Thesis (Ph. D.)--Lehigh University, 2004. / Includes vita. Includes bibliographical references (leaves 179-194).

Advance composite materials based mainly on epoxy resins are being used in increasing amounts in aerospace components due to their high strength:weight ratio. Such components have to survive in a range of temperature and humid environments in different parts of the world. The current generation of epoxy resins used in high performance fibre reinforced laminates absorb moisture from the atmosphere. Moisture absorption by the epoxy resins leads to a reduction in glass transition temperature and to a softening of the resin with a loss of resin stiffness and strength. In certain applications the components have to survive low impacts from dropped tools and rough handling during maintenance. Low energy impacts of this nature are considered potentially dangerous mainly because the damage might be left undetected. Even where no visible impact damage is observed at the surface, matrix cracking and interlaminar failure can occur, and the load carrying properties of the composite components is considerably reduced. A compression after impact (CAI) test is widely used in industry as the major screening parameters for materials selection. The aim of the work reported in this thesis was to determine the influence of thermohumid conditions on CAI properties and to assess the degradation behaviour of composite laminates under these thermohumid conditions.

Comparative studies were carried out on the curing kinetics, physical and mechanical properties of conventionally and microwave cured epoxy resins. Epoxy resins Araldite LY 5052 and DLS 772 were used for this study. 4 4' Diaminodiphenyl sulfone was used as a hardener in the preparation of both systems. Nuclear magnetic resonance and gel permeation chromatography were used to identify the chemical structure of the resins. Differential scanning calorimetry was used to monitor the curing kinetics of conventionally cured epoxy samples while a microwave heating calorimeter was used to monitor the curing kinetics of microwave cured epoxy samples 'in situ'. These studies were carried out under non-isothermal and isothermal conditions. For both conditions, there was a significant increase in the fractional conversion of the microwave cured samples compared to the conventionally cured samples. The curing reactions for samples cured using microwave heating took place over a smaller temperature range. Higher reaction rates were observed in the samples cured using microwave heating.There were some differences in the kinetic parameters of the non-isothermal curing reactions of samples cured using microwave and conventional heating. For the Araldite LY 5052 / 4 4' DDS epoxy system, the microwave cured samples had higher activation energy than conventionally cured samples, while for the Araldite DLS 772 / 4 4' DDS epoxy system, the microwave cured samples had lower activation energy. The activation energies of the microwave isothermal curing of both Araldite LY 5052 / 4 4' DDS and Araldite DLS 772 / 4 4'DDS epoxy systems were lower than the activation energies of the conventionally cured samples.Infrared spectroscopy showed that the curing reaction followed the same path during conventional and microwave heating. It also revealed that the reaction rate of the microwave cured samples was higher than the conventionally cured samples.For both epoxy systems, the microwave cured samples had a higher glass transition temperature (Tg) , higher cross-link density (v) and lower molecular weight between cross-links. These showed that the microwave cured samples had a more compact network structure than the conventionally cured samples, which is an indication of better mechanical properties.A microwave reaction system was used to successfully dissolve conventional and microwave cured samples of Araldite DLS 772 / 4 4' DDS epoxy system. The chemical structure of the decomposed product was determined.

This study was made to determine the advantages of the use of epoxy resins in the industrial arts laboratory. The purpose of this study was to determine the feasibility of using epoxy resins as a wood adhesive. Data was gathered from texts, periodicals, and unpublished data. Tests were conducted using epoxy samples acquired from three epoxy manufacturers on three different woods and joints. The study discusses the advantages and disadvantages of using epoxy resins as a wood adhesive and the material and equipment necessary for the use of epoxy resins. Strength tests were performed on the joints adhered with epoxy and on joints adhered with white glue. A hand operated high tensile strength machine was used to conduct the tests. Epoxy Resins were found, in most cases, to give a more durable bond than white glue. Further studies should be made using epoxy resins as adhesives for metal, glass, plastic, and other materials used in the industrial arts laboratory.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.