Flattening a visco-elastic-plastic material (Abaqus)

[Satiar]

Hello members
I am modeling flattening of a ball using Abaqus. It consists of three steps: flattening (load control, static), creep (visco, constant load) and tangential loading (static, displacement). My 3D model converged for elastic(v=0.46)-viscoplastic (power-law) material and the results are good, but when I introduce yielding it doesn't converge in the second step (creep) and interrupted at very initial increments (<1.0E-6). I am validating my model with another model defined in Ansys so I can only use power law and elastic-plastic parameters. I am wondering what is the problem and should I used UMAT or VUMAT subroutines? or Can I use the default material properties of Abaqus? Can Abaqus handle creep and plastic deformation together?
Thank you in advance

 

[DanStro]

Just to make sure, are you using hybrid elements?

 

[Satiar]

Yes to be exact i use C3D8RH

 

[FEA way]

Can you attach an input file of this analysis or at least describe the details of the simulation (loads, BCs and in this case especially material data) ? In case of convergence problems everything should be checked and we can't help without more details.

 

[Satiar]

** MATERIALS
**
*Material, name=Deformable
*Creep
1.6036e-05, 2., -0.789
*Elastic
700., 0.46
*Plastic
14., 0.
14., 0.4
**
** INTERACTION PROPERTIES
**
*Surface Interaction, name=IntProp-1
1.,
*Friction, rough
*Surface Behavior, penalty
**
** BOUNDARY CONDITIONS
**
** Name: Bot Type: Symmetry/Antisymmetry/Encastre
*Boundary
Deformable-1.Bot, PINNED
** Name: Sym Type: Symmetry/Antisymmetry/Encastre
*Boundary
Deformable-1.Side, ZSYMM
**
** INTERACTIONS
**
** Interaction: Int-1
*Contact Pair, interaction=IntProp-1, type=SURFACE TO SURFACE
Deformable-1.Surf-1, Flat-1.Surf-1
** ----------------------------------------------------------------
**
** STEP: Step-1
**
*Step, name=Step-1, nlgeom=YES, inc=1000
*Static
0.0001, 1., 1e-08, 1.
**
** BOUNDARY CONDITIONS
**
** Name: RP Type: Displacement/Rotation
*Boundary
Flat-1.RP, 1, 1
Flat-1.RP, 3, 3
Flat-1.RP, 4, 4
Flat-1.RP, 5, 5
Flat-1.RP, 6, 6
**
** LOADS
**
** Name: Load-1 Type: Concentrated force
*Cload
Flat-1.RP, 2, -19.464
**
** OUTPUT REQUESTS
**
*Restart, write, frequency=0
**
** FIELD OUTPUT: F-Output-1
**
*Output, field, variable=PRESELECT
**
** HISTORY OUTPUT: H-Output-1
**
*Output, history, variable=PRESELECT
*End Step
** ----------------------------------------------------------------
**
** STEP: Step-2
**
*Step, name=Step-2, nlgeom=YES, extrapolation=PARABOLIC, amplitude=RAMP, inc=10000
*Visco, cetol=1e-05
1e-05, 600., 1e-08, 600.
**
** OUTPUT REQUESTS
**
*Restart, write, frequency=0
**
** FIELD OUTPUT: F-Output-1
**
*Output, field, variable=PRESELECT
**
** HISTORY OUTPUT: H-Output-1
**
*Output, history, variable=PRESELECT
*End Step
** ----------------------------------------------------------------
**
** STEP: Step-3
**
*Step, name=Step-3, nlgeom=YES, inc=1000
*Static
0.0001, 1., 1e-08, 1.
**
** BOUNDARY CONDITIONS
**
** Name: RP Type: Displacement/Rotation
*Boundary
Flat-1.RP, 1, 1, 2.
**
** OUTPUT REQUESTS
**
*Restart, write, frequency=0
**
** FIELD OUTPUT: F-Output-1
**
*Output, field, variable=PRESELECT
**
** HISTORY OUTPUT: H-Output-1
**
*Output, history, variable=PRESELECT
*End Step