If the aluminum was 2 times the thickness of a cast iron panel ignoring
modulus of elasticity for the moment stiffness would be about 100 times
stiffer as it is a fourth power function of the panel thickness. We are
not talking tensile stiffness here. We are taking about panel stiffness.
Roughly thickness to the fourth power. You cannot go to half the
thickness of cast iron with steel and expect it to be as stiff.

http://www.engineersedge.com/beam_bending/beam_bending1.htm
This is a simplistic way of looking at it because I can't find
simple steel panels uniform pressure loaded on the internet so far.

Plus the panel support structure enters into the equation.
Nothing less than a good FEA is going to help us out here.
A simple FEA would be a 3 by 3 by 3 box with one side open.
A constant pressure applied to the opposite panel would give
good insight. What we are really interested in is the panel resonant
frequency.

Paul Lamar

Paul,
I think you really hit upon the possible problem in that last sentence.
The resonant frequency is the MOST important factor in the the use of a
thin
section, built up rotor. The simple tensile strength of the material is
more than
adequate. A regular flexure at anything near a harmonic frequency will
be the
biggest problem to watch out for. Personally I like the idea of the 2
piece rotor
either e-beam welded or brazed. I believe several Ti grades can be
brazed. Steel
could be done this way too. I think you can rib the rotor as well and
help break up
harmonics on the combustion wall.
Bill Jepson


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