Thanks to all who provided info and suggestions.
I plan to run some tests, starting with a modification to my 20T "H"
frame press so I can tension test specimens up to 10k lbs or so and
measure force with a simple Dillon mechanical 5k# force gauge I have. A
lever arm will give me 2x and maybe 4x tension. I've also talked with
West Coast Wire Rope and Rigging here in Seattle, they have a 5k to
500k# pull stand for up to 180' long cables that costs $150 per test
hour. 6 to 8 tests can be run in that time for short/small cables (my
home test samples will be 4 to 5' long). If I can't break a test
specimen, then they will. With my press setup I can leave the tension
on for a few days and check for slippage and cycle the test to some max
tension value.
It appears that one solution to be able to use "old" Phillystran is to
use wire rope clips and HD thimbles at the right quantity and tightening
torque. So, I plan an experiment with differing numbers of clips, 4 to
6, and tightening torques (5/8" clips) from 35 to 95 ft-lbs (95 is the
recommended wire rope value). I think 3/4" heavy duty thimbles are the
correct size for all experiments.
So the plan is to test 3 "corner conditions" assemblies to 10k# then to
20k# (if I can), measuring the slippage or failure each time and then
pull test whatever survives to failure at WCWR. (I hope I can watch!)
Since "new" Phillystran (11.2k# vs what I have is 45k#) will set me
back well over $4k for this tower (65G, 150'), this seems a reasonable
way to find out if what I have can be made reliable for $200 of steel,
clips, and some welding.
So, if you know more about designing a such a test or clips on
Phillystran let me know.
Tom's multi-turn wrap termination is an interesting idea, it works for
line and monofilament on fish-hooks. Any suggestions on what the
"thimble" would look like? Kevlar is bend radius sensitive and fatigue
prone.
Grant KZ1W
On 1/14/2014 7:54 AM, Tom W8JI wrote:
I would never design and especially never test for the maximum steady
working load at a wind speed. The shock load of a bounce can strip the
ends. I had a friend who lost a tower from a straight line wind in a
normal thunderstorm because the outer layer stripped off. He used
three saddle clamps. I told him he should have wrapped the insulator
(he used insulators to transistion to steel) two or three turns before
clamping.
This is not much different than getting hold of copperweld twinlead,
or anything else with a soft outside and hard core.
Has anyone thought of a long rectangular bar with multiple champhered
holes, with the Phillystran woven through from side-to-side? With
enough weaves, this should self-tension with just a single clamp on
the far end. Regardless, I would test pull and see what breaks first
at what tension.
73 Tom
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|