Ok guys, here are the material densities:
mild steel - 0.283 lbs/cu. inch
stainless stell - 0.295
Aluminum - 0.100
Magnesium- 0.065
So Dave, you are about right - Aluminum is roughly 1/3 the weight, but
is also has exactly 1/3 of the tensile strength of steel.
Cheers,
Cale
98cc318sporty
Mike Schwall wrote:
>
> At 02:39 PM 2/3/2000 -0600, you wrote:
> >Hey Mike,
> >
> >Without measuring the shafts and calculating the second moment, there is
> >no way to say which shaft is easier to accelerate. You could be right
> >that the aluminum shaft still comes out ahead despite a thicker wall,
> >but the OD is really quite a bit more than the steel, which levels the
> >playing field again. In the calculations for inertia:
> > 4
> > (pi) x density x Length x (Outside Radius-Inside Radius)
> >I= ---------------------------------------------------------
> > 2
> >
> >The R is the shaft radius, density is material density, Length is shaft
> >length, I is inertia about the central axis. You can see that Radius is
> >to the 4th power which makes it 4 times more critical to the inertia as
> >does the material (density).
> >
> >As per usual, anybody whose brain is full, head hurts, or brain exploded
> >messily may be excused.
> >
> >Cale
>
> Ok, I like it. Next question, what is the density index of steel and
> aluminum. I see your point. Makes perfect sense - even though the
> material is lighter, making the diameter larger reduces the advantage of a
> lighter material.
>
> Good stuff
>
> Mike
>
> __________________________
> mschwall@flash.net
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