Civil Engineering Reference
In-Depth Information
0 to 550 °C, and checked at room temperature, with a spatial resolution (IFOV) of
1.3 mrad. The temperature was measured for three tests: (i) stationary tests, when
electricity is applied through the specimen, but when there is no deformation, just
preloading to ensure contact and no electrical spark, (ii) an EAF compression test,
and (iii) a conventional compression test. In order to measure the temperature rise
during the tests, no lubricant was used during these tests. The specimens were
cylindrical, with the same diameter as the outer diameter of the ring samples, and
a height of 4 mm. The same material and same test conditions as for rings were
used. For a higher emissivity factor and more accurate readings, the specimens
were painted black. The thermal profiles were calculated using ThermaCAM soft-
ware. Specifically, the software allowed for the selection of an area on the speci-
men. Then the maximum value in the area was recorded at a frequency of 1/250 s
until the user ended the recording.
For the stationary test and a current density of 25 A/mm
2
, the temperature
increased rapidly up to approximately 310 °C (Fig.
9.40
). The second test, which
was an EAF compression test, exhibited a different behavior. The temperature
increased initially up to 105 °C, and then it started to decrease, before turning off
the electricity. During the conventional compression test, an increase of maximum
10 °C was recorded. A few conclusions are reached from these tests:
The temperature measurements during the EAF test agreed with other studies
that indicated a temperature between 100 and 200 °C [
20
]. The low temperature
rise during the conventional compression test suggests that the increase in tem-
perature in the electrical tests is due to the resistive heating. The large difference
in temperature rise between stationary and EAF tests can be partially attributed to
the change in specimen surface area during the deformation, which affects the heat
transfer through convection and conduction. Note though that the change in total
350
300
Stationary test
EAF test
250
200
Conventional
test
150
100
50
0
0
5
10
15
Electricity applied
(25 Amps/mm
2
) for
Stationary/EAF tests
Time [sec]
Fig. 9.40
Temperature profiles of stationary electrical and EAF tests [
13
,
14
]. The stationary
electrical test at the same current density is much hotter than the EAF test. This supports the idea
that the electrons aiding with the plastic deformation of the material
