Compressive Electrically Assisted Forming Model - Electrically Assisted Forming - page 91

the experimental setup and procedures used to calibrate the model for accuracy, a
discussion of the experimental/analytical results, an efficiency analysis comparing
the magnitude of applied electrical power to the decreases in the forming stress,
and finally conclusions on the EA forging model [ 11 ]. The resulting stress-strain
profiles, after the EEC values are fed into the thermo-mechanical model, will be
displayed and explained. Additionally, the efficiency of applying electricity to the
deformation process and the benefits gained will be provided.

5.2.2 Modeling Strategy Overview

As part of the modeling strategy, an EEC was previously created to represent the
efficiency of the applied electricity (i.e., how much of the applied electrical power
contributes toward plastic deformation vs. how much contributes toward resistive
heating). EAF tests were performed on SS304 specimens, while varying the die
speed and the starting current density (i.e., the current magnitude was held constant
throughout each test, and density varied according to the instantaneous cross-sec-
tional area). The “current density” values are based on the initial cross-sectional area
of the specimen. As the part is deformed, the cross section will increase. However,
in this chapter, the current magnitude (i.e., the current selected at the beginning of
the test in order to produce a particular starting current density) will remain constant
throughout the test. This means that the current density will decrease as deforma-
tion takes place and the workpiece diameter increases. In Chap. 4 , the results from
these experiments were used to determine the EEC for stainless steel using the
mechanical- and thermal-based approaches, and the results from both methods were
compared. Now, the EECs will be fed into a thermo-mechanical model in order to
predict stress-strain profiles comparable to the experiments.
The hybrid modeling strategy introduced by Bunget et al. [ 1 ], accounts for the
thermal, mechanical, and coupled thermo-mechanical aspects of the direct electri-
cal effects witnessed during EAF. Further, the EEC was conceptualized to quantify
the “usable” direct electrical effects. The interrelations between the thermal and
mechanical aspects of EAM, and how they relate to the workpiece temperature
and force profiles are depicted in Fig. 5.5 .

5.2.3 Coupled Thermo-Mechanical Modeling

As stated, the electroplastic effect is the fraction of electrical power imparted into
the plastic deformation process, as shown below in Eq. ( 5.19 ):

P e = P heat + P def = η( 1 − ξ ) VI + ηξ VI

(5.19)

where P e is the electric power ( I · V ), η is the efficiency, and ξ is the EEC [ 12 ].
P heat represents the amount of electric power that will dissipate into heat through