[TowerTalk] Springiness of materials

[Kurt Andress]

Mark Lowell, N1LO wrote:

> Greetings from Virginia's Middle Peninsula,
>
> At the risk of boring some, I will make an attempt to describe and quantify
> 'stretching' for those who are interested. Forgive me if the majority have
> no interest in this level of detail or consider the topic already beaten to
> death. Reviewing it sure helps me, anyway.

Big Snip

> The relationship between the size of the load and the amount of deflection
> (elastic movement) is controlled by the size and shape of the part

(insert) cross sectional area

> and the
> "Modulus of Elasticity" (modulus for short) of the material that the part is
> made from. Just as the yield stresses can vary for different materials, the
> modulus is also dependent on the type of material. The higher the modulus,
> the *less* a part will change shape elastically. The modulus of steels is
> well known, and varies very little for different steels. I don't have data
> for aramid fiber. Perhaps Kurt can find this or someone will contact
> Phillystran's manufacturer for this data.

Big Snip

Hi Mark,
Good explanation!
Found some info on the aramid cable. Just had to ask one our spar designers, and
he immediately whipped it out. The data was provided by one of our rigging
suppliers in Portsmouth, RI. They specialize in marine rigging and will be too
pricy for amateur use. All of their calbes are supplied with a variety of High
Strength (17-4) stainless terminations. But, I know they buy the cable from
Philadelphis Resins Co. as all the cables say Phillystran.

For the sake of others who haven't been exposed to modulus values, here is a
list:

Note: Msi stands for millions of Psi

Fiberglass    3.5- 4.0 Msi     Epoxy/E-glass Mil Spec G-10 material.

Aluminum    10 Msi        Common 6061 & 6063 alloys

Aramid        18 Msi    Kevlar 49 used for most aramid guying cable

Aramid        25 Msi    Kevlar 149. I only found listings for 8600Lb - 32500 Lb
cable

Steel            29 Msi        Commonly used steels mild, Chrome Moly, and
stainless

I think the bulk of aramid cable sold to amateurs is Kevlar 49, the 149 is more
expensive, but it can be had.

73, Kurt

--
YagiStress - The Ultimate Software for Yagi Mechanical Design
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