jonathon schuh: university of illinois at urbana-champaign · jonathon schuh: university of...
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Jonathon Schuh: University of Illinois at Urbana-Champaign
Yong Hoon Lee: University of Illinois at Urbana-Champaign
James Allison: University of Illinois at Urbana-Champaign
Randy Ewoldt: University of Illinois at Urbana-Champaign
Decrease friction in lubricated sliding contact
Decrease shear stress
Increase normal force
Approach: surface textures and Non-Newtonian fluids
Determine optimal design of surface textures and
lubricant
22015 Fluid Power Innovation & Research Conference
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[1] Pipkin. Lectures on Viscoelastic Theory. 1972.
No
n-lin
ear:
Am
plit
ud
edependent
pro
pert
ies
Viscoelastic: Time-dependent properties
Weissenberg
Deborah
De = l / tchar
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Controlled by geometry Geometry+Fluid
Pipkin space [1]
[1] Pipkin. Lectures on Viscoelastic Theory. 1972.
De = l / tchar
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Newtonian
Fluid
Generalized
Newtonian
Fluid
Linear Viscoelastic
Ordered
Fluid
Expansion
Non-linear models
Experimental precision and challenges
Experimental results surface textures and
Newtonian fluids
Origin of the Pipkin space
Experimental results surface textures and Non-
Newtonian fluids
Exploring more of Pipkin space
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Non-
dimensional
ratios govern
behavior [2]
[2] Johnston, King, and Ewoldt. Tribology International. 2015.
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Gap controlled rotational rheometer
DHR-3 by TA instruments
Precision aligned for tribo-rheometry [2]
Parallel disks D=40 mm
Top: flat (RRMS=3.33 μm), rotating, stainless
Bottom: textured, 1018 steel, attached with
Crystalbond
Key Challenges:
• Gap error
• Non-texture
normal forces[2] Johnston, King, and Ewoldt. Tribology International. 2015.
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h = ha + e
ha =ht
1+e
ha
1
ha
=1
ht
+e
ht
1
ha
Risk of misinterpreting shear stress
reduction that is not due to the
textures [3,4]
Gap zeroing calibration based on
contact force
Squeeze flow of air produces force
Calibrated ε=19.0±0.69 μm using
Newtonian oil with η=0.14 Pa s
[3] Connelly and Greener. Journal of Rheology. 1985.
[4] Pipe, Majmudar, and McKinley. Tribology Letters. 2008.
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F
N
Risk of misinterpreting normal
forces that are not due to the
surface textures [5-7]
a) Inertia:
b) Surface Tension:
c) Non-Parallelism:
[5] Andablo-Reyes, Hidalgo-Álvarez, de Vicente. Journal of Non-Newtonian Fluid Mechanics. 2010.
[6] Andablo-Reyes, de Vicente, and Hidalgo-Álvarez. Journal of Rheology. 2011.
[7] Macosko, C.W. Rheology: Principles, Measurements, and Applications. 1994
Fnp = WhR4
h20.256
a
h
æ
èçö
ø÷
FN = C
Finertia = -3 / 40prR4W2
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ha =2 ha + e( )
pR4
M
W
Real shear stress
reduction through
use of textures
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Asymmetric textures produce
forces above experimental limit
through viscous effects.
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m* ºFt
FN
=M / R
FN
Asymmetric textures
decrease friction.
Optimal β.
Surface textures decrease shear stress
Symmetry must be broken in order to produce
normal forces above experimental limit
Sign of force depends on direction of motion
Normal forces are produced by viscous effects
up to Reh=1.21
Optimal angle β exists for decreasing friction
with asymmetric surface textures
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Non-Newtonian?
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Polyisobutylene (PIB) has been used as an additive for enhancing mechanical
properties [8] and modifying viscosity [9]decrease temperature dependence of viscosity
Dissolves in mineral oil
0.5wt% PIB (MW~1,000,000) in mineral oil (highly refined, S6, η=9.62 mPa s)
c/c*=0.0774 (dilute solution)
[8] Fuks, Bakaleinikov, and Samgina. Chemistry and Technology of Fuels and Oils. 1974.
[9] Totten. Fuels and Lubricants Handbook: Technology, Properties, Performance, and Testing. 2003
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Surface textures
reduce viscosity
beyond shear thinning
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Asymmetric surface
textures produce normal
forces above viscoelastic
response
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m* ºFT
FN
=M / R
FN
Asymmetric textures
decrease friction.
Optimal β
Surface textures decrease shear stress beyond
shear thinning
Symmetry must be broken to produce normal
forces above viscoelastic response
Normal forces are always positive
Optimal angle β exists for decreasing friction
with asymmetric surface textures
Friction coefficient is smaller with Non-Newtonian
fluids than Newtonian
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Examine relaxation time scale effects
Change concentration of polymer in solution
Explore more of Pipkin space
Mathematically model surface textures
and Non-Newtonian fluids
2nd order fluid
3D flow theorem of Giesekus
with Reynolds equation solver
Determine optimal design of textures and fluid
Direct optimization with Reynolds equation
Adaptive surrogate modeling techniques [10]
Experimentally test optimal texture and fluid
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[10] Rao et. al. iDETC 2015.
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Ewoldt Research Group Funding
Specific PeopleMichael Johnston (MS UIUC, 2014)
Nathan Bristow (BS UIUC, 2014)
Nikita Dutta (REU summer 2014)
Feargus MacFhionnlaoich (REU summer 2015)
Jonathon Schuh ([email protected])
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hD
R
Rc
Rtj
W
h,r
FN ,ha( ) = f h, R, Rc, Rt , D,j,h,r,W( )
By Buckingham Pi Theorem:
FN
pR2 hWR / h( ),ha
h
æ
èç
ö
ø÷= F j,
h
R,
h
Rc
,h
Rt
,h
D,rWh2
h
æ
èçö
ø÷
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h = 1.4 Pa s
r=846.4 kg/m3
h = 1.4 Pa s
r=846.4 kg/m3
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h = 1.4 Pa s
r=846.4 kg/m3
h = 1.4 Pa s
r=846.4 kg/m3
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m* ºFT
FN
=M / R
FN
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M =Ntex tqzdr rdq( )( )Ri
Ro
ò-j /2
j /2
ò r
ha =2 ha + e( )
p R4
M
W
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