This paper presents results of a comparative study of the effects of moisture and temperature on tensile properties of Kevlar 49/epoxy, graphite/epoxy, single fiber and Kevlar 49-graphite/epoxy hybrid composites. The work reported here shows variations in tensile strength, elastic modulus and Poisson's ratio with changes in the hygrothermal conditions. A temperature range of 23°C to 150°C was considered for both dry and wet specimens exposed to moisture for 200 days. Moisture was introduced into the specimen by immersion in distilled water. Effects of the kind of outer fiber of the same hybrid system was also studied for better understanding of the behavior of hybrid composites. Variation in the tensile modulus determined by various test methods is also reported.The results indicate that moisture and temperature degrade the tensile strength of hybrid and single fiber composites. The tensile modulus of Kevlar 49-graphite/epoxy is comparatively higher than that of Kevlar 49/epoxy. The degradation of the tensile modulus is mostly temperature dependent. The presence of moisture either increases or decreases the tensile modulus depending upon the laminate and exposure conditions. Poisson's ratio in general appears to increase with temperature. In the presence of moisture the Poisson's ratio further increases between the temperatures of 45°C to 150°C.

This research consists of experimental load tests and numerical simulations of structural steel connections with various filler materials to study the effect of non-steel fillers on the connection strength. Non-steel fillers are used in the steel connections to provide thermal insulation by reducing thermal bridging. Eight specimens having steel and polypropylene filler plates of various thicknesses were tested in the laboratory. The collected data were compared to a Finite Element Analysis (FEA) using ABAQUS to validate the numerical results. After validation, three parametric studies were conducted using ABAQUS to provide insight into general behavior of connections with a variety of fillers that could be used as thermal breaks. In addition, an extreme case of having air gaps instead of alternative fillers was also considered. The Research Council on Structural Connections (RCSC 2014) suggests a reduction in the bolt shear strength when undeveloped fillers with a thickness of more than 0.25 inch are used while using any non-steel material is prohibited due the limited research available. Most research studies have investigated the mechanical behavior of thermal breaks in either end-plate moment connections or slip-critical connections. No data is available for thermal breaks in bearing-type connections up to failure. This research aims to study the effects of filler material properties such as modulus of elasticity and strength on bolt strength, as well as investigate whether the current equation in RCSC 2014 is applicable for alternative filler materials like polypropylene that has less than 0.5% of the steel modulus of elasticity and less than 10% of steel strength. This work would not have the spirit it has without the guidance and support provided by my academic advisor Dr. Thomas Schumacher. First and foremost, I would like to show my sincere gratitude to Dr. Schumacher for his expert advice, immense knowledge, encouragement, motivation and for funding the experimental test. Throughout the rough road to finish this thesis, Dr. Schumacher's support was not limited to the academic assistantship only, but also emotionally. I would like to extend my gratitude to my thesis committee member Dr. Peter Dusicka for his ideas and feedback. I would also like to thank committee member Dr. Hormoz Zareh for his invaluable advice. The knowledge I gained from his classes along with his advice were of great help in numerous aspects of this research. I would like to thank the Higher Committee of Education Development in Iraq (HCED) for giving me this scholarship and the opportunity to pursue my Master's degree. I would also like to thank Portland State University for their financial support.

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