hello,
lammps-users
I want to study the micro-mechanical behavior of metallic foam i.e some porous material by using molecular dynamics if I allow some shock wave with huge velocity to pass through this material,I have come to know from lammps documentation that this type of research can be done by Lammps,am I correct ?
Assuming that I am using proper code(Lammps),primarily I have prepare some input structure just as msst example with some modifications in the .in file,I have introduce a pour in the simulation box which is full of Al fcc structure.Here i have confusion I am introducing pour by using delete_atom command,is it proper ? if not, is there another way to invoke pour in a structure without deleting any atom ?
My input script is here …
Energy in eV, time in ps, distance in angstroms.
units metal
boundary p p p
atom_style atomic
variable latparam equal 4.050
reset_timestep 0
timestep 1e-4
lattice fcc {latparam}
region box block -20 20 -20 20 -20 20
region void sphere 0 0 0 20 units box
create_box 1 box
create_atoms 1 box
group bulk region box
group void region void
lattice fcc {latparam} orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
delete_atoms group void
mass 1 26.981539
Initial velocities correspond to around 300.0K.
velocity all create 600 12345 mom yes rot no
pair_style lj/cut 10
pair_coeff 1 1 0.01032 3.405
reset_timestep 0
timestep 2e-4
compute csym all centro/atom fcc
compute peratom all pe/atom
Equilibrate the system
fix 2 all nve
thermo 20
Store final cell length for strain calculations
variable tmp equal “lx”
variable L0 equal {tmp}
print "Initial Length, L0: {L0}"
run 200
unfix 2
MSST fix
fix msst all msst z 120.0 q 200 mu 3e2 tscale 0.00001
fix_modify msst energy yes
thermo 10000
variable srate equal 1.0e10
variable srate1 equal “v_srate / 1.0e12”
fix 2 all deform 1 x erate ${srate1} units box remap x
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 10 “{p1} {p2} {p3} {p4}” file Al_SC_100.def1.txt screen no
variable dhug equal f_msst[1]
variable dray equal f_msst[2]
variable lgr_vel equal f_msst[3]
variable lgr_pos equal f_msst[4]
thermo_style custom step v_strain temp v_p2 v_p3 v_p4 ke pe lx ly lz pxx pyy pzz etotal &
v_dhug v_dray v_lgr_vel v_lgr_pos f_msst vol enthalpy dt
dump 1 all custom 100 dump.msst_*.xyz type x y z
dump_modify 1 element Al
run 10000
*as this for just trial so the parameters is not actual
It’s run fine but when i visualize the dump file and make animation the I am seeing that the pour is breaking,it’s fine but I expect that the pour should break from one side i.e Z direction,as well as it should not be symmetric when it breaks but from video it is showing that the pour breaks symmetrically i.e it starts breaking from all direction simultaneously, where the fallacy is?
As the shock velocity is quit high I expect Z direction should be compressed and at the same time X& Y should expand but log file shows that Z compressed and X expand but Y remain same,why this is happening ?
My last question with such porous structure when I equilibrate it the pour would be collapsed, isn’t it? so what should I do ?
As I am in primary level in this research so it may be very basic problems.
Thanks in advance.
Best
