Effect of Fiber Architecture Parameters on Deformation Fields and Elastic Moduli of 2-D Braided Composites

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.

Numerical and Experimental Investigation of the Hydrostatic Performance of Fibre Reinforced Tubes

“…Under uniaxial static load, an increase in braid angle leads to a decrease in the longitudinal modulus and an increase in transverse modulus. In addition, the shear modulus and the in-plane Poisson's ratio increase with an increase in braid angle with a maximum peak at ±45 • [19]. The transverse moduli, strength, and dimensional stability of braided composites arise from helical fibres and the damage tolerance results from the locking mechanism between the intertwined fibres of the braid architecture that helps in preventing or limiting the yarn delamination [2].…”

“…19 Representative images of burst filament wound tubes of all reinforcement angles Table 3 illustrates the estimated fibre volume fraction for each wind angle along with the density of the composite. The density and elastic properties of a unidirectional fibre reinforced ply at a specific fibre volume fraction (f ) were calculated through the HalpinTsai equations.…”

Elastic properties of large tow 2-D braided composites by numerical and analytical methods

“…The fiber bundles of the large tow composites used by automotive industry typically contain on the order of 1Ok filaments. (Naik et al, 1994) Figure 2.2 shows two sectional micrographs of a multi-ply braided composite laminate (Dadkhah et al, 1995). It can observed that the fiber geometry exhibits many irregular features that are difficult to model.…”

“…This required that the diameter of the axial braider, d,, be larger than that of the 4, braiders db,. Their ratio was: 5 = case da (b) (1) (Naik et al, 1994), and (d) cross sectional micrographs along the axial and f8 braiders (Dadkhah et al, 1995). Also, the model only incorporated the undulation of the +0 braiders, and the lenticular cross section of the braiders were simplified to be rectangular to preserve the flattened and expansive characteristic of the fiber tows.…”

“…The geometry of the braided architecture was modeled using idealizations similar to those presented by Naik (1994) and others (e.g., Vandeurzen et al, 1997) in which the composite was idealized as an array of repeating unit cells. The homogenized elastic properties of the unit cell were determined by finite element analysis (FEA).…”