Is wood stronger than metal per weight?

No big deal, but I want to know. Partly curious.
I want to use a crosswise board or an aluminum rectangular tube (or whatever
other metal would be appropriate) as a two wheel platform, for the rear end
of a tricycle.
I want more intelligent/experienced guesses about the situation. Not
concerned about workability, weather resistance, etc.
I see some opinions on the Internet that go both ways.
Thanks.
Reply to
John Doe
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Look for discussions on homebuilt wooden airplanes.
Reply to
Jim Wilkins
John Doe wrote in news:nnatdo$g7p$ snipped-for-privacy@dont-email.me:
What's your definition of "stronger"? Compression or tension or shear? Resistance to flex (i.e. stiffness) or ability to take multiple cycles of flex (fatigue resistance)?
I'm going to guess for your tricycle application that stiffness is a key parameter, in which case a tube is probably the stronger structure.
John
Reply to
John McCoy
Is your bike made of metallic tubing or wood?
Reply to
Cydrome Leader
Balsa is both the lighest wood *and* the strongest wood for its weight. Black Widow Spider webs are stronger than steel.
What you want is an oval balsa tube externally braced with spider webs.
Reply to
Felix
As usual it depends. The nose fairings on the A3 Polaris , C4 trident , an d D5 Trident missiles are all made of sitka Spruce. And the missiles are l ifted by the nose fairing. So for that application wood is best. On the o ther hand the rocket cases are made of kevlar and carbon fiber.
Dan
Reply to
dcaster
Ha!
Reply to
Cydrome Leader
John Doe should look into a field of endeavor called "stress analysis". From there he should be able to find his own answer.
Reply to
J. Clarke
Properly used, wood is capable of excellent performance, for example the Mosquito airplane, longbows, stagecoaches, skis, wood-framed birchbark canoes and Egyptian chariots, which are remarkably light for a fast off-road vehicle.
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Improperly used it's dangerous because the properties of individual pieces are unpredictable and strong joints require experience to design and skill to make.
Wood, steel and aluminum have all been used to build light and strong airplanes, even jet fighters. It's up to you to learn how to apply them.
--jsw
Reply to
Jim Wilkins
Well, this is true, ipe is stronger than aluminum foil but Balsa is weaker than titanium.
Reply to
Leon
This is a manageable question if you specify acceptable dimensions and how the axle is loaded (it depends on the structural section and dimensions -- either one can be stonger per pound -- except that it also depends on whether the load is applied in a point), but wood is so complicated, from a structural standpoint, that just asking "which is stronger" just leads around in circles.
Here's an example: Douglas Fir is three times stronger than aluminum per pound in compression -- parallel to the grain axis. Perpendicular to the grain axis, fir is 1/3 as strong as aluminum in compression. Tension is much more complicated because of the difficulty of attaching a load to wood in tension.
If you want to get serious about comparing the two, the easy way is to look up construction tables for bending horizontal wood beams, and then getting the specs on an aluminum section that you choose. That is, one you can *get*.
They're both on the same order or close to it. But arranging the design for applying loads will give aluminum the advantage. That's one of the problems with engineering with wood, unless your loads are purely in compression.
If you want to get into it, this will occupy you for a while:
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This one has good stuff on beams:
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The Forest Products Laboratory has a wealth of information, if you have nothing else to do with your life.
BTW, aside from aircraft, a very successful race car from around 1960 had a chassis made of plywood (the original Marcos GT). And the stiffness and strength of fir plywood is roughly equivalent to a cored composite made from polyurethane foam, ordinary S-fiberglass, and polyester resin.
Not bad.
Reply to
Ed Huntress
Here's how to determine the modulus of elasticity value for the tables:
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Reply to
Jim Wilkins
"Sandwich-structured composites" (see refs) are one way to build a light but stiff panel or beam. Some pieces I've tested are stiffer than steel or aluminum beams weighing ten times as much. You may be able to buy 2'x4' aluminum honeycomb-core panels online or if you live near an aircraft factory can get cutoffs that would be large enough. If you have any fab skills you could make a beam with steel, aluminum, fiberglass, kevlar, or carbon fiber skins over balsa core.
Refs:
Reply to
James Waldby
...
There's also the torsion box...
Reply to
dpb
Japanese Spider Crab is horrific.

Reply to
Felix
Ewww!
Makes me wonder why all those monster movies of the 50s needed to show magnified or prop monsters (Tarantula, Mysterious Island, etc). ;)
nb
Reply to
notbob
Ask any Fire Fighter which building he would prefer to enter - a timber framed structure or one framed with structural steel.
Reply to
geraldrmiller
Gunner Asch wrote in news: snipped-for-privacy@4ax.com:
Technically that is a grass.
John
Reply to
John McCoy
Which is grass. ;-)
Reply to
krw

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