Civil Engineering Reference
In-Depth Information
4.2.3 EEC Thermal-Based Determination
Within this section, true stress-strain plots and temperature plots are used to
emphasize several EAF relations and effects. First, the reductions in flow stress
due to EAF are shown. Of note is that since this work focused on modeling EAF,
only one current was used, so the reductions in flow stress from EAF could be
much greater if larger currents were utilized. Second, the model prediction pro-
cess and accompanying experimental results are discussed. The steps required
for model prediction are outlined in the previous section. From the creation of
the model and analysis of several of the main input variables, EAF can be bet-
ter understood and more accurately predicted through this variety of influencing
factors.
4.2.3.1 Force Reduction Due to EAF
From many experimental works over the last several years, it has been shown
that EAF reduces a metal's flow stress compared to conventional forming [
6
].
Figures
4.8
and
4.9
show the true stress-strain profiles of a conventional compres-
sion test (at room temperature) and an EAF test for Ti-G2 and Ti-G5, respectively.
A die speed of 12.7 mm/min was used and a constant current of 300 A was applied
during the EAF test [
4
]. Both figures show that the flow stress was reduced sig-
nificantly due to EAF. In Fig.
4.8
, one can see that the difference in the flow stress
is offset by about 150-200 MPa throughout the test. Conversely, in Fig.
4.9
, the
difference in flow stress increased slightly as the test progressed. Additionally,
the Ti-G5 in the conventional compression test failed before the end of the test.
However, in the electrically assisted compression test, the material was able to be
completely formed without failure. The results in Fig.
4.9
are comparable to EAF
compression test results of the same alloy run by [
2
]. In particular, a small amount
of strain weakening is apparent at the beginning of the test, and in both works, the
elongation of Ti-G5 is increased using EAF.
Fig. 4.8
Flow stress
reduction due to EAF
(Ti-G2) [
4
]. The flow
stress was notably reduced
in comparison with the
conventional stress-strain
profile
1000
Conventional Test
Conventional Test
800
600
EAF Test
EAF Test
400
200
0
0
0.1
0.2
0.3
0.4
0.5
0.6
True Strain
