Elastic Response of Porous Matrix Plain Weave Fabric Composites: Part II—Results

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Abstract
In this second of a two-part series of papers, the analytical and three-dimensional finite element models developed in Part I are implemented to predict the effective elastic response of both Stiff-porous ceramic and Soft-dense polymer matrix plain weave fabric composites. Analytical results obtained using a Modified Lamination Theory (MLT) model and which are based on four methods of unit-cell property averaging are presented. Effective elastic in-plane properties predicted via the finite element method for a single woven ply and for a laminate comprised of symmetrically arranged woven plies are also reported. Comparisons between the analytical estimates and the numerical predictions suggest that the Parallel (P-MLT) property averaging scheme yields, in an overall sense, good unit-cell effective property estimates. Thus, the P-MLT model was employed to conduct extensive parameter studies aiming at assessing the effects of the woven geometry and the overall microstructure on the effective elastic properties of Soft- and Stiff-matrix woven composites. Soft-matrix systems were shown to exhibit higher sensitivity to the unit-cell woven morphology and fiber/matrix elastic mismatch when compared to their Stiff-matrix counterparts. On the other hand, the effective elastic properties of Stiff-matrix systems were shown to be substantially reduced with increasing interbundle matrix porosity, and were also shown to be rather sensitive to the elastic properties of the thin fiber and bundle coatings. Surface contour data obtained from 3-D finite element analysis provide strong evidence of local micro-bending and stress concentrations within the unit cell. In both Soft- and Stiff-matrix systems, the out-of-plane normal and shear stresses along the bundle/matrix interface surfaces were shown to be at least an order of magnitude smaller than the predicted normal bundle stress along the fiber direction. This work presents detailed analytical and numerical parameter studies, and explores for the first time the relations between the microstructure and macromechanical woven composite response.