The thermal expansion behavior of Graphite/Epoxy Laminates between 116 and 366 degrees Kelvin was investigated using a novel implementation of the Priest interferometer concept. This thesis describes the design, construction and use of the interferometer along with the experimental results it was used to generate. The experimental program consisted of 25 tests on 25.4 mm and 6.35 mm wide, 8-ply quasi-isotropic T300/5208 graphite/epoxy specimens and 3 tests on a 25.4 mm wide unidirectional specimen. Experimental results are presented for all tests along with a discussion of the interferometer's limitations and some possible improvements in its design. / Master of Science

This investigation concerns the validity and feasibility of using moduli reduction to monitor the effect of fatigue damage in graphite epoxy composites. Five laminate orientations were considered, [O]₄, [90]₄, [±45]_s, [0,90]_s, [0,90,±45]_s, and four inplane-stiffness properties were monitored for each. The stiffness parameters were E_xx, E_yy, G_xy, and v_xy, and were measured using a longitudinal tension test, a rail shear test and a transverse bend test. Nondestructive testing techniques such as C-scan and edge replication were also performed to aid in the observation of damage development. Results describe the response of each laminate orientation in tension-tension fatigue, including a record of changes in the stiffness properties at intervals during fatigue. Longitudinal stiffness (E_xx) and shear stiffness (G_xy) were shown to significantly decrease for the [0,90,±45]_s, laminate following fatigue loading. The inplane stiffness properties for the other four laminates remain essentially unchanged following fatigue loading. Matrix cracking and delamination appears to contribute to the stiffness reductions that occur in the [0,90,±45]_s laminate. / Master of Science

This study consisted of two main parts, the thermoviscoelastic characterization of Kevlar 49/Fiberite 7714A epoxy composite lamina and the development of a numerical procedure to predict the viscoelastic response of any general laminate constructed from the same material. The four orthotropic material properties, S₁₁, S₁₂, S₂₂, and S₆₆, were characterized by 20 minute static creep tests on unidirectional ([0]₈, [10]₈, and [90]₁₆) lamina specimens. The Time-Temperature-Superposition-Principle (TTSP) was used successfully to accelerate the characterization process. A nonlinear constitutive model was developed to describe the stress dependent viscoelastic response for each of the material properties. A new numerical procedure to predict long term laminate properties from lamina properties (obtained experimentally) was developed. Numerical instabilities and time constraints associated with viscoelastic numerical techniques were discussed and solved. The numerical procedure was incorporated into a user friendly microcomputer program called Viscoelastic Composite Analysis Program (VCAP), which is available for IBM ‘PC’ type computers. The program was designed for ease of use and includes graphics, menus, help messages, etc. The final phase of the study involved testing actual laminates constructed from the characterized material, Kevlar/epoxy, at various temperature and load levels for 4 to 5 weeks. These results were then compared with the VCAP program predictions to verify the testing procedure (i.e., the applicability of TTSP in characterizing composite materials) and to check the numerical procedure used in the program. The actual tests and predictions agreed, within experimental error and scatter, for all test cases which included 1, 2, 3, and 4 fiber direction laminates. The end result of the study was the development and validation of a user friendly microcomputer program that can be used by design engineers in industry to predict thermoviscoelastic properties of orthotropic composite materials. / Ph. D.

Montmorillonite reinforced polymers are a new development in the area of nanocomposite materials. Since reinforcement of epoxy is important to the development of high strength adhesives and composite matrices, the introduction of montmorillonite to epoxy is of interest. Compositional effects on epoxy reactivity, on molecular relaxation, and on mechanical properties were investigated. Change in reactivity was determined by Differential Scanning Calorimetry. Tensile properties at room temperature indicated improved modulus and retention of strength of the epoxy matrix but a decreased elongation to failure. Depression of dry nanocomposite glass transition was observed for nanocomposites beyond 5% by weight montmorillonite. Samples that were saturated with water showed lower moduli due to the epoxy matrix. The greatest moisture absorption rate was found at 7%, the least at 3%.

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / M.S.

Thesis (Ph.D.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering.. / Title from title screen. Includes bibliographical references.

The structural response of unreinforced masonry elements strengthened with hybrid elastomeric/fiber materials was investigated through material characterization and flexural experiments. Material characterization tests were performed on various unreinforced and reinforced elastomeric materials to identify those materials that were best suited for use as structural retrofits. After material characterization was completed, the three most promising material systems were selected for further investigation, including one unreinforced elastomer film and two reinforced elastomer films with fiber orientations at 0/90° and +/- 45° relative to the major axis of the masonry elements. A series of four-point bending tests were performed on the selected masonry and epoxy bonded elastomer/fiber hybrid retrofits to determine the structural response of the composite systems. The experimental load-deformation response was used, along with material characterization results, in the development of a semi-empirical model to predict the static moment capacity of the strengthened masonry system. This model will be used in the development of reliable design criteria for masonry walls strengthened with these advanced materials.

Cysteine proteases are important drug targets due to their involvement in many biological processes such as protein turnover, digestion, blood coagulation, apoptosis, cell differentiation, cell signaling, and the immune response. In this thesis, we have reported the design, synthesis and evaluation of clan CA and clan CD cysteine protease inhibitors. Aza-peptidyl Michael acceptor and epoxide inhibitors for asparaginyl endopeptidases (legumains) from the bloodfluke, Schistosoma mansoni (SmAE) and the hard tick, Ixodes ricinus (IrAE) were designed and synthesized. SARs were similar, but with some notable exceptions. Both enzymes prefer disubstituted amides to monosubstituted amides in the P1' position and potency increased as we increased the hydrophobicity of the inhibitor in this position. Extending the inhibitor to P5 resulted in increased inhibitory potency, especially against IrAE, and both enzymes prefer small over large hydrophobic residues in the P2 position. Aza-peptide Michael acceptor inhibitors are more potent than aza-peptide epoxide inhibitors and, for some of these compounds, second order inhibition rate constants are the fastest yet discovered. We have also synthesized aza-peptidyl Michael acceptor and epoxide inhibitors for the parasitic cysteine proteases; cruzain, rhodesain. We have found that monosubstituted amides were favored over disubstituted amides indicating the involvement of the amide hydrogen in a H-bond network. We have shown that aza-peptide epoxides were as potent as Michael acceptors and we have obtained compounds with IC50 values as low as 20 nM. We have worked on the synthesis of heterocyclic peptidyl α-ketoamides, peptidyl ketones and aza-peptidyl ketones as calpain inhibitors. We have synthesized peptidyl α-ketoamides with nucleotide bases in the primed region to create compounds that can cross the blood-brain barrier. We have improved the potency by introducing a hydrophobic group on the adenine ring. We have obtained compounds with Ki values in the nanomolar range. We have designed peptidyl aminoketones as a new class of inhibitors for calpain. Peptidyl aminoketones were less potent than peptidyl α-ketoamides but still reasonable inhibitors of calpain that have the potential to cross the BBB.

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.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy