Finite element micromechanical strength modeling of stitched 3d-orthogonal composites

Three-dimensional reinforcement is often employed in thick composite parts to increase delamination resistance and through-thickness properties. In the current study, a three-dimensional orthogonal woven S2-glass composite is investigated using finite element micromechanics. A detailed series of photomicrographs has been taken to ensure a precise representation of the layout and dimensions of the weave geometry under consideration. This allows for the development of a representative volume element (RVE) that will accurately depict the chosen material. The RVE structure is modeled directly through three-dimensional FEM. Stiffness and strength are determined using a series of simulated characterization tests upon the RVE with a detailed analysis of the resulting microstress field. Modeling results are verified by comparison to experimental data. Tensile tests and Iosipescu shear tests have been performed to determine in-plane and transverse shear properties. In-plane stiffness and strength are predicted with 90% or better accuracy. Transverse shear properties were less well predicted, but strength was still predicted within 86% accuracy. The micromechanical methods are then employed towards a parametric study of the effect of stitch density on potential improvement of delamination resistance and shear properties, as well as loss of in-plane properties.