This minisymposium will focus on the application and development of computational models and methods to study and elucidate the behavior and properties of nanomaterials (nanowires, nanotubes, thin films, nanocrystalline materials, biological materials, polymers, etc).  Topics of interest will include, but are not limited to:  (1) Computational models and methods that enable multiphysics modeling of nanomaterials, such as coupling mechanical deformation to electrical, thermal or optical properties.  (2) Deformation and fracture mechanisms in single and polycrystalline nanomaterials.  (3) Interactions of nanostructures, such as adhesion, tribology and energy dissipation.  (4) Advances in spatial and temporal multiscale computational methods. (5) Size and surface effects on the behavior and properties of nanomaterials.  (6) Deformation and failure mechanisms in soft/amorphous/non-crystalline materials. 

Conference Organizers: 

Harold S. Park
University of Colorado
Harold.park@colorado.edu

Gregory M. Odegard
Michigan Technical University
gmodegar@mtu.edu

H. Eliot Fang
Sandia National Laboratories
hefang@sandia.gov
 

Abstract of paper recently accepted for publication in Journal of Applied Physics:

The purpose of the present work is to quantify the coupled effects of surface stresses and boundary conditions on the resonant properties of silicon nanowires.  We accomplish this by using the surface Cauchy-Born model, which is a nonlinear, finite deformation continuum mechanics model that enables the determination of the nanowire resonant frequencies including surface stress effects through solution of a standard finite element eigenvalue problem.  By calculating the resonant frequencies of both fixed/fixed and fixed/free <100> silicon nanowires with unreconstructed {100} surfaces using two formulations, one that accounts for surface stresses and one that does not, it is quantified how surface stresses cause variations in nanowire resonant frequencies from those expected from continuum beam theory.  We find that surface stresses significantly reduce the resonant frequencies of fixed/fixed nanowires as compared to continuum beam theory predictions, while small increases in resonant frequency with respect to continuum beam theory are found for fixed/free nanowires.  It is also found that the nanowire aspect ratio, and not the surface area to volume ratio, is the key parameter that correlates deviations in nanowire resonant frequencies due to surface stresses from continuum beam theory. 

There has recently been a great deal of discussion on imechanica regarding the effects of surface stress on the resonant properties of nanostructures such as nanowires.  The controversy has revolved around the strain-independent part of the surface stress, which can be shown, i.e. by Gurtin et al. APL 1976, 529-530, or by Lu et al, PRB 2005, 085405, to have no effect on the resonant frequency of the nanobeam.  The reason is because in taking the moment, and differentiating the moment to get the beam equation of motion, the strain-independent part of the surface stress drops out as it is constant, while the strain-dependent (surface elastic) part survives the differentiation.

However, the corresponding analysis has not been done, to-date, for finite deformation kinematics, which is critical in nanowires due to the large surface-stress-driven deformation that the nanowires undergo, particularly for sub-20 nm cross sections.  The attached paper, recently accepted in JMPS, addresses this issue for the first time.  As the paper is long, Section 5 of the paper is the relevant one, where we discuss the methodology we employ and the results; additional commentary is given in the conclusion.  

To summarize the key findings:  (1) The residual surface stress does impact the resonant properties of nanowires under finite deformation kinematics; in fact, the effect can be comparable to or larger than the effect of the strain-dependent part of the surface stress, depending on boundary condition.  (2) Knowledge of the state of deformation in the nanowires is not sufficient to predict their resonant frequencies.  

I should also note that ZP Huang and co-workers have recently shown analytically that the residual surface stress does impact the elastic properties of nanostructures if finite deformation kinematics are considered; portions of this discussion are also on iMechanica.

I certainly welcome any feedback and discussion from the imechanica community regarding the results, or the approach taken to obtain the results.

I would like to invite everyone attending the 2008 ASME IMECE next week in Boston to attend a keynote lecture given by Prof. Ted Belytschko of Northwestern University.  The lecture will occur at 1:45 PM on Tuesday, November 4, and will be entitled "Multiscale Computations of Fracture - When Does Flaw Tolerance Occur?" 

