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[lammps-users] Problem regarding uniaxial tension test
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[lammps-users] Problem regarding uniaxial tension test


From: Selesta Oxem <oxemselesta@...24...>
Date: Thu, 3 Aug 2017 12:14:14 -0400

Hi all,
I was just trying to do some uniaxial tension test by using fix_deform and as a specimen sample I took single crystal Al. I use the available lamps script at https://icme.hpc.msstate.edu/mediawiki/index.php/Uniaxial_Tension

But, surprisingly I do not see any fracture even after the strain value of over 200%. The sample is stretched unusually at that high strain. I have seen a recent post about this type of behaviour but do not see any comments over it.

Could anybody please make some suggestion what I'm missing.

Thanks for your help in advance.

Best,
O  

# Input file for uniaxial tensile loading of single crystal aluminum
# Mark Tschopp, November 2010

# ------------------------ INITIALIZATION ----------------------------
units 		metal
dimension	3
boundary	p	p	p
atom_style	atomic
variable latparam equal 4.05

# ----------------------- ATOM DEFINITION ----------------------------
lattice		fcc ${latparam}
region		whole block 0 10 0 10 0 10
create_box	1 whole
lattice 	fcc ${latparam} orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
create_atoms	1 region whole

# ------------------------ FORCE FIELDS ------------------------------
pair_style	eam/alloy
pair_coeff	* * Al99.eam.alloy Al

# ------------------------- SETTINGS ---------------------------------
compute csym all centro/atom fcc
compute peratom all pe/atom 

######################################
# EQUILIBRATION
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 

# Set thermo output
thermo 1000
thermo_style custom step lx ly lz press pxx pyy pzz pe temp

# Run for at least 10 picosecond (assuming 1 fs timestep)
run 20000
unfix 1

# Store final cell length for strain calculations
variable tmp equal "lx"
variable L0 equal ${tmp}
print "Initial Length, L0: ${L0}"

######################################
# DEFORMATION
reset_timestep	0

fix		1 all npt temp 300 300 1 y 0 0 1 z 0 0 1 drag 1
variable srate equal 1.0e10
variable srate1 equal "v_srate / 1.0e12"
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 Al_SC_100.def1.txt screen no

# Use cfg for AtomEye
dump 		1 all cfg 250 dump.tensile_*.cfg mass type xs ys zs c_csym c_peratom fx fy fz
dump_modify 1 element Al

# Display thermo
thermo 	1000
thermo_style	custom step v_strain temp v_p2 v_p3 v_p4 ke pe press

run		20000

######################################
# SIMULATION DONE
print "All done"