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Mystical contact problem

Mystical contact problem

Mystical contact problem

(OP)
Hello everyone!

I am doing a nonlinear simulation of a compression test of a 2D geometry with round inclusions.
Matrix is modeled as hyperelastic material, material of inclusions is chosen to be a lot stiffer then matrix. Geometry is compressed between two analytical rigid horizontal lines. Contact between rigid lines and matrix has Normal Behaviour with Hard Contact pressure-overclosure and Tangential Behaviour with friction of 0.5. Contact between inclusions and the matrix is the same, but friction is equal to 0.9. Compression is imposed by displacement of a top rigid line.
I used Plane Stress triangular elements from standart Abaqus Library (CPS3: A 3-node linear plane stress triangle.)
The task seems to be easy (The geometry and mesh is presented on the first picture), but each time I run calculation, at the first step I have always the same error following by the same warnings:

Excessive distortion at a total of 25 integration points in solid (continuum) elements
Excessive distortion at a total of 3207 integration points in solid (continuum) elements

And after:
Too many attempts made for this increment

So, I started to investigate the problem, and what I found:
1) If I insert only few inclusions in the middle of geometry - calculation runs;
2) If I add any inclusion close to the geometry border - calculation fails on the first step with the above mentioned error;
3a) If I use geometry with all inclusions, but incline the top rigid line (so the contact starts at the corner) - calculation runs
3b) If the slope of inclined rigid line is small - calculation runs, but result is extrusion of the geometry from the area between of two rigid lines (in simple words - geometry flies away).


I am using Abaqus 6.11-2/Standart

Hope someone will help,
Than you in advance

Attachements:

Problem, initial geometry: http://files.engineering.com/getfile.aspx?folder=c...

Case of a inclined line - resulting geometry: http://files.engineering.com/getfile.aspx?folder=d...

Case of 3 inclusions - resulting geometry: http://files.engineering.com/getfile.aspx?folder=2...

RE: Mystical contact problem

Don't use 3 noded tet elements, they're useless. If you spend a little time and partition the geometry you can used hex elements and get better results.

RE: Mystical contact problem

(OP)
Thank you for your suggestions. I have few additional questions:

to corus: why 3 node elements are bad and useless? Are they less stable in the meaning of possibility of distortion?

to IceBreakerSours: what do you mean under "high quality" element? Fine meshing?

to all:
1) I understand the distortion of the element, but what does the distortion of integration point means?
2) Is it normal to have small penetration of master surface into slave surface?

Additionally I tried to model "compression plates" by deformable geometry: in this case calculation runs. I thought that normally rigid object can simplify the problem, not the opposite.

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