Hi,

I have been trying to solve a large 3D biomechanics problem using ABAQUS. 
There are 57277 nodes in total from which 30595 are defined by me and the 
rest are internal nodes generated by the program. The input file is 
attached. The model represents a medium composed of fat and soft tissues 
which is exposed to about %20 static compression. The soft tissue is
considered incompressible, therefore I used C3D8H hybrid elements. Currently 
I am considering the fat and soft tissues as linear elastic materials and 
with the NLGEOM option off, there is no problem, however when I activate this
option to take into account the large deformation occurring in this case, the 
convergence rate becomes extremely slow after reaching a total time of about
0.65. I wonder if relaxing the convergence criteria is advisable. Any 
suggestion would be highly appreciated.


Abbas Samani, PhD
Bioengineering Research  
 



*HEADING

3-d soft tissue problem

Elastic piece wise homogeneous medium

*RESTART, WRITE, FREQUENCY=10

*NODE, INPUT=soft123.inp

**

*NSET, NSET = BASE, GENERATE

1, 3584

*NSET, NSET = TOP, GENERATE

57345, 60928

**

** Elements data

**

*ELEMENT, TYPE = C3D8H, ELSET = FAT, INPUT=fatelem.inp

*ELEMENT, TYPE = C3D8H, ELSET = FIBGLN, INPUT=fibelem.inp

**

*ELSET, ELSET = ALL

FAT, FIBGLN

**

** material data

*SOLID SECTION, MATERIAL = ELS1, ELSET = FAT

*SOLID SECTION, MATERIAL = ELS2, ELSET = FIBGLN

*MATERIAL, NAME = ELS1

*ELASTIC

0.25, .49

*MATERIAL, NAME = ELS2

*ELASTIC

1.50, .49

**

** boundary conditions

*BOUNDARY

BASE, 1, 3

** the default maximum number of increments in a step INC=10

*STEP, NLGEOM=YES, INC=100

*STATIC

*BOUNDARY

TOP, 3,  , -10.0

*EL PRINT, ELSET = ALL, POSITION = AVERAGED AT NODES, FREQUENCY=10

S

*NODE PRINT, FREQUENCY=10

U, RF

*END STEP