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Does wood grain have one strong direction, or does it depend on the force type?

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HumanPoweredDesigner

Well-Known Member
Joined
Sep 6, 2009
Messages
1,030
Location
Arizona
OK, force parallel to the grain, where if you go in the direction of the force, you are moving parallel to the grain (I think that is how they define it). Tensile strength is strongest in this direction. 10% as strong perpendicular to the grain.
But what about compression strength? Wouldn't it be much weaker parallel to the grain? I'd think it would be stronger perpendicular to the grain. I could see parallel compression causing the wood to split and rupture both directions perpendicular to the force. Am I right that the max strength for tensile and compression are in different directions? So if I need the top of the wing to be under high tension when landed, and high compression when in the air, does that mean there is no wood grain direction that gives me good strength both times?
I'm tempted to go aluminum for this reason. Problem with aluminum is the same weight and strength is much thinner, so I'm worried it would be like pushing on a string.

http://www.hardwoodinfo.com/species_guide/brochure_44-45.pdf

This chart says compression parallel to the grain is much stronger, but I don't know if I got my definitions wrong.
 
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