Biomimetic Textiles - Engineered Biomimicry - page 246

made of polymers , which are long chain-like mol-
ecules. These molecules are, of course, very thin,
to say the least, but the transverse dimension of
fibers is somewhat larger, ranging from as large
as 100 μ m down to the nanometer scale. Yarns ,
whose diameter is again increased in relation to
that of fibers, are composed of these long, thin
fibers. This type of hierarchy of form is a domi-
nant feature in textiles, as it is in nature. Because
of this development of structure, yarns and fib-
ers have many of the same properties, such as
high aspect ratio and good flexibility, but the
yarn is stronger and may be much longer. In
fact, the length of natural fibers ranges from
about 1 in. for cotton to up to 6 in. for wool, so
spinning makes the natural material more
useful.
Fibers and yarns are, in a sense, one-dimen-
sional. To provide the function of protection
mentioned earlier, the dimensionality must be
increased. Fabric-forming processes provide
higher dimensions, from the two-dimensional
clothing fabric to robust three-dimensional
structures. Fabrics that are composed of yarns
have the most broad application field, and the
three basic classes of yarn-based fabrics are
woven, knitted, and braided. These are briefly
covered in Section 10.3.1.3 .
It is generally agreed that there are two essen-
tial methods of fabric formation from yarns:
interlacing and interlooping . Knits basically are
formed by connecting loops of yarn. There are
several types of knits, and each has a specific set
of properties, but the basic idea is represented
by the simple jersey knit. This fabric structure
exhibits a great deal of dimensional fluidity and
flexibility. Some other knit structures offer
increased control over the dimensional stability
and also impart a higher flexural modulus [5] .
In contrast with knits, woven fabrics and
braids are formed by the interlacing of yarns. The
quintessential braiding process is that of a
maypole celebration, where two or more groups
of people dance in opposite-directed twirling
and interlacing circles around a pole, each person

holding the end of a ribbon of a (woven) fabric,
the other end of which is tied to the top of the
pole. In manufacturing a braid, yarns or mono-
filaments are used. There are multiple rotating
yarn carriers, determining the desired complex-
ity of the braid [5] . Renderings of two braids are
shown in Figures 10.2 and 10.3 , one with 6 yarns
( Figure 10.2 ) and one with 16 ( Figure 10.3 ).
The braid structure, sometimes referred to as
a plait , has a resulting dominant property best
represented by the monkey trap. When the braid
is pulled (lengthened), the inner diameter of the
tube reduces and tightens onto whatever is

FIGURE 10.2 Rendering of a braid comprising six yarns.
(Used with permission: Kevin John, www.kevinjohn3d.com. )

FIGURE 10.3 Rendering of a braid comprising 16 yarns.
(Used with permission: Kevin John, www.kevinjohn3d.com. )