2012 Morton Antler Lecture – Sept. 25, 2012
Additional resources
58TH IEEE HOLM CONFERENCE ON ELECTRICAL CONTACTS
Website:
http://web.mit.edu/mbuehler/www/index.html
http://cee.mit.edu/buehler
Computational materials
science — From atoms to
structures
Publications:
http://web.mit.edu/mbuehler/www/research/publications.htm
Markus J. Buehler
MIT Profiles:
http://web.mit.edu/newsoffice/2012/profile-buehler-0403.html
http://web.mit.edu/newsoffice/2012/spider-web-strength-0202.html
http://web.mit.edu/newsoffice/2010/biomaterials-1022.html
http://ilp.mit.edu/newsstory.jsp?id=18292 (MIT Industrial Liaison Program)
http://ilp.mit.edu/videodetail.jsp?id=580 (series of five videos)
http://www.asme.org/kb/news---articles/media/2012/11/podcast-thenanomechanics-of-spider-webs (ASME podcast)
Laboratory for Atomistic and Molecular Mechanics
Department of Civil and Environmental Engineering
Massachusetts Institute of Technology
E-mail:
mbuehler@MIT.EDU
URL:
http://web.mit.edu/mbuehler/www/
Funding: DOD-ONR, AFOSR, ARO, ARO-MURI, PECASE, NSF, NIH
1
Advanced manufacturing: overview
Enabling the next industrial revolution
Conventional: “Top-down approach”
- Requires many different raw materials
- Limited structural control & flexibility
Material
Design
Van Vliet, Yip, Buehler, Ulm et al., MRS Bulletin, 2012
Feedback to improve material design (requirements, performance in use, etc.)
Material design is a critical component in Advanced Manufacturing
Source: O. De Weck, MIT
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New: “Bottom-up approach”
- Few raw materials
- Enhanced flexibility through structure
- Integration of material synthesis
with manufacturing of product
(system perspective)
- Bioinspired
A new paradigm of material design
“bottom-up approach” – example: spider silk, self-assembled solid that’s
stronger than steel
spinning
Steel: strength ~1 GPa: strong bonds
Spider silk: strength: ~1-2 GPa & 60% strain @ failure extreme toughness
weak bonds; made @ room temperature via self-assembly
Key science question: how weakness is turned to strength
spider
web
Copyright Dennis Kunel
Microscopy
DNA
protein
4 ‘letters’
ACGT
20 building blocks
(amino acids)
material/
tissue
(spider) silk spinning
liquid to solid
strength of steel
M. Buehler et al., Nano Letters, 2011; Nature, 2012; Kaplan, Buehler, Wong, et al., 2012
Source: M. Buehler & NSF
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Concept: universality-diversity paradigm (UDP)
Diverse material properties, same building block
M. Buehler, MRS Bulletin, 2013
silk
proteins
underwater adhesive
(mussels)
H. Waite/USCB
actin, intermediate
filaments (cell)
Multifunctionality
(diversity) created
by changing
structural
arrangements of few
(universal)
constituents
silk fibers (spider web)
Architecture/structural engineering
collagen
(tendon)
No need to invent
new building blocks
http://www.olympusmicro.com
ultrascale structural engineering
Materials composed from a library of only 20 amino acids (proteins)
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Powerful paradigm
for innovation
- Fewer resources
- More flexibility
- Wider design
space
Buehler, Nature Nanotechnology, 2010
Ackbarow, Buehler et al., Materials Today, 2007
Thin copper films deposited on silicon wavers
Material failure – across the scales
metal film
on substrate
(e.g. silicon waver)
microcrack
Electrical contacts: failure due to temperature, corosion, cyclic loading
Balk, Dehm, Arzt, 2003
Earthquake: failure of the earth’s crust
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thermal expansion
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Buehler and Xu, Nature, 2010; M. Buehler and S. Keten, Rev. Mod. Phys. 2010
Integration of experiment and computation
Connecting the virtual to
the physical world
Exploiting a hierarchical bio-inspired
approach enables us to manufacture
‘materials by design’
From chemical structure to
engineering properties
Three-pronged research
approach: “materiomics”
1. Simulation and
experiment of different
systems
2. Generalize insight
through comparative
study
3. Analytical models,
mathematical tools
Combine first principles computation and
experimental approaches
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Funding: NSF CAREER 0642545, AFOSR, ONR
Quantum
mechanics
Buehler et al., Nature Materials, 2009;. Z. Qin et al., 2010, 2012
Linking chemistry, structure and mechanics
Molecular simulation – movie
Molecular dynamics:
Fundamental model of materials
“bottom-up”
electrostatic
bonds
covalent bonds
weak bonds
Large-scale simulation of complex biomolecules now possible
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M. Buehler, Atomistic Modeling of Materials Failure, Springer, 2008
Enables a multi-scale approach