Further information on Prof. Belytschko's talk can be found here: 

http://www.asmeconferences.org/Congress08/PlenarySessions.cfm

Graphene has recently become one of the most studied materials in the world, mainly due to its unique 2D crystal structure and its exceptional electrical and mechanical properties.  One of the most exciting applications for graphene is as a basic building block for NEMS.  In particular, due to its extremely small mass and exceptional stiffness, it is being investigated extensively as an ultra-sensitive nanoscale element for sensing incredibly small amounts of mass, force, pressure, etc.  Recently, Bunch et al. (2007) (http://www.sciencemag.org/cgi/content/abstract/315/5811/490) suspended graphene and measured its quality (Q)-factor, which was found to be extremely low; low Q-factors are critical as they place fundamental limits as to the mass, force and pressure sensitivity of the graphene NEMS.

More recently, we have studied, using classical molecular dynamics, possible intrinsic (extrinsic effects such as gas damping and clamping losses were neglected) loss mechanisms that may be responsible for the experimentally observed low Q-factors.  In doing so, we have found interesting results, recently published in Nano Letters (http://pubs.acs.org/doi/abs/10.1021/nl802853e), which suggest that free edge effects (analogous to surface effects in nanomaterials, and thus surface losses in nanowire-based NEMS) dominate the intrinsic losses, and thus the Q-factors of graphene nanoresonators.  

Horacio Espinosa and I welcome the submission of new abstracts for a minisymposium on "Mechanics of Crystalline Nanostructures", to be held at the 2010 US National Congress on Theoretical and Applied Mechanics (USNCTAM 2010), June 27-July 2 at Penn State University. 

The minisymposium will focus on the development and application of both experimental techniques and computatiohnal models and methods to study and elucidate the mechanical behavior and properties of crystalline nanostructures, including nanowires, thin films, carbon nanotubes and graphene.  Topics of interest will include, but are not limited to:  (1) Deformation and fracture mechanisms in crystalline nanostructures.  (2) Interactions of nanostructures, such as adhesion, tribology and energy dissipation.  (3) Experimental and computational studies of size and surface effects on both the elastic and inelastic behavior and properties of crystalline nanostructures.  (4) Development and application of atomistic and multiscale models for crystalline nanostructures. 

Minisymposium Organizers:

Horacio D. Espinosa (Northwestern University)

espinosa@northwestern.edu

Harold S. Park (University of Colorado)

harold.park@colorado.edu

Registration Information:

Please submit an abstract to Technical Track 4-4:  "Mechanics of Crystalline Nanostructures" at the following website:  <http://www.conferencetoolbox.org/USNCTAM2010/Author/NewAbstract.cfm>

The Department of Mechanical Engineering at the University of Colorado
at Boulder invites applications for two full-time positions beginning
fall 2010. The positions are for tenure-track assistant professors with
disciplinary expertise in the areas of (1) Bioengineering (posting #808181), and (2) Solid Mechanics/Materials Physics (posting #808182);
higher rank may be considered for experienced candidates. Candidates
are expected to strongly complement and strengthen existing
departmental research in biomechanical/biomaterials engineering, energy
and environmental engineering, micro/nanosystems engineering, materials
engineering or solid/fluid mechanics. Candidates must have an earned
doctorate in Mechanical Engineering or a closely related field with a
strong background in research in their area of specialization.

Successful candidates must have a strong commitment to scholarship, the
development of an externally funded research program, and teaching at
the undergraduate and graduate levels in mechanical engineering.
Exceptionally well-qualified candidates with outstanding credentials
may be considered for appointment at an appropriately higher academic
level. Post-doctoral or similar professional experience is highly
desirable but not required.

Interested persons should apply through the web site (http://www.jobsatcu.com)
using the appropriate posting numbers and submit electronic files (pdf
format) containing a cover letter, curriculum vita, two-page statements
of research and teaching interests, respectively, and the names,
addresses, and telephone numbers of at least three references.

Review of applications will begin as they are received, and will
continue until the positions are filled. Additional information
regarding the Mechanical Engineering Department search process as well
as our research and academic programs can be found at (http://www.colorado.edu/mechanical/). The University of Colorado is committed to diversity and equality in education and employment. 

We have recently been studying the effects of strain on the optical properties of metal nanoparticles, which have become of significant interest to the materials, physics, biology and chemistry communities due to the fact that they exhibit unique optical properties, specifically surface plasmon resonance and surface enhanced raman scattering, which are being used primarily for optical sensors at the single molecule level, but for many other applications, including photothermal cancer treatment and optical imaging.  While strain engineering of bandstructure in semiconductors is a well-established and important area, similar types of studies on metals have not been performed despite the immense potential of metal nanoparticles.  We have performed such fundamental studies of strain effects on gold nanospheres, with the results having been accepted for publication in Journal of the Mechanics and Physics of Solids (http://dx.doi.org/10.1016/j.jmps.2009.12.001).  The basic finding is that both the plasmon resonance wavelength, as well as the magnitudes of the plasmon resonance and surface enhanced raman scattering, can all be tuned and enhanced using mechanical strain.

Dear Colleagues:

We would like to invite you to submit an abstract for the 2010 ASME IMECE in Vancouver, to be held November 12-18, 2010.  Our minisymposium is on "Multiphysics Simulations and Experiments for Solids", and is the continuation of a very successful minisymposium held at the 2009 IMECE that resulted in more than 50 presentations.  This year's focus areas are:

1.Multiphysics modeling, simulation and experiments of electromechanical materials and systems

2.Multiphysics modeling, simulation  and experiments of optomechanical materials and systems

3.Multiphysics modeling, simulation and experiments of biomechanical materials and systems

4.Multiphysics modeling, simulation and experiments of thermomechanical materials and systems

5.Multiphysics modeling, simulation and experiments of fracture in solids

Abstracts can be submitted at the conference website:  (https://www.asmeconferences.org/Congress2010/Author/NewAbstract.cfm), where our minisymposium is Track 12-22.  Please note that the abstract submission deadline is fast approaching, March 1, 2010.

Sincerely,

Gang Li, Harold Park, H. Eliot Fang, Hanqing Jiang, Aman Haque, Dong Qian, Ting Zhu and Spandan Maiti

The computational nanomechanics laboratory (http://people.bu.edu/parkhs/), which is based at Boston University under the direction of Prof. Harold Park, is looking to recruit a highly motivated and independent postdoctoral researcher to study, via the development of new computational methodologies, various scientific issues surrounding the mechanics of crystalline nanostructures.  The position is available for a 1-year duration, with possible extension to future years depending on the availability of funding.  

Requirements for the postdoc position include:

1.  A strong background in computational solid mechanics, programming and implemeneting finite element-based methodologies

2.  A strong background in topology optimization techniques

3.  A strong background in the extended finite element method and level sets

If you are interested in the postdoc position, please contact Prof. Park via email at (parkhsAT_bu.edu); please email with the subject entitled "Postdoc Position", and send a CV with the contact information of two references.

Dear Colleagues:

We would like to invite you to submit an abstract for the 2011 ASME
IMECE in Denver, to be held November 11-17, 2011.  Our minisymposium
is on "Multiphysics Simulations for Solids", and is the
continuation of a very successful minisymposium held for the past 4 years
that have resulted in more than 50 presentations at the 2009 and 2010 IMECE conferences.  This year's focus areas
are:

1.Multiphysics modeling, simulation and experiments of electromechanical materials and systems

2.Multiphysics modeling, simulation  and experiments of optomechanical materials and systems

3.Multiphysics modeling, simulation and experiments of biomechanical materials and systems

4.Multiphysics modeling, simulation and experiments of thermomechanical materials and systems

5.Multiphysics modeling, simulation and experiments of fracture in solids

6.Multiphysics modeling, simulation and experiments of coupled diffusion and deformation in solids

Abstracts can be submitted at the conference website:  (http://www.asmeconferences.org/Congress2011/Author/NewAbstract.cfm),
where our minisymposium is Track 12-31.  Please note that the abstract
submission deadline is fast approaching, February 28, 2011.

Sincerely,

Gang Li, Harold Park, H. Eliot Fang, Hanqing Jiang, Aman Haque, Dong Qian, Ting Zhu and Spandan Maiti

Dear Colleagues:

We would like to invite you to submit an abstract for the upcoming 2011 Annual Technical Meeting of the Society of Engineering Sciences (SES 2011), to be held October 12-14, 2011, at Northwestern University in Evanston, Illinois (http://ses2011.org/).  The area of the minisymposium is "Mechanics of Crystalline and Composite Nanostructures", and we anticipate having a diverse and well-respected group of theoreticians and experimentalists give presentations on this subject.  Abstracts can be submitted by going to the following conference website:

http://ses2011.org/submit_abstracts.php

where our minisymposium is labeled 3.1.  We look forward to seeing you at Northwestern in the fall of 2011!

Best regards,

Harold S. Park (parkhs@bu.edu)
Jeffrey T. Paci (jpaci@chem.northwestern.edu)

Dear Colleagues:

We would like to invite you to submit an abstract for the 2011 ASME
IMECE in Denver, to be held November 11-17, 2011.  Our minisymposium
is on "Multiphysics Simulations for Solids", and is the
continuation of a very successful minisymposium held for the past 4 years
that have resulted in more than 50 presentations at the 2009 and 2010 IMECE conferences.  This year's focus areas
are:

1.Multiphysics modeling, simulation and experiments of electromechanical materials and systems

2.Multiphysics modeling, simulation  and experiments of optomechanical materials and systems

3.Multiphysics modeling, simulation and experiments of biomechanical materials and systems

4.Multiphysics modeling, simulation and experiments of thermomechanical materials and systems

5.Multiphysics modeling, simulation and experiments of fracture in solids

6.Multiphysics modeling, simulation and experiments of coupled diffusion and deformation in solids

Abstracts can be submitted at the conference website:  (http://www.asmeconferences.org/Congress2011/Author/NewAbstract.cfm),
where our minisymposium is Track 12-31.  Please note that the abstract
submission deadline is fast approaching, February 28, 2011.

Sincerely,

Gang Li, Harold Park, H. Eliot Fang, Hanqing Jiang, Aman Haque, Dong Qian, Ting Zhu and Spandan Maiti

Dear Colleagues:

We would like to invite you to submit an abstract for the upcoming
2011 Annual Technical Meeting of the Society of Engineering Sciences
(SES 2011), to be held October 12-14, 2011, at Northwestern University
in Evanston, Illinois (http://ses2011.org/). 
The area of the minisymposium is "Mechanics of Crystalline and
Composite Nanostructures", and we anticipate having a diverse and
well-respected group of theoreticians and experimentalists give
presentations on this subject.  Abstracts can be submitted by going to
the following conference website:

http://ses2011.org/submit_abstracts.php

where our minisymposium is labeled 3.1.  We look forward to seeing you at Northwestern in the fall of 2011!

Best regards,

Harold S. Park (parkhs@bu.edu)
Jeffrey T. Paci (jpaci@chem.northwestern.edu)

Since 2005, researchers have known via molecular dynamics simulations that ultra-small (i.e. < 5 nm diameter) FCC metal nanowires can exhibit unique shape memory and pseudoelastic behavior driven by surface stress effects resulting from their very small cross sectional dimensions - see (http://prl.aps.org/abstract/PRL/v95/i25/e255504) and (http://pubs.acs.org/doi/full/10.1021/nl0515910).  The process involves tensile loading of a rhombic <110> nanowire with {111} transverse surfaces that, after about 40% tensile strain, can reorient to a <100> nanowire with {100} transverse surfaces, and a square cross section.  The shape memory effect or pseudoelasticity is determined by whether the nanowire is stable in the new <100> orientation, or whether additional thermal energy is required to cause the surface-stress-driven reorientation back to <110>/{111}.  

Experimental studies of these deformation paths have not existed until recently, when in the attached paper recently published in Nano Letters (http://pubs.acs.org/doi/abs/10.1021/nl2022306), we found that <110> gold nanowires with {111} transverse surfaces can indeed reorient under tensile loading to <100> wires with {100} surfaces.  The reorientation occurs through ~40% tensile strain, is driven by coherent and long range (micrometer scale) propagation of twin boundaries, and occurs for the range of nanowire diameters tested (40-150 nm).  The results are novel and demonstrate the gold nanowires to uniquely be both superstrong and superplastic.  

The objective of this paper is to examine the instability characteristics of both a bulk FCC crystal  and a (100) surface of an FCC crystal under uniaxial stretching along a <100> direction using an atomistic-based nonlocal instability criterion.  By comparison to benchmark atomistic simulations, we demonstrate that for both the FCC bulk and (100) surface, about 5000-10000 atoms are required in order to obtain an accurate converged value for the instability strain and a converged instability mode.  The instability modes are fundamentally different at the surface as compared to the bulk, but in both cases a strong dependence of the instability mode on the number of atoms that are allowed to participate in the instability process is observed.  In addition, the nonlocal instability criterion enables us to determine the total number of atoms, and thus the total volume occupied by these atoms, that participate in the defect nucleation process for both cases.  We find that this defect participation volume converges as the number of atoms increases for both the bulk and surface, and that the defect participation volume of the surface is smaller than that of the bulk.  Overall, the present results demonstrate both the necessity and utility of nonlocal instability criteria in predicting instability and subsequent failure of both bulk and surface-dominated nanomaterials.

