pxx and pyy are not zero with free bc

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1

dear lammps users,
i am using free boundary conditions (boundary s s s) for cylindrical pillar in all 3 directions (x,y & z), compressing it using fix indent plane command,
the pxx, pyy are not becoming zero, they are coming equivalent to pzz value. whereas for free bc stress should be zero in that direction are much less than other directions stresss in which we applied pressure.

why pxx and pyy values are zero?

thanks in advance

2

Maybe you aren't giving it time enough to relax. Maybe
there are oscillations in the pressure that you have to
average over. If the lateral dimensions are free surfaces,
then there is the question of what volume to normalize
by. Not all systems are able to sustain a large tensile
stress in one dimension and fully relax in the others.

Steve