Honeycomb
Honeycomb
(OP)
I,m looking for hints on how to optimize the design of a vacuum vessle (cylindrical) with a honeycomb, or foam core
wall.
I would like to minimize the density & thickness of the walls.
Thanks
wall.
I would like to minimize the density & thickness of the walls.
Thanks
RE: Honeycomb
Terry Drinkard
terrydrinkard@yahoo.com
RE: Honeycomb
The problem is not very simple, as, to some extent, the formulas used in pressure vessel calculations contain practical coefficients based on experiment.
As a starting point you can take the formula for the critical external pressure of a long thin cylinder (elastic buckling only!) and adapt it as follows (all the symbols have their commonest meanings, r is some average radius):
p=3*D/r^3
where
D=E*t^3/12(1-ni^2) for a solid wall
Now I suppose (but this is only my opinion!) that for a sandwich one can take for E and ni (Poisson) their equivalent values (ni=0 is a safe choice) and for t^3/12 the moment of inertia of the sandwich per unit length.
The result is a theoretical pressure and a safety coefficient of at least 3 is normally taken for practical applications. Of course it is also essential that the cylinder has uniform bending resistance around the circumference (the longitudinal joint, if any, is a critical point).
This may only be a starting point. The actual length of the cylinder need be accounted for (but a shorter cylinder has of course a higher buckling pressure): the formula is more complicated, but the procedure is exactly the same. Also plastic collapse conditions need be examined: a rough check is obviously that the hoop load (p*r) is not higher than the allowable load in the sandwich. Finally one should examine the heads and perhaps other special points.
You should also consider that in pressure vessel technology a normal solution is to use stiffening rings welded to the vessel wall: this might offer a safer, simpler and already available way to your mass optimization problem!
prex
motori@xcalcs.com
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