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Modeling the Bauschinger Effect: Metal-Forming and Viscoplasticity
Under Phase I SBIR efforts from the USAF and NSF, we have successfully implemented axis-symmetric
and plane-strain versions of a new, strain-rate- and temperature-
dependent viscoplasticity material model which incorporates kinematic
hardening and captures the Bauschinger Effect. This effect is
manifested as a reduction in flow stress after a reversal in
strain direction. The model and the implementation have been
tested, and have been used to simulate a number of classic metals
forming problem including the upset forging of an iron billet
and the rolling of a thick aluminum plate.
Comparisons of these results with those of a widely accepted
isotropic model (also implemented) indicate that kinematic hardening
produces phenomena critical to proper design of common industrial
metal forming processes. Neglecting the Bauschinger effect appeared
to produce non-conservative designs in some cases, and overly
conservative in others. Thus, the incorporation of kinematic
hardening into viscoplasticity produces phenomena of critical
importance to proper design of common industrial metal forming
processes.
The underformed and deformed grids for the forging problem. The
bottom and left hand edges of the mesh represent reflection-symmetric
and axis-symmetric boundaries, respectively. Simulated with kinematic
hardening, isothermally with an initial temperature of 800C.
Our work to date has included:
- Successfully implementing our new kinematic hardening material
model.
- Successfully implementing a well-accepted isotropic model.
- Fitting model parameters to data for both 2% SiFe and 1100-O
Aluminum.
- Testing the models using single element, plane-strain tests.
- Performing a range of simulations with both models for the
upset forging of a 2% SiFe billet
- Simulating the rolling of thick 1100-O Aluminum plates with
both models.
- Critically comparing the results of the two models.
The implementation functioned beyond expectations over five
orders of magnitude of strain-rates and a temperature range from
near room temperature to over 90% of the melting temperature.
Commercial
Potential
There is no other current model having all of the capabilities
we have shown. Further, we know of no software able to simulate
all of the material behaviors of which we are capable. Our work
has resulted in a computer code which could provide the economic
benefits of reduced initial design to product time, and reduced
energy and material costs for metal forming industries. It further
appears to have bearing on safety-critical features of design.
Such results would be highly beneficial for key industries including
the metal fabrication and metal forming sectors, as well as to
commercial software firms producing codes used to simulate metal
forming processes and to perform computer aided design.
Phase
III Sponsorship and Commercialization
We are actively seeking other sponsors, collaborators, and
commercialization partners in this topic for both Phase III sponsorship
and beyond.
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