In 12.0.1, the userfric.F user-defined friction subroutine was introduced to allow users to write their own friction law. The out-of-the box friction models in ANSYS include static-dynamic transitional frictional model as well as orthotropic friction. Uses for userfric.F include situations where you want two frictional directions to be independent of each other (the built-in orthotropic friction model assumes an elliptical ‘yield’ surface) or separate frictional models in different directions.

To include user-defined friction, the userfric.F must be coded, compiled, and linked. The TB,FRIC,,,,USER APDL command defines the user-defined friction for a given material ID number, and parameters can be passed via TBDATA. (The subroutine can also access real constant data as well.)

Only the penalty-based method (acting in tangential direction) is used for this feature (KEYOPT(2)=0, 1, or 3), so the important item to keep in mind is the ‘elastic’ slip calculations. Namely, the tangential contact stiffness KT parameter needs to be defined by the user, and it will influence the elastic slip calculations.  The output from the subroutine is documented in the example userfric.F, but note that in addition to the status, slip, and frictional stress output, the derivatives (“dt” array) also need to be supplied.