Learning Forum

[STAVROS PAPIGKIOTIS]

Hello ! I would like to ask for help for configuring this simulation in Workbench.
The problem is a contact between a hemi-sphere and a plate in which I want to evaluate stresses and contact radius when a downforce is applied to the hemi-sphere ,to compare to the analytical solution. I am simplifying it to a 2D problem with symmetry.When I have a frictionless model I get Hertzian contact stresses.But when I put friction in it ,instead of JKR ,MG or DMT model , I get again  the Hertzian model .I don't know how to continue. Here is the result where I get the von Mises stress without  , and with friction applied





Thank you and Im waiting for your response!

[John Doyle]

I do not understand your problem statement or your question.

What does "...JKR, MG or DMT model..." refer to?

[STAVROS PAPIGKIOTIS]

JKR ,MG ,DMT model refer to contact with adhesion .
For example , the theorytical solution for Hertz ,when the contact is frictionless is this

When  the contact is frictional  , the stresses should follow this model

or this model

[John Doyle]

Thanks for the clarification. 

The coulomb friction model used in Ansys does not include local surfacce adhesion effects due to micro material intermingling and entanglement (as described by JKR Theory).  Frictional surfaces in Ansys are always free to separate at zero surface pressure.  You might be able to achieve something similar to JKR by defining a nonzero cohesion real constant with RMODIF,cid,13, in a command object.  See Section 3.9 of the MAPDL Contact Technology Guide for details.  If that does not work, you would likely have to write a customized user routine to capture this effect.

[STAVROS PAPIGKIOTIS]

See my comment below!

[STAVROS PAPIGKIOTIS]

Hello again,I tried this simulation on Mechanical APDL , and I face some difficulties.First ,I want to have as an input the Force.In this photo below ,  I have put an area displacement in the plate ,  and a line displacement (ALL DOF) in the upper  line of the circle, in order to see if the contact is detected.But I do not want to do this , I want to put a force like the HERTZ model and see the stresses of both of the surfaces .
Secondly , Could u help me a little bit with the JKR case? I do not know how to use the command window, cause I work with the menu toolbar.Is it a way to achieve the JKR model with the menu only ? 
Waiting for ur response, thanks!