OVERVIEW OF TEXTILES
of a textile as nonlaminar in describing its passage to ultimate failure, even though in the
elastic regime it is clearly quasi-laminar.
Whether a textile is quasi-laminar or nonlaminar is a crucial question in choosing an
appropriate approach to modeling its properties. Quasi-laminar composites can generally be
modeled accurately by some modification of standard laminate theory. Nonlaminar textiles
require a model that computes the distribution of stresses in all tows, which is a much more
difficult problem.
2.1.2 Preforms
2.1.2.1 Weaving
Weaves have been used in composites for many years. They offer a low cost
method of fabricating large areas of material, with only a small sacrifice in the properties
that would have been obtained with laminates of unidirectional tape. Weaves are made by
interlacing two or more orthogonal sets of yarns (warp and weft) on a loom. Most weaves
contain similar numbers of fibers and use the same material in both warp and weft.
However, hybrid weaves [2.4] and weaves dominated by warp yarns (Sect. 2.2.2.4) have
important roles in textile composites .
Woven broadgoods may be purchased either as a dry preform or pre-impregnated
with a B-staged epoxy matrix. In most applications, multiple layers of 2D weaves are
laminated together. As with tape laminates, the layers are oriented to tailor strength and
stiffness.
3D woven fabrics are created on a multiwarp loom. As in a conventional loom,
harnesses alternately lift and lower the warp yarns to form the interlacing pattern. In the
multiwarp loom, separate harnesses lift different groups of warp yarns to different heights,
so that some are formed into layers while others weave the layers together.
2.1.2.2 Flat Braiding from Cylindrical Mandrels
Traditional braiding involves a series of yarn carriers that follow intersecting
circular paths so that the yarns interlace to form a tubular fabric (Fig. 2-3). A mandrel that
passes through the braider may be used to control the final fabric configuration. The
rotational speed of the yarn carriers relative to the transverse speed of the mandrel controls
