How to unload the sample in lammps?

Dear all,

I performed an atomistic simulation of uniaxial tensile loading of an aluminum single crystal oriented in the <100> direction, same as the performance of Makr Tschopp in LAMMPS tutorial. Now I would like to unload the sample at a certain point of the stress-strain curve of uniaxial tension. I fulfill this by applying an identical negative deform rate (comparing with uniaxial tensile stage) on the sample, and i got some results. When unloading from a point in the linear elastic stage of tension, the stress-strain curve exactly backtracks along the tension path. but if unloading from a point in the plastic deformation stage (the stress-strain curve declining stage, the plastic deformation can be viewed by VMD) , the stress-strain curve does not backtrack along the tension path, and producing a residual strain of about 0.1. I think these observations agree with the deformation mechanism of materials that plastic deformation produces residual strain but elastic deformation does not. Now what i want to ask is that the unloading method by applying a negative deform rate is reasonable? Thank you very much for advance! Any tips will be gratefully appreciated!


This is not a LAMMPS question, but a question for your advisor and colleagues.


Dear Ray:
Thank you very much for your kindly comments! As you said, this is not a lammps question, i asked here is to find if someone unloading in this way. If any, I hope he or she could give me some comments. If no one did this, I also wish my experience could provide some guidance to someone else. Thank you very much!