On 7/13/21 4:46 PM, Grant Saviers wrote:
Calibrating against the actual fiber is *probably* good enough for ham
tower work, BUT
Be aware that the Kevlar fibers of Phillystran behave very differently
than steel wire. The Kevlar fiber is very strong axially with about
60% the modulus of steel. The fiber also has very complex lower
modulus behavior longitudinally, the fibers are anisotropic.
The Loos gauge is based on the isotropic (equal in all directions)
modulus of steel, approximately the deflection of a beam center loaded
and simply supported at both ends. A simple equation that can be
looked up on the web, that doesn't apply to Phillystran.
If the Kevlar "beam" was isotropic, then the Loos gauge on Kevlar
would deflect 1/0.6 more on the same diameter as EHS (IE the exact
diameter of the actual fiber or wire bundle if all air was removed -
weight per foot is the easiest means to get the value for both). A
0.22" diameter of the PE Phillystran sheath, isn't that value.
So perhaps the best use of a Loos gauge is to get all guy tensions
equal and use a simple force gauge to measure the tension. Sometimes
cheap on ebay ("dillon force gauge") and all mechanical (D shaped
steel ring and dial gauge).
They can be made on a milling machine, google for instructions. Like
these. They work in tension or compression.
https://scienspec.com.tw/userfiles/files/MODEL%20X.PDF
Grant KZ1W
And if you want to get fancy, there's plenty of load cells for sale at
remarkably low prices.
(I was looking for <200 lbs, so the ones I found are probably not
suitable, but they were <$50) You could monitor the tension in your
guys at all times, and tell when the wind has shifted. I found some
ones rated at 2000kg for $42 (they're used in weighing applications,
among others) - "Load Cell Sensor S type"
And there's also things like "Digital Crane Scales" (which are basically
tension sensors, with a display, and sometimes, a USB or BT interface.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|