Re: [ATM] Aluminium or stainless steel?

[Dale Eason <atmpob@yahoo.com>]

Ok try the reverse.
Suppose I take a metal tube and stuff it with Gum
rubber.  Does the tube become stiffer?

What Bob May said holds true for most combinations of
Aluminum outter tube and anything else you can put
inside it.  It depends on the properties of the two
materials and thier diameters.  When the modulus of
elasticity is about the same it depends on the
diameter of the rods.

>From Kriege and Berry page 56.
deformation = (force x length^3)/(3xExI)
where E is the modulus of elasticity
and I = (OD^4 - ID^4)/64
and OD = outside diameter ID = inside diameter.

You can see from these equations that length and
diameter or the important factors when E is about the
same.

By increasing the diamter 1.5 times you increase the
stiffness 1.5^4 = 5 times.

So you can work out for youself how much stiffnes you
can add by placing a stiff rod in the center.
 
Dale Eason

--- Woodchuck <djv@bedford.net> wrote:
> On Sun, 8 May 2005, Bob May wrote:
> 
> > Putting stuff in the tubing won't really reduce
> the deflection - that is
> > taken care of in the outside diameter of the
> tubing.
> 
> Huh?
> 
> Suppose the tubing is made of gum rubber.  I stuff
> it with a
> tight-fitting rod of steel.  Doesn't it become
> stiffer?
> 
> Instead, suppose I plug each end and then fill the
> tube with something
> under pressure, doesn't it become stiffer also? 
> (V14gra effect,
> so to speak).
> 
> When a piano string is tightened, does it require
> more force to deflect it?
> 
> Dave
> 
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