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Setting Up Initial Contact

I am trying to set up a sort of indentation test. I have an indenter with a round tip, which will be indenting a specimen that is split in two as seen in the attached picture below. For the sphere - specimen contact I am using a type7 contact which is fine because there is a small initial gap between the indenter and specimen pieces, however, for the contact between the two specimen pieces, I have tried with type7 with inacti = 6 and tried again with inacti = 1. inacti = 6 gave penetration errors, where inacti = 1 gave penetration warnings. I also tried with Type3 contact but I got some element deformations that shouldn't have occurred. Therefore, for this situation would Type3 or Type 7 be better, and how do I go about getting rid of the initial penetration errors? And do I need to set-up a contact group from Specimen1 to Specimen2 and then another as Specimen2 to Specimen1 or would a single contact group take care of that?

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Altair Forum User

Hi Brandon,

For type 7 interface you can try with Fpenmax=0.75 and Inacti=5 and any node that is penetrated more then 75% of the gap is removed from the contact and nodes penetrated < 75% gap have their gap reduced due to Inacti=5. Or reduce your Gapmin to a very small amount if you are using constant gap or for variable gap set Igap=2 and Fscalegap=0.999.

If issue persist please share the model file.

Altair Forum User

thanks, I have tried these values, and I am now just getting penetration warnings instead of errors. Upon reviewing the OUT file, they appear to just be stating that the nodes are now at zero stiffness.

I am however, now getting a 'total mass error limit reached' error and the run is then terminated. Any idea why this is occurring? I will attach all the files if you need them.

Unable to find an attachment - read this blog

Altair Forum User

Hi Brandon,

Total mass error occurs when the imposed time step is high in the model.

Can you try running with the attached engine file.

Unable to find an attachment - read this blog

Altair Forum User

I have tried with the new engine file you attached, however I got an error after a few animation files were written that said the Time Step Less Or Equal Zero.

So i saw you chose a time step of 2.5e-6 so I tried increasing that to 2.5e-3, and then 2.5e-2, but still am getting the 'Time Step Less Or Equal Zero' termination. Any ideas?

Is this occurring because of the initial contact that is going on? If so, is there any alternative for initial contact aside form Type7? I could put a tiny gap between the two specimen, but ideally they'd stay contacted.

Altair Forum User

Hi Brandon,

'Time Step Less Or Equal Zero' error termination will happen when the time step of the model goes very low.

Penetrations in the model can result in the same.

I would recommend you to fix the penetrations. You can try with HyperCrash penetration tool or in HyperMesh. Please see the below post which shows the same.