Contact Traction very high

Hello,

I have performed a simple non-linear quasi static analysis to study a ball-plate contact. Optistruct was used as a solver. Contact is modelled as node to surface, slide contact.

I am wondering why Contact Traction (Normal) is resulting in a very high number? As far as I understand, Contact Traction (Normal) is supposed to represent a pressure in a contact.

In such a simple example (ball-plate contact) it is easy to verify the results with analytics, which in fact yields more than 100 times smaller values for the contact pressure in comparison to the Contact Traction results.

As a 'workaround' to plot the contact pressure, I am checking Element Stresses, where the option Pressure is chosen (I have CONTF card enabled in a solver). The results are correct here.

Could you please give me more insight of what Contact Traction is representing? I haven't found anything in a Reference guides.

Thank you in advance,

Matej

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Rahul Rajan_21763

Could you please let us know the version of OptiStruct you are using at your end? Also please check the vector plot of contact force and try with S2S method instead of N2S as the penalty method is different for both the case.

Altair Forum User

I am using Optistruct 2017.2.2 and just tried with S2S contact and I get much better results. They are still about 40% higher from analytical values; however, this might be due to quite coarse mesh I am using right now. Additionally, also the contact forces are for about the same factor lower than before, which gives much more logical results. Thanks a lot for your help!

Anyway, what is the difference between the Contact Traction and the Contact Stress (Pressure option)? Because the results differ a bit (even when observing corner data for stress).

Altair Forum User

Hi,

When bodies come in contact this gives rise to normal traction. Contact traction needs to be determined for say admissible velocity for example.