Simulation of Deformation Behavior in Amorphous Polymer
This is a LAMMPS input to study deformation mechanisms during uniaxial tensile deformation of an amorphous polyethylene polymer. The stress-strain behavior comprised elastic, yield, strain softening and strain hardening regions that were qualitatively in agreement with previous simulations and experimental results.
# Deformation mechanisms during uniaxial tensile deformation of an amorphous polyethylene polymer. # Dr. Mark A. Tschopp, 2010. # VARIABLES variable fname index PE_nc10_cl1000.dat variable simname index PE_nc10_cl1000 # Initialization units real boundary p p p atom_style molecular log log.${simname}.txt read_data ${fname} # Dreiding potential information neighbor 0.4 bin neigh_modify every 10 one 10000 bond_style harmonic bond_coeff 1 350 1.53 angle_style harmonic angle_coeff 1 60 109.5 dihedral_style multi/harmonic dihedral_coeff 1 1.73 -4.49 0.776 6.99 0.0 pair_style lj/cut 10.5 pair_coeff 1 1 0.112 4.01 10.5 # Equilibration Stage 1 (Langevin dynamics at 500 K) velocity all create 500.0 1231 fix 1 all nve/limit 0.05 fix 2 all langevin 500.0 500.0 10.0 904297 thermo_style custom step temp press thermo 100 timestep 1 run 10000 unfix 1 unfix 2 write_restart restart.${simname}.dreiding1 # Equilibration Stage 2 (NPT dynamics at 500 K) fix 1 all npt temp 500.0 500.0 50 iso 0 0 1000 drag 2 fix 2 all momentum 1 linear 1 1 1 thermo_style custom step temp press thermo 100 timestep 0.5 reset_timestep 0 run 50000 unfix 1 unfix 2 write_restart restart.${simname}.dreiding2 # Equilibration Stage 3 (NPT dynamics from 500 K --> 100 K) fix 1 all npt temp 500 100 50 iso 0 0 1000 drag 2 fix 2 all momentum 1 linear 1 1 1 thermo_style custom step temp press thermo 10 timestep 0.5 reset_timestep 0 run 50000 unfix 1 unfix 2 write_restart restart.${simname}.dreiding3 # Equilibration Stage 4 (NPT dynamics at 100 K) fix 1 all npt temp 100 100 50 iso 0 0 1000 drag 2 fix 2 all momentum 1 linear 1 1 1 thermo_style custom step temp press epair ebond eangle edihed pxx pyy pzz lx ly lz thermo 10 timestep 0.5 reset_timestep 0 run 50000 unfix 1 unfix 2 write_restart restart.${simname}.dreiding4 # Uniaxial Tensile Deformation run 0 variable tmp equal "lx" variable L0 equal ${tmp} variable strain equal "(lx - v_L0)/v_L0" variable p1 equal "v_strain" variable p2 equal "-pxx/10000*1.01325" variable p3 equal "-pyy/10000*1.01325" variable p4 equal "-pzz/10000*1.01325" variable p5 equal "lx" variable p6 equal "ly" variable p7 equal "lz" variable p8 equal "temp" variable t2 equal "epair" variable t3 equal "ebond" variable t4 equal "eangle" variable t5 equal "edihed" fix 1 all npt temp 100 100 50 y 0 0 1000 z 0 0 1000 drag 2 fix 2 all deform 1 x erate 1e-5 units box remap x fix def1 all print 100 "${p1} ${p2} ${p3} ${p4} ${p5} ${p6} ${p7} ${p8}" file ${simname}.def1.txt screen no fix def2 all print 100 "${p1} ${t2} ${t3} ${t4} ${t5}" file ${simname}.def2.txt screen no thermo_style custom step temp pxx pyy pzz lx ly lz epair ebond eangle edihed thermo 100 timestep 1 reset_timestep 0 run 171800 unfix 1 unfix 2 unfix def1 unfix def2 print "All done"
1. In this LAMMPS input, “Initialization” section defines the style of units, the dimension (3D here), and LAMMPS data file reading.
2. We need to define the interatomic potentials for particles interactions. Simulation is run with the DREIDING interatomic potential in this study.
3. It’s now time for simulation to actually run, which begins with the energy equilibration. The simulated polymeric structure has to be equilibrated before the deformation in 4 stages.
4. “Deform section” is last section of the simulation, but not the least. This is where deformation is actually carried out. Different variables such as strain rate, pressures, stress has been defined and then later printed in the log files.
Here is an example “data file” for a polyethylene system with 10 chains of 1000 monomers each. Download this file and add this to the directory with the LAMMPS input script above: Media:PE_nc10_cl1000.dat
Reference
https://icme.hpc.msstate.edu