Hi,
I am trying to apply a force on a clamped-clamped beam using a virtual cylindrical indenter using LAMMPS.
My units are metals and the force constant of indenter is K = 10 ev/A^3. My beam is made of Cu and modeled with EAM potential and simulated under NVT ensemble.
I am scaling the forces on the indenter by a factor of 1.60288 to convert forces from ev/A to nN. Is this the correct way to get the forces in nN ?
I need these forces to get the F-d curve. However, I have noticed that my forces (in F-d curve) are 1.5 times higher than those reported in literature.
Any suggestions or help in this regard are highly appreciated...
Best
Hi Mohd,
If you change the indenter geometry or indenter size, it is expected that you observe such reasonable change in your (F-d curve). Did you change any of Them?
Best
Hi Iyad,
I modeled the indenter size and the beam simulation according to the literature problem. And I was expecting similar results through my simulation. However, my forces are 1.5- 1.6 times higher than those reported in literature. My deformation behavior matches well with the literature one. Here I'm scaling my forces obtained in ev/A (in Metal units) by a factor 1.60288 to convert to nN (in SI units).
I will try to change the indenter size as you said and let you know my results.
Any suggestions on why my forces are higher ??
Thanks
Best,
In addition to what Iyad said, I would like to point out that the indentation rate may be playing a significant role to explain the difference you are finding. If you are comparing your LAMMPS results to quasi-static experimental results, then the indentation rate is probably the cause of the differences you are finding.
LAMMPS typically performs indentation in a displacement-controlled mode with penetration rates that are orders of magnitude higher than the typical experimental ones.
Which penetration rate are you using? You can copy the fix indent line of your script here and we can help you.
Best,
Carlos
Thanks Carlos:
I am trying to plot force-displacement curve (with forces on the indenter and the displacement of center of indenter). I am using a virtual cylindrical indenter. The simulation of nano wire is done in NVT ensemble with SSS Bcs at 0.01 K temperature. The penetration rate is 0.01 A/ps. Following are the commands of LAMMPS:
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variable y0 equal 25.305
variable x equal "xlo + 0.5*(xhi-xlo)"
variable y equal "v_y0 - step*dt*0.01"
fix 33 all indent 10 cylinder z v_x v_y 10.845 units box
variable fyy equal "f_33[2]*1.602889105" ( To convert forces in ev/A to nN (nano Newton) )
fix 34 all print 1000 "${tstep} ${disp} ${fyy} " file bending.txt screen no ( I am plotting disp Vs fyy obtained using this fix)
run 100000
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I have one difficulty, my forces are around 1.6 times higher than those reported in literature.
I have attached my F-d curve graph. Green curve represents the scaled values of forces in nN and Red curve represents forces in ev/A units. My Red curve matches with literature, but the literature results (as said) are reported in nN.
Can anyone comments or suggest were I might be going wrong or I might be correct ??
Best,
Also,
The simulation and all the values of the parameters used to generate the F-d curve are taken from the literature (which is used to compare the F-d curve).
Thanks
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