Estimation of in-plane elastic properties of stitch-bonded, non-crimp fabric composites for engineering applications

Stitch-bonded, non-crimped fabric composites are among the most common forms of structural fiber-reinforced polymer composites. A complex three-dimensional finite element model is usually required for the accurate prediction of the mechanical properties of these composites. The objective of this work was to develop a model to predict the in-plane elastic properties of non-crimped fabric composites (without structural stitching) with no inputs from the experimental characterization of the composites themselves. The motivation for this work was to develop a swift, accurate methodology that would be very beneficial with ever reducing design cycle times (for screening different fabrics) and as these fabrics find new application areas. The modeling approach used only the properties of the dry non-crimped fabric and the resin as inputs. Models were constructed to account for the geometrical aspects of the non-crimped fabric such as yarn width and yarn spacing, which depend on the stitching pattern employed. They included regions of pure matrix between fiber tows as well as between fabrics parallel to the stacking plane. The stitching threads, voids, crimping of the fiber tows and damage or disturbances to the fiber due to the stitching were not modeled. The effective elastic properties of uni-directional, bi-axial and tri-axial non-crimped fabric composites are computed using classical composite lamination theory and finite element analysis. The predicted results are found to be in good agreement with experimental results obtained using composites fabricated by vacuum-assisted resin transfer molding.