No description available.

No description available.

The study described in this thesis examines how modification with different thermoplastics affects the structure and properties of a tetrafunctional epoxy re5ín_ Polyetherimide (PEI) is found to give the best improvement in fracture properties without loss in Youngs Modulus and the PEI/epoxy system is used as the basis for further study. The influences of PEI concentration, initial cure temperature, test temperature and the presence of a second thermoplastic additive, are investigated. The information provided gives insight into the likely mechanisms of toughening in tetrafunctional epoxy/thermoplastic blends. Flory-Huggins Lattice Theory is used to describe miscibility behaviour for a number of curing thermoplastic/epoxy blends and the predictions compared with the actual morphologies observed. Further, the sensitivity of the expected miscibility behaviour to fluctuations in Flory Huggins interaction parameter X12 and number-average molecular weight Mn of the thermoplastic, is considered. Dynamic mechanical analysis is used to monitor the changing viscoelastic properties of curing thermoplastic/epoxy blends, allowing investigation of the way different thermoplastics influence the state transformation profile of a curing epoxy resin.

This thesis presents the results of an investigation into the effects of hygrothermal conditioning on the mechanical properties, and fatigue properties of epoxy based composites reinforced with carbon, glass and Kevlar 49 fibres. Cross-plied laminates (0/90) of these materials of nominal volume o fraction 60% were conditioned by drying at 60°C, by exposure to a 65% RH atmosphere at room temperature and by boiling in water. The effects of conditioning on the tensile and shear strengths and on the tensile fatigue response are discussed. The effects of exposure to an extreme diurnal cycle and to the ultra violet in isolation on the tensile properties are also discussed. The 0/90 tensile properties of the three laminates are relatively little affected by the environmental conditioning except for the case of GRP exposed to boiling water, when corrosion damage to the glass fibres significantly reduces the composite strength, and in the KFRP in which the strength is reduced by complete drying. The +/-45 strengths are more sensitive to the effects of moisture, however, it appears that the optimum strength is obtained after conditioning in the 65% RH environment. Acoustic emission monitoring of the tensile tests shows distinctive differences between KFRP and the two other types of composite and permits the identification of characteristic effects of moisture on the tensile failure mechanisms of all three materials. Tensile fatigue tests have been carried out on the laminates in the 0/90 orientation. The CFRP shows no effect of conditioning on the fatigue behaviour, and in the GRP only the boiling water conditioning affects the results. The tensile fatigue of the KFRP is affected both by boiling and by drying, the latter being the most severe. The fatigue response of the KFRP shows a dramatic down turn at lives in excess of 105 cycles. This effect appears to reflect the ease with which mechanical damage is sustained by the aromatic polyamide fibres. The residual strengths of the laminates after fatiguing is discussed and possible mechanisms for the damage accumulation in the materials during fatiguing are given.

The static and fatigue properties of advanced epoxy-based composites reinforced with carbon, glass or aromatic polyamide (Kevlar-49) fibres have been measured for a range of different loading and environmental conditions. Cross-plied laminates were tested in tension in the 0/90 and +/-45° orientations and also under flexural loading. The laminates were similar, except for the type of fibre. The effects of environmental exposure were assessed by preconditioning test specimens to equilibrium by either drying at 60°C, storage at 65%RH at ambient temperature or boiling in water. Moisture absorption was through the resin alone for CFRP and GRP and by additional absorption by the fibres for KFRP. Fatigue testing revealed that the tensile performance in the 0/90 orientation is strongly dependent on the level of cyclic strain. 0/90 CFRP has excellent fatigue and environmental resistance but GRP exhibits a steep fatigue curve and the static and low cycle fatigue strengths are both reduced by boiling. The fatigue strength of 0/90 KFRP is reduced by drying, more so than by boiling, and in all conditions the stress/log-life curves are characterised by a downward curvature or 'knee'. Tensile preloads do not significantly affect the residual fatigue properties or the equilibrium levels of moisture uptake, although extensive damage involving cracking in both longitudinal and transverse plies may lead to increased absorption rates. A tendency for Kevlar fibres to split or 'defibrillate' plays an important role in most failures of KFRP. It limits the shear strength and causes flexural failures to occur at the compression surface at low stress levels. 0/90 CFRP also fails at the compression surface in flexure but GRP fails at the tensile surface, the environmental fatigue performance resembling that under axial tensile loading. The +/-45° tensile and low cycle fatigue strengths are sensitive to the effects of conditioning, all laminates exhibiting optimum performance after conditioning at 65%RH, although generally these effects become insignificant at long lives.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Two evaporative-cooling materials were studied which are (i) salt hydrates and (ii) polyacrylic acid for the purpose showing proof of concept of being able to put evaporative-cooling materials into a composite with the Air Force polyimide AFR-PEPAN. The salt hydrates were observed to absorb water and then evaporate water, but due to having a collapsible lattice, made them incapable of reabsorbing water. Polyacrylic acid was mixed into an epoxy sheet at polacrylic acid weight percentages of 5, 10, 12.5. For each weight percentage there was a hydrated epoxy specimen and a dry epoxy specimen. All specimens were individually shot with a hot air stream (temperature approximately 1300C). Temperature readings were taken for each sheet. The hydrated specimen exhibited greater evaporative cooling over its dry counterpart. 12.5 wt% was shown to have the best evaporative cooling mechanism. Experiments were repeated to show that the polyacrylic could reabsorb water. This study illustrates proof of concept utilizing polyacrylic acid as an evaporative cooling material.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 220-231).

Thesis (Ph. D.)--Lehigh University, 2003. / Includes bibliographical references and vita.

Thesis (M.S.)--Florida State University, 2003. / Advisor: Dr. Zhiyong Liang, Florida State University, College of Engineering, Dept. of Industrial Engineering. Title and description from dissertation home page (viewed Mar. 2, 2004). Includes bibliographical references.