Optimum braid type for bending stress in square tube?

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#1

Hi, I am new to the forum, and carbon fiber. I wish to make my own square tube, about 3/4" x 3/4" and very light. I have a reasonable understanding of the principles that underlie fiber orientation and how it affects strength characteristics in various directions, but I am uncertain about specific terminology or how to go about asking suppliers for exactly what I want.

In short, virtually all of my stresses will be in bending, and thus I want a braid (some sources call it tube) that is mostly unidirectional, but with some hoop strength. Exactly what kind of braid or weave should I be asking suppliers for? And is there any supplier that specializes in this particular kind of braid?

Edit: I would imagine I could use two layers, a unidirectional and a regular braid for hoop strength, but for simplicity and weight, I really want only one layer, of an optimum braid for bending strength.

#2

Basicly you want +/-45 on the sides, and unis on top and bottom.

The first is simple, these are standard braids. The second is a bit more complicated, I would revert to unidirectional tapes, not braids.

The nice thing is you can bury the unis in a couple of layers of braid, so you get some stability for the unis in compression.

#3

Thanks for the reply. Admittedly, I did not clarify that the bending stress may come from any side, so the uni would have to be on all four sides. I was really hoping for a braid that could do both things in one step, in effect, a braid that is comprised mostly of unidirectional fibers in the warp direction (I hope warp and weft are applicable terms for braids and tape :))

If such is not possible, what do you think about a uni tape 3.5" wide, wrapped around the mandrel with aproximately .5" overlap, and then a lightweight braid over top?

#4

I would prefer braid-uni-braid. This keeps the uni in column better. (although most tubes indeed have uni on the inside, so it might not be a problem)

Due to the nature of a braid it is impossible to effectively introduce a uni into that. So you will have to live with separate materials, or have the mandrel overbraided.

#5

Thanks. What exactly do you mean by “have the mandrel overbraided”? can you explain this phrase?

#6

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