Yanhua Xu

Geometrical analysis of co‐woven knitted preform for composite reinforcement

In this paper, a co‐woven knitted (CWK) structure for composite reinforcement is presented. Based on the experimental observations, its unit cell and representative volume element (RVE) geometries were identified along with the idealized cross‐sectional shapes of the weft, warp and stitch yarns. A geometrical model for the RVE was proposed and the mathematical equations were derived to describe the relationships between the geometrical parameters and process variables. The model was verified with the experimental data and good agreements were obtained between the calculations and measurements of different yarn lengths in a RVE. The inserted and stitch fiber volume fractions as well as total fiber volume fraction were calculated and their variations with the stitch‐to‐inserted yarn linear density ratio under different fabric tightness factors were discussed. The geometrical model provides a basis for the establishment of process windows for the CWK preforms as well as for the prediction of the mechanical behavior of the CWK‐reinforced composites.

Analysis and prediction of elastic constants of co-woven-knitted fabric (CWKF) composite

This paper presents an analytical and numerical model for the prediction of tensile elastic constants of a novel textile structural composite, namely co-woven-knitted fabric (CWKF) composite. Based on the CWKF geometry model previously developed, the direction angles of basic-cells of the weft, warp, and stitch yarn components in a representative volume elementary were determined. The micromechanics method and both isostrain and isostress conditions were applied to the yarn and the pure resin components, and the overall stiffness or compliance matrix of the composite was obtained. The normal elastic constants were calculated and compared with the experimental ones. The results showed that the relative errors between the calculated and the tested values are at an acceptable level (<10%). Thus, the proposed model can be used for the predictions of other elastic constants of the CWKF reinforced composite and effects of structural parameters.