Abstract not available

The main source of the time-dependent behavior of fiber-reinforced composites is their polymeric matrix, which causes concerns about their long term durability. Although for composites where organic fibers such as Graphite are used, the fibers are also a contributing factor. A composite material may exhibit an appreciable amount of creep, depending on the state of stress and temperature. Viscoelastic flow in the matrix and internal flaw formation and growth are the main sources of this creep. Thus a study was made on the viscoelastic behavior of GI/BMI fiber reinforced composite. An experimental method for testing a large number of composite materials in compression was developed. The samples were tested according to the test matrix consisting of combinations of static and cyclic loads and temperatures. The fixtures were calibrated to check the validity of measurements and reproducibility of results. Stress gradients were caused by frictional effects between the fixture and samples. The modulus change of samples over a period of time were studied. Bending parameters in samples were measured and analyzed for different stresses, clamping forces, temperatures and time. Mechanical models were used to explain the basic principles behind creep of a viscoelastic material followed by a theoretical explanation and study of creep. The linear and non-linear viscoelastic constants were studied and a methodology to analyze these results was presented. The linear and non-linear constants were used in a prediction model and predictions of a composite creep strain with time were made. Creep data obtained tor [45/0/-45/90]������ for a period of three months were compared to the prediction model. / Graduation date: 1994

No description available.

No description available.

Single Wall Carbon Nanotubes (SWNTs), discovered in 1993, have good mechanical, electrical and thermal properties. Polyacrylonitrile (PAN) is an important fiber for textiles as well as a precursor for carbon fibers. PAN has been produced since 1930s. In this study, we have processed SWNT/PAN fibers by dry-jet wet spinning. Purified SWNT, nitric acid treated SWNTs, and benzonitrile functionalized SWNTs have been used. Fiber processing was done in Dimethyl Formamide (DMF) and coagulation was done in DMF/water mixture. The coagulated fibers were drawn (draw ratio of 6) at 95 oC. Structure, orientation, and mechanical properties of these fibers have been studied. The cross-sections for all the fibers are not circular. Incorporation of SWNT in PAN results in improved mechanical properties, tensile modulus increased from 7.9 GPa for control PAN to 13.7 GPa for SWNT/PAN composite fiber, and functionalized SWNTs result in higher improvements with tensile modulus reaching 17.8 GPa for acid treated SWNT/PAN composite fibers. The theoretical analysis suggests that observed moduli of the composite fibers are consistent with the predicted values.

The material properties of fibre networks and fibre reinforced composites are strongly influenced by fibre-fibre interactions. Stress transfer between load bearing elements in such materials is often dictated by the nature of the fibre-fibre interface. Inter-fibre bonding is solely responsible for internal cohesion in paper, because all stresses transferred between fibres operate through fibre-fibre bonds. . The future development of cellulosic fibre materials will require an improved understanding of the fibre-fibre interface. Fluorescence resonance energy transfer (FRET) was proposed as a new tool for the study of fibre interfaces. A protocol for covalent linkage of fluorophores to natural and regenerated cellulosic fibres was developed and the absorptive and emissive properties of these dyes were characterized. The fluorescent response of these dyed fibres in paper sheets was studied using steady-state fluorescence spectroscopy. Fluorescence micrographs of fibre crossings on glass slides were analyzed using the FRETN correction algorithm. Energy transfer from coumarin dyed fibres to fluorescein dyed fibres at the interface was observed. The FRETN surfaces for spruce and viscose rayon fibre crossings were distinctly different. The FRET microscopy method was able to detect statistically significant differences in spruce fibre interface development when fibre fraction and wet pressing were varied. The coalescence of natural cellulosic fibre interfaces during drying was also observed with the technique. Polysaccharide films were employed as model systems for the natural and regenerated cellulose fibre interfaces. It was found that pressing cellulose films did not result in significantly increased FRETN either due to resistance to deformation or the inability to participate in interdiffusion. Conversely, xylan films demonstrated a drastic increase in the FRETN signal with increased wet pressing. These results support the previously observed differences between regenerated cellulose fibres and natural wood fibres. The results of the FRETN analysis of the polysaccharide film model systems suggest that lower molecular weight amorphous carbohydrates are likely to be significant contributors to fibre interface development.

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.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2008. / Title from PDF title page (viewed Jan. 28, 2010). Additional advisors: Michael Anderson, Fouad Fouad, Wilbur Hitchcock, Virginia Sisiopiku. Includes bibliographical references (p. 203-208).

Thesis (M.S.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed Jan. 29, 2010). Includes bibliographical references (p. 66-70).

Thesis (M.S.) in Civil Engineering--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 115-121).