This is a technical paper made by the people developing the Sag 10, and it is about the compressive stress of the aluminum part of an ACSR.
Consider an ACSR that has been subjected to some initial loading, following whuch the load is reduced. The unloading will follow the final stress-strain curve, and at some point the tension in the aluminum portion will go to zero.
Since the aluminum will have experienced some plastic deformation, while the steel will have experienced little if any, the steel will be under tension while the aluminum goes slack.
Read the rest of the technical paper on the down load link below: