Abaqus convergence error due to plasticity

[banassa]

Hello,

I have an error massage in abaqus (6.12-1) and I can't figure out what's wrong with my model.
I have a simple cube made out of soil and I used the element type C3D20RP (Standard) because I have pore pressure.
My Step-1 (Geostatic) consists only of gravity as load. The error message says that there are
TOO MANY ATTEMPTS MADE FOR THIS INCREMENT. I thinks it's due to the warning
THE PLASTICITY/CREEP/CONNECTOR FRICTION ALGORITHM DID NOT CONVERGE AT 7452 POINTS.
While I deleted the Mohr Coulomb Plasticity and used only Elasticity (+ Permeability and Density)
as material behaviour everything worked just fine. Here an extract of my input file of this simplified model:


** MATERIALS
**
*Material, name=Material-1
*Density
1800.,
*Elastic
1e+09, 0.45
*Permeability, specific=10000.
0.0001, 0.111
*Mohr Coulomb
35., 17.5
*Mohr Coulomb Hardening
1.,0.
**
** PREDEFINED FIELDS
**
** Name: Predefined Field-1 Type: Void ratio
*Initial Conditions, TYPE=RATIO
Part-1-1.Set-1, 0.111
** Name: Predefined Field-2 Type: Saturation
*Initial Conditions, type=SATURATION
Part-1-1.Set-1, 1.
** Name: Predefined Field-3 Type: Geostatic stress
*Initial Conditions, type=STRESS, GEOSTATIC
Part-1-1.Set-1, 0., 50., 450000., 0., 0.43, 0.43
** Name: Predefined Field-4 Type: Pore pressure
*Initial Conditions, TYPE=PORE PRESSURE
Part-1-1.Set-1, 0., 50., 500000., 0.
** ----------------------------------------------------------------
**
** STEP: Step-1
**
*Step, name=Step-1, nlgeom=YES
*Geostatic, utol
0.1, 1., 1e-20, 1.
**
** BOUNDARY CONDITIONS
**
** Name: BC-1 Type: Displacement/Rotation
*Boundary
Set-1, 1, 1
Set-1, 3, 3
** Name: BC-2 Type: Displacement/Rotation
*Boundary
Set-2, 2, 2
** Name: BC-3 Type: Pore pressure
*Boundary
Set-3_PP_, 8, 8
**
** LOADS
**
** Name: Load-1 Type: Gravity
*Dload
, GRAV, 10., 0., -1., 0.



In 2D there is no such error. Besides, I already minimized my increment size. I hope you can help me.

Thanks!!

Banassa