f := interface.node.stress.normal.add(in)
interface.node.stress.normal.add(in) := f

Get/set the additional normal stress. The normal stress used in the calculation is equal to the penetration × stiffness + additional normal stress. This function can be used to initialize (or pre-stress) the interface normal stress or to counteract the stresses induced by interpenetration.

Returns:f - additional normal stress
Accepts:f - additional normal stress
Arguments:in - interface node pointer