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Computational%20Nanotechnology

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Pre/Post processing for single/multi-walled CNTs with selected diameters, ... Determined mechanical properties of CNTs for various chiralities, with and ... – PowerPoint PPT presentation

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Title: Computational%20Nanotechnology


1
Computational Nanotechnology
A preliminary proposal
N. Chandra Department of Mechanical
Engineering Florida AM and Florida State
University
Colloborators
  • Proposed Areas
  • Nanoscale composites
  • Nanoscale interface Mechanics
  • Defect Engineering in CNTs
  • Hydrogen Storage
  • Parallel computing, Time extension algorithms

Professor Ashok Srinivasan, Dept. of Computer
Science, FSU Professor Leon van Dommelen, Dept.
of Mechanical engineering, FAMU-FSU
2
Application of Carbon Nanotubes (CNTs) to
Nanocomposites and Hydrogen Storage
  • Significant Results
  • Developed atomic level stress measures (3
    types), and strain measures (new) and validated
    the mechanical response of CNTs
  • Determined mechanical properties of CNTs for
    various chiralities, with and without defects
    (Stone-Wales)
  • Evaluated the effect of a single and multiple
    interacting and non-interacting defects on the
    mechanical properties using stress/strain
    measures
  • Role of functionalization (attachment of radical,
    e.g. vinyl)on the in-situ mechanical properties
    of CNTs and their effect on evolution of defects
  • Identification of the optimal set of parameters
    that maximizes the hydrogen storage? Parameters
    include chirality and diameter of
    single/multiwalled tubes, temperature, pressure
    and geometrical defects
  • Parallelization of codes in IBM-p690-512
    processors

3
Research Areas
  • NanoScale Interfaces
  • Nano-Composites
  • Hydrogen Storage
  • Parallel Algorithms

4
Nano-Scale Interfaces
  • Issues
  • How does the thermo-mechanical load transfer take
    place at nano-scale?
  • Can the macro theories (chemical bonding,
    mechanical serrations Kelly-Tyson) be applicable
    and if not how they should be modified?
  • What methods enhance strength, stiffness and
    fracture behavior of nanocomposites ?
  • Will any addition of short radicals to smooth
    surface enhance bonding? Will the nature of
    bonding be chemical, mechanical or electronic ?
  • How will the application of mechanical loading
    (tension, compression, shear or combination
    thereof) and thermal loading affect the load
    transfer?
  • What is the equivalence of thermal residual
    stresses at the nano-scale interfaces?
  • Functionalized CNT have higher stiffness.
  • High temperature deformation- defects are formed
    at lower strains (6 strain) .
  • Fracture occurs at lower strains in
    functionalized tubes.

Functionalization a possible mechanism to
increase interface strength ? Different numbers
and groups of hydrocarbons were attached and
tested in tension
5
Defect Engineering in CNTs
Background Defects (missing atoms, rotated
bonds, diameter/chiralty transition) arise during
processing and loading. They are either
deleterious or beneficial
Results
  • Issues
  • Effects of defects on elastic and also inelastic
    properties (strength, stiffness and elastic to
    plastic transition and failure)
  • Role of chirality, diameters and location of
    single and multiple interacting/non-interacting
    defects and their effect on properties
  • Aligned defects in single/multi-walled CNTs and
    their effect on mechanical properties and
    hydrogen storage
  • Interaction of defects and functionalization in
    load transfer
  • Origin of defects as a function of combined
    thermal and mechanical load application

6
Hydrogen Storage
Back ground Interest in hydrogen as a fuel has
grown dramatically since 1990. However, hydrogen
storage technologies must be significantly
advanced if a hydrogen based energy system is to
be established. Nanotubes have been long heralded
as potentially useful for hydrogen storage to
meet energy densities at values of 6.5wt set by
DOE.
  • Issues
  • Mechanism of hydrogen adsorption is it a purely
    physical or chemical interaction or is it
    somewhere in between.
  • Optimize a given carbon adsorbent system
    simulation of different parameters such as
    temperature, pressure, diameter and chirality.
  • Simulation of adsorption considering nanotube
    with defects , disorder, diameter polydispersity,
    and functionlization.
  • Simulation of adsorption of Li-doped nanotube
  • Simulation of high energy hydrogen atoms
    implanting into nanoutbe.
  • In theory, close ends nanotube can have a
    volumetric densities of 142kg/m3 storage since
    nanotube has a high tensile strength.

7
Hydrogen Storage-MD Simulation
Preliminary Results
Results After 100ps simulation, about 3.18 wt
hydrogen absorbed within the intratube spacing.
Initial condition Carbon nanotube (10,10)
periods4 Pressure, 15atm. Temperature 77K
hydrogen atoms160 carbon
atoms480 Periodic box size60x78x9.84 A. Time
step0.25 fs.
Work in progress What forces are required to
separate the tubes (magnetic?) to store and
release hydrogen?
8
Nanocomposites
  • Process modeling of nanocomposite fabrication
    using multi-scale methods to enhance alignment
  • Modification of nanoscale interfaces to improve
    load transfer through functionalization or/and
    defect engineering or/and surface modification
  • Large-scale simulation of nanocomposites to
    determine thermo-mechanical properties
    optimization studies for strength, stiffness and
    fracture
  • Enhance longitudinal and transverse stiffness by
    improved interfacial bonding
  • Mechanics of defect formation- loss in strength
    and stiffness

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9
Computational Issues and Large scale parallel
computing
Issues
  • Use FSUs 512 processor IBM 690p server
  • Third fastest university owned supercomputer in
    the US
  • Science-aware parallelization
  • Predict regions likely to experience short
    time-scale phenomena and concentrate
    computational resources there
  • Avoid fine granularity where possible
  • Use Monte Carlo techniques for rare-event
    simulation when required, to avoid fine
    granularity
  • Efficiently parallelizable through replication
  • Faster versions of traditional parallelization
    techniques
  • Stochastic versions of traditional domain
    decomposition techniques
  • Trade computation for communication
  • Mixed shared and distributed memory
    parallelization
  • Optimize sequential component too
  • Cache-aware computation

Solutions
  • Large time scale
  • Small system size
  • Fine grained parallelization
  • High communication cost
  • Adaptive computations
  • Regions experiencing short time-scale phenomena
    simulated with a finer resolution
  • Spatial decomposition and granularity change
    dynamically, and quickly, with time
  • Need fast and efficient load balancing strategies

Resources Third largest computer in U.S
universities (IBM-p690-512 processors)
10
Nanocomposite simulation-prelim. results
  • Model
  • Matrix-nanotube interface modeled with springs
  • An extra force term computed for atoms attached
    to springs
  • Springs can break, requiring substantial increase
    in computations in that region

Polymer matrix
Spring
  • Experimental parameters
  • Nanotube with 1000 atoms
  • Spring probability 0.05
  • Probability of a spring breaking in an iteration
    0.01
  • Load increase factor due to spring break 200
  • Disturbance region depth 3
  • Number of time steps 100

11
Detailed information on each of the topics
Click on the arrow for any topic for direct link
Mechanics of Defects (presentation)
Interaction of Defects in nanotubes
Nanoscale interface mechanics
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