Advanced Approach for Determining Equivalent Orthotropic Elastic Properties of Glass Non‐Crimp Fabrics/Polymer Matrix Composites

ABSTRACT Non‐crimp fabrics (NCFs) enable the cost‐effective manufacturing of large composite structures. Due to backing fiber bundles and stitching threads, the elastic properties measured from NCF specimens correspond to those of an unsymmetric laminate rather than an orthotropic lamina. Thus, measured strain data, which represent the average surface strain within the gage area, do not accurately reflect the overall strain in the test section. This study developed an advanced, systematic approach to determine the equivalent orthotropic elastic properties of unsymmetric glass NCF/polymer matrix composites. After fabricating specimens using NCFs combined with an epoxy system for resin infusion, their longitudinal, transverse, and shear stiffnesses, as well as Poisson's ratios, were measured. An iterative back‐calculation approach, integrating periodic microstructure micromechanics and 3D finite element solid modeling of the test specimens, was employed to determine the isotropic elastic properties of the fiber and epoxy as well as correction factors for the measured data. This approach enabled accurate predictions of polymer composite elastic properties across various fiber volume fractions. Notably, compared to the experimentally measured properties of the neat epoxy, the back‐calculated stiffness and Poisson's ratio for the epoxy exhibited errors of only −0.18% and 3.48%, respectively, demonstrating the high accuracy of this iterative approach.