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A micro-meso-scale model is proposed to predict shear deformation and strength of textile-reinforced composites, considering shear non-linearity, strain-rate dependent elastic and visco-plastic behavior, and 3D geometrical nonuniformity of the reinforcement. The matrix and fibers are combined using bridging-model micromechanics into composite tows. Combined with the geometrical characteristics of the reinforcement, a composite with orthotropic rate-dependent visco-plastic behavior is obtained. A damage model detects damage in the composite tows and interstitial matrix, introducing stiffness reduction and stress redistribution. The model constants are measured by experiments on neat epoxy matrix and unidirectional glass/epoxy specimens. Model predictions are validated with independent experiments. [ABSTRACT FROM AUTHOR]

The objective of this work is to develop a methodology to predict matrix damage initiation and evolution in laminated composites subjected to monotonic cooling using discrete damage mechanics and a careful characterization of the required temperature-dependent material properties. Since prediction of thermo-mechanical damage requires precise knowledge of the temperature-dependent properties of the material, back-calculation of fiber and matrix properties from different sources is included. The proposed methodology is flexible, in that it can be adapted to the availability of experimental data. A compilation of literature data is developed to estimate the properties of several fiber and matrix systems. Prediction of lamina and laminate temperature-dependent properties are compared with available data. Furthermore, temperature-dependent fracture toughness of four material systems are estimated from available crack density data. For the material systems studied, it is found that temperature-independent fracture toughness is satisfactory for prediction of damage initiation, evolution, and saturation. [ABSTRACT FROM AUTHOR]

Abstract: A model to predict the effective stiffness of woven fabric composite materials is presented. Taking advantage of the inherent periodicity of woven fabric architecture, periodic microstructure theory is used at the mesoscale for the case of a two-phase heterogeneous material with multiple periodic inclusions. For plain weave fabrics, the representative volume element (RVE) is discretized into fiber/matrix bundles and the pure matrix regions that surround them. The surfaces of the fiber/matrix bundles are fit with sinusoidal equations using two approaches. The first is based on measurements taken from photomicrographs of composite specimens and the second is based on an idealized representation of the plain weave structure. Three-dimensional sinusoidal surfaces are generated from the face equations and weave shape for the real and idealized cases in order to mathematically describe the fiber/matrix bundle regions, which are treated as unidirectional composites. Model results from the idealized geometry are compared to experimental data from the literature and show good agreement, including interlaminar material properties. From a comparison of the real and idealized geometry results for similar material RVE dimensions, it is seen that the model is capable of predicting significant changes in the in-plane material properties from slight mismatch in the fiber/matrix bundle shape and crimp, which can be captured using the geometric surfaces generated from photomicrograph measurements. [Copyright &y& Elsevier]

Micro-buckling of unidirectional fiber-reinforced composites is investigated in this paper by means of an explicit representation of a geometrically imperfect fiber within the context of kinematical and material non-linear behavior. Two types of fiber imperfections are considered: a helicoidal shape, identified as 3D imperfection; and a sinusoidal plane shape (2D imperfection). Both imperfection models are characterized by a maximum misalignment angle of the fiber with respect to the ideal or perfect configuration, as is usually considered in this field. A total of 816 cases were computed in terms of imperfection type (either 2D or 3D), fiber volume fraction, fiber arrangement (square or hexagonal array), orientation for 2D models, matrix yield stress, and misalignment angle. Two load cases, with constrained and unconstrained transverse strain, were considered. Assuming periodic boundary conditions, homogenization was carried out to obtain macroscopic stresses. Numerical results are compared with an analytical model available in the literature. The results show a high imperfection-sensitivity for small misalignment angles; on the other hand, the type of imperfection and the fiber arrangement do not have a large influence on the results. In addition, it was found that this problem is governed by fiber volume fraction and matrix yield stress only for small imperfections, whereas for large misalignment angles, a change in fiber volume fraction produces small changes in micro-buckling stress. [ABSTRACT FROM AUTHOR]