| The design of polymer matrix composite joints is strongly influenced by the presence of out-of-plane or through-the-thickness stresses. These stresses can be critical, since out-of-plane interlaminar tension and shear strengths, as well as moduli, are strongly influenced by the low strength and stiffness of the polymer matrix constituents as well as the fiber matrix interface. To aid in the design of these structures, this research develops a methodology for predicting structural adequacy of composites in the presence of through-the-thickness loadings. Specifically, this work details guidelines for the design of resin fillet tee-joints for use in marine applications.;A combination of finite element analyses and analytical approximations are used to create these practically oriented design guidelines. A parametric study, utilizing finite element models, was conducted examining the effects of changing various material and geometric variables on the stresses and failure modes of the tee-joint structure. In conjunction with this examination, the tee-joint structure was sectioned in order to facilitate the creation of analytical approximations to predict the failure stresses in the various sections.;Some important design guidelines have been successfully created, whereas other features are more challenging and represent important areas for future research. Changes in the tee-joint design configuration precipitate a wide variation in structural behaviour covering a wide range of responses. Finite element methods are shown to be valuable in guiding the analytical effort by determining boundary conditions.;The second chapter of this dissertation deals with a different type of composite system and deals with the micromechanics of failure. In this section, the longitudinal tensile strength of the fiber reinforced metal matrix composite SCS6/Ti 15-3 was investigated for different loading configurations and specimen volumes. It was found experimentally that the strength had a modest volume dependence for specimens of the same loading configuration, while the strength is substantially affected by the loading type. These characteristics are encapsulated in an analytical model for the strength. In the model, it is assumed that fiber-breaks occur upon loading in a statistical manner. Due to the nature of the breaks, they cluster in certain regions and form macroscopic defects that dictate the strength of the composite. |
