OVERVIEW OF TEXTILES
2.3 The Geometry of Textile Reinforcement
2.3.1 Ideal geometry
2.3.1.1 Unit Cells
The geometry of a periodic textile is conveniently described in terms of unit cells,
following the example of crystallography ([2.6]; see also section 5.1.5). The unit cell is
defined by the requirement that the entire textile can be constructed from spatially translated
copies of it, without the use of rotations or reflections. The unit cell is not unique.
Nevertheless, as in crystallography, symmetry in the textile usually suggests a preference.
2.3.1.2 2D Weaves
Weaves may be classified by the pattern of interlacing. The simplest pattern is the
plain weave shown in Fig. 2-10(a). A disadvantage of the plain weave is the frequent
exchanges of position from top to bottom made by each yarn. This waviness or yarn crimp
reduces the strength and stiffness of the composite. Other weave patterns reduce the
number of exchanges and increase the lengths of straight segments of yarn (known as the
“float”). Of particular interest are the satin weaves shown in Fig. 2-10(b), (c), and (d). The
satin weave pattern is defined by the number of yarn widths between exchanges. For
example, the five harness satin weave shown in Fig. 2-10(c) has a 4-over, 1-under pattern.
In addition, the exchanges are arranged so as not to connect; or in the case of the crow's-
foot pattern (Fig. 2-10(b)), so as not to lie on continuous diagonals.
Individual layers of satin weave fabric are asymmetric. One side of the fabric is
predominantly warp yarns; the other fill. Exchange sites also break symmetry because they
bend yarns in an asymmetric way. Bending and stretching in a satin weave ply are
consequently coupled. There is also coupling between stretching and in-plane shear,
because exchange locations are not symmetric about either in-plane axis (Fig. 2-11).
Coupling between bending and stretching will tend to cause warping during cure because
of thermal strains. Warping can be minimized in a multilayer laminate by considering which
side of each ply should face the tool.
The selection of a weave involves manufacturing considerations as well as final
mechanical properties. The type of weave affects dimensional stability and the
conformability (or drape) of the fabric over complex surfaces. Satin weaves, for example,
exhibit good conformability. Unfortunately, good conformability and resistance to shear
