# Modeling a thermomechanical bending process

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December 14, 2016, 17:07
Modeling a thermomechanical bending process
#1
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Guillaume
Join Date: Dec 2016
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Hi,
I'm writing on this forum because I'm a bit at a lost with an analysis conducted with ANSYS workbench.

I've got creep response data and springback data: I used a test bench consisting of a constant weight pulling laterally a polypropylene flat bar (somewhat in the manner of a cantilever beam but pulled honrizontally)

SEE PICTURES in attachment

For the creep test: The heat gun warms the flat bar while the force is pulling on it: the magnitude of the angular deformation is measured as a function of time.

For the recovery test: The heat from the heat gun and the force are both removed and the recovery is measured as a function of time.
I've developped a creep equation for the creep test that also figures in the ATTACHMENT.

With matlab, I've fitted the equation and found the right parameters to fit my data.

I am now trying to model this experiment in ANSYS workbench. I've read a bunch on the subject but I'm having a hard time finding where to start and what should be included in my analysis.
From what I understand, I need to make a static structural analysis with the right temperature profile. That I can do. But I need to include material properties that'll allow a permanent deformation and also the viscoelastic behavior.

All I have is series of data of angular deformation (in rad) as a function of time (seconds). SEE PICTURE in attachment

The general question is: How should I make an FEA analysis of this experiment using Ansys Workbench? I'm a bit familiar with command snippets in mechanical but I know next to nothing of mechanical APDL (Ansys classic)

+++++++++++++++++++++++++++++++++++++++++++++++
The angular deformation at

lim = 4.5 Degrees
t -> ∞

Question #1a:

I've been advised to use the Extended Drucker-Prager model to model that experiment.

I can't find Extended Drucker-Prager model in any of the tabs in the workbench material toolbox. From what I understand, I must use Extended Drucker-Prager material model via command snippets in mechanical. Considering my experimental results, which form of the EDP model would you advise to use, linear, power law or hyperbolic? And how would you go in coding the command to define the model?

MP,GXY or ALPD ?,MAT,C0?
MP,NUXY,MAT,C0?
TB,EDP,1
TBDATA,1,2.9,32,0 ???

Question #1b:

I don't know how to compare my experimental curve with the model proposed by ANSYS once it has been defined. How can I see if the model fits my data?

Question #1c:

Also, would that model be applicable to both parts of the experiment? (before AND after the removal of the force)

Question #2:

Is Extended Drucker-Prager model considered a creep model?

Question #3:
Do I have to include another model besides EDP? Such as a standard plasticity model in the "Plasticity Tab" from the workbench material toolbox? Or a standard viscoelastic model in the "Viscoelastic Tab" from the workbench material toolbox? Or maybe another model altogether via a command snippet? I'm just having a hard time figuring what type of non-linear material property has and doesn't have to be included in this experiment in order to get good numerical approximations.

Attached Images
 ForumShematics.jpg (40.1 KB, 5 views) Graph and Data.png (54.0 KB, 2 views)

 Tags ansys, bending, creep, fea, polymer