Civil Engineering Reference
In-Depth Information
Fig. 11.4
Electrical
parameters varied in EAB
investigation [
1
,
2
]. The
electrical parameters that
can be varied are the current
magnitude, the pulse
duration, and the time period
between electrical pulses
t
0
p
p
Time, t
decreasing over the test, and therefore, the current density is increasing. The pulse
parameters that were varied during the tests are current density,
C
d
;
pulse duration,
Δ
t
; and pulse period,
p
(Fig.
11.4
).
11.1.4.1 Energy Effect
When electricity is applied during plastic deformation, a part of the electrical
energy is imparted into the mechanical deformation process. The total power con-
sumed by the deformation process is given by Eq. (
11.12
):
J
total
=
J
m
+
J
e
=
J
m
+
ξ
P
e
(11.12)
where
J
m
is the mechanical component related to the applied forming load applied
and die velocity,
J
e
is the effective electric power that aids deformation,
P
e
is the
electrical power (
I
·
V
) passing through the workpiece, and
ξ
is the electroplastic
effect coefficient (EEC). The EEC depends on the material, applied current den-
sity, time, and strain rate and can be determined through tests. The remaining elec-
tric energy,
(
1
−
ξ)
P
e
, is converted into heat through resistive heating.
11.1.4.2 Temperature Rise Effect
The global heating from the electricity will result in some degree of thermal sof-
tening, thereby lowering the flow stress of the material and contributing to the
decreased required work. At room temperature, the flow stress is given by the
power law presented earlier, but as the temperature rises, the flow curve depends
strongly on the temperature. The investigations conducted by previous researchers
indicated that the temperature is lower than the temperature at which recovery and
recrystallization take place; thus, the strain-rate dependency may be neglected, but
the influence of the temperature on the strength of the material, given by the tem-
perature-dependent coefficient function,
C
(
T
), is still significant. The flow stress
is given by equation in Eq. (
11.13
). When considering all metals, the strength
coefficient is reduced as they are heated. However, each metal has a specific
strength-temperature relationship and has a specific temperature range where this
