Civil Engineering Reference
In-Depth Information
Fig. 4.9
Flow stress
reduction due to EAF (Ti-
G5) [
4
]. The flow stress
was reduced to EAF, and
the specimen was able to
be completely formed to
the desired length without
failure, unlike with the
conventionally formed test
1500
1200
Conventional Test
900
EAF Test
600
300
0
0
0.1
0.2
0.3
0.4
0.5
0.6
True Strain
Although the displacement varies linearly in time due to a constant die speed, the
force for the EAF test showed some variation (“noise”). The frequency analysis of
the data indicated a frequency response at ~22.29 Hz and its multiples for G2, and
1.02 Hz and its multiples for G5, which are not found in the conventional tests. The
behavior observed may be due to a cyclic softening/hardening phenomenon present
during EAF. It is hypothesized that the input of electric energy may result in alternat-
ing of electroplastic softening of the material (thus, reduction in the forming load)
and hardening of the material due to deformation (thus, increase in load).
4.2.3.2 Model Prediction and Experiments
The first step in the model prediction process is to compare the model to a simple
stationary electrical test, to isolate the resistive heating effects and validate that the
heat transfer relationships within the model are correct.
Figure
4.10
displays both an experimental test and the model output for a stationary
electrical test on Ti-G2. The model tends to slightly underestimate the temperatures in
Fig. 4.10
Ti-G2 Stationary
electrical test at L
0
. The
stationary electrical tests
were run by applying
electricity without deforming
the workpiece. The model
assumes 100 % of the
electrical power contributes
toward heating the workpiece
Experimental Output
(no def.)
Model Output
(no def.)
