Civil Engineering Reference
In-Depth Information
After completing this test, another sample was tested where the same electrical
treatment was performed, and then, the sample was deformed at room temperature
to failure (refer to Fig. B.7 in Appendix B). This result is compared to the room
temperature deformation sample (Sample 2). The micrographs for the electrically
treated deformed sample in orientations 1 and 2 are shown in Figs. C.14 and C.15,
respectively.
From a visual comparison of orientation 1, the grain size of the electrically
treated sample deformed at room temperature appears to have a smaller average
grain size with approximately an equal amount of twinning. From the statisti-
cal analysis, it is said that the means are not equivalent, but the variances are the
same. The average equivalent grain size of the stationary electrical test in orienta-
tion 1 is 5.43 µm with a standard deviation of 1.74 µm as compared to 6.73 µm
with a standard deviation of 2.29 µm for the deformation test of the as-received
material in orientation 1.
For orientation 2, a visual analysis suggests that grain size is slightly larger and
the grains have become more elongated. The statistical analysis concluded that
the means are not equal, but the variances are the same. The average equivalent
grain size of the stationary electrical test in orientation 2 is 6.78 µm with a stand-
ard deviation of 2.13 µm as compared to 6.15 µm with a standard deviation of
2.33 µm for the deformation test of the as-received material in orientation 2. The
variation in the mean and grain shape as compared to the as-received deformation
sample (Sample 2) may be a result of the additional strain that was imposed on the
material before failure (approximately 24 %) which is greater than that of Sample
2. This additional deformation could explain the greater amount of grain elonga-
tion and directional alignment shown in orientation 2 (Fig. C.15). As a result of
the grains in orientation 2 becoming elongated more, the grains in orientation 1
reduced in grain size to maintain approximately the same grain volume. Thus, this
additional amount of deformation could explain the observed micrograph differ-
ences despite the stationary electrical pre-treating not altering the grain size/shape
as described above.
8.3.4.2 EAF with Square Wave Current Application During
Deformation
To examine the influence on an applied electrical current during EAF testing with
a square wave current application, different electrical conditions were tested and
analyzed. This section varies from the prior section in that the electrical square
wave is applied during deformation.
The test summarized in this section applied 800 A at intervals of 60 s for the
duration of 0.5 s, and this application was continued until the specimen fractured
(refer to Fig. B.3 of Appendix B). In addition to examining the microstructure
at the fracture location (L1), this section examines a section at the middle of the
specimen (L2) and a section from the region near the specimen fillet (L3). This
was performed to determine whether a microstructure gradient is present as a
