How can I specify friction coefficient in the contact interface?

The friction coefficient is usually obtained from experiment. However, this coefficient might vary for different conditions. For example, for the same material, the friction coefficient might be larger when small dir radii are used. Also the friction coefficient is affected by the interface pressure, etc.

Many users tend to pick one friction coefficient, such as 0.1, for all the simulation. Sometimes, small variations on friction coefficient will make big difference on the final result, especially for springback analysis.