Biomedical Engineering Reference
In-Depth Information
inside. One very common use of a braid is to
enclose a collection of elastic strips to make bun-
gee cord. When the braid is extended to the
point where the yarns are pressed against one
another, the braid cannot be extended further
and is quite strong and rigid.
Simple plaiting results in one component
lying over and under its nearest neighbors, with
the number of interlacings depending on the
complexity of the braid. It is thus structurally
analogous to a woven fabric, with the two major
differences being that the plain weave is a flat
structure (although it is possible to weave com-
plex 3D shapes), whereas the braid is intrinsi-
cally a tube and there is a skew angle of the
structure relative to the major axis. In a plain
weave, nearest neighbors cross over one another,
whereas the yarn interlacing may occur with
some complexity in braids. The mechanical
properties are, of course, significantly different
between the two. Tension at 45° applied to a
plain weave results in a skew deformation
(square to diamond). Tension (compression)
applied axially to a braided tube, which is analo-
gous to the skew load on a plain weave because
the plaiting lies at 45° to the tube axis, results in
an extension (shortening) with associated nar-
rowing (expansion) of the tube. These actions
have been exploited in making artificial pneu-
matic muscles. These artificial muscles have an
elastic membrane (hose) inside the braid, which,
when inflated with air, expands, causing the
braid to shorten
[6]
. Although perhaps not a per-
tinent example of biomimetics
per se
, this is
nonetheless an application of a textile material
to mimic a biological function. Some plant struc-
tures do resemble braids
[7]
.
Woven fabrics, perhaps the most ubiquitous of
all fabrics, are produced by interlacing yarns on
a weaving loom. The most basic weave is a plain
weave, shown in
Figure 10.4
. There are two sets
of yarns (at the most essential level), called the
warp
and the
weft
. The warp runs the length of
the fabric, and the weft is in the cross-wise direc-
tion. In the rendering shown in
Figure 10.4
, the
FIGURE 10.4
A visual model rendering of a plain-weave
fabric. (J. Manganelli, personal communication. Used with
permission.)
larger-diameter element depicts the weft yarn; in
real fabrics, the warp and weft yarns are more
nearly matched in size. This is a representation of
a woven structure as it would be produced on a
shuttle loom. The weft yarns are continuous, so
the edges of the fabric (the
selvedge
) are neat,
without loose ends. Fabric formed using shuttle-
less weaving machines—there are several types
of these looms and they are faster—have loose
selvedges.
The word
textile
is often assumed to be syn-
onymous with cloth used for apparel, sheets,
towels, and similar items. Admittedly, the pre-
dominant and most venerable use of fibers and
yarns is for apparel fabric and bed sheeting.
Nonetheless, there is a broad range of common
textiles that sometimes goes unnoticed, ranging
from floor coverings and upholstery to tenting
material. Beyond these textile materials, we find
fibrous materials in industrial and architectural
applications, some with structures and func-
tions very different from everyday textiles. The
commonly used fibers and some of the specialty,
high-performance fibers are discussed in Section
10.3.1.1
.
Development in the field of modern textiles
parallels that of synthetic fibers. The cost and
limited survivability of natural fibers, with the
possible exception of mineral fibers, limit their use
in demanding environments. Extremely high
loads and rates of loading, high temperatures or
