Originally Posted by
Canaboo
A lot more can be done with hemp or flax without just putting a gob of random fibers around the lug like the BBS used to do.
Their lugs were more likely failing because of lack of sufficient orientation of the fibers.
No matter what fiber choice you use an underlay of cloth in the chosen fiber makes more sense than just straight wrapping.
Unidirectional carbon cloth layed along the lines of the tubing and spanning the miter joints before wrapping goes a long way towards lasting lug integrity.
You can buy high grade Linen artist's canvas as an underlay for a natural fiber lug.
The source of your natural fiber is very important also. The way the fibers are grown and processed are crucial to the strength.
Keep in mind that modern phenolics used in very high stress areas are often based on Cotton or linen canvas or even paper in a resin binder.
I agree that fiber orientation is all important in a composite layup schedule. The "chop" method is borderline stupid. I've tried laying the hemp in using the orientation you describe for carbon and then over wrapping that as one would with tow, and it worked for a while. That said, I've been using hemp cord, string, cloth and raw fiber for various things for about 10 years now and the problem with the hemp is that it stretches under heavy impact and then doesn't recover. Over time the bike (or whatever) turns floppy, or fits loosely, etc. It is simply not the best option for structural applications. I use hemp as an overlay (money layer) over a carbon structural layup.
I guess I should add that the BBS tests tested 5 different layups (if memory serves) and experienced failure due to repetition in all cases. As a result of the testing they developed the carbon tow method that they use today.