Steve,
I forgot to address your question about elongation over time.
I my industry, it is called "Creep." It is most prevalent in synthetic
materials.
Creep is a material property that causes it to take a permanent set in a
new condition, after being subjected to loads over a certain time
period.
The Phyllistran folks know that the aramid cable does this, and offer
the information to help us understand how to properly use it.
Steel does not have the same tendency for creep behavior. To get steel
to take a permanent set in in a new configuration, one usually needs to
exceed the the materials yield strength.
The steel wire moves and slides about itself until the heilical wraps
get pulled down around the bundle, where it starts to actually begin to
work.After the initial tensioning, to pack the wrapped bundle into a
tight package, nothing else much happens, except for the cable stretch
that is defined by the cable wire count and heilical winding angles.
So, I guess that the answer is that synthetic materials (mostly plastic
alloys) are going to take a permanent set over time. The steel does not.
A professional com tower rigger that attended the Polyphaser seminar I
was at told me over coffee, one morning, that he always set the guy
grips and cable on the ground with a come-along device. This meant that
he had fewer calls to go back and re-tune the tower guys.
73's, Kurt
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