Civil Engineering Reference
In-Depth Information
Fig. 8.12
Stress-strain
profiles (20 %CW/annealed,
EAF at 800 A) [
5
]. The EAF
stress-strain profiles show
the same differences as the
conventional compression
tests; however, the stress-
strain profile of the worked
specimens is still slightly
higher than the annealed
profile at the end of the tests
4500
4000
3500
3000
2500
EAF - 20% CW
2000
1500
EAF - 20% Anneal
1000
500
0
0
0.1
0.2
0.3
0.4
0.5
0.6
Engineering Strain
dimensions. As the percent cold work is increased, the metal has a higher disloca-
tion density (i.e., a greater number of dislocations per area of lattice). With more
lattice obstacles, it is understandable that the worked specimens would be hotter
because there are more lattice obstructions for the flowing electrons.
In an attempt to correlate the different levels of cold work with different dis-
location densities, the following was performed. First, a static load of the magni-
tude that it took to deform the specimens to the desired height was applied to each
specimen, while 300 Amps of electrical current was run through the specimen. A
value of 300 A was chosen such that there was sufficient current to cause a heat-
ing effect, but not so much current to resistively heat the specimen to tempera-
tures above the maximum temperature of the thermal camera. While the current
was applied, the voltage between the top and bottom dies was recorded using a
multimeter. This procedure was performed for each level of cold work, and the
resulting voltages are shown below in Table
8.5
. In addition, Fig.
8.13
provides a
way to compare the voltages of the annealed and worked specimens at the same
Table 8.5
Stationary
electrical voltage
measurements of worked and
annealed specimens [
5
]
Height (%)
Designation
Static load (N)
Voltage
(mV)
Worked
22,250
70
10
57
Annealed
20
Worked
32,040
58
30
Annealed
30
Worked
42,275
31
17
Annealed
40
Worked
50,063
24
15
Annealed
50
Worked
62,300
15
Annealed
8
