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Metal Foams: A Design Guide

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(b) (continued)<br />

Appendix: Catalogue of material indices 243<br />

Function and constraints a Maximize b<br />

CYLINDER WITH INTERNAL PRESSURE<br />

elastic distortion, pressure and radius specified; wall<br />

thickness free<br />

SPHERICAL SHELL WITH INTERNAL PRESSURE<br />

E/<br />

elastic distortion, pressure and radius specified, wall<br />

thickness free<br />

E/⊲1 ⊳<br />

a To minimize cost, use the above criteria for minimum weight, replacing density by Cm ,whereCm is the material cost per<br />

kg. To minimize energy content, use the above criteria for minimum weight replacing density by q where q is the energy<br />

content per kg.<br />

b E D Young’s modulus; G D shear modulus; D density.<br />

(c) Strength-limited design at minimum mass (cost, energy a )<br />

Function and constraints a,c Maximize b<br />

SHAFT (loaded in torsion)<br />

Load, length, shape specified, section area free<br />

Load, length, outer radius specified; wall thickness free f/<br />

Load, length, wall thickness specified, outer radius free<br />

BEAM (loaded in bending)<br />

Load, length, shape specified; section area free<br />

Load, length, height specified; width free f/<br />

Load, length, width specified; height free<br />

COLUMN (compression strut)<br />

Load, length, shape specified; section area free f/<br />

PANEL (flat plate, loaded in bending)<br />

Stiffness, length, width specified, thickness free<br />

2/3<br />

f /<br />

1/2<br />

f /<br />

2/3<br />

f /<br />

1/2<br />

f /<br />

1/2<br />

f /<br />

aTo minimize cost, use the above criteria for minimum weight, replacing density by Cm ,whereCmis the material cost per<br />

kg. To minimize energy content, use the above criteria for minimum weight replacing density by q where q is the energy<br />

content per kg.<br />

b<br />

f D failure strength (the yield strength for metals and ductile polymers, the tensile strength for ceramics, glasses and brittle<br />

polymers); D density.<br />

cFor design for infinite fatigue life, replace f by the endurance limit e.

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