Bid Strength

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proppastie

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Guess what guys, the links on the FAQ no longer work......

Yes I know I should read the book, but I am kind of busy so I hope if you can answer a quick question off the top of your head you will save me a lot of time. If not just do not answer.

Bid.... Bi-Directional Fiber say 90 Degree weave, Only 1/2 the fibers are going in the right direction for say a cap of a spar, .... is the conclusion that the cap is only 1/2 as strong as the thickness might suggest were it Uni-direction or say metal.
 

BJC

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BID will not be as strong as uni because of the weave. The fibers at 90 degrees to the load should not be considered as load carrying, although they may have a stabilizing effect.


BJC
 

proppastie

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BID will not be as strong as uni because of the weave. The fibers at 90 degrees to the load should not be considered as load carrying, although they may have a stabilizing effect.


BJC
1/2 " thickness of Bid... 1/2 (1/4") strength of Uni? 1/2 strength of published strength specifications?
 

Marc Zeitlin

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1/2 " thickness of Bid... 1/2 (1/4") strength of Uni? 1/2 strength of published strength specifications?
BID and UNI are weave types. To compare, you will need to determine the amount of glass (of what type) in each weave in each direction in order to compare strengths. If you look at:

https://www.aircraftspruce.com/catalog/cmpages/rutan.php

for the standard Rutan BID/UNI cloths, see the "Q&A" section on that page for the relative strengths.
 

proppastie

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The breaking strength of P/N# 01-00642 is warp- 440 lbf/in,Filling- 366 lbf/in. BID
P/N# 01-00641 is warp- 650 lbf/in, 70 lbf/in. UNI
 

BoKu

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The breaking strength of P/N# 01-00642 is warp- 440 lbf/in,Filling- 366 lbf/in. BID
P/N# 01-00641 is warp- 650 lbf/in, 70 lbf/in. UNI
Others have pretty much covered it, but:

* The tensile strength of the raw fibers doesn't really tell you all that much.

* But, in general, yeah, uni tapes will have about twice the tensile strength of the same weight BIDs when pulled along the fiber axis.

* A lot of sailplane design problems are bounded by stiffness, not strength. And with carbon, it's fairly easy to get handbook stiffness properties unless you really abuse it.

* The gorilla in the room is compression strength. In carbon, fiber alignment and resin strength and stiffness have a huge impact on compression, and it can be hard to get anywhere near the theoretical maximums. It can be distressingly easy to not reach half of what you think you ought. That's why those Graphlite pultruded rods, ribbons, and strips are so valuable, especially for upper spar caps.

--Bob K.
 

Topaz

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... Only 1/2 the fibers are going in the right direction for say a cap of a spar, .... is the conclusion that the cap is only 1/2 as strong as the thickness might suggest were it Uni-direction or say metal.
Which is why BID is not generally used for spar caps. UNI tapes, pultruded rods, etc. are more normal for that usage.
 

autoreply

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* A lot of sailplane design problems are bounded by stiffness, not strength. And with carbon, it's fairly easy to get handbook stiffness properties unless you really abuse it.

* The gorilla in the room is compression strength. In carbon, fiber alignment and resin strength and stiffness have a huge impact on compression, and it can be hard to get anywhere near the theoretical maximums. It can be distressingly easy to not reach half of what you think you ought. That's why those Graphlite pultruded rods, ribbons, and strips are so valuable, especially for upper spar caps.

--Bob K.
The LBA allowables are pretty much the standard. They have twice the rating for UNI as for BID. Their values (600/300) are slightly conservative for properly hand laid-up structures with a Vf of around 40%. Most of the industry (including me) has just ignored the difference between tensile and compressive strength and uses compressive for everything; KISS. Not for Kevlar obviously.

I've tested pultrusion and failed them in compression with over 3 times the normal allowable stress. Other pultrusions were worse than the allowables for UNI, so make sure you know the resin and fiber (T700 or equivalent).

But as you say; save spar caps pretty much anything is plenty strong in terms of stress and ruled by buckling.

Would help if the links in Stickys worked,
Which links are you specifically referring to?
 

proppastie

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Which links are you specifically referring to?
In the FAQ....Do not remember exactly and so hit a bunch but not all of them, when looking before I hit two and both came up bad so I figured it was related to the problems with the server change and that all were bad... but no not all are bad, but I got tired of checking.

This was a side trip because of the "spar failure" thread, ......

HBA - Graphlite structural bending
Fiberglass - discussion of different weaves
HBA - Laminating resin and resin prices
HBA - Composite fuel tanks and ethanol
HBA - Orion gives a good overview of available literature and their strong and weaker points

Online - R&G handbook of composites, excellent start (German and English)
Online - NIAR - AGATE material properties database
 

proppastie

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They're all older than that tie the forum software was updated, so all the links back to HBA forum posts are broken. All the external links are fine, I think.
in the interest of improvement, I could go though all of them, I can not fix them, At least two pointed out post 10 are external links. Do you need me to check them all?.....and there is a whole lot of data lost as regards to broken links with the software update.....is there a fix?
 

pictsidhe

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in the interest of improvement, I could go though all of them, I can not fix them, At least two pointed out post 10 are external links. Do you need me to check them all?.....and there is a whole lot of data lost as regards to broken links with the software update.....is there a fix?
Admin could theoretically find and replace links. It would be really good if they would. Nothing us users can do, other than petition admin to fix it.
 

autoreply

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lr27

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Uni being only twice as strong as bid seems a bit odd. Bid fibers are all bent to get around each other. Depending on the quality of the layup, and the type of cross stitching, uni can be fairly straight. OTOH, if you use multiple layers of that kind of uni held together with little strips of glue, it's less stiff than you'd expect because the fibers zigzag a bit. I don't know the numbers, but my guess is that the strength of uni layups in compression varies greatly depending on how straight you can keep the fibers.

autoreply:
I'm guessing your 300/600 figures are in megaPascals? (43500/87000 psi)
 

proppastie

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