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M. Buehler, MRS Bulletin, 2013
Emergence of opportunity
The basis of multi-scale methodology is the parameterization of
“coarse-grain” models through analysis of more complex and
sophisticated “fine-grain” models.
Already a common practice to “train” atomistic force-fields for
molecular dynamics simulations via results from quantum mechanics
(e.g. DFT), extended across all scales
S. Cranford, M. Buehler, Biomateriomics, Springer, 2012
Source: TIME magazine
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cell membrane rupture at micrometer scale
Structure prediction and functional properties
Genetics
…GGLGGQGAGAA
AAAAGGAGQG …
Amino acid
sequence
Validation
(experimental
results)
Replica
Exchange
Simulations
Ensemble
of final
structures
Folding
—structure
S. Cranford, M. Buehler,
Biomateriomics,
Springer, 2012

Mechanical characterization
(multiscale)
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Mechanics
(functionality)

What happens when we stretch fibers
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Smaller is stronger
~2-3 nm (nanocrystal)
detailed study:
hydrophobic,
form crystals
(don’t mix w/
water) = A
hydrophilic
(mix w/ water) = B
Smaller crystals (left) are stronger: Larger crystals (right) are fragile, crack easily
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Keten, Buehler et al., Nature Materials, 2010
Mechanics of web from molecular principles
What happens when we stretch fibers
Silk structure identified
using statistical methods
Constitutive behavior
(derived from molecular
principles, w/ mechanisms:
Unfolding, slip, failure)
Nanomechanics
characterization
Macroscale system (web)
Silk protein
sequence
Nature
Materials, 2010;
Nature, 2012
Simple model: interplay of two “particles” allows us to describe
material properties of silk from “first principles”
31-helices
(semi amorphous)
beta-sheet
nanocrystal
Web failure (simulation,
model and in situ
experiment)
Link macroscale
web failure back
to molecular
mechanisms
stiffening:
robust system
Key result: Explains source of great strength of silk (comparable to steel)
despite material being constructed from weak H-bonds (e.g. water)
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Nova et al., Nano Letters, 2010
Case study:
protein
music
Creating enhanced functionality out of simple
building blocks
A = hydrophobic domain
BA3
B = hydrophilic domain
AB3
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M. Buehler, Nano Today, 2010
Funding: NIH/U01 EB014976
Kaplan, Wong, Buehler et al., 2012
How sequence controls structure & mechanics
Manufacturing synthetic silk fibers
Forms fibers from microfluidic
spinning device
BA3
Design sequence
AB3 vs. BA3
Novel
biomaterial
Gronau, Kaplan, Wong, Buehler et al., 2012
AB3
20 m
Kanahan, Kaplan, Wong, Buehler et al., 2012
Microfluidic model of the spider’s spinning duct
Joyce Wong, S.B. ‘88, Ph.D. ’94, Boston Univ.
David Kaplan, Tufts Univ.
Clogging and no fiber formation
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Gronau, Kaplan, Wong, Buehler et al., 2012
Microscopic insight from molecular simulation
Shifting gears: metals, ceramics, etc.
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Fracture is a multi-scale phenomenon
Fracture of silicon: problem statement
M.J. Buehler,
Atomistic
Modeling of
Materials Failure,
Springer, New
York, 2008
Crack dynamics in silicon
Fracture initiation and instabilities: movie
Buehler et al., Phys. Rev. Lett., 2007
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Atomistic fracture mechanism: 5-7 defects
