Micromechanical Models for Bending Behavior of Woven Composites

Thin woven composites have been popular for space structures due to the symmetrical and balanced properties. Although in-plane properties of these materials can be calcu- lated accurately using the classical lamination theory (CLT), the corresponding bending properties lack any accuracy for one or two-ply woven laminates. Experiments on thin laminates made from woven composites disagree with the estimates of bending stifiness and strains using CLT. Such estimates can result in errors of up to 200% in the maximum bending strains or stresses, and up to 400% in the bending stifinesses. This is because CLT assumes that the flbers and the matrix are uniformly distributed in each lamina, and relies on this uniformity in the integration of the transformed laminate stifinesses over the thickness of the laminate. However, a thin laminate made from fabrics in fact con- sists of bundles of flbers that are typically much thinner than the overall thickness of the laminate; these bundles are not homogenous through the thickness. This paper presents micromechanical models for bending behavior of woven composites considering the flber bundles and the matrix and their interactions. Finite element models are developed to estimate the bending properties of plain weave composites. The results are compared to experimental data, showing very good agreement particularly for a lamina.