Learning Forum

[holmesthinking]

Hi, all material models I have checked, required strain hardening. So my question is which material model in Ansys, allow to input stress strain curve with softening of material?

[Sandeep Medikonda]

Are you trying to simulate progressive damage? If so, please look at the following document.

Regards,
Sandeep

[jj77]

Not for concrete, where there is a microplane model for cracking and softening of concrete in tension.

Also other type of damage models Sandeep mentions should capture the softening of some material.

 

Also in general FEA one should be able to use a softening stress strain curve using max principal stress criteria (not VM), of course this is for nonlinear elastic material, and not plastic. (This is called MELAS in ansys).

 

[holmesthinking]

Ok, I refine my question. Consider material stress-strain curve like this:

Which material model should I use for that?
Also which model can describe softening after yieldnig point and strain rate dependence of material?

[jj77]

As described above it would be nonlinear elastic curve not plastic. Using max stress not VM yield criteria. Think this is Melas in Ansys, not sure because I have used this type of curve in Strand7 for cracking concrete.

If you are looking on strain rate then this is different to standard plastic models. The above does not have strain rate dependence.

Ofcouse I do not know all models so there might be some out there. Perhaps someone else has more tips

[jackhero]

@jj77

Also in general FEA one should be able to use a softening stress strain curve using max principal stress criteria (not VM), of course this is for nonlinear elastic material, and not plastic. (This is called MELAS in ansys).

 

with reference to your reply above, could you please provide guidance on how to input MELAS in Ansys workbench under engineering data? Also, the max principal stress criteria, is it already included in MELAS or it should be defined separately?

[jj77]

As far as I can see it is not possible to do that in WB, also very limited use in apdl (say MELAS can not be used with a 8 node brick element, think it is solid185),

So I am not sure how it can be used in ansys, as I have never used it there, only in Strand7 where it is used in some cases to model cracking in concrete.

 

Have in mind that this type of model is nl. elatsic, this when it is unloaded it goes back to the undeformed shape (thus no plasticity).

 

In Strand7 it is very tricky to get this to converge for failing concrete structures (say due to cracking).

 

Finally, as say standard plastic models uses often VM stress for the nonlinear calculations (say yield occurs when VM stress is equal yield stress of the mat.), in Strand7 the stress used for such a model (MELAS type), is of Ranking type, so max/min principal stress/strain, that is what is used for the nonlinear material calculations. Not sure what ANSYS uses (not read the theory manual).

 

Have a look in the chapter about element support for material models, but I do not think many elements support this model anymore (MELAS).

 

Sorry I can not give much help, on this. 

[peteroznewman]

In the Geomechanical materials library is the Menetrey-Willam model. It has two versions of material softening: linear and exponential, but has a different response in tension than in compression. This material model was developed for concrete which has little tensile strength.

Note: you have to add Linear Elasticity for the linear elastic response, and also the Menetrey-Willam model, and after you add that, the Softening option becomes available in the Toolbox.

Regards, Peter

[holmesthinking]

This is what I search for. Thank You for help.

[jj77]

Good one Peter, reminds unforgettably a bit about CONCR material model that seems similar.

Be aware that this is for modelling geomaterial like concrete that has a brittle failure (say cracks in tension), and not a ductile behaviour.