Civil Engineering Reference
In-Depth Information
Fig. 3.7
Experimental EAF flow stress results (Parameter Set 8) and effect of specimen cooling
during EAF
to dislocation or pinned dislocations such that they could continue the process of
slip. As a result, this reduced the necessity for twin-boundary formation, which
was necessary for the room temperature deformation test to continue. Hence, the
current application supplied energy directly to the regions of high stress or the
areas with very high dislocation densities. Also, for the tests where cooling was
compared to non-cooling (Fig.
3.7
), a small difference in flow stress reduction was
noted while the cooled test quickly increased in strength after the application of
the current. This is in agreement with the “hot spots” improving the mobility of
the dislocations, while the remainder of the material was not at such an elevated
temperature. Once the current was discontinued, the electrical energy imparted to
the dislocations was removed and the strength quickly increased as shown experi-
mentally (e.g., Fig.
3.8
).
Moreover, this theory is also in agreement with Ross et al. where isothermal
tests were performed at temperature greater than that reached in the electrical tests
[
18
]. The results from this work showed that the isothermal testing did not create
near the flow stress reductions or the increases in fracture strain as compared to
the electrical tests. The results are given in Fig.
3.9
.
This work directly speaks to the aforementioned difference between heating by
external convection and with a direct electrical current, where the convection does
not allow for localized “hot spots” within the lattice. Additionally, early works in
EAF using very short-duration pulses produced large flow stress reductions with
very small bulk temperature increases [
19
,
20
]. Thus, this work also coincides
with the theory in that the short-duration pulse allowed for high local temperatures
at defects, while the bulk of the lattice remained at a reduced temperature.
