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Mechanics of surface damage:
A new look at the old problem of wear
Ramin AghababaeiÉcole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Aarhus University, Denmark (from September)
Collaborators: J.-F. Molinary (EPFL) and D.W. Warner (Cornell)
12-14 June 2017, Kiev
Material resistance to extreme conditions for future energy systems
Sliding
Sliding
PloughingDebris particle
Subsurface cracksPlasticity
Adhesion
Contact
FractureFriction
Fatigue
Wear is Extreme
The process of surface damage and eventual material degradation
Farias et al (2007) Wear, Kotzalas and Doll (2010) Phil. Trans. R. Soc. A
Wear in a shaft bearing
10 μm100 μm
Surface damageWear debris
2
The process of surface damage and eventual material degradation
Wear in a shaft bearing
10 μm100 μm
Surface damageWear debris
2
Temperature VelocityEnvironment
ExtremeMechanics
Wear is Extreme
A major source of materials and energy loss
with serious economic, environmental and industrial impacts.
Wear importance in energy systems
3
Cause: wear in brake system
Vestas Wind Turbine Collapse Hornslet, Denmark (2008)
A major source of materials and energy loss
with serious economic, environmental and industrial impacts.
Wear importance in energy systems
3
J.F. Archard (1953) JAP
V=KN×S
HN
4
Archard’s wear law (1953)
Wear coefficient: (10-10 - 1)The probability of particle detachment
J.F. Archard (1953) JAP
V=KN×S
HN
Archard’s wear law (1953)
1950 1960 1970 1980 1990 2000 2010 2020
Year 4
Wear coefficient: (10-10 - 1)The probability of particle detachment
J.F. Archard (1953) JAP
V=KN×S
HN
Archard’s wear law (1953)
1950 1960 1970 1980 1990 2000 2010 2020
Year 4
Sliding
Sliding
PloughingDebris particle
Subsurface cracksPlasticity
Adhesion
Contact
FractureFriction
Fatigue
Wear coefficient: (10-10 - 1)The probability of particle detachment
J.F. Archard (1953) JAP
V=KN×S
HN
Archard’s wear law (1953)
How and when do wear particles arise?
Archard (1953) JAP, Archard and Hirst (1957)
4
Wear coefficient: (10-10 - 1)The probability of particle detachment
Liu et al.,(2010) ACS Nano Chung and Kim, (2014) Tri. Let.
Fracture-induced debris
Exp
eri
men
ts
200 nm
Irregular surface due to fraction
500 nmFracture of
the apex
DLC Si
Vahdat et al., (2013) ACS Nano
Gradual plastic smoothing
10 nm
Si
Bhaskaran et al., (2010) Nat. Nanotech
Wear Experiments vs. Simulations
5
Liu et al.,(2010) ACS Nano Chung and Kim, (2014) Tri. Let.
Fracture-induced debris
Wear
Frac
ture
Plasticity
Contact
Exp
eri
men
tsS
imu
lati
on
s
Too complex for continuum approach
200 nm
Irregular surface due to fraction
500 nmFracture of
the apex
DLC Si
Vahdat et al., (2013) ACS Nano
Gradual plastic smoothing
10 nm
Si
Bhaskaran et al., (2010) Nat. Nanotech
Wear Experiments vs. Simulations
5
Si
Kim and Falk (2010) PRB
Liu et al.,(2010) ACS Nano Chung and Kim, (2014) Tri. Let.Vahdat et al., (2013) ACS Nano
Fracture-induced debris Gradual plastic smoothing
10 nm
Wear
Frac
ture
Plasticity
Contact
Exp
eri
men
tsS
imu
lati
on
s
Too complex for continuum approach
Sha, J. et al., (2013) APL
Stoyanov, et al., (2014) Acta Mat.
DLCDLC
W
200 nm
Irregular surface due to fracture
500 nmFracture of
the apex
Gradual plastic smoothing
DLC SiSi
Bhaskaran et al., (2010) Nat. Nanotech
Wear Experiments vs. Simulations
5
r p=βK c
2
π σ y2
r p Plastic zone size, Rice (1972)
Fracture at the atomic scale
6
r p=βK c
2
π σ y2
LDPE
HDPE
PsPMMA
Nylons
Mg alloys
Al alloys
Cu alloys
Ni alloys
Ti alloys
W alloys
Steels
MgO
ZrO2Al2O3 SiC
Si3N4 C
RocksGlasses
BMGs
Foams
Polymers
Metals
Ceramics
100 nm
1 um
100 um
10 um
1 mm10 mm100 mm
PVC
10 nm
1 nm
1 A?Model
Materials
r p
Ashby Map
Plastic zone size, Rice (1972)
Fracture at the atomic scale
6
● Identical lattice structure
● Identical elastic properties
● Tunable inelastic properties
Ductile Soft
Brittle Hard
0 5 10 15 20 25 30 35
(r o)
Con
tact
pre
ssur
e(ε
/ro3)
Indentation Depth
F
AP6 (cleavage cracking)P1 (crack blunting)
HardnessFracture Toughness
Model inter-atomic potential
Aghababaei et al., (2016) Nat. Comm. 7
Thermostat region
Displacement
Constant pressure
Thermostat region
lx
Asperity size
Surfacespacing
Fixed region
Rigid atoms
Idealized wear simulation
8
Ductile potential
Gradual plastic smoothing
Idealized wear simulation
9
Ductile potential Brittle potential
Gradual plastic smoothing Fracture-induced debris
Idealized wear simulation
9
Ductile potential Brittle potential
Gradual plastic smoothing Fracture-induced debris
?
Idealized wear simulation
9
Gradual plastic smoothing
Fracture-induced debris
Energy balance criterion
10
En
erg
y
d
Ead∼d2
Eel∼−d3
Energy balance criterion
11
En
erg
y
Critical junction size
Idealized case (α=β=1)
in 2D
in 3D
d
Ead∼d2
Eel∼−d3
Wear transition occurs when:
Energy balance criterion
11
Δ w
σ j2/G
Junc
tion
size
, d
Characteristic length scale,
Gradual plastic smoothing
Fracture-induced debris
1.5
Model vs. Simulations
12
~ 4 Million atoms~ 10 Millions time-steps~ 2 weeks of calculation on 240 processors
Gradual plastic smoothing Fracture-induced debris
3D simulations
d < d* d > d*
13
SiNx Si Au Ag
Asp
erity
tip
size
(nm
)
Critical junction size (nm)
Fracture-induced debris
Gradual plastic smoothing
14
Model vs. Experiments
A critical length scale controls wear mechanisms at the asperity level
Surface roughness
Bulk properties
Interface properties
d*=λ
G×Δ w
σ j2
d>d * d<d *
Empirical fitting Mechanics of interfaces
Aghababaei et al., (2016) Nat. Comm. 15
New mechanistic look at wear
Summary and outlook
● A new methodology to simulate wear phenomena
● A critical length scale controls adhesive wear mechanisms at the asperity level
● Revising empirical wear laws at different scale
● Develop new physics-based wear models
● R. Aghababaei et al, (2016) Critical length scale controls adhesive wear mechanisms, Nature Communications, 7, 11816.
● R. Aghababaei et al, (2017) On the debris-level origins of adhesive wear: Did Archard get it right?, appears in PNAS
● Frérot (2017) Emergence of wear law: from single-asperity to multi-asperity, Submitted.
