Hello all,
I am trying to make a uniaxial loading of a Fe-Mn binary system, however, when I started to deform my simulation box, the stress appeared to be negative.
Here is my input script
LAMMPS Input File for Deformation Induced Martensitic Transformation
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SYSTEM INITIALIZATION
clear
units metal
dimension 3
boundary p p p
atom_style atomic
ATOMIC STRUCTURE
read_data Fe_5Mn_10w.lmp
INTERATOMIC POTENTIALS
pair_style meam/c
pair_coeff * * library.meam Fe Mn FeMn-para.meam Fe Mn
SIMULATION SETTINGS
compute csym all centro/atom fcc
compute eng all pe/atom
compute eatoms all reduce sum c_eng
######################################
VARIABLE DEFINE
variable n_iter equal 20000
variable srate equal 1.0e10
variable srate1 equal “v_srate / 1.0e12”
MINIMIZATION 1 (UNDER 0K)
reset_timestep 0
fix 1 all box/relax iso 0.0 vmax 0.001
thermo 100
thermo_style custom step pe lx ly lz press pxx pyy pzz c_eatoms
dump 1 all cfg 25 dump.Fe_5Mn_minimization_*.cfg mass type xs ys zs c_csym c_eng fx fy fz
dump_modify 1 element Fe Mn
min_style cg
minimize 1e-18 1e-18 10000 10000
unfix 1
MINIMIZATION 2 (UNDER 300K)
reset_timestep 0
timestep 0.001
velocity all create 300 12345 mom yes rot no
fix 1 all npt temp 300 300 1 iso 0 0 1 drag 1
thermo 1000
thermo_style custom step lx ly lz press pxx pyy pzz pe temp
run ${n_iter}
unfix 1
Store final cell length for strain calculations
variable tmp equal “lx”
variable L0 equal {tmp}
print "Initial Length, L0: {L0}"
UNIAXIAL DEFORMATION
reset_timestep 0
fix 1 all npt temp 300 300 1 y 0 0 1 z 0 0 1 drag 1
fix 2 all deform 1 x erate ${srate1} units box remap x
Output strain and stress info to file
for units metal, pressure is in [bars] = 100 [kPa] = 1/10000 [GPa]
p2, p3, p4 are in GPa
variable strain equal “(lx-v_L0)/v_L0”
variable p1 equal “v_strain”
variable p2 equal “-pxx/10000”
variable p3 equal “-pyy/10000”
variable p4 equal “-pzz/10000”
fix def1 all print 100 “{p1} {p2} {p3} {p4}” file Fe_5Mn_tens.def1.txt screen no
DUMP THE RESULTS
dump 1 all custom 1000 Fe_5Mn_tensile.dump mass type xs ys zs c_csym c_eng fx fy fz
dump_modify 1 element Fe Mn
DISPLAY THERMO
thermo 1000
thermo_style custom step v_strain temp v_p2 v_p3 v_p4 ke pe press
run 20000
ALL DONE
unfix 1
unfix 2
undump 1
print “ALL DONE”