Civil Engineering Reference
In-Depth Information
4.3
Aluminum Testing and Properties
Typical properties are provided in Tables 4.4 and 4.5 for non-heat-treatable
and heat-treatable wrought aluminum alloys, respectively. Typical proper-
ties for cast aluminum alloys that may be used for structural applications are
given in Table 4.6. These values are only an indication of the properties of
cast aluminum alloys. Material properties of cast members can vary through-
out the body of the casting due to differential cooling rates.
Tests performed on aluminum are similar to those described for steel.
These typically include stress-strain tensile tests to determine elastic
modulus, yield strength, ultimate strength, and percent elongation. In con-
trast to steel, aluminum alloys do not display an upper and lower yield
point. Instead, the stress-strain curve is linear up to the proportional limit,
and then is a smooth curve up to the ultimate strength. Yield strength is
defined based on the 0.20% strain offset method, as shown in Figure 4.5.
As indicated earlier, the modulus of elasticity of aluminum alloys is on the
order of 69 GPa (10,000 ksi) and is not very sensitive to types of alloys or
temper treatments.
Sample Problem 4.1
An aluminum alloy rod with 10 mm diameter is subjected to a 5-kN tensile load. After
the load was applied, the diameter was measured and found to be 9.997 mm. If the
yield strength is 139 MPa, calculate the Poisson's ratio of the material.
Solution
5000
p
d
2
4
10
6
Pa
s =
=
63.7
*
=
63.7 MPa
It is clear that the applied stress is well below the yield stress and, as a result, the de-
formation is elastic. Hence, assume that
E
=
69 GPa
10
6
s
E
=
63.7
*
e
axial
=
=
0.000923 m/m
10
9
69
*
ยข
d
=
9.997
-
10.000
=
0.003 m
e
lateral
=-
0.003
=-
0.0003
m/m
10.000
-
e
lateral
e
axial
0.0003
0.000923
=
=
0.33
n
=
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