Is tube stiffer than bar?
On Tue, 28 Nov 2006 23:05:52 GMT, Tony Bryer
wrote:
On Tue, 28 Nov 2006 22:02:41 GMT T i m wrote :
Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube (I'm guessing it would still be a
function of the overall x sectional area)? This probably sounds like a
perpetual motion question ;-)
So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?
Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?
For a solid bar, stiffness is proportional to D^4, bending strength (in
simple terms) to D^3 and weight to D^2. For a tube substitute D^x -d^x
where D is the OD and d the ID.
So if your tubes are of 1/16" material the numbers are (work in 1/16" for
ease of calculation)
3/8: Stiffness 6^4-4^4: 1040 Weight 20 Stiffness/weight 50.2
1/2: Stiffness 8^4-6^4: 2800 Weight 28 Stiffness/weight 100.0
But it's not quite as simple as just making it as big and thin as
possible as you reach a point where the tube buckles before its
theoretical strength is reached.
Note that no reliance should be placed on any calculations done at this
time of night g
lol.
Thanks and all the best ..
T i m
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