Hi SFS and SFM are stifness factors which has to be adjust to achive appropoate contact stifness and it is governed by the follwing equation
k = max(SLSFAC * SFS * k0, SOFSCL * k1)
so you need to tune this parameter via trail and error method. untill you are satisfied with the contact forces which might be affected due to contact stifness. In fact the defaults are great to start. Check the follwing study to see how the SFS and SFM affected the resultant contact force.
https://www.researchgate.net/publication/236866498_Delamination_of_impacted_composite_structures_by_cohesive_zone_interface_elements_and_tiebreak_contact
Cheers, Ram
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