Drucker-Prager-cap model

[wucy]

Hi, I am learning to simulate powder compaction with Drucker-Prager-cap model. And got the follwoing error messages. Does anyone know the possible reasons that cause this problem. Thank you very much!

***WARNING: THE SYSTEM MATRIX HAS 3 NEGATIVE EIGENVALUES.
IN AN EIGENVALUE EXTRACTION STEP THE NUMBER OF NEGATIVE EIGENVALUES IS
EQUAL TO THE NUMBER OF EIGENVALUES BELOW THE CURRENT SHIFT POINT.
THIS MAY BE USED TO CHECK THAT EIGENVALUES HAVE NOT BEEN MISSED.

IN OTHER CASES, NEGATIVE EIGENVALUES MEAN THAT THE SYSTEM MATRIX IS
NOT
POSITIVE DEFINITE:
FOR EXAMPLE, A BIFURCATION (BUCKLING) LOAD MAY HAVE BEEN EXCEEDED.

***WARNING: OVERCLOSURE OF CONTACT SURFACES WALLFE and WALLFACE IS TOO
SEVERE
-- CUTBACK WILL RESULT. YOU MAY WANT TO CHANGE THE VALUE OF
HCRIT
ON THE *CONTACT PAIR OPTION.

***WARNING: OVERCLOSURE OF CONTACT SURFACES WALLFE and WALLFACE IS TOO
SEVERE
-- CUTBACK WILL RESULT. YOU MAY WANT TO CHANGE THE VALUE OF
HCRIT
ON THE *CONTACT PAIR OPTION.

***WARNING: CONVERGENCE JUDGED UNLIKELY. INCREMENT WILL BE ATTEMPTED AGAIN
WITH A TIME INCREMENT OF 9.10069E-12


Thank you very much!

Charley

 

[Max78]

I do the same Thame for Mg Powder, but i have setup the friction as Subroutine.

 

[gwolf]

I don't think this error has anything to do with your material model.

At a wild guess it is one of the following:

1) You are using basic second order elements for contact - try using the "M" variants of these elements of better still the C3D8I element which is excellent at contact.

2) You have an unconstrained rigid body mode.

 

[A1AMKI]

Hello

I am planning to use ABAQUS to simulate the liquefaction of saturated loose sand under undrained condition (monotonic load) . I am not sure if It has a constitutive model which can dublicate the stress path in this case.

Thanks