# Lammps-uni-axial tension\compression, simple shear , and loading/ unloading questions

Dear All,

I am going to do uni-axial tension, uni-axial compression, simple shear , and loading/ unloading (cyclic loading) for glassy polymers using Lammps with period boundary conditions along 3 dimensions.

I have 2 questions:

(1) During the deformations mentioned above, I would like to output stress-strain information not only on the surfaces of the simulation box, but some inter-planes within the box, so I have to divide the box into parts. Is it allowed in Lammps? If so, what is the command for the it?

(2) During applying the deformations, for example, uni-axial tension, I need to measure the temperature rise due to the deformation, so I can’t use NPT ensemble since I don’t want to keep the temperature constant. But I do have to control the stress (pressure) on the

lateral directions, they should be zero in uni-tension tests. What ensemble do you think is suitable for my tests? Can pressure control be used independently from the ensembles? Or maybe I shouldn’t use any ensemble at all, just need to apply the deformations and control some components of the stress.

Thank you for your time and advise.

Lili Zhang

PhD student, Mechanical and Materials Engineering
University of Nebraska-Lincoln, Lincoln, NE 68588-0526