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Re: [lammps-users] Stretching test for mechanical property
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Re: [lammps-users] Stretching test for mechanical property

From: Ray Shan <rshan@...1795...>
Date: Tue, 22 Aug 2017 22:06:34 +0000

Please make good use of the doc page. 


On Aug 22, 2017, at 14:57, Arun Bikram Thapa <aaron.thapa143@...24...> wrote:

---------- Forwarded message ----------
From: Arun Bikram Thapa <aaron.thapa143@...24...>
Date: Tue, Aug 22, 2017 at 4:36 PM
Subject: Re: [lammps-users] Stretching test for mechanical property
To: Vanessa Oklejas <voklejas@...92......>
Cc: lammps <>

Hi Ray,

In this script file. I am getting this error message

thermo_style    custom step etotal evdwl lx v_eps v_sxx pe temp press time
WARNING: New thermo_style command, previous thermo_modify settings will be lost (../output.cpp:690)
thermo_modify    temp new3d
WARNING: Temperature for thermo pressure is not for group all (../thermo.cpp:480)

reset_timestep    0.0001
ERROR: Expected integer parameter in input script or data file (../update.cpp:419)
Last command: reset_timestep    0.0001

What might be the possible reason behind this?


On Tue, Aug 22, 2017 at 3:47 PM, Vanessa Oklejas <voklejas@...29....> wrote:
Can you post the error message? I don't see one in your original post. Thanks

On Tue, Aug 22, 2017 at 1:38 PM Arun Bikram Thapa <aaron.thapa143@...12...24...> wrote:
I am getting error in stress calculation section in this script.

On Tue, Aug 22, 2017 at 3:33 PM, Arun Bikram Thapa <aaron.thapa143@...24...> wrote:
Hello everyone,

I am doing mechanical test by stretching a nano tube. The two end of nano tubes are clipped and one end is kept fixed and other end is stretched by applying displacement. In between stretching the system is relaxed (quasi static loading).  Apart from velocity what can I use for loading. the all boundary is periodic so I though velocity command would be suitable for this. 
Am I correctly applying quasi static loading. Please suggest me some better approach if there is any.
This is my script

## ----- setting-------------------------
units metal
atom_style atomic

boundary p p p
newton on

dimension 3

##----- Read input ------------------------

read_data 1tube.txt


## -------- pair potential --------------
pair_style airebo 3.0 1 1
pair_coeff      * * CH.airebo C


timestep 0.0001
thermo_style custom step pe etotal press temp density vol time pxx pyy pzz pxy pxz pyz
thermo 1000
reset_timestep 0
restart 100000 NICYCLESTAT.STA
dump SWCNT all xyz 10000
min_style cg
minimize 1.0e-6 1.0e-8 1000 10000

##-------- equlibration-------------------

neighbor 2.0 bin
neigh_modify every 3 delay 3
region lowerclip block -63.6 63.6 -36.5 36.5 0 2.84
region upperclip block -63.6 63.6 -36.5 36.5 48.25 51.12
region midclip block -63.6 63.6 -36.5 36.5 2.85 48.25
group lower region lowerclip
group upper region upperclip
group mid region midclip
group cliped union lower upper 
group mobile subtract all cliped
#set group lower type 2
#set group upper type 3

# temp controllers
compute new3d mobile temp

velocity mobile create 50.0 49284121 temp new3d

fix 1 all nvt temp 50.0 50.0 0.1 
fix 2 cliped setforce 0 0 0

compute stressperatom mobile stress/atom
compute stgb mobile reduce sum c_stressperatom[1]       

variable    sxx equal c_stgb/vol
variable    eps equal (lx-51.12)/51.12

dump        1 all xyz 100 tens1
thermo        100
thermo_style    custom step etotal evdwl lx v_eps v_sxx pe temp press time
thermo_modify    temp new3d
timestep    0.0001
run        2000000

# tension
velocity    upper set 0 0 0.163
velocity    mobile ramp vz 0 0.163 z 2.85 48.25 sum yes

thermo        100
thermo_style    custom step etotal evdwl lx v_eps v_sxx pe temp press time
thermo_modify    temp new3d

reset_timestep    0.0001
run        2000000

#equilibration after first loading step

unfix 1
fix   1 all nvt 300 300 0.01
reset_timestep  0.0001
run             250000
Inline image 1


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