A study to investigate the factors that contribute to the variation among the stiffnesses of consolidated composite plates reinforced by plain-weave fabrics with various degrees of in-plane shear is presented. The first part of the two-part study focuses on the experiments performed. Threepoint bend tests were used to measure the effective stiffness of the composite plates along the global X and Y axes, which were aligned with the weft and warp orientations, respectively, in the undeformed configuration at 0° of shear. The warp yarns were sheared 0°, 10°, 20°, 25° and 30° toward the weft yarns. It was observed that as the shear angle in the plates increased, the thickness of the plates also increased. An increase in stiffness for bending in X-direction with increasing shear angle was observed as was expected, but the change in stiffness for bending in Y-direction was observed to be inconsistent with the expected decrease with increasing degree of shear.

Numerical investigations were pursued in an effort to understand the relationship between changes in the stiffness of plain-weave fabric-reinforced plates and the degree of in-plane shear within the fabric reinforcement. These numerical studies were motivated by an experimental study where the measurable geometric changes discerned among plates with different levels of in-plane shear were (1) the reorientation of the fibers within the plane of the plate, (2) an increase in thickness with increasing in-plane shear, and (3) the change in width of the fiber tows as function of in-plane shear. Finite element models were used to investigate the individual contributions of these geometric changes on the bending stiffness of the plates. For the material system considered in this study, the reorientation of the fibers and the change in plate thickness as a function of the state of shear were concluded to be the dominant factors affecting the bending stiffness of the plates. The change in cross-section orientation about the tow axis was determined to be insignificant.