A study has been made of glass fibre reinforced plastic beams in three-point bending. In recent years, the importance of flexural loading in composites has manifested itself in the form of composite leaf springs, helicopter rotors, and other applications. This study is directed at the initiation, growth, characterization and measurement of damage in unidirectional and cross-ply composite beams. Beams were tested in three-point static and cyclic bending. Following damage initiation, either by a machined notch or by repeated cycling, damage growth has been characterized by two damage parameters: a damage depth encompassing a number of broken fibres on the tensile surface at the central load point, and a damage length or delamination parallel to the beam longitudinal axis. A model was developed to predict the compliance, or deflection under applied load, as a function of beam properties and damage dimensions. The model is able to predict the compliance of damaged beams with reasonable accuracy. From fracture mechanics concepts it is shown that the two damage dimensions, depth and length, are related. It is concluded that the increase in compliance, a result of the growing damage dimensions, is related to the growth of the damage depth; the damage length follows from the relation between damage parameters and the compliance follows from the compliance model. The damage state can thus be determined by compliance measurements if the relevant material properties and loading conditions are known. However, in service, compliance measurements may not be practical. Therefore a section of this study is devoted to an alternative damage measurement technique, namely acoustic emission monitoring. Damage initiation, compliance, damage length and damage depth were measured with AE monitoring techniques. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Prestressing a steel girder reduces the required structural steel weight, limits tension stresses in the section, increases the ultimate strength, and increases the fatigue resistance. The technique of prestressing with tendons can be used for strengthening of existing bridges as well as for construction of new bridges. This thesis presents an analytical study of the behavior of simply-supported and continuous prestressed composite girders and describes the benefits of prestressing steel in composite construction. Analytical models are developed and used as a basis for a computer program that calculates the stresses and displacements in the cables and the girder at discrete number of nodes along the length of the girder. The effects of design variables such as prestress force, tendon profile, eccentricity and tendon length are studied. The results indicate that prestressing is an effective means of increasing the load carrying capacity of simple-span as well as continuous composite girders.

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Thesis (Ph. D.)--School of Aerospace Engineering, Georgia Institute of Technology, 2003. Directed by Erian A. Armanios. / Vita. Includes bibliographical references (leaves 209-212).

Thesis (M.S.) in Mechanical Engineering--University of Maine, 2002. / Includes vita. Bibliography: leaves 109-113.

Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Hodges, Dewey; Committee Member: Bauchau, Olivier; Committee Member: Volovoi, Vitali; Committee Member: White, Donald; Committee Member: Yu, Wenbin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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