Using non linear elasticity in Drucker Prager Cap Model for Code-Aster

[sameenmustafa]

Dear Dr. Helfer,
I writing here as I have been trying to implement the DPC model created by you in MFRONT. I have succeeded in compiling and implementation in code-aster. However, I have to simulate powder compaction using DPC model, for this, I have with me the Elastic Modulus and Posisson's coefficient as a function of pressure. This comes from the mechanical testing and calibration of the powder itself.
I have noticed that changing these properties in Code-aster doesn't affect the results as the simulation is being governed by the mfront library. To verify this, I have simulated using both the linear elastic properties as well as pressure dependent properties. Thus, I am writing my problems below:

1. How can I implement the varying E and nu in the Drucker Prager Cap Model code. I don't have a proper function, but I have the values of E and nu corresponding to different pressures (SIGM). To better explain this, I have the density of the powder as a function of the applied pressure but, I cannot implement the density as a function of pressure in code-aster as it only accepts density variation based on the co-ordinates. In the end, every varying input parameter needs to be inserted as a function of pressure. I am also attaching the .comm files of the simulation results for your reference.
2. While in powder compaction, in consideration with the DPC model, other parameters also vary as a function of density and in turn, as a function of pressure. For example, in my case, I would be having d, beta and R as constant while pa and pb needs to be varied in accordance with the callibration data. At this point I would also like to ask how can I use pa and pb as a user defined function based on pressure.
3. I would also like to implement a modified version of the DPC model, which includes a transition surface to smoothen the transition from the shear line to the cap. Since you are the main developer of the DPC model, can you please help me in defining the modified DPC model in MFRONT?

I am attaching here different files to refer to the simulations I have carried out so far. I am also new to MFRONT and Code-Aster as well, and after reading several discussions and watching different videos by Mr Cyprian and Dr Nicolo Grilli, I am writing here.

Thanks and Regards,
Yours Sincerely,
Sameen Mustafa.
DPC.zip

[thelfer]

@sameenmustafa Thanks for you interest to MFront.

This matter already have been discussed on this forum: #391

You may want to read the following tutorials:

• https://thelfer.github.io/MFrontGallery/web/CrushedSaltKorthausBehaviour.html
• https://thelfer.github.io/tfel/web/MohrCoulomb.html

[sameenmustafa]

@thelfer
I am working on powder compaction. For now I Plan to input the displacement at each time step, like 1mm at 0.1 sec. So the instantaneous density at a particular time step would be (mass/instantaneous volume), where the mass is constant throughout. But I am using Salome-Meca to impose these displacements. I am able to compile mfront code and generate the library, then I pass the required material properties using MFRONT module in salome itself.
This would work fine if the E and nu were a constant value, but in the case of powder these value vary with density. I am a bit confused as how to proceed now.

[thelfer]

As stated by @Asocie13, the evolution of the density is known locally based on either the total strain or the plastic strain depending on the hypothesis that you want to use. See: https://thelfer.github.io/MFrontGallery/web/CrushedSaltKorthausBehaviour.html for example, but there are other resources on the TFEL website: https://thelfer.github.io/tfel/web/StandardElastoViscoPlasticityBrick-PorousPlasticity.html

[Asocie13]

Thomas also specify how change the DPC mfront file in https://github.com/thelfer/tfel/blob/master/docs/web/drucker-prager-cap.md

With Salome, you can manage how to model powder compaction (imposed displacement or pressure, matrix-powder contact) and mfront file models the local material behavior. Depending on the local compaction you will model the volumetric strain variation and thus the density variation.

[sameenmustafa]

@thelfer
Hello Sir,
I was simulating on Salome using the DPC Mfront code from the repository, I am getting an error which I tried to resolve but it does not work. Could you help in this regard:
EXCEPTION> <CALCUL_46> !
! !
! Il y a une incohérence entre les paramètres matériaux et la loi de comportement. !
! On ne trouve pas les paramètres matériaux associés à la relation MFRONT !
! !
! pour la maille M3433. !
! !
! Conseils : !
! Vérifiez la mise en données de la commande DEFI_MATERIAU : il faut définir !
! les paramètres matériau pour la relation utilisée. !
! Vérifiez que la maille M3433 est bien affectée par le matériau. !
! !
! -------------------------------------------- !
! Contexte du message : !
! Option : RIGI_MECA_TANG !
! Type d'élément : MECA_TETRA4 !
! Maillage : mesh !
! Maille : M3433 !
! Type de maille : TETRA4 !
! Cette maille appartient aux groupes de mailles suivants : !
! !
! Position du centre de gravité de la maille : !
! x=0.003428 y=0.000398 z=0.009936 !

DC.py : ERREUR WITH THE EXECUTION - INTERRUPTION

JDC.py: DEBUT CR of execution of JDC in MIXTE
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! Exception user raised but not interceptee. !
! The bases are fermees. !
! Type of the exception: error !
! !
! Il y a une incohérence entre les paramètres matériaux et la loi de !
! comportement. !
! On ne trouve pas les paramètres matériaux associés à la relation MFRONT !
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
fine CR of execution of JDC in MIXTE

[thelfer]

I think that the DEFI_MATERIAU command has an MFRONT keyword to define the properties associated with the material properties.

I don't know with version of aster you used, but for old versions, there is a long standing bug in the code_aster interface that requires the MFront behaviours to have two material properties at least, so you may have to add:

@MaterialProperty real dummy1, dummy2;

[sameenmustafa]

@thelfer
Sir, Could you please have a look at the last message...

[thelfer]

@sameenmustafa, I don't know what happened, I did make comments. Let me see again.

[sameenmustafa]

@thelfer
Thankyou for replying. I had not recieved the previous message.