Civil Engineering Reference
In-Depth Information
in order to continue plastic deformation. With this being said, this investigation
should be able to provide the same type of information as the grain size research
was intended to provide, such as how the different dislocation densities affect the
EAF technique. The specimen preparation, the experimental setup and procedure,
and the results and discussion of thermal profiles and stress-strain profiles of
worked/non-worked specimens are described.
8.2.1 Importance of Percent Cold Work on EAF
Effectiveness
The interactions between electrons and dislocations within a metal are responsible
for the electroplastic effect. The percent cold work, or prior plastic deformation
imposed on a metal before forming it again, has a correlation with the dislocation
density within a material. Depending on the material, as it is pre-worked to a greater
degree, the dislocation density within the metal increases potentially up to 10
12
mm/
mm
3
[
7
]. More specifically, as the percent cold work within a metal is increased, the
dislocation density within that metal is also increased. Since the flowing electrons
interact with dislocations, different amounts of dislocations within a metal should
have an effect on the efficiency of the EAF technique. Depending on the number of
preexisting dislocations, the flowing electrons will have more or less of an effect on
reducing the flow stress and extending elongation of the workpiece.
8.2.2 Specimen Preparation
All of the specimens used in this research work were derived from the same
9.5-mm-diameter rod of 304 Stainless Steel. This rod was sectioned off into
approximately 125-mm-long increments. These increments were then centerless
ground to 6.35 mm diameter, along with five other larger diameters which are rep-
resentative of the diameters which would be reached at various levels of cold work
(10 to 50 % in increments of 10 %—see Table
8.2
). Now, having all the different
diameter rods, two types of specimens could be made: one without any cold work
(i.e., in the annealed state) and one with cold work (i.e., in the worked state). The
worked specimens were fabricated by simply taking a 6.35-mm-diameter speci-
men and physically compressing it to 10, 20, 30, 40, and 50 % cold work. The
non-worked specimens were created using the other rods which were centerless
ground to the same diameters as the cold-worked specimens at each cold work
percent (neglecting the barreling effect). The length of these specimens was sized
using an EDM operation. In the end, cold-worked and non-worked specimens
were fabricated from the same rod to the same dimensions and were ready for test-
ing and evaluation. Table
8.2
displays the length and diameter changes required to
produce each level of cold work.
