Re: Boron safety data sheet

From: leop12345 <leop_at_lyradev.com>
Date: Thu, 06 Jan 2011 00:28:50 -0000

Well, there is carbon and there is carbon. For our planes we care about the stiffness or modulus of elasticity of the fibers (aka Young's Modulus). Actually, we care about the modulus in both tension and compression (which are different for both carbon and boron fibers) but discussing the modulus in tension is sufficient.

Boron fibers have a modulus of around 400 GPa (58 million psi) and this value is consistent and uniform (the properties of the boron fibers that we can buy from Ray are listed in the www.specmaterials.com website). The boron fibers have a density of about 2.5 g/cc.

Carbon fiber properties vary greatly depending on the heat treatment after the initial fiber is produced. Most of the commonly available carbon fiber has a modulus of about 230 GPa (33 million psi). There are higher modulus carbon fibers available (normally 290 Gpa, 42 million psi, to 380 Gpa, 55 million psi, with some, rare, up to 520 GPa, 77 milion psi) but they are much more expensive and hard to find (and harder for us to verify their properties). Thus, even with a carbon fibers' lesser density, 1.8 g/cc, the boron fibers are stiffer per unit weight than the normally available carbon fibers.

Also, the carbon fibers are much smaller in diameter, about one tenth the diameter of the boron fibers. Mark is correct to worry about the amount of glue needed to hold down the carbon fibers. In good carbon fiber epoxy composites, the carbon fiber is usually just over 50% of the total weight. The very best composites have 70% carbon fiber by weight but this takes molding with high pressure or an autoclave and careful techiniques to remove excess epoxy resin. So, the glue, Ambroid or Duco, to hold down the carbon fibers will probably weigh as much as the carbon fibers. I do not know how much glue is needed to hold down the boron fibers (I hope to remember to weigh a wing spar before and after sometime). Maybe Mark or someone else knows.

The bottom line, in my amateur opinion, is that boron fibers are the best stiffener material available for indoor planes at the current time.

Leo

--- In Indoor_Construction_at_yahoogroups.com, "Mark F1diddler" <f1diddler@...> wrote:
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> --- In Indoor_Construction_at_yahoogroups.com, "Bill Gowen" <wdgowen@> wrote:
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> > Or for a different solution carbon tow pulled from Russian unidirectional carbon fabric weighs 8.4 mg for 24". Probably not as strong as boron but is breakage a problem for boron on wing spars?d\
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> That's an attractive weight. But no, *tensile strength* for a pair of .004" borons is not a problem with spars--if anything, overkill maybe. The bigger consideration for me is adhesive weight vs. attachment lifespan, meaning I often have to add more glue (weight) later in the model's life. So, what is a common glue weight for attaching the above carbon fiber? And are you able to pull out a single strand 24" long? My attempts with carbon tow years ago amounted to getting smaller fuzzy tow out of bigger tow. Does "fabric" more or less mean tow impegnated with some epoxy, baked in order to get straight, unidirectional fabric?
> Mark F1diddler
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Received on Wed Jan 05 2011 - 16:28:52 CET