Civil Engineering Reference
In-Depth Information
• At the same die speed, some metals in this work expressed a low-threshold
current density, while others showed a higher-threshold current density (up to
4-times higher than others).
• The EAM technique produced similar results on two different size specimens,
leading to the conclusion that the effects are related to current density and not
current amplitude.
11.4.1.2 Effects of Different Die Speeds on EAM Effectiveness
Work by Jones and Roth [
17
] determined that this electroplastic effect is strain-
rate-dependent. More specifically, in this work, Mg AZ31B-O specimens were
compressed, while a constant current was applied. As the die speed was increased,
while the current remained constant, the magnitude of the electroplastic effect
decreased, as shown in Fig.
11.36
.
The final geometries for the same test series are depicted in Fig.
11.37
. The
25.4, 19.05, and 12.70 mm/min tests fractured by shear, whereas the 6.35 mm/min
test only had cracking and was able to be formed to a much greater extent. As seen
for the specimens which failed by shearing, the fracture once again occurred on a
45° plane. As mentioned in the previous subsection, the “threshold” effect can also
be categorized as a significant improvement in formability. From Fig.
11.37
, one
can see that the “electrical threshold” for this particular current density is between
die speeds of 6.35 and 12.70 mm/min.
Conclusions from this work are as follows:
• The higher current densities produced greater formability improvements, how-
ever, the same benefits could be produced from lower current densities if the
platen speed was slowed down.
• A threshold current density was noticed where the formability was considerably
improved compared to the other lower current densities.
• The EAM technique in compression was found to be strain-rate dependent.
Fig. 11.36
EAM die speed
dependence (CD
=
20 A/
mm
2
) [
17
]. For the same
electrical settings, as the
die speed is increased, the
amount by which EAM
has an effect on the metal's
formability becomes reduced
