not exhibit any damage. However, in the balsa core of the sandwich skin, the von Mises stress exceeded its allowable at wind speeds ranging from 11.0 m/sec to 12.6 m/sec. In the blades with composite tubular reinforcement, two different types of damage are observed: a. Stress concentrations at the tubular-skin attachments, and b. Highest von Mises stress caused by the flapping bending moment. The vibration studies revealed a strong coupling mode, bending and twist, at the higher natural frequencies of the blade with tubular truss configuration. The weight saving measures in developing lighter blades in this study did not detract from the blades structural response for the selected load cases.

Zeolites are nanoporous crystalline aluminosilicates that are tasteless, odorless and nontoxic to humans. They can be tailored into antibacterial agents that are more cost effective than other conventional alternatives. Considering the increasing demand for enduring antibacterial agents, the potential uses of antibacterial zeolites are numerous in medical applications and for everyday household products. To produce antibacterial zeolites, the extra framework cations in the zeolite structures can be exchanged with silver ion (Ag+), the most commonly used antibacterial heavy metal ion due to its high stability, strong activity and broad spectrum. Utilization of antibacterial zeolite powders can be diversified when they are used as fillers in a polymer matrix. Polyurethanes (PU) are a class of polymers which can be prepared in wide range of physical structures with excellent mechanical properties. Ag+ loaded zeolites used as fillers in the PU matrix would contribute to the diversity and efficiency of the PU utilization in many applications including biomedical uses and consumer products. In this study, three types of zeolites, namely / zeolite Beta, X and A with different pores sizes and SiO2/Al2O3 ratios were synthesized hydrothermally and treated with Ag+ containing solution for the exchange of cations. Composites were prepared by incorporation of sieved Ag+ exchanged zeolite particles into biomedical grade PU prepolymers which were prepared either in film or as sponge forms. Films were prepared by molding and foams were prepared in the presence of water as the blowing agent. Liquid media antibacterial tests showed that all of the Ag+-zeolite powders were effective against E. coli at a concentration of 500 ppm zeolite in deionized water. To assess the antibacterial effect of composites against E. coli, disc diffusion tests were carried out. Bacterial growth inhibition zones formed around the composite samples were the evidence of the antibacterial activity in the vicinity of the surface. All three kinds of zeolites successfully introduced the desired antibacterial property to the biomedical grade PU both in elastomeric film and in the foam form. Mechanical characterization of the composites yield higher ultimate tensile strength, modulus of elasticity and elongation at break values compared to control PU. No significant change in thermal properties of the composites was observed. Hence mechanical and thermal characterization of the composites showed that zeolites serve for the reinforcement of the mechanical properties of the polymer and did not cause any deterioration in thermal properties.

The purpose of the work is to employ molecular simulation to further extend the understanding of Self-Assembled Monolayers (SAMs), especially as it relates to three particular applications: organic-inorganic composite membranes, surface treatments in Micro-Electro-Mechanical Systems (MEMS) and organic-surface-modified Ordered Mesoporous Materials (OMMs). The first focus area for the work is the use of SAMS in organic-inorganic composite membranes for gas separations. These composite membranes, recently proposed in the literature, are based on the chemical derivatization of porous inorganic surfaces with organic oligomers. Our simulations achieve good qualitative agreement with experiment in several respects, including the improvement in the overall selectivity of the membrane and decrease in the permeance when increasing the chain length. The best improvement in the overall solubility selectivity is reached when the chains span throughout the pore. The second application focus is on the use of SAMs as coatings in MEMS devices. The work focuses on the modeling of adhesion issues for SAM coatings at the molecular level. It is shown that as the chain length is increased from 4 to 18 carbon atoms, the adhesion forces between two monolayers at the same separations decreases. The third application focus is on the use of SAMs for tailoring surface and structural properties of OMMs, in particular, porous silicas. A molecular study of structural and surface properties of a silica material with a 5 nm pore size, modified via chemical bonding of organosilanes with a range of sizes (C4, C8 and C18) is presented. Grand canonical MC simulations are employed to obtain nitrogen adsorption isotherms for unmodified and modified MCM-41 material models. Furthermore, the density profiles of alkyl chains and nitrogen molecules are analyzed to clarify the differences in the adsorption mechanisms in unmodified and modified materials. The position of the capillary condensation steps gradually shifted to lower pressure values with the increase in size of the bonded ligands, and this shift was accompanied by a gradual disappearance of the hysteresis loop. As the length of the bonded ligands is increased, a systematic decrease in the pore diameter is observed and the multi-layer adsorption mechanism in modified model materials diminishes.

