contact stress

[zain22]

Hello everyone,
I apologize if this is a very basic question but I really need help in this. in my Biphasic model I would like to plot the contact stress (xplt and logfile.) which I could not find in FEBio variables.
thank you
Ali

[maas]

Hi Ali,

The contact traction or contact pressure (i.e. normal component of contact traction) can be stored to the plotfile only. There is no option to store that information to the logfile, but you can store it to the plotfile and then use PostView to export the data to a text file. To store these variables to the plotfile, find the "Output Request" item in the Model Viewer in PreView, right-click it and select "Edit". In the dialog box that appears you can select the output variables.

Cheers,

Steve

[zain22]

Hi Steve,
Thank you very much for your detailed reply. If I understand correctly, the contact pressure is resulted from the applied load on the whole contact area area (solid + fluid). However, I was wondering how can I calculate the contact stress on the solid phase alone?

thanks again
Ali

[ateshian]

Hi Ali,

The biphasic normal contact traction is t = -p + te, where p is the fluid pressure and te is the traction on the solid. You can calculate te from this formula. Keep in mind that contact stress is |t| (absolute value of normal contact traction). Also, you may find that the contact stress is a noisy variable. A better choice might be the minimum principal normal stress (3 Principal stress), which is evaluated a the center of the element. If your elements at the contact surface are thin, then minimum principal normal stress is a good measure of the contact stress. In that case, the elastic part of the contact stress is simply the minimum principal normal solid stress (3 Principal solid stress).

Best,

Gerard

[zain22]

Hello Prof. Ateshian,
Thank you very much for your prompt reply. It is very clear now.
Bests
Ali