Threaded Connection (Contact) 1

[AriaCole]

Hello all. I'm new to the group, but I've been browsing trying to find helpful hints for my abaqus model. I am very new to abaqus.

I'm modeling a threaded connection (box and pin) including contact. My model has 4 steps (initial, make-up, internal pressure and compression) which simulate the loading of the connection based on a Von mises criterion (standard VME curve) for my material, steel. I am having a few issues with my model:

1. Some parts of my model appear to be floating when I examine the viewer. How do I fix this?

2. Errors in the msg file include:

***WARNING: SOLVER PROBLEM. NUMERICAL SINGULARITY WHEN PROCESSING NODE
BOX-1.14 D.O.F. 2 RATIO = 17.2549E+12 .


***WARNING: SOLVER PROBLEM. NUMERICAL SINGULARITY WHEN PROCESSING NODE PIN
TOP-1.453 D.O.F. 2 RATIO = 442.136E+12 .

***WARNING: DISPLACEMENT INCREMENT FOR CONTACT IS TOO BIG.


***ERROR: TIME INCREMENT REQUIRED IS LESS THAN THE MINIMUM SPECIFIED


Any help is greatly appreciated. When I try to edit my model I get more errors of excessive distortion and severe contact overclosures exist. THANK YOU!

 

[corus]

If a part appears to be 'floating' then it hasn't made contact and has moved off into space. You'll need to review your contact surfaces and conditions to find out why that is.

 

[DanStro]

You should also check the deformation scale factor in the visualization view. If it's very large than the parts could look like they are in contact, or even moving away from each other, when they are really not in the simulation.

This has bitten me a couple of times.

Han primo incensus

 

[AriaCole]

Thanks to you both for the tips. The deformation scale was set at one. However, I discovered that I needed to redefine the interactions and turn the auto stabilization on. My model has successfully made it through step 1, make-up. Make-up includes 7 interactions.

Currently, the model halts during step 2, internal compression. I notice (in the viewer) that around step 20 the extra length of pipe included in my model for analysis purposes turns red (high plastic deformation). This seems odd to me because this portion of the pipe should see minimal deformation during the entire analysis. I expected to see more localized deformation in the threads and seal but not on the pipe. It seems to be an error.

The internal pressure step includes the same 7 interactions as make-up but I have now applied 3 loads, internal pressure (values from VME plot), external pressure, and tension. The model has 3 parts; field end, mill end, and coupling. Tension is applied to the field end, internal pressure to the field and mill end (left side), external pressure to the coupling, field and mill end (right side). 1 BC of no rotation/displacement is present.

The warning I receive when monitoring the message file are shown below. The file runs until step 2 increment 34.


***NOTE: THE SOLUTION APPEARS TO BE DIVERGING. CONVERGENCE IS JUDGED UNLIKELY.


***ERROR: TIME INCREMENT REQUIRED IS LESS THAN THE MINIMUM SPECIFIED

Any suggestions on how to fix the model?

 

[corus]

Have you also got *Contact controls, automatic toleramces set?
To check the results from a model I always find it best to check the displaced shape to see if the contact is working properly. If
it seems fine and you have a lot of non-linearity in the model (ie. contact, large displaemenet, plasticity) then it might be better to switch to an explicit model, which is less strict in applying static equilibrium everywhere.

 

[AriaCole]

Yes corus, during the analysis I have one contact control set for automatic over closure tolerances, friction to be onset immediately and the automatic stabilization is on.