Learning Forum

[Vasco Rasemann]

Hello members of the forum,
I've been using the multilinear hardening model to try to describe the behavior of a material I've tested. First and foremost, I need to ask if using the the multilinear model is the correct choice, considering the little plastic strain that the material suffered. Second of all, I get the warning on picture 2 after a while, which means the amount of points I've put in the multilinear model are not enough. Taking into account that I'm performing a tensile test, I'm simply inducing a displacement, so there is a chance I go over the plastic limits from the stress-strain curve. May I just ignore the warning or do I need to put more points in the table?

[Armin]

Hi Vasco,

I have a few questions regarding your model: Could you describe how the hardening curve was obtained? Is it from a tensile experiment? If so, is the last data point in the table associated with the onset of necking in the tensile experiment?

 

[Vasco Rasemann]

Tbh this is a bit of an experiment I'm doing for my study. Yes, the curve obtained was from a tensile test, but the material did not experience strain hardening. It experienced strain softening, but in some cases only subtle and in others more aggressive. But since ANSYS does not deal with strain softening and the values are somewhat consistent, I've opted into using a multilinear hardening model and observe the error between the experimental test. 

To answer the second question, no necking occurred. The material presented that strain softening behavior and then ruptured. 

[Armin]

 

Hi Vasco,

Thanks for this description. I’ve seen materials (mostly metals) that display a prolonged region of strain softening and almost no strain hardening but that occurs at elevated temperatures. I look forward to hearing how you incorporate this only-softening response for your specific material.

For the warning of out-of-range plastic strain, I recommend that you fit a curve to your current data and extrapolate it at larger plastic strains. From the shape of the curve you showed in your image it appears to me that a “power-law” or “Voce” type function should be able to capture the behavior properly.  

 

[Vasco Rasemann]

Thank you so much for your help, I will try to do the curve fitting. Regarding the behavior of the material and the incorporation of the only-softening response, it is presenting a real challenge, since ANSYS does not allow for strain softening. But, in due time, the results will show if my approach is the proper one or not.