On Aug 31, 6:39*pm, DougC wrote:
For a project I can use either kevlar cord or thin steel cable.



And what is the % for kevlar rope? The same, or higher or lower?

(-I know that there are other factors like kevlar's higher price, lower
abrasion resistance ect, but those aren't significant in this instance-)

You could probably also use uhmw polyethylene. The plastic fibers
have some advantages over steel in that they do not rust , are lighter
and do not stretch as much as steel. But have some disadvantages
too. Kevlar degrades from ultraviolet. UHMW loses strength if
heated. You can get uhmw fiber from places that sell fishing line. I
suspect people use 20% of breaking strength for working load in pretty
much all cases.

Dan


From WIKI.
Fiber applications

Ballistic vests can be made of UHMWPE.

Dyneema and Spectra are gel spun through a spinneret to form oriented-
strand synthetic fibers of UHMWPE, which have yield strengths as high
as 2.4 GPa (350,000 psi) and specific gravity as low as 0.97 (for
Dyneema SK75).[4] High-strength steels have comparable yield
strengths, and low-carbon steels have yield strengths much lower
(around 0.5 GPa). Since steel has a specific gravity of roughly 7.8,
this gives strength-to-weight ratios for these materials in a range
from 10 to 100 times higher than steel. Strength-to-weight ratios for
Dyneema are about 40% higher than for aramid.

UHMWPE fibers are used in armor, in particular, personal armor and on
occasion as vehicle armor, cut-resistant gloves, bow strings, climbing
equipment, fishing line, spear lines for spearguns, high-performance
sails, suspension lines on sport parachutes and paragliders, rigging
in yachting, kites, and kites lines for kites sports. Spectra is also
used as a high-end wakeboard line.

For personal armor, the fibers are, in general, aligned and bonded
into sheets, which are then layered at various angles to give the
resulting composite material strength in all directions.[5] [6]
Recently developed additions to the US Military's Interceptor body
armor, designed to offer arm and leg protection, are said to utilize a
form of Spectra or Dyneema fabric.[7] Dyneema provides puncture
resistance to protective clothing in the sport of fencing.

Spun UHMWPE fibers excel as fishing line, as they have less stretch,
are more abrasion-resistant, and are thinner than traditional
monofilament line.

In climbing, cord and webbing made of combinations of UHMWPE and nylon
yarn have gained popularity for their low weight and bulk, though,
unlike their nylon counterparts, they exhibit very low elasticity,
making them unsuitable for limiting forces in a fall. Also, low
elasticity translates to low toughness. The fiber's very high
lubricity leads to poor knot-holding ability, and has led to the
recommendation to use the triple fisherman's knot rather than the
traditional double fisherman's knot in 6mm UHMWPE core cord to avoid a
particular failure mechanism of the double fisherman's, where first
the sheath fails at the knot, then the core slips through.[8][9]

Owing to its low density, ships' hawsers and cables can be made from
the fibre, and float on sea water. "Spec Lines" as they are called in
the towboat community are commonly used for face wires.

It is used in skis and snowboards, often in combination with carbon
fiber, reinforcing the fiberglass composite material, adding stiffness
and improving its flex characteristics. The UHMWPE is often used as
the base layer, which contacts the snow, and includes abrasives to
absorb and retain wax.

High-performance lines (such as backstays) for sailing and parasailing
are made of UHMWPE, due to their low stretch, high strength, and low
weight.[10]

Dyneema was used for the 30-kilometre space tether in the ESA/Russian
Young Engineers' Satellite 2 of September, 2007.

The extremely low friction coefficient of UHMWPE makes it a common
topsheet for boxes in terrain park.[citation needed]
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