summer school: granular materials – from simulations to ...€¦ · friction in granular material...
TRANSCRIPT
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Summer School: Granular Materials –from Simulations to Astrophysical Applications
Hosted by CSCAMM and the University of Maryland Burgers Program in Fluid Dynamics
Organizers:Derek Richardson, AstronomyWolfgang Losert, PhysicsEitan Tadmore, CSCAMM
Support:Burgers Program for Fluid DynamicsCenter for Theory and ComputationNational Science FoundationEuropean Space Agency[NASA support requested]
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Labtours Friday June 17th
2pm Neutral Buoyancy Facility (test of weightless robotics)
2.30pm Dynamo Experiment (self generation of magnetic fields)
3pm Three dimensional imaging of granular flows
3.30pm Fluid Dynamics Lab (tentative)
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Granular materials
SandCoffee
Gravel Rocks
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Astrophysical granular matter
MARS ASTEROID
Mars rock avalanche. The landslide fell 5 miles and ran out 65 miles.
McEwan, 1989
Regolith migration on Eros
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Static Granular Materials
http://www.photos-voyages.com/selection/sand-dune.html
Nature, 387 (1997)
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Flow of Granular MatterAvalanches
http://video.google.com/videoplay?docid=4401583576558606021#
http://www.youtube.com/watch?v=6qVwIuznFW0&feature=relatedhttp://www.youtube.com/watch?v=UOFMIjDmw6A&feature=fvst
http://www.youtube.com/watch?v=2IItP7dVoYc&playnext=1&list=PL7E11AEC3A4A077BE&index=3
http://www.youtube.com/watch?v=5Xw0NPSviAk
Shear Flows
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Granular MaterialsMade up of many solid particles >> 1 micron.
1210 mgd
Tk bLifting 1 mm bead by one bead diameter:
Motion requires energy input >> thermal energy Interaction between grains (Friction and inelastic collisions) dissipates kinetic energy.
System not in thermal equilibrium
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Static granular matter: jammed state
From
Cor
ey O
’Her
n
Significant progress in past 10 years to define and characterize an idealized jamming transition for hard spheres without friction.
(Liu, Makse, Nagel, O’Hern, Radjai, Snoijer, Saarloos, etc)
Blue line: Contact force brightness ~ Magnitude
Without energy input, in confinement, granular matter is jammed
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Challenges in modeling jamming
Since kT is too small to move grains noticeably, the system does not equilibrate
Physical principles that rely on a thermal equilibrium reference state (e.g. minimization of free energy, maximization of entropy) do not apply.
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Experiments on Aging and Strengthening
Plate weight: 10-50 gGranular material: Glass beads 70-100 µm DIA
Layer depth: 3 mmSpring constant: 189.5 N/m
Vertical sensor
Sliding plate
Horizontal displacement sensorSpring Target
granular layer
Frame
W. Losert et al Phys. Rev. E. 61, 4060 (2000)
Displacement sensors: h = 0.1 µmForce measurement: F / F = 0.01 %
High Sensitivity Measurements
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Friction between two solid objects
Static friction coefficient:
Dynamic friction coefficient:
/S S NF F
/D D NF F
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Dynamics: Stick-slip motion
500
400
300
200
100
0
d (µ
m)
20151050
t (s)
L0VA
B
C
0 X
A
B
C
L + d0 M
L + d0 m
sd
Dynamics: Stick-Slip Motion
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Friction in granular material kept under shear stress for 10 hours
Stick-Slip motion: m=26.6g, k=189 N/m 11/29/98 experiment
Strengthening of granular layer under stress
500
450
400
350
300
250
d
2520151050
time (s)
s of first slip larger than s of other slips
Shear Stressfor 10 hours
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Friction between two solid objects
Static friction coefficient: Dynamic friction coefficient:
*The above are (very good!) approximations.
