Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes Page: 72 of 108

Maximum effective strain and strain rate experienced by the material was determined from the FEM
simulations for the regions of microstructure examined after extrusion. This was performed by
determining the position of the material in the un-extruded billet in reference to its final position in
the extrudate using point tracking in the FEM simulation. Two points were measured for each
simulation-one starting on the interface between the stainless and plain carbon steel, and one at the
mid-thickness of the core material (stainless steel), which was 5.7 mm from the plain carbon steel
surface. For the low-extrusion ratio sample, the maximum strain and strain rates were 1.2 and 2.0 s-1,
respectively (Figs. 4.39 and 4.40). For the high-extrusion ratio sample, the maximum strain and strain
rates were 2.9 and 22.0 s-1, respectively (Figs. 4.41 and 4.42).
4.3.4 Gleeble Simulation of Extrusion Process
Samples of the two materials were machined into 6-mm-thick by 10-mm-diam cylinders. The
materials were butted together at a force of 445 N, held at the preheat temperature for the extrusion
ratio conditions for the corresponding time, and deformed at the corresponding extrusion temperature
using a Gleeble Hydrawedge system. The grips were displaced a total of 11.3 mm, and the final
sample height was 0.7 mm for the high extrusion ratio Gleeble simulation; the grip displacement and
final sample height were 8.4 mm and 3.6 mm for the low extrusion ratio simulation. The samples
were allowed to air cool to room temperature while still in the grips. Additionally, the low extrusion
ratio simulation sample was placed back into a box furnace at 11000C and allowed to furnace cool to
2000C (time versus temperature shown in Fig. 4.43) and then was air cooled to room temperature.
Samples from the Gleeble simulations were sectioned and prepared in a similar manner to the tubes
produced from extrusions carried out at ORNL.
Point Tracking Effective Strain Low1
1.4-
1

c
S0.8
0.6
w
0.4
0.2
n

I

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Time (s)
- Interface point - Mid-core point
Fig. 4.39. Effective strain measurement from point tracking in finite element modeling of the Lowi
sample (total time).

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Misiolek, W. Z. & Sikka, V. K. Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes, report, August 10, 2006; United States. (digital.library.unt.edu/ark:/67531/metadc884646/m1/72/ocr/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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