Civil Engineering Reference
In-Depth Information
• EAF reduced the low stress in the 304 Stainless Steel specimens for both the
die speeds.
• The EEC proiles determined using both methods were consistent to each other
throughout the entire stroke range for both die speeds.
• The mechanical-based approach to determining the EEC only required force versus
position data to generate the EECs, whereas the thermal-based approach required
there to be thermal data taken, which required the use of a thermal camera.
• The mechanical-based approach does not solely isolate the effects of thermal sof-
tening, since there will be some extent of thermal softening contributing to the
mechanical power reduction of the EAF tests due to the increased temperature.
4.5 Empirical Modeling Strategies
The following two sections present empirical modeling for compression EAF
forming. The first section contains a model that is only based off the nominal cur-
rent density where the second section takes into account the non-steady state cur-
rent density during forming.
4.5.1 Non-constant Current Density
For the development of the electrical current and flow stress model, previously
performed continuously applied stress versus strain data was analyzed. The fol-
lowing sections discuss the methodology used in creating the stress predictor func-
tion and the observed comparison between empirical results and actual testing.
4.5.1.1 Relationship Development
When examining the relationship between the flow stress and applied strain with
the addition of current, a range of the strain equivalent to the baseline fracture
strain was examined. This is shown in Fig.
4.20
for the different initial current
densities.
The next step was to determine the difference or ratio between the baseline and
each of the electrical tests. To perform this, a ratio was determined, which would
relate the electrical test back to the baseline. The stress ratio with respect to strain
for each nominal current density is shown in Fig.
4.21
. After seeing the relation-
ship for each current density, an exponential fit (dashed line) was utilized as the
transfer function between the electrical test and the baseline. This type of equation
was utilized as it best represented the observed ratio functions. To better character-
ize the relationship, the different current density's stress ratio converged to one at
an approximate strain value of 0.018, thus an additional offset parameter in the
