Metal Foams: A Design Guide

Properties of metal foams 47
foams. Metal foams have some capacity as acoustic absorbers (Chapter 12),
although polymer foams and glass wool are generally better.
As in other materials, cyclic loading causes fatigue damage in metal foams.
High-cycle fatigue tests allow a fatigue limit 1 e to be measured (1 e is
the cyclic stress range at which the material will just survive 10 7 cycles)
Typical data for compression-compression fatigue with an R-value of about
0.1 are shown in Figure 4.5. A detailed description of fatigue behavior of
metal foams is given in Chapter 8.
σ max
σ pl
1.4
1.2
1
0.8
0.6
Compression (R = 0.1)
Compression (R = 0.5)
Tension (R = 0.1)
1 10 2 10 3 10 4 10 5 10 6 10 7 10 8
Cycles
Fatigue
limit
Figure 4.5 Fatigue data for Alporas foams. Chapter 8 gives details
The toughness of metal foams can be measured by standard techniques. As
a rule of thumb, the initiation toughness JIC scales with density as:
� �p JIC ³ ˇ y,s Ð ℓ
⊲4.3⊳
s
where ℓ is the cell size with p D 1.3 to1.5andˇ D 0.1 to0.4.
The creep of metal foams has not yet been extensively studied. The theory
and limited experimental data are reviewed in Chapter 9.
Thermal properties
The melting point, specific heat and expansion coefficient of metal foams
are the same as those of the metal from which they are made. The thermal
conductivity scales with density approximately as:
� �q ⊲4.4⊳
³ s
with q D 1.65 to 1.8.
s