Biomedical Engineering Reference
In-Depth Information
is the
shuttle loom
, so named because the weft
yarns are woven into the warp yarn sheet by
being carried across the width of the fabric on a
shuttle. Other means of weft insertion include
the airjet, projectile, and rapier, each of which
has its own benefits and liabilities. For example,
weaving speeds can be very high on a loom with
airjet insertion in comparison with a shuttle, and
so the airjet is most often used for commodity
flat goods such as bedsheets and pillowcases.
For our purposes, let us consider only the
shuttle loom. For the weft to interlace with the
warp, the relative position of neighboring warp
yarns must be changed; the term for this is that
a
shed
must be formed in the warp through
which the weft yarn is inserted. The most ele-
mentary manner of accomplishing this is
through a
harness-and-heddle
system. The
heddle
is a wire-like structure with a hole in it through
which a warp yarn is passed. There is one hed-
dle for each warp yarn (in a plain weave). The
heddles are collected in a set of
harnesses
, the
number ranging from two or four up to eight.
The harnesses are raised and lowered
programmatically by a
cam
; the machinery limi-
tations of space preclude a loom from having
more than eight harnesses when using a cam
mechanism. Other shed-forming methods do
exist
[5,17]
. Two harnesses are used to weave the
plain weave, with nearest-neighbor warp yarns
passing through every other harness. The
harnesses are raised and lowered in an alternat-
ing fashion, forming a simple alternating shed.
With each pass of the shuttle the shed is reversed.
The final step after weft insertion is
beating up
by the reed, during which the weft is pressed
against the prior weft, forming the
fell line
of the
cloth. The force with which the reed is pressed
to the fell line determines of the tightness of the
weave.
With the use of more than two harnesses,
other weaves may be produced. Each type of
weave has its own set of properties. For exam-
ple, the
satin weave
(
Figure 10.5
) has the very
characteristic feel of satin-smoothness because of
FIGURE 10.5
A visual model rendering of a satin-weave
fabric. (J. Manganelli, personal communication. Used with
permission.)
the long floats, i.e., yarns that are not interlaced
with each neighbor, in the warp direction. (The
satin weave identifies the long floats as being in
the warp direction.) Of course, this structure is
prone to snagging, also as a consequence of the
long float. This weave has been used as the rein-
forcement in composites because there is not so
much bending stress on the warp yarns. Many
other woven structures are possible
[17]
.
10.3.2 Bioinspiration as it Informs
Engineering
There are many popular examples of nature-
inspired engineering. The most common exam-
ple is Velcro
®
, modeled as it is after the hook
shape of burrs. The most recent entry is the gecko,
with a multitude of small hair-like appendages
on its feet
[18]
. The question remains, however,
as to the order of, or the route to, the inspiration.
Consider bamboo as a composite. It seems
clear, at least in terms of the time sequence of
events, that the field of fiber-reinforced compos-
ites research was not predicated on a morpho-
logical study of bamboo; if anything, the
language of composites has been used to
describe the observed structure of bamboo. Or,
take synthetic fiber spinning, discussed in Sec-
tion
10.3.1.1
. Again, this technology was devel-
oped through scientific and engineering research,
