# Setting a coefficient of friction

#1

When doing a non-linear thermomechanical study, we have the option of choosing a friction interface between bodies but I can not see where to define the coefficient of friction? I do understand that since the thermomechanical solver first solves for temperature and then for forces, the friction functionality is limited, but still, I don’t understand how it can calculate a frictional force without a coefficient of friction

#2

Hi Roy and sorry for the late response!

Some pictures to demonstrate how you would set up/ find the Coulomb Coefficient:

\underline{\text{1. Set up a Physical Contact}} \underline{\text{2. Set Coulomb Coefficient}} Is that what you were looking for? Let me know if you need anything else, happy to help you out!

Jousef

#3

Hi @jousefm

Thanks for the reply. I didn’t get as far as the 2nd screen so did not see that. What is the penalty coefficient and friction penalty coefficient?

#4

Hi Roy!

As for the difference the penalty method produces a small interpenetration whereas the Augmented Lagrange method is quite exact (almost). The penalty coefficient is something between 1-100x the Young’s Modulus of your material (anything too big will lead to an ill-conditioned matrix). In the same way the friction penalty coefficient is assigned to the tangential direction. The penalty parameter is a scaling factor to calculate the normal pressure, but only when there is contact or interpenetration.

Cheers,

Jousef