Civil Engineering Reference
In-Depth Information
Fig. 4.27
G5 titanium NCCD empirical modeling
Using this model for a constant current density (CCD) where the current den-
sity does not change during the test as described by Eq. (
4.10
), hence reduces the
flow stress predictor in Eq. (
4.11
) to an approximate linear flow stress modifier.
Thus, this does not allow for an effective estimator of the flow stress for CCD as
there are significant reductions in flow stress and great variation when increasing
from current density to current density. Using the present data, an alternate rela-
tionship is introduced and based off of the CCD data. The proposed relationship
for a CCD tests is presented in Eq. (
4.12
). The new predictor function is based off
of a power function relation that corresponds to the strain imposed in the material
and the CCD value.
σ
predicted
=
K
′
ε
n
ε
m
(
A
+
B
)ε
C
D
(4.12)
where
σ
predicted
is the predicted flow stress with the application of electricity,
K
′ is
the strength coefficient,
ε
is the strain,
n
is the strain hardening exponent,
ε
is the
strain rate,
m
is the strain rate sensitivity exponent,
is the current density, and
A
,
B
,
C
, and
D
are material specific constants for this model.
The resultant model material specific constants are shown in Table
4.5
and the
predicted flow stress for the SS304 and the Grade 5 titanium is shown in Figs.
4.28
and
4.29
, respectively. Of note is the fact that the titanium results were only pre-
dicted until the baseline fracture.
Table 4.5
CCD model
constants
A
B
C
D
−
0.018
1.101
−
0.00061
1.592
SS304
G5 titanium
−
0.015
1.053
−
0.00048
1.560