Static friction increases with stick time
Dynamic friction decreases with sliding speed
/S S NF F
/D D NF F
0 0ln /S S is O(10-2)
0 0( ) ln /D DV V V
Hahner and Spencer, Phys. Today 51, 23 (1998)Krim, MRS Bull. 23, 20 (1998)
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Waiting time strengthening(Shear stress during waiting time)
1.20
1.15
1.10
1.05
1.00
F max/F
norm
10 2 10 3 10 4
waiting time (s)
Friction increases roughly logarithmically with waiting time(for t > 500 s)
Waiting Time Strengthening
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Geophysical friction laws for granular materials: Dietrich/Ruina
00
0
( ) ln lnD DC
VVVV D
Time dependent StrengtheningJ.H. Dieterich, J. Geophys. Res. 84, 2161 (1979)
(1) lnC C
d V Vdt D D
(2) 1C
d Vdt D
Strain dependent strengtheningA. Ruina, J. Geophys. Res. 88, 10359 (1983):
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Waiting without shear stress for 16 hours
450
400
350
300
sprin
g di
spla
cem
ent (
µm)
4035302520
time (s)
•No strengthening without applied stress•No strengthening, if direction of shear stress during waiting and during motion are opposite (not shown)
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Aging under thermal cycling
Glass beads and plastic container
OVEN
From: Peter Schiffer, Penn State
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System: glass container filled with plastic beads (or vice versa)
Heating expands plastic more than glass (Schiffer group, Nature, 2006)
Slow compaction of granular matter (without giving individual grains significant kinetic energy)
Compaction through thermal cycling
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Simple thermal cycling results
0 20 40 60 800.0
0.5
1.0
1.5
C
hang
e in
Pac
king
Fra
ctio
n (%
)
Change in temperature (C)
0.5mm 0.9mm 2mm
From: Peter Schiffer, Penn State
Clear and systematic change in packing fraction!
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Thermal packing dependence on repeated cycles
0 5 10 15 20 25 30 35 40
59
60
61
62
P
acki
ng F
ract
ion
(%)
Cycle number
T = 107 oC
T = 41 oC
Peter Schiffer, Penn State
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Effect of repeated cycles can be understood through simple two-component model
0 5 10 15 20 25 30 35 40
59
60
61
62
Pac
king
Fra
ctio
n (%
)
Cycle number
T = 107 oC
T = 41 oC
1 2max 1 2
n n
PF PF A e A eBarker and MehtaPeter Schiffer, Penn State
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Granular Flow
Inertia Number I
d: particle diameter: particle density
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Effects of mesoscale structure
Observations- Notable rolling/sliding during steady shear- Significantly different motion during shear reversal
SchematicContact network
steady shear
SchematicContact network shear reversal
Masahiro Toiya
Toiya et al. PRL 2004
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Small initial torque during shear reversal
shear
reversal
Derek Updegraaf with E. Wandersman, J. Dijksman, M. van Hecke
DEMO
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Excited Granular MatterAn example of a granular gasEnergy input into a granular gas
Vertical Shaker(20-120 Hz)
32 cm
CCD Camera (up to 10,000 frames/s)
granular material: spherical beads, 4 mm Dia
Experimental Setup
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Velocity Distribution
P ( v ) e v 1 . 5
Granular gases have non-Gaussian velocity distribution
Acceleration= 5g ; frequency = 100Hz ; coverage = 0.42
Velocity distribution best fit byin agreement with recent theoretical predictions.
Gaussian
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Energy of particle mixtures
No Equipartition of energy
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Bistability
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Granular Segregation
Flowing granular materials segregate according to particle properties (size, density, shape, and more).
(Image by H. Makse)
(Image by H. Makse)
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Axial BandsSee Newey et al. Europhysics Letters 2004
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Particle Speed on Surface
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]
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Anisotropic yield surface
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Aging/Strengthening in Astrophysics?
Thermal Cycling on the MoonDaytime: +120oCNight: -150oC[lunarpedia.org]
The pole is a regions not exposed to thermal cycling. Will it be equally compacted? DEMO
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Long Runout Rock AvalanchesThe Blackhawk event
in California
Field Data: Rock avalanche probabilities are correlated with the direction of prior shear (Friedmann, Kwon & Losert, J. Geophys. Res 2003)
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Forces in Astrophysical Applications
Holding Granular Matter together:
GravityVan der WaalsCharges
Rearranging Granular Matter:
Tidal forcesSeismic forcesCentrifugal forces
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Outline
Intro: What are granular materials?Granular Materials JamGranular Materials Age and StrengthenGranular FlowGranular GasSegregationAstrophysical Applications
Wolfgang Losert [email protected]