Making a fiber rod with certain tension strength and thickness

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Aviator168

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To make a fiber rod with certain strength in tension. Do I just need to calculate the area needed and stack the layers up the desired heigh according to manufacturer data?

The following is the data sheet of an uni carbon fiber product
https://s3.amazonaws.com/cdn.fibreglast.com/downloads/00962.pdf

My second question is, how come the 12k fabric is not 4 times the 3k fabric in thickness and in weight?
https://s3.amazonaws.com/cdn.fibreglast.com/downloads/00459.pdf
https://s3.amazonaws.com/cdn.fibreglast.com/downloads/00101.pdf
If I stack each one of them up to the same cross section area, will I get the same strength?


Thnx in advance
 

wsimpso1

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For a uni rod in pure tension, it is like any other material. Find the tensile strength of the material and multiply by cross section area to get tensile strength of built up section.

The trick comes in several areas. First is that a laminate has both fiber and matrix, with the laminate strength dependant upon a bunch of things including fiber fraction, fiber straightness, strain to failure of fiber and resin chosen, and how you get the loads into the laminate and what the combination of loads is.

For instance, simply loading a rod in tension can easily be more a test of the termination than the rod. Winding eyes into the end is frequently done. Strength reduction due to winding/laminating defects is also a huge contributor.

Pultruded rod is frequently of superior fiber fraction, modulus, and strength to hand laminated rod. Where you can buy pultruded rod overstrength to your needs, you will likely find it to be both economical and comparable on weight. Where they are too large, the can likely be machined to modest oversize.

If such rods are to be used in larger assemblies, as in spar caps, you would do well to look into shear stresses at free edges and their tendency to edge delamination. Jones has an excellent discussion in his book on the topic as well as prevention methods.

Billski
 

wsimpso1

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3k and 12k indicate the number of fibers combined to make a strand. In woven cloth, how that tow is formed makes all kinds of difference. If the tow was round, yeah 12k would be twice as thick and use half as many strands across any given width of fabric. But if 3k is a round strand and 12k is a flat strand, you can get the same thickness but use only a quarter as many strands to cross a given width of fabric.

The big deal is knowing carbon per square yard (or square meter), modulus and strength used, fiber orientations, fiber fraction of the lamina. Other significant effects are fiber straightness and crimping of fibers.

The best practice is to scheme out your intended processes and test for strength and elastic properties of sample parts, then iterate design based upon results. This avoids surprises of the bad kind.
 

fixnflyr

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Mar 7, 2009
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Springfield, Ga. USA (2ga2) Swaids Field
A friend and I need some per-cured Protruded carbon rods 20 foot long for a Reno racing SnoShoo project we are building. We are having trouble finding a source because of the Covid shutdown. Does anyone have a source they know of?
Thanks, Swaid.
 

dukkbutt

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Jan 9, 2021
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Thinking about buying his book.
The book is expensive for something with a relatively low number of pages but the information is very interesting and useful. I'm happy with my purchase and recommend the book.

VJ
 
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