1. The document summarizes a molecular dynamics simulation study of the tribological properties of diamond and silicon dioxide nanoparticles confined between two iron blocks. 2. The simulation found that both nanoparticles separated the rubbing surfaces and acted as ball bearings, reducing wear and friction. Diamond nanoparticles performed better than silicon dioxide at high loads and velocities due to its greater hardness. 3. At high velocities and loads, both nanoparticles failed to prevent contact and instead formed a transfer layer, leading to greater plastic deformation and friction.

1. Molecular Dynamics
Simulation On The Tribology
Properties Of Two Hard
Nanoparticles Confined By
Two Iron Blocks
By: Brij Nandan Tripathi
MET (Mechanical Engineering)
17MT001599
Chengzhi Hua, Minli Bai, Jizu Lv, Zhihai Kou, Xiaojie Li

2. Introduction
 Tribology behaviour of Diamond and
Silicon Dioxide nanoparticles
examination via Molecular Dynamics
(MD) Simulation

3. Why Nanoparticles
 Over past two decades
nanomaterials have attracted
great interest for their confirmed
:
 Friction performances
 Wear performances
 Important tribological
applications

4. Statistical data by ISI ( Institute for Scientific
Information ) database on 22 Feb 2017

5.  Studying tribological properties of all
nanoparticles is impractical and a
classification into soft and hard
particles represents more efficient
manner of performing investigation for
simulation
 Hard particles: diamond and silicond
dioxide

6. Why diamond and SiO2
 Many experiments have reported
improvement in friction properties,
due to their addition
 Lubrication mechanism of these
two additives exhibits similar
characteristics
a) They act as billions of rolling
particles between the rubbing
surfaces
b) They separate the rubbing
surfaces and prevent direct
contact

7. Model Setup
 Two similar iron blocks are used as
friction pair
15Å
300K

8. Molecular Dynamics
Simulation
 It is a computer simulation method for
studying the physical movements of
atoms and molecules.
 The atoms and molecules are allowed
to interact for a fixed period of time,
giving a view of dynamic evolution of
the system.
 Trajectories are determined using
Newton’s equation of motion
 Forces are determined by EAM
 LAMMPS MD is used

10. EAM (Embedded Atomic
Method)
 It is an approximation describing the
energy between atoms, an interatomic
potential
 C-C interaction: Tersoff potential
method
 SiO2 : BKS potential model
 Fe-C, Fe-Si, Fe-O : Lennard Jones
model

11. Simulation Procedure
 The simulation were performed using
the classical open source MD
LAMMPS code.

12. Results and Discussion
• Under low load (500 Mpa)
• Under High load (1000 MPa)
Friction
state with
low velocity
(10 m/s)
• Under low load (500 Mpa)
• Under High load (1000 MPa)
Friction
state with
high velocity
(500 m/s)

13. 1.1 Low Velocity + Low Load

14. Inference
1. Both nanoparticles separate the rubbing faces
and hence prevent direct contact by acting as ball
bearings.
2. Hard nanoparticles reduce both the wear and
smooth the worn surfaces more than pure base
oil when used as additives.
3. Direct contact between the friction surfaces and
plastic deformation results into adhesive and
contact fatigue.

15. 4) Figure shows that nanoparticles (np) rotated
clockwise for most of the sliding process.
This is an evidence of mechanism of anti-wear and
friction reduction by np which converted sliding
friction to rolling plus sliding.
A positive
value
suggests the
CW rotation
V=10 m/s
P= 500 MPa

16. 5) Under boundary lubricating conditions the two hard
nanoparticles have a polishing effect on the friction surfaces.
Morphology
changes of friction
surface of lower
block
Surface roughness
asperities are polished
by np.
Diamond is harder
than SiO2

17. 6) Hard np added lubricants were
effective in reducing the temperature of
friction pair due to less shear than that
in direct contact
Temp profile along
Y dimension at a
sliding time of
400ps ,
V=10 m/s
P= 500 MPa

18. 1.2 Low Velocity + High Load
Under high load of 1000 MPa , owing to hardness of diamond its
shape didn’t change and rolling occurred where as in SiO2 it distorted
Even the digging was less in later case

19. Most of the SiO2 points are negative.
Diamond particles constitute rolling + Sliding
SiO2 only sliding
V = 10m/s
P= 1000
MPa

20. Friction Force
Friction force
without np= 5GPa
V=10 m/s
Friction force for
diamond is lower
in both case due
to smaller
interaction
strength Fe-C as
shown earlier in
slide

21. 2.1 High velocity + Low Load
SiO2
V=500 m/s
P=500 MPa

22.  SiO2 prevented direct contact initially
but later it developed transfer layer
 Diamond remains unaffected and is
more effective than SiO2 in improving
the high velocity low load tribological
properties.

23. Temp distribution at 800 ps
Middle region
(transfer layer)

24. 2.2 High velocity + High load
 Both of the np were trapped into
transfer layer only after a short sliding
time.
V= 500 m/s
P= 1000 MPa

25.  Formation of early transfer layer
results into high plastic deformation,
frictional heating, amorphization, non-
equilibrium material flow

26. Conclusion
 Tribological behaviour of two np was
quite similar under low load and low
sliding velocity
: Improved temp distribution and friction forces
: np acted as ball bearing
: hard np had polishing effect
 At high load diamond properties were
least affected

27.  At high velocity low load only diamond
prevented direct contact
 At high velocity and load both failed
and formed transfer layer.

28. REFRENCE
 [1] TangZ,LiS.Areviewofrecentdevelopmentsoffrictionmodifiers forliquid lubricants
(2007–present). CurrOpinSolidStateMater2014;18:119–39.
 [2] Choi Y,LeeC,HwangY,ParkM,LeeJ,ChoiC,etal.Tribologicalbehaviorof copper
nanoparticlesasadditivesinoil.CurrApplPhys2009;9:124–7.
 [3] Guo D,XieG,LuoJ.Mechanicalpropertiesofnanoparticles:basicsand applications.
JPhysD:ApplPhys2014;47:013001–25.
 [4] Qiu S,ZhouZ,DongJ,ChenG.PreparationofNinanoparticlesandevaluation of
theirtribologicalperformanceaspotentialadditivesinoils.ASMEJTribol
2001;123:441–3.
 [5] KolodziejczykL,Martínez-MartínezD,RojasTC,FernándezA,Sánchez-López JC.
Surface-modified Pdnanoparticlesasasuperioradditiveforlubrication. J
NanopartRes2006;9:639–45.
 [6] Chou R,BattezAH,CabelloJJ,ViescaJL,OsorioA,SagastumeA.Tribological
behaviorofpolyalphaolefin withtheadditionofnickelnanoparticles.Tribol Int
2010;43:2327–32.
 [7] Pan Q,ZhangX.Synthesisandtribologicalbehaviorofoil-solubleCu nanoparticles
asadditiveinSF15W/40lubricatingoil.RareMetMaterEng 2010;39:1711–4.
 [8] Sánchez LópezJC,AbadMD,KolodziejczykL,GuerreroE,FernándezA. Surface-
modified PdandAunanoparticlesforanti-wearapplications.Tribol Int 2011;44:720–6.