Civil Engineering Reference
In-Depth Information
Fig. 4.1
Mechanical
power profiles (12.7 mm/
min) [
1
]. The mechanical
power profiles decrease in
magnitude as a higher current
density is applied
12
CD15
10
CD10
8
Baseline
6
CD25
4
CD20
2
0
0
5
10
15
20
Time (s)
mechanical work with respect to time, thus aiding the deformation (i.e., imparting
energy onto the dislocations and facilitating their movement by providing enough
energy to overcome lattice obstacles). The specific steps to solve for the EEC
using the mechanical-based method are as follows. Within the following sections,
these steps will be carried out using EAF compression tests on Al 6061-T6511.
1. Run a conventional and an EAF compression test. Note that these tests need
to be run at the same parameters (i.e., die speed, deformation stroke, initial
preload, and starting specimen size), with the exception of the applied current
for the EAF test. It is also recommended to run several replicates of each test to
verify that the results are repeatable.
2. Plot the mechanical power versus time profiles. In Fig.
4.1
, four different start-
ing current densities were tested; therefore, four different sets of EAF tests and
one set of conventional compression tests were needed to construct the profiles.
3. Determine the difference between the two power profiles and normalize it with
respect to the conventional forming power profile.
4.1.1 Experimental Setup and Procedure
The experiments for this section involved running conventional compression tests
and EAF compression tests at several starting current densities. The experimen-
tal data used in determining the EEC are from EAF compression tests run on Al
6061-T6511 specimens, by Perkins et al. [
2
]. The initial billets had a diameter
of 6.4 mm and a height of 9.5 mm. The compression tests were deformed to a
maximum stroke of 6.4 mm at a speed of 25.4 mm/min. The material parameters
and the friction conditions were determined by solving the model for a classical
test. After fitting the data, the following values were determined:
C
=
348 MPa,
n
=
0.04,
and
ยต =
0.08.
