Civil Engineering Reference
In-Depth Information
• The contribution that thermal softening had on reducing the mechanical proile
of the process was dependent on the specific material (since each metal has a
different strength vs. temperature relationship) and the specific temperatures
reached during the EAF process.
• Factors such as die speed and current density signiicantly affect the eficiency
of the EAM technique. The concept was highlighted in the previous experimen-
tal work for tensile processes. This particular section shows that the current den-
sity and die speeds also need to be “balanced” in order to optimize results in
compression as well.
5.3 Specific Heat Sensitivity
Although the heating effects from EAF are not a major contributor to the formability
enhancements (as highlighted from the work by Ross et al.), these effects are utilized
in the thermal-based EEC determination method, where differences in temperatures
between stationary electrical and EAF tests were used to quantify the EEC profile.
Therefore, it is important to understand the effect that the temperature has on the spe-
cific heat of the material, and ultimately on the EEC profile (i.e., the efficiency of the
applied electrical power). In this analysis, specific heat sensitivities for both SS304
and Ti-G5 are evaluated at three different temperatures respective of the temperatures
reached during three different tests (conventional forming, EAF tests, and stationary
tests). Figure
5.15
displays the relationship between the specific heat values and the
temperatures for each metal (note that the maximum temperature that was reached
during stationary testing at 25 A/mm
2
for each material is denoted by a black dot).
Additionally, Table
5.2
lists the exact specific heat values used for each test
description in the model per material [
17
]. The maximum temperature observed in
750
304 SS
700
Ti - G5
650
600
550
500
450
400
0
100
200
300
400
500
600
700
800
900
Temperature (° C)
Fig. 5.15
Specific heat versus temperature profiles (SS304 and Ti-G5) [
17
]. Relationships
between the specific heat values and temperatures for SS304 and Ti-G5
