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.
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.
On Wednesday, July 27, 2016 at 3:16:49 PM UTC-4, John McCoy wrote:
If the user will be riding the tricycle like we did when I was young,
"multiple cycles of flex (fatigue resistance)" is also very important.
If it wasn't the driver riding with one foot on the rear platform, pushing
with the other, it was a friend/sibling standing on the platform.
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.
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
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:
This one has good stuff on beams:
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
Gunner, we usually only call dicots 'wood'. 'Woody' monocots are not
usually included in that genre. A weird exception might be palm trunks
used as fence posts, but they're _barely_ 'woody', at their best.
On Sat, 30 Jul 2016 01:15:40 -0000 (UTC), John McCoy
Do you call particle board "lumber"? I suppose bamboo is closer to
butcher block but I wouldn't call it "lumber", I don't think. The
point being that it's made up of a bunch of small pieces (strips)
glued together to make something of a useful size.
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