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APPENDIX A

MATERIAL PROPERTIES FOR DESIGN

To estimate the masses of components for alternate configurations, nominal design values for a variety of physical properties must be assumed for the materials involved. Only a few "standard" metal alloys are shown in Table 4-4, chosen to give good weldability, corrosion resistance, and forming properties. A more careful specification of specific alloy percentages for structural components in a final design is expected to reduce the actual structural mass somewhat from that derived from this conservative approach. For particular applications where, for example, cyclic stress reversal may induce fatigue, high temperatures cause creep, or low temperatures cause brittleness, special materials must be used.

TABLE 4-4 (gif format)

Table 4-4.- MATERIAL PROPERTIES OF SOME METAL ALLOYS

Tensil strength Conductivity
Metal types Ultimate

MPa
Yield

MPa
Working

MPa
Brinell
hardness
number

Density
G,
10^3 kg/m^3
Modulus
E,
MPa
Poisson
ratio
Coefficient
of expansion

10^-6 X C^-1 (degrees)
Electric
10^-6 X ohm-m^-1
Thermal
W/m degrees C
Aluminum
(150 Degrees C)
i) Pure (99.5 percent)
83 41 28 30 2.70 70,000 1/3 24 36 230
ii) Heat treated alloy:
Al 12 Si 0.5 Mg
303 248 165 95 2.65 76,000 1/3 19 21 157
iii) Cold form wire
or plate
455 352 234 140 2.65 76,000 1/3 20 31 163
Titanium
i)Heat treated alloy:
Ti 5 Al 2.5 Sn
620 517 345 105 4.54 110,000 1/3 10 - 22
Cold formed wire
or plate
1030 931 620 110 4.54 110,000 1/3 9 - 23
i) Magnesium
Heat treated castings:
Mg 8.5 Al
138 83 55 48 1.8 43,000 0.35 27 7 93
ii)Thin plate or wire
Mg 3 Al 0.5 Mn 0.1 Zn
207 152 110 52 1.8 43,000 .35 25 8 81
Steel
i) Wrought iron
352 207 138 70 7.8 207,000 .3 12 9 93
ii) Rolled - heat treated 538 352 234 120 7.8 200,000 .3 12 8 81
iii) Cold drawn 1380 1240 830 200 7.8 200,000 .3 12 8 81

A safety factor of 1.5 is applied to the yield stress to give safe working values. This corresponds to the standard for large civil engineering structures combining dead- and live-load factors. In all large structures the material is proof-tested before use, so that, in reality, the end result of processing and fabrication is not a dubious variable but can be a controlled parameter. At least one good machine for static and dynamic testing of the strength of materials must be included in the laboratory equipment brought from Earth to the colony site.

The strength properties of ceramic-type materials and "soil" if (table 4-5) are low, and experimental results from any pilot study for processing lunar ores should help define them more precisely. While it should also be possible to grow long glass fibers having great structural strength, such materials are not assumed for construction of the first colony.

TABLE 4-5 (gif format)

TABLE 4-5.- MATERIAL PROPERTIES OF SOME CERAMICS AND SOILS

Flexural working stress

MPa
Untempered Tempered Brinell
hardness
number
Density
G,
10^3 kg/m^3
Poisson
ratio,
Coefficient
of expansion

10^-6 C^-1degrees
Thermal
conductivity,
W/m C (degrees)
Ceramics
i) Silica glass
3.4 6.9 400 2.2 0.18 80 15
ii)Window sheet 8.3 16.5 500 2.45 .23 850 .9
Rock
i)Fused
3.4 200 2.8 .15 - -
ii)Soil (dry) - - 1.4 .1 - -
iii)Soil
(60 percent
moisture)
- - 1.68 .5 - -

a Compressive strength is about 10 times greater.

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