Apply shear stress by 'fix aveforce'

Dear LAMMPS community,

I am trying to apply a constant stress by using ‘fix aveforce’ command.
I define two regions ‘upper’ and ‘lower’, where I apply aveforce. The shear stress is derived as stress=force_total/Area.
The following inscript seems to lead a shear stress of about 160 MPa.
However, the shear stress is actually too large, so that it catastrophically destroys my model.

Any idea about applying a stress with reasonable magnitude?

Thank you.


Your cut out piece of script is too short to understand what you are trying to accomplish. You have two oppositely forced groups of atoms, so what?