Gardner, "This got me to thinking about box beam construction. I have not been clear if the harryproa beams are all fiberglass/carbon or if they are sandwich construction as well. I have never seen any mention of core material for masts, so is coring used for box beams, and if so, why is that different than for a circular section."
Yes the beams are sandwich construction. The answer to the second part of your question is more difficult. To a first approximation a circular mast is no different than a square beam. But, a smaller (lighter) round carbon fiber (non sandwich) mast is stiffer (8 -13 times stiffer) because of its modulus of elasticity than a fiberglass mast and the shear strength of the core becomes very important.
It turns out cost, weight and size wise that going with solid carbon fiber is the best compromise, because the interior foam and glass of a sandwich 'beam' doesn't do much for a mast except add weight. The sandwich works best for preventing oil canning, which makes it ideal for a hull or deck.
Gardner, "How would I calculate the strength of a box beam, based on the dimensions, wall thickness and material, with and without a core?"
Join the club : ) First you have to know the forces applied and the strength of your materials. Then you have to determine the strength depending on the shape of the structure and the load points. Pretty much you either copy existing structures, pay an engineer, or do the FEA yourself with a computer program.
And after all of that I can assure you it will be wrong : ) but maybe close enough.
Gardner, "
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Posted by: taladorwood@yahoo.com.au
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