elastic constatnts

Hi Dear

I use Lammps to calculate elastic constants of vinylester. I use following commands to calculate it:

fix tensile all deform 1 x scale 1.005 y volume z volume remap x
compute mystress all stress/atom
compute fx all reduce sum c_mystress[1]
thermo 10
thermo_style custom step temp c_fx[1] lx ly lz xy press vol
run 10
unfix tensile

But the results of c_fx[1] is very much, for example the value of it in step of 10000 is

Hi Dear
I use Lammps to calculate elastic constants of vinylester. I use following
commands to calculate it:

fix tensile all deform 1 x scale 1.005 y volume z volume remap x
compute mystress all stress/atom
compute fx all reduce sum c_mystress[1]
thermo 10
thermo_style custom step temp c_fx[1] lx ly lz xy press vol
run 10
unfix tensile

But the results of c_fx[1] is very much, for example the value of it in
step of 10000 is 2.38E+09.

is very much what?

Hamzeh,

I don’t know much about vinyl ester, but I see that it is a resin and behaves like a low-viscosity polymer. Computing elastic response of a soft polymeric materials is not straightforward. For starts, the response is strongly time dependent. Second, at each strain state you have to perform a time-average over the equilibrium distribution of stress values. There are many more complicating factors that you will have to learn about yourself.

These are not LAMMPS questions, they are questions about the statistical mechanics of polymers. I suggest the following program:

  1. Read the literature
  2. Teach yourself how to reproduce published (visco-)elastic properties of a particular polymer
  3. Apply the same methodology to vinyl ester

Aidan