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Abaqus 2d contact model not working

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Hi

 

Sorry in advance, but this will be a long story...
Thank you for taking the time to look at it! :)

 

I have a 2D model that worked fine until a couple of
days ago where I tried changing the mesh a bit. Now when I try to run it aborts
calculation and gives some of the following errors:

 

- There are 14 unconnected regions in the model.

- There is zero MOMENT everywhere in the model based
on the default criterion. please check the value of the average MOMENT during
the current iteration to verify that the MOMENT is small enough to be treated
as zero. if not, please use the solution controls to reset the criterion for
zero MOMENT.

- The strain increment has exceeded fifty times the
strain to cause first yield at 5 points (reappears several times with various
numbers)

- The strain increment is so large that the program
will not attempt the plasticity calculation at 8 points.

 

Now, even if I try to go back to my original setting,
it still will not calculate. :(

 

A little bit about my setup (.inp file at: http://files.engineering.com/getfile.aspx?folder=7f9ccad1-9b8c-4375-a702... ):

It is a 2D deformable plate with 12 bolt holes at the
right side and 1 larger pin hole at the left side. The bolts and pin are
modeled as rigid circular wires, elements R2D2, and have a rigid body
constraint to its reference point in the center. The plate uses CPS6M elements.

Material is steel with E=216.5Gpa and v=0.3. I have
the yield and ultimate strength from tensile tests and also the final strain at
ultimate strength, so for the plasticity module I use: 274.5 MPa at 0 plastic
strain, 377.7 MPa at 0.35 plastic strain and set another point of 377.7 MPa
with 1.0 plastic strain just to ensure no stresses above the ultimate.

I use surface-to-surfacce contact between the rigid
bolts/pin and the respective plate holes. The rigid bolts/pin are set as the
master surface.

First fitting step: BCs are at each bolt for both main
directions and rotation. Initially I set a displacement of the plate of 0.5mm
to close the gap to the bolts and create contact. The pin is moved 1.0mm down,
also to create contact. Next step: Bolts are kept supported, plate displacement
is deactivated and the load is applied through displacement control of the pin.
I.e. the pin at the left hand side moves downwards causing the plate to bend,
but it is supported by the bolted connection at the right hand side.

 

I have tried both making a new mesh, using other
elements, utilizing stabilization through contact control, using small sliding,
reducing the displacement load, lowering step length and various other things.
I have even tried starting over with a former version of this file, using only
the geometry but resetting everything else. But nothing works... :(

 

I hope someone has an idea why this will not work. I
an completely out of ideas. Thank
you so much in advance! :)

 

Best regards,

Steen

 

P.S. A hint might be
that if I look at the result file, there are very large stresses at the end of
the fitting step, indicating that the plate might be pushed too much down?
However, if I reduce it contact will not be established.

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