Abstract

The effects of various braiding parameters for 2-D triaxially braided textile composites were systematically investigated both experimentally and analytically. Four different fiber architectures designed to provide a direct comparison of the effects of braid angle, yarn size and axial yarn content were tested. Moiré interferometry was employed to study the effect of these parameters on the surface strain fields in the material. Moiré results for the surface strain fields were found to be strongly influenced by all of the three parameters. Larger yarn sizes led to higher normal strains and led to early cracking under transverse loading. Increasing the axial yarn content by using larger axial yarns also led to premature cracking under transverse loading. The mechanical tests showed that stiffness properties were not a function of yarn size. However, they were strongly influenced by braid angle and axial yarn content. A simple analysis that explicitly models the fiber architecture was developed. The analysis technique successfully predicted mechanical properties and also the trends in the test data. Increasing the braid angle led to decreasing longitudinal modulus, increasing transverse modulus, and in-plane shear modulus values that peaked for a braid angle of ±45°. Increasing the axial yarn content led to increasing longitudinal modulus, decreasing in-plane shear modulus and Poisson's ratio values. Out-of-plane Young's modulus and shear moduli were insensitive to variations in braid angle and axial yarn content. Composite properties were found to be more sensitive to variability in braid angle than to variations in axial yarn content.