Metal Foams: A Design Guide

Cost estimation and viability 215
Conventional alloys (cast irons, steels, aluminum alloys) lie in the lower part
of the diagram. Beryllium alloys, CFRPs and Al-based MMCs lie in the central
and upper parts.
The trade-off surface for conventional, fully dense, materials is shown by
the shaded band. Metal foams lie in the unpopulated sector of the diagram – all
three classes of foam offer non-dominated solutions to this problem. But even
so, they are viable only if the mass/value exchange constant lies in the right
range. To explore this question for the panel of specified stiffness we define
the value function
�
V D ˛1P1 C ˛2P2 D ˛1
E 1/3
� �
C
C
E 1/3
�
⊲16.16⊳
(since ˛2, relating value to cost, is unity). Values of ˛1, relating value to
mass, are listed in Table 16.2. The equation is evaluated in Table 16.3 for
two extreme values of ˛1 for a set of materials including cast irons, steels,
aluminum alloys, titanium, beryllium and three metal foams. When ˛1 has the
low value of 0.5£/kg, nodular cast irons are the best choice. But if ˛1 is as
Table 16.3 The selection of panel materials: stiffness constraint
Material E Cm P1 P2 V V
Mg/m 3 GPa £/kg ˛1 D ˛1 D
£0.5/kg £500/kg
Cast iron,
nodular
7.30 175 0.25 1.31 0.33 0.99 655
Low-alloy
steel (4340)
7.85 210 0.45 1.32 0.59 1.25 660
Al-6061-T6 2.85 70 0.95 0.69 0.66 1.01 345
Al-061–20%
SiC, PM
2.77 102 25 0.59 14.8 15.1 309
Ti-6-4 B265
grade 5
4.43 115 20 0.91 18.2 18.7 473
Beryllium
SR-200
1.84 305 250 0.27 67.5 67.6 202
Alporasa 0.25 1.0 40 0.23 10.0 10.1 125
Alulighta 0.30 0.8 16 0.3 5.2 5.4 155
Alcana 0.25 0.4 5.8 0.34 2.0 2.2 172
a All three types of metal foam are made in a range of densities, with a corresponding range of properties. These three examples
are taken from the middle of the ranges. The costs are estimates only, broadly typical of current prices, but certain to change
in the future. It is anticipated that large-scale production could lead to substantially lower costs.