excessive distortion when the model has't deformed at all!

[MrSamuel]

I have a general static step that has a boundary condition that forces one body into another. One material is steel, the other is hyperelastic. The contact is frictionless. I get the error excessive distortion soon after they contact each other but before there is any significant deformation of the model, so how can this error make any sense at all?

I have searched the web for solutions to this error to no avail. I did read that the error can be given in contact problems because of sudden accelerations, but I don't know how to fix this either. Any tips at all, anyone?

I can post the file and provide a more detailed explanation if that would be helpful.

Thanks!

Sam

 

[Timusop]

If you are using Abaqus Standard, try "nudging" the parts together using displacement control before switching to force control. This normally solves this problem. I hope that helps.

 

[MrSamuel]

Currently I use a displacement/rotation boundary condition and set a displacement (in a general static step) that results in contact and a small amount of deformation.

Is this a "nudge" or is it something else? How do I do a nudge? I'm finding references to nudging on the web, but no explanation on how to set it up.

Thanks,
Sam

 

[corus]

A'nudge' just means a very small displacement.

Another problem with contact is when you specify that initial overclosure should be removed. Some times that can cause excessive distortion as the two contact surfaces are brought together, but before any displacements or forces are applied.

 

[MrSamuel]

Thanks guys for your support so far.
I'm trying to simulate a toe pushing into a surface including two bones connected by springs and covered with skin (hyperelastic material). I seem to have it working OK so far.

One problem though, an option is turned on that I don't want turned on:

for the BoneBone interaction, "tie adjusted surfaces" is on. (see the attached model for details)

I need to have it off to better simulate bone bone interaction, but soon as I turn this off, the simulation fails.

Could someone please open up my CAE file and give it a try? Why might it be failing when this option is turned off? One thing I noticed is that when the option is turned off and a different material is used (rubber in my model) instead of skin, it works... very confusing...

Please let me know if you need more information.

Thanks,
Sam

 

[MrSamuel]

Just when I finally ask someone to open the actual model, I get it working, go figure. Simply by using a bigger nudge, it seems to work. Man is Abaqus ever fussy...

Thanks guys!

Sam

 

[corus]

I think the problem was that you didn't have the parts initially in contact in the assembly. Given the curved surface it's difficult to translate the parts so that they are touching, In these cases I tend to zoom in on the contact point and guess at a translation value until they're more or less in contact and then run the job removing any overclosure and applying a small nudge that I know will bring the parts into contact.

 

[abqMaster]

Two solutions:
1) add stabilizie to *step
2) add contact controls,stabilize