On Sun, 6 Jul 2003 22:54:03 +0100, "sniffer" wrote
something
.......and in reply I say!:

Ted. I did not get your message direct, bu7t can read it here. SO.

I am not sure if you were among those that guided me through this
maze, but the Elastic modulus is not the whole story, from my
extensive blundering about on this subject. High tensile steel is
"stronger" than mild steel mainly because it can withstand more
distortion before Elastic Modulus (Young's) is overcome and the metal
reaches its permanent deformation point. Young's then no longer
applies.

My favourite examples are spring steel and mild steel. The spring is
actually no "stiffer" than the mild steel, but continues to resist
permanent deformation for a long time, while also applying Young's
modulus to a greater and greater strain. Both will have a YM around
210 MPa.

So the "tested stress maximum" is often more important than the
Elastic modulus.

How does this apply to aluminium vs say, mild steel? From the Beam.exe
programme it appears about the same using a 100mm tube, with a 6 mm
wall of alum and a 2mm wall of steel. Both reached approixmately the
same proportion of their failure strain under a given load.



"Ted Edwards" wrote in message
...
sniffer wrote:

According to that program, steel weighs 3 times more than aluminium. My

That's about right.

question is, how much stronger will steel tubing be than aluminium, if
the
steel tubing is 1/3 of the wall thickness of aluminium tubing?

Strength depends on the alloys being considered. There are aluminum
alloys up to about 75Ksi tensile and steels up to about 250Ksi but
whether they are practical in a given situation ...

However if you can come up with a strong enough design, the deflection
would be about the same. Steel has 3 times the weight and 3 times the
elastic modulus.

Ted

Thanks Ted.




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