Crushable Foam Plasticity Model (Abaqus)

[shaldar]

Hi, I am a new user of Abaqus (using v6.10). I am trying to implement Crushable Foam Plasticity Model. People have used it, however, I could not use this model. I have uniaxial compressive test data from which others have implemented the model.
Can anyone please help! What am I doing wrong!
I can not insert picture, otherwise I could show my input and experimental data.

Helps are a lot appreciated.
I could upload the images here:

http://files.engineering.com/getfil...6b-0eb9779d7f4c&file=Crushable_Foam_Input.JPG

 

[compositesFEAguru]

Hi shaldar,

I could not see your experimental data. By looking at your material inputs, the first thing that I noticed is your compressive crush strength (2nd row Yield stress) value is the same as your uniaxial compressive strength (1st row Yield stress). I would expect the compressive crush strength to be lower than the uniaxial compressive strength and this may be what is causing model complications.

Hope this helps,

Firehole Composites

http://www.firehole.com

 

[shaldar]

Thank you so much for your reply. I have seen some plots that show lower compressive crush strength and few with similar. I will try modifying that. I am attaching the experimental data here for your reference and to show how I took them.

 

[shaldar]

Also compositesFEAguru,
I tried with lower crush strength than the compressive strength as attached here. The same error is coming! The convergence is no occurring! Please let me know what do you think!

Regards,
shaldar

 

[compositesFEAguru]

Hi shaldar,

What error message are you getting? Are you sure it is related to your crushable foam material card? Try removing rows 2-4 so that you don't repeat the same yield stress values for multiple uniaxial plastic strain values.

Best wishes,

Firehole Composites

http://www.firehole.com

 

[shaldar]

Thanks a lot for helping out! I am pretty much sure, the error is for Crushable Foam Model (CFM) since, I have CFM right after Elastic portion and the elastic portion works.
The error mssg is like:
CONVERGENCE CHECKS FOR EQUILIBRIUM ITERATION 4


AVERAGE FORCE 2.677E-02 TIME AVG. FORCE 2.220E-02
LARGEST RESIDUAL FORCE 2.863E-04 AT NODE 2352 DOF 3
INSTANCE: FOAMCORE
LARGEST INCREMENT OF DISP. -6.330E-05 AT NODE 2416 DOF 2
INSTANCE: FOAMCORE
LARGEST CORRECTION TO DISP. -1.094E-04 AT NODE 2351 DOF 1
INSTANCE: FOAMCORE
FORCE EQUILIBRIUM NOT ACHIEVED WITHIN TOLERANCE.


***NOTE: THE SOLUTION APPEARS TO BE DIVERGING. CONVERGENCE IS JUDGED UNLIKELY.


***ERROR: TOO MANY ATTEMPTS MADE FOR THIS INCREMENT



ANALYSIS SUMMARY:
TOTAL OF 8 INCREMENTS
11 CUTBACKS IN AUTOMATIC INCREMENTATION
60 ITERATIONS INCLUDING CONTACT ITERATIONS IF PRESENT
60 PASSES THROUGH THE EQUATION SOLVER OF WHICH
60 INVOLVE MATRIX DECOMPOSITION, INCLUDING
0 DECOMPOSITION(S) OF THE MASS MATRIX
1 REORDERING OF EQUATIONS TO MINIMIZE WAVEFRONT
0 ADDITIONAL RESIDUAL EVALUATIONS FOR LINE SEARCHES
0 ADDITIONAL OPERATOR EVALUATIONS FOR LINE SEARCHES
5 WARNING MESSAGES DURING USER INPUT PROCESSING
20 WARNING MESSAGES DURING ANALYSIS
0 ANALYSIS WARNINGS ARE NUMERICAL PROBLEM MESSAGES
13 ANALYSIS WARNINGS ARE NEGATIVE EIGENVALUE MESSAGES
1 ERROR MESSAGES

 

[compositesFEAguru]

This issue could stem from your *Foam Hardening material input card, but the error message seems to me to be related to the nonlinear behavior of the model. In your case, you have material nonlinearity and possibly geometric nonlinearity (if it is turned on, NLGEOM=ON in step card) and/or contact nonlinearity (if there is contact in your model). The first thing you could try is to set NLGEOM=OFF if it is indeed on to help diagnose the problem. Otherwise, resolving nonlinear model issues can be quite complex. A few things you could try are:

- Increasing the number of increments so that smaller loads/displacements are applied per increment

- Increasing the number of equilibrium iterations allowed for each increment using the *CONTROLS, PARAMETER=TIME INCREMENTATION card

- Ensure your model runs with just the *Elastic material definition and not the CFM parameters

Hope this helps,

Firehole Composites

http://www.firehole.com

 

[shaldar]

Thank you so much for the reply.
I tried them. It seems the solver goes past the yield point (i.e. in Crushable Foam Plasticity) but meets the error within the plastic deformation regime.

However, in the process, I had to rethink about my plan. Another question is, may I use a damage model with the crushable foam plasticity model? The Abaqus manual does not say that explicitly. However, I was reading the damage models and they have mention to use the damage model with several plasticity models like JC, vonMises but no mention of crushable foam plasticity was found!
Looking forward to your comment!