Metal Foams: A Design Guide

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Creep
p e
p e
•
Area A
u F
2r
Tube
a
p i
b
Sphere
b
a
p i
Figure 6.8 Creep
t
•
δ
s
•
F
Constitutive law
Cantilever
•
δ
=
Punch
Tube
•
ρ = 2
Sphere
•
•
εo
•
o
n+2
Design formulae for simple structures 79
• •
= o
s
s o
n
(2n+1) F
n +1
nsο bt t
•
u = C1 o
n
• C2F √A
soA •
o
ρ (1 − ρ)
1
n
1− (1 − ρ)
( ) n
( ) n
= 0.6
(n +2)
n
2 (pe − pi) n σο n
• •
ρ =
3
2 o
ρ (1 − ρ)
1
1− (1 − ρ) n
3 (ρe − ρi) 2n sο Foam constitutive law
ε
n 3n+1
⎛1.7
(2n+1) s ⎛ρs
2
⎝ n so ⎝ ρ
This is correct for simple tension and compression, and a reasonable approximation
for bending and torsion, but it breaks down for indentation and
hydrostatic compression because volumetric creep-compression of the foam
has been neglected.
Reference
Young, W.C. (1989) Roark’s Formulas for Stress and Strain, 6th edition, McGraw-Hill,
New York.
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⎝
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