I did a set of loading-unloading uni-axial tension tests on polymers, i.e. first use “fix deform” to deform the box to 100% strain along one direction, then unload the box by setting the pressure along all three directions equal to zero.
Please see the figure attached for the stress vs time curve, time = 1ns is the point of unloading.
My question is: the stresses along all directions seem reasonable during the loading part,
but the stresses don’t go to zero during the unloading part although I set them all equal to zero at this part.
Does anyone have experience on this problem?
Thanks for your comments and suggestions.