Dear Colleagues:

We would like to invite you to submit an abstract for the 2012 ASME
IMECE in Houston, to be held November 9-15, 2012.  Our minisymposium
is on "Multiphysics Simulations and Experiments for Solids", and is the
continuation of a very successful minisymposium held for the past 5 years
that have resulted in more than 40 presentations at the 2009, 2010 and 2011 IMECE conferences.  This year's focus areas
are:

1.Multiphysics modeling, simulation and experiments of electromechanical materials and systems

2.Multiphysics modeling, simulation  and experiments of optomechanical materials and systems

3.Multiphysics modeling, simulation and experiments of biomechanical materials and systems

4.Multiphysics modeling, simulation and experiments of thermomechanical materials and systems

5.Multiphysics modeling, simulation and experiments of fracture in solids

6.Multiphysics modeling, simulation and experiments of coupled diffusion and deformation in solids

Abstracts can be submitted at the conference website:  (http://www.asmeconferences.org/Congress2012/Login.cfm)
where our minisymposium is Track 9-32.  Please note that the abstract
submission deadline is fast approaching, February 27, 2012.

Sincerely,

Gang Li, Harold Park, H. Eliot Fang, Hanqing Jiang, Aman Haque, Dong Qian and Albert To

Dear Colleagues:

We are happy to announce a minisymposium to be held at the 2012 ASME IMECE in Houston (November 9-15) entitled "Symposium on Multiscale Computational Mechanics:  Bridging Scales and Physics in Honor of Prof. Wing Kam Liu's 60th Birthday".  

As a world-renowned scholar in the field of computational mechanics, Professor
Liu has made fundamental contributions to nonlinear finite element methods and
pioneering work in meshfree particle methods, multiple scale analysis and
multiresolution methods, and coupling of atomistic with continuum simulations.
To reflect these important contributions, the major theme of this symposium is to
address topics in multiscale modeling and simulation of multiphysical phenomena
involved in modern engineering applications.  Contributions from all aspects related to this major theme
are invited. In addition, we welcome work that presents validation, verification,
and uncertainty quantification of the multiscale methodology through analytical
and experimental work.

Abstracts can be submitted until February 27, 2012, at the following website:

http://www.asmeconferences.org/Congress2012/Login.cfm

where the Liu minisymposium is 9-12.

Best regards from the symposium co-organizers:

Professor Shaofan Li, UC Berkeley

Professor Albert To, University of Pittsburgh

Professor Sukky Jun, University of Wyoming

Professor Harold Park, Boston University

Professor Lucy Zhang, RPI

Professor Yaling Liu, Lehigh University

Dr. Gregory Wagner, Sandia National Lab

Professor Eduard Karpov, University of Illinois

Professor Dong Qian, University of Cincinnati

We presenta three-dimensional nonlinear finite
element formulation for dielectric elastomers.  The mechanical and electrical governing equations are solved
monolithically using an implicit time integrator, where the governing finite
element equations are given for both static and dynamic cases.  By accounting for inertial terms in
conjunction with the Arruda-Boyce rubber hyperelastic constitutive model, we demonstrate
the ability to capture the various modes of inhomogeneous deformation,
including pull-in instability and wrinkling, that may result in dielectric
elastomers that are subject to various forms of electrostatic loading.  The formulation presented here forms
the basis for needed computational tools that can elucidate the
electromechanical behavior and properties of dielectric elastomers that are
used for engineering applications.

 <http://dx.doi.org/10.1016/j.ijsolstr.2012.04.031>

Recently published in JMPS:

<http://dx.doi.org/10.1016/j.jmps.2012.07.009>

In the past 5 or so years, analytical studies of surface effects on the mechanical properties of nanostructures such as nanowires have been performed predominantly using one-dimensional models like the Young-Laplace model.   While many such analytical studies have been performed, what has been lacking until now is a systematic study of such analytical models as compared to benchmark atomistic studies for a range of nanomechanical boundary value problems. 

This work performs such a study, and also develops a new theoretical model to calculate the flexural rigidity of nanowires from three-dimensional elasticity theory that incorporates the effects of surface stress and surface elasticity.  It is very similar to a seminal work by Dingreville et al <http://dx.doi.org/10.1016/j.jmps.2005.02.012>, but is different in that it incorporates, through the second moment, the heterogeneous nature of elasticity across the nanowire cross section due to the effects of free surfaces.  We use this approach to study the boundary value problems of surface-stress-induced axial relaxation, transverse vibrations and buckling.  The benchmark comparisons demonstrate the need for a three-dimensional continuum formulation while pointing out the errors introduced by taking a one-dimensional model.