Analysis of advanced thin-walled composite structures

The use of fiber reinforced composites is increasing in engineering applications. One of the major issues in composite structures is the understanding of the role of the material's anisotropy on the deformation modes, damage modes and failure mechanisms. This research work addresses these stiffness and strength related issues by developing analytical models for the prediction of deformation modes and their coupling effects and damage onset and growth in laminated composites. Accurate prediction of stiffness, response, damage modes and failure mechanisms is bound to lead to the design of efficient and damage tolerant composite structures.; In the first part of this work shear deformation models including hygrothermal effects are developed for the analysis of mid-plane edge delamination and local delamination originating from transverse cracks in 90{dollar}spcirc{dollar} plies. The results of these models are combined with a previously developed shear deformation model for mixed-mode edge delamination to yield a unified analysis of delamination and the ability to identify the critical failure modes and loads.; In the second part, a variationally and asymptotically consistent theory for thin-walled beams that incorporates the anisotropy associated with laminated composites is developed. The theory is based on an asymptotical analysis of 2D shell energy. The major advantage of this approach lies in the fact that the displacement function is not assumed a priori and is determined as a result of the minimization of the energy functional. As a result, two nonclassical contributions to the warping emerge. While these new contributions vanish for isotropic and orthotropic materials, they have a significant influence on the response of generally anisotropic materials. The accuracy of previously developed theories is assessed by comparing the resulting displacement fields and an assessment of the significance of shear deformation is presented. Comparison of predictions with finite element simulation and test results illustrate the consistency and accuracy of the developed theory.