TM 1-1500-204-23-11
ability to place iber in the component exactly where
it is required and in the optimum quantity desired.
UD ibers are straight and uncrimped. This results
in the highest possible structural properties in fabric
composite construction. As with other fabrics, the
surface quality of a unidirectional fabric is determined
by two main factors: the combination of iber bundle
size and thread count of the primary iber as well
as the amount and type of the secondary iber. The
drape, surface smoothness, and stability of a fabric
are controlled primarily by the construction style, while
the areal weight, porosity, and (to a lesser degree)
wet-out are determined by the number of ibers per
inch or centimeter.
(3) Braids. Braiding is a system of three or
more yarns intertwined in such a way that no two
yarns are twisted around one another. In practical
terms, braid refers to a family of fabrics continuously
woven on the bias. There are four main braid forms
and four main braid architectures available. The acute
angle measured from the axis of the braid to the axis
of the bias yarns is called the braid angle. This angle
is also referred to as the iber angle or the bias angle.
The braiding process allows for the introduction of
axial yarns between the woven bias yarns. These
axial yarns are not crimped by the weaving process.
(a) Braid is most commonly manufactured
and used as a freestanding, tubular
fabric with a constant braid angle for a
given diameter. In this form, it is sup-
plied on reels or festooned in cartons.
In composite manufacturing, tubular
braids are typically expanded open dia-
metrically, applied to a molding tool or
core, snugged down (using the Chi-
nese inger trap effect), impregnated
with resin, and then consolidated. For
pultrusion, tubular braids are continu-
ously fed over a die mandrel to produce
hollow cross sections. Flat braids are
used primarily for selective reinforce-
ment, such as tabbing in boat building
and strengthening speciic areas in pro-
truded proiles.