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3/4 .035 4130 round

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wanttobuild

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What would a square carbon tube 3/4 in on PVC foam look like, approx comparable to 4130 strength.
Looking for weight of reinforcement, fiber orientation.
Also, S glass. The foam will have the corners knocked with a 1/8 in radius.
 

Vigilant1

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What would a square carbon tube 3/4 in on PVC foam look like, approx comparable to 4130 strength.
Looking for weight of reinforcement, fiber orientation.
Also, S glass. The foam will have the corners knocked with a 1/8 in radius.
Are you asking somebody to do the math for you, to help with the layout schedule, or to walk through the steps (or give a citation of a source that walks through the steps) of figuring this out so you can do the layout/calculations yourself?
Not to be a wiseacre, but it would "look like" a black (or white) squarish tube.
And why PVC foam vs XPS? The strength will be the same in this case, and XPS will weigh/cost less.
 
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Vigilant1

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PVC foam I have is 5 times the compressive strength for 3 times the weight.
Is the compressive strength of the foam significant in this application? It serves as a form for the CF/epoxy, but (I believe) the CF/epoxy will be doing all the work in actual use. The foam certainly won't be taking any pure axial compressive or tensile loads on the tube, and in bending one surface of the tube will be in compression while the other is in tension, the other "side" skins will transfer loads between them (like a spar web). I suppose the foam might see local buckling loads from the skins, but in a tube of this size the side skins would be close enough to handle them and would do so because they are much stiffer.
With most foams the manufacturers cite a compressive load that occurs at 10% compression or yield. I'd think that by the time foam compressed 10% anywhere due to buckling that the game would be over and the part would be in the process of failing rapidly.
Dragonplate and other manufacturers of CF tubing don't sell it with an included foam core. If the core added any significant strength, I'd think these products would include it.
All of the above is subject to revision or outright disavowal in the likely instance of counterarguments by more knowledgeable persons (which is a big group).
 
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