Advanced techniques for constituent-based progressive failure analysis of composite structures

Progressive failure analysis of composite structures is an extremely challenging problem demanding numerical efficiency while transcending geometric length scales extending over several orders of magnitude. These two attributes place fundamentally opposite demands on the development of such analyses. The premise of this thesis was to investigate and implement pragmatic numerical techniques to enhance progressive failure analysis of composite structures with particular attention paid to addressing the impact of thermomechanical loads that may arise in structural problems.A hexagonally packed micromechanics model was implemented with an in-house finite element code, and optimized for speed, to allow macroscopic material property calculation on the order of milliseconds. Solution speeds were reduced by three orders of magnitude over previous models. Linear elastic micromechanics modeling capabilities were then extended to allow for time and temperature dependent material properties through a viscoelastic material model. A typical cure cycle for a glass/epoxy and carbon/epoxy composite was modeled. The constituent stresses generated during the cure cycle were then used to conduct a detailed analysis on the effects of residual stresses from cure cycles on lamina failure predictions at room temperature. It was found that the effects of thermal residual stresses from a cure cycle are negligible for room temperature failure predictions of unidirectional composite materials.A detailed analysis of cryogenic failure predictions was also conducted for unidirectional laminae and multidirectional laminates. It was found that cryogenic thermal loadings have a pronounced effect on failure predictions for both unidirectional laminae and multidirectional laminates.Finally, an orthotropic degradation scheme was used to simulate transverse matrix cracking in multidirectional laminates. A series of progressive failure predictions were modeled and compared to experimental data to show that orthotropic degradation of the matrix material under transverse loadings predicts the progression of failure in good agreement with experimental data.