Crack speed: experiment vs. simulation
Load: normalized by critical energy release rate to initiate fracture
Buehler et al., Phys. Rev. Lett., 2007
M.J. Buehler et al., Phys. Rev. Lett., 2007
Brittle-to-ductile transition
Simple “continuum” model
Explanation: Increased barrier due to 5-7 defect that forms under stress
and “locks” the crack (increased surface energy)
 0
v0
G    G0
cR
1  G
G  G0,MD
G0,MD   57
G  G0,MD
G0   0
 57   0
M.J. Buehler et al., Phys. Rev. Lett., 2007
36
M.J. Buehler et al., Phys. Rev. Lett., 2010
Brittle-to-ductile transition
Atomistic modeling studies of
dislocation plasticity in thin films
Experimental work by G. Dehm, J. Balk, E. Arzt (MPI),
C.V. Thompson (MIT), B. Nix (Stanford), et al.
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M.J. Buehler et al., Phys. Rev. Lett., 2010
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Thin films: geometry
Dislocations in TEM
metal film
on substrate
(e.g. silicon waver)
Grain
boundaries
constant yield
stress
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Balk, Dehm, Arzt, 2003
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Balk, Dehm, Arzt, 2003
Dislocations in TEM
Atomistic details of dislocation nucleation
[111]
top view
• Dislocation nucleation from a traction-free
grain boundary in an ultra thin copper film
• Atomistic results depict mechanism of
nucleation of partial dislocation
stretch 10x
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Thin copper with Al-oxide layer on surface
“Threading
dislocations”
Dislocations
inclined with
respect to
surface plane;
appear as
straight lines on
surface
Shear stresses & dislocation nucleation
Passivated


Nonpassivated
T

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Balk, Dehm, Arzt, 2003
44
T
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Buehler, Gao, et al. JMPS, 2004
[112]

Buehler, Gao, et al. JMPS, 2004
Balk, Dehm, Arzt, 2003
(time
sequence)
z
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Diffusion leads to insertion of lattice planes in grain
boundary, yields stress field of a crack
48
Buehler, Gao, et al. JMPS, 2004
Key mechanism: From grain boundary to crack
Buehler, Gao, et al. JMPS, 2004
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Plot: displacement of atoms in the z-direction (red=large displacement)46
Buehler, Gao, et al. JMPS, 2004
How is it possible that a thin film with
no cracks behaves like one with
cracks?
Ritchie, Buehler et al., Annual Rev. Mat. Sci., 2011
Sen, Buehler, Scientific Reports, 2011
Hierarchical composites
Bio-inspired hierarchical
composites
J-integral analysis
Modeling/simulation, design and
manufacturing
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Fracture mechanism
bone-like
*90% of fracture strength
Summary: Universality-diversity paradigm
Paradigm uncovered:
• Create multifunctionality
(diversity) by changing structural
arrangements of few (universal)
constituents: geometry controlled
by confinement/scaling laws
• No reliance on invention of new
building blocks
• Departure from widely used
engineering approach: Turn
weakness to strength
Dimas, Buehler, Bioinspiration & Biomimetics, 2012.
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Engineering impact: Bioinspired materials; i.e. define
properties, geometry etc. of materials other than
protein, e.g. metal-polymers by applying scaling laws:
Use silica (sand), clay, and soy beans transformed to
create high tech materials
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M. Buehler, Nature Nanotechnology, 2010; Nano Today, 2010