Fracture Mechanics of OneDimensional Nanostructures

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Fracture Mechanics of One-Dimensional
Nanostructures
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Carbon Nanotube Source
Arc-grown Multi-wall Carbon Nanotubes (MWCNTs)
from MER Corp. AZ. were studied in this work. A
simple fractionation process was used to remove
some impurities and increase nanotube
concentration.
SEM image of powdered cathode deposit core
material with 30-40 MWCNT content from MER Corp.
SEM image of separated MWCNTs on a silicon wafer,
after fractionation.
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Testing Tool Nanomanipulator
A home-built nanomanipulator is used to perform
mechanics study inside vacuum chamber of an
scanning electron microscope (SEM).
Nanomanipulator inside vacuum chamber of FEI Nova
600 SEM (Ruoff group)
Home-built nano-manipulator
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Nanoscale Tensile Test
Atomic force microscope (AFM) cantilevers are
used as manipulation tools and force-sensing
elements.
Tensile Test Schematic
Experimental Setup
MWCNT
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In situ Clamping - EBID
Electron beam induced deposition (EBID) is the
process of using a high-intensity electron beam
to deposit structures on a scanned surface. EBID
is commonly used to make clamps in situ inside
SEM.
EBID clamp
Hydrocarbon molecules
Exposure area
A CNT in contact with an AFM tip, before and
after EBID clamping
EBID principle
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Sword-in-sheath Fracture
Multi-wall carbon nanotubes fracture in a
sword-in sheath manner during tensile test.
Cross-sectional area
? inter-layer separation of graphite, 0.34 nm
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MWCNT Diameter Measurement
Cantilever holders were designed to hold a
shortened AFM chip for nanotube diameter
measurement in TEM.
AFM cantilevers
(a) AFM chip holder model
(c) Gatan TEM straining holder (model 654)
(d) SEM and TEM images of a MWCNT fragment
attached to an AFM tip.
(b) An AFM chip in the AFM chip holder
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Stress Strain Measurements
The whole tensile testing process was recorded by
taking SEM images at each loading step.
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MWCNT Tensile Testing Result
Fracture Strength
Elastic Modulus
Average elastic modulus 910 GPa
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Multiple Loading (Tube 6)
(1)
(2)
(3)
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Nanoparticle Chain Aggregates
Stretching a chain
Tensile Testing
Contact Force Measurement

• Carbon nanoparticle chain aggregates
• Nanoparticle diameter 25-35 nm
• Chain length 2 ?m

• Breaking Force 42 ? 25 nN
• Tensile Strength 40 -100 MPa
• Elastic Modulus 200 - 600 MPa
• Particle Contact Force 8 ? 4 nN

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Nonlinearity Large Deflection Misalignment
where FxF?sin? and FyF?cos?
(Transformation Converting to elliptic integrals)
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Experimental Data Analysis

• AFM cantilevers were used as force-sensing
  elements in our nanoscale tensile testing
  experiments on templated carbon nanotubes inside
  SEM.
• Large deflection of the cantilever beam was
  encountered in the tests along with non-ideal
  alignment of the specimens.
• The linear analysis underestimated the applied
  load up to 15 .

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Error in Linear Estimation
Normalization
Linear analysis
Analytical analysis