Metal Foams: A Design Guide

60 Metal Foams: A Design Guide
More generally, if the performance metrics for a reference material M0 are
known, those for competing materials are found by scaling those of M0 by
the ratio of their material indices. There are many such indices. A few of
those that appear most commonly are listed in Table 5.3. More are listed in
the Appendix.
Table 5.3 Material indices a
Function, objective and constraint Index
(and example)
Tie, minimum weight, stiffness prescribed
(cable support of a lightweight stiffness-limited tensile structure)
Tie, minimum weight, stiffness prescribed
(cable support of a lightweight strength-limited tensile structure)
Beam, minimum weight, stiffness prescribed
(aircraft wing spar, golf club shaft)
Beam, minimum weight, strength prescribed
(suspension arm of car)
Panel, minimum weight, stiffness prescribed
(car door panel)
Panel, minimum weight, strength prescribed
(table top)
Column, minimum weight, buckling load prescribed
(push-rod of aircraft hydraulic system)
Spring, minimum weight for given energy storage
(return springs in space applications)
Precision device, minimum distortion, temperature gradients
prescribed
(gyroscopes; hard-disk drives; precision measurement systems)
Heat sinks, maximum thermal flux, thermal expansion prescribed
(heat sinks for electronic systems)
Electromagnet, maximum field, temperature rise and strength
prescribed
(ultra-high-field magnets; very high-speed electric motors)
˛/
˛/
/E
/ y
/E 1/2
/ 2/3
y
/E 1/3
/ 1/2
y
/E 1/2
E/ 2 y
1/ Cp
Note: D density; E D Young’s modulus; y D elastic limit; D thermal conductivity; ˛ D thermal expansion coefficient;
D electrical conductivity; Cp D specific heat.
a The derivation of these and many other indices can be found in Ashby (1999).