friction subroutine

Hi,

i want to simulated a compression and sliding of rubber block on a rough rigid substrate (i want optain a friction coefficient as output by abaqus simulation)

i wnat implement a friction subroutine,

Wher i can read about?

are there tutorial abaout friction subroutine?

How i can create a friction subroutine or use a frct subroutine?

thanks a lot