The mechanical reliability of electronic components has become harder and harder to predict due to the use of composite materials. One of the key issues is creating an accurate model of the delamination mechanism, which consists in the separation of two different bounded materials. This phenomenon is a very challenging issue that is investigated in the Nano Interface Project (NIP), in which this thesis is involved. The macroscopic adhesion force is governed by several parameters described at different length scales. Among these parameters, the roughness profile of the interface has a pronounced influence. The main difficulty for an accurate delamination characterization is then investigating the effects of this roughness profile and the modifications it implies for the overall cohesion. The objective of the NIP is to develop an interface model for the numerical testing of electronic components in a finite element software. The problem is that a direct modeling of all the mechanisms described previously is really expensive in term of computation time, if possible at all. This difficulty is increased by the huge mismatch of the mechanical properties of the materials in contact. A scale transition method is therefore required, which is provided by homogenization. The idea is to consider the delamination at a wider scale. Rather than modeling the whole roughness profile, the adhesion at the interface will be described by homogenized, or macroscopic, parameters extracted from a representative model at the micro-scale, the RVE. This thesis will deal with the determination of these homogenized parameters.

The effects of reactive metal particles on the microstructure and mechanical properties of epoxy-based composites are investigated in this work. To examine these effects castings of epoxy reinforced with 20-40 vol.% Al and 0-10 vol.% Ni were prepared, while varying the aluminum particle size from 5 to 50 microns and holding the nickel particle size constant at 50 microns. In total eight composite materials were produced, possessing unique microstructures. The microstructure is quantitatively characterized and correlated with the composite constitutive response determined from quasi-static and dynamic compressive loading conditions at strain-rates from 1e-4 to 5e3 /s. Microstructures from each composite and at each strain rate were analyzed to determine the amount of particle strain as a function of bulk strain and strain rate. Using computational simulations of representative microstructures of select composites, the epoxy matrix-metallic particle and particle-particle interactions at the mesoscale under dynamic compressive loading conditions were further examined. From computational simulation data, the stress and strain localization effects were characterized at the mesoscale and the bulk mechanical behavior was decomposed into the individual contributions of the constituent phases. The particle strain and computational analysis provided a greater understanding of the mechanisms associated with particle deformation and stress transfer between phases, and their influence on the overall mechanical response of polymer matrix composites reinforced with metallic particles. The highly heterogeneous composite microstructure and the high contrasting properties of the individual constituents were found to drive localized deformations that are often more pronounced than those in the bulk material. The strain rate behavior of epoxy is shown to cause a strain rate dependent deformation response of reinforcement particle phases that are typically strain rate independent. Additionally, the epoxy matrix strength behavior was found to have a higher dependence on strain rate due to the presence of metal particle fillers. Discrepancies between experimental and simulation mechanical behavior results and these findings indicate a need for epoxy constitutive models to incorporate effects of particle reinforcement on the mechanical behavior.

In vielen technischen Anwendungen werden Faserverbundwerkstoffe mit Hochleistungsfasern aus Carbon und AR-Glas eingesetzt, die aufgrund ihrer physikalischen und chemischen Eigenschaften ein hohes Festigkeitspotential aufweisen. Damit eröffnen sich neue Anwendungsgebiete, z. B. als textile Bewehrungen für Betonbauteile. Die Garnmaterialien müssen hohe sicherheitstechnische Anforderungen erfüllen. Dazu gehören u. a. eine ausreichende Tragfähigkeit unter Dauerlastbeanspruchung und eine hohe Temperaturbeständigkeit im Brandfall. Zur Spezifizierung dieser Eigenschaften wurden experimentelle Untersuchungen durchgeführt, deren Ergebnisse nachfolgend vorgestellt werden. / Due to their strong mechanical and chemical properties, fiber composite materials composed of high performance carbon and AR-glass fibers lend themselves to many technical applications. Potentially new and innovative application fields should be considered, such as textile reinforcements for concrete components. The yarn materials must meet high technical and safety standards, specifically sufficient load-bearing capabilities under long-term conditions and acceptable strength at high temperatures should fire occur. Research was conducted to document these characteristics. The results are presented in this paper.

Nowadays, high demands are made on filling materials in modern dentistry: Durability, Reliability &Aesthetic Requirements Thus, a group of physicists and an independent practicing dentist investigated 11 different teeth fillings (composite materials) as used in modern dental practices according to their stability and ability to withstand contact loadings.