Civil Engineering Reference
In-Depth Information
Fig. 5.20
Stainless Steel
304 die conduction length
sensitivity [
11
]. Different die
conduction lengths were used
in the model to determine the
significance and sensitivity
of the die conduction length
value
L
dc
=0.0065m
L
dc
=0.0085m
Exp.
L
dc
=0.0105m
length of the die that contributes toward drawing heat from the workpiece (
L
dc
).
Figure
5.20
displays workpiece thermal profiles for several different die lengths,
along with the actual experimental data for EAF tests run at a starting current den-
sity of 20 A/mm
2
and a die speed of 12.7 mm/min. Currently, the authors use the
thermal images to estimate the die conduction lengths, where the excessive heating
was apparent when electricity was applied. The die conduction length used for the
model in this case was 0.0085 m. This was determined visually from the thermal
camera profiles of the EAF tests. From the figure, where the conduction lengths
are moved in increments of 2 mm, the overall thermal profile is extremely sensi-
tive to the die conduction length value. By varying the conduction length by about
0.004 m, there is about a 40 °C difference in the maximum temperatures within
the thermal plots. Overall, when modeling the electroplastic effect, it is critical to
devise a consistent and accurate method of approximating the conduction length.
5.5 EEC Profile—Material Sensitivity Comparison
In this subsection, the general shape of the EEC profiles for the Stainless Steel 304
and Ti-G5 specimens will be discussed. Figures
5.21
and
5.22
display the EEC
profiles for Ti-G2 and SS304, respectively (both tests run at a starting current den-
sity of 25 A/mm
2
with a die speed of 12.7 mm/min) [
11
]. The EECs are plotted
here as a function of stroke. Other parameters could be used as well, e.g., strain
or displacement, but the overall observations are still valid. From the two figures,
it can be seen that the percentage of “usable” electricity increases throughout the
test; however, the increase is different for each material. In particular, the majority
of the EEC profile increase for the Ti-G2 material occurs in the initial part of the
stroke (about 50 % of the maximum EEC value occurs over about the first 5 % of
the compressive stroke), whereas the majority of the EEC profile increase for the
SS304 material occurs at the end of the stroke (about 50 % of the maximum EEC
value occurred in the final 25 % of the stroke). Both of these EEC profiles were
approximated using the power law, and the value of the exponential term is what
