Metal Foams: A Design Guide

144 Metal Foams: A Design Guide
Weight Index
ψ = W /2πR 2 Lρ s
Optimum density
ρc /ρs 0.004
0.003
0.002
0.001
0.08
0.06
0.04
0.02
a
b
Axially stiffened
Buckling
yielding
&
wrinkling
Buckling & wrinkling
0
0 0.2 0.4 0.6
Global weight minima
E c /E s = (ρ c /ρ s ) 2
Buckling & yielding
E c /E s = 3(ρ c /ρ s) 2
E c /E s = 3(ρ c /ρ s ) 2
E c /E s = (ρ c /ρ s ) 2
/R = 1
0.8 1 1.2 1.4 1.6 1.8 2
N/E fR (×10 5 )
Load index
Figure 10.17 Global weight minima for cylindrical sandwich shells
Imperfection sensitivity
An important consideration for strength-limited thin-walled construction
concerns the influence of imperfections. In most cases, imperfections reduce
the buckling loads, sometimes considerably. In shells, imperfections cause
out-of-plane bending, which lowers the maximum support load due to two
effects: (1) by advancing non-linear collapse and (2) by causing premature