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Xiaoyan Li's picture

Simulating Fullerene Ball Bearings of Ultra-low Friction

We report the direct molecular dynamics simulations for molecular ball bearings composed of fullerene molecules (C60 and C20) and multi-walled carbon nanotubes. The comparison of friction levels indicates that fullerene ball bearings have extremely low friction (with minimal frictional forces of  5.283×10-7 nN/atom and  6.768×10-7 nN/atom  for C60 and C20 bearings) and energy dissipation (lowest dissipation per cycle of  0.013 meV/atom  and  0.016 meV/atom  for C60 and C20 bearings). A single fullerene inside the ball bearings exhibits various motion statuses of mixed translation and rotation. The influences of the shaft's distortion on the long-ranged potential energy and normal force are discussed. The phonic dissipation mechanism leads to a non-monotonic function between the friction and the load rate for the molecular bearings.

Micromechanical Exfoliation and Graphene: 1999 papers and brief discussion of them

The discovery of a new material type, graphene and extremely thin platelets of graphite, was discussed in several articles from my research group published in 1999:

Lu XK, Huang H, Nemchuk N, and Ruoff RS, Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, APPLIED PHYSICS LETTERS, 75, 193-195 (1999).

Jinglei Yang's picture

A good beginning of 2007

In the very beginning of 2007 I have four papers published or accepted (one is independent research and others are collaborated). All of them are the work done in my doctoral period. The topic is focusing on the enhancement of creep resistance of polymers by incorporating of nanofillers including particles and CNTs.

Teng Li's picture

Journal Club Theme of March 2007: Mechanics of Flexible Electronics

Choose a channel featured in the header of iMechanica: 

Flexible electronics is an emerging technology with an exciting array of applications, ranging from paper-like displays, skin-like smart prosthesis, organic light emitting diodes (OLEDs), to printable solar cells. These potential applications will profoundly impact various facets of our daily life, and excite our curiosity on: what's the future of newspapers and books? Will OLEDs replace light bulbs and fluorescent lamps, and emerge as future lighting source? Can we power electronic devices everywhere cordlessly? Significant progress has been made in the past several years, especially as sizable investments flux in. For example, Polymer Vision just released the first commercial product of rollable display (as shown in the figure) after secured $26M investment in January 2007. The future success of this emerging technology largely relies on:

Three-dimensional anisotropic elasticity - an extended Stroh formalism

Tom Ting and I have recently developed a method of extending Stroh's anisotropic formalism to problems in three dimensions. The unproofed paper can be accessed at http://www-personal.umich.edu/~jbarber/Stroh.pdf .

Vikram Gavini's picture

Quasi-continuum orbital-free density-functional theory : A route to multi-million atom electronic structure (DFT) calculation

I would like to share the research work I have been pursuing over the past four years. I believe, through this forum, I will be able to reach researchers with various backgrounds and expertise. Suggestions and comments from members will be very useful. I am also attaching links to preprints of manuscripts describing this work. Please follow these links:

http://www-personal.umich.edu/~vikramg/academic/Preprints/QC-OFDFT.pdf

Ashkan Vaziri's picture

Multi-Axial Failure Models for Fiber-Reinforced Composites

The increasing use of fiber-reinforced composites accentuates the need for developing multi-axial fatigue failure models for these materials. In this article (attached), we proposed several multiaxial fatigue failure models for fiber-reinforced composites considering the contribution of mean and cyclic normal stress/strain and shear stress/strain at the plane of failure and examined their capability for predicting the fatigue life of the E-glass/epoxy composite materials.

Accuracy and error estimation in extended finite element methods

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Stephane Bordas, Marc Duflot and Pierre-Olivier Bouchard announce the WCCM8 mini-symposium Link to detailed pdf description 3d error estimation by extended moving least squares

Which phenomenological flow stress model is the best?

A couple of years ago a colleague who wanted to simulate high-speed machining asked me: " Which is the best phenomenological flow stress model for metals?" I wasn't able to give an answer right away and decided to look in the literature.

What I found was, every ten years or so, a new model appears in the literature that tries to solve some of the problems of older models. However, a clear ranking of models has not been established yet.

eXtended Finite Element Method: Short Course Notes

I taught a short course some time ago on the eXtended Finite Element Method, and thought many people would find the notes useful.  

So I've posted them here, in .mov format (as exported with the Apple software keynote).  The advantage of this format is that, when you click on one of the .mov files, it should open a separate browser.  Clicking in the window will advance the slide. This way you see all the movies, etc, as well as the sequence as it appears when I gave the talk.  There is a way to add audio to this format as well - something I may pursue in the future.  

Second XFEM short course, July 2007, Lausanne, Switzerland

After the success of the course in 2005 (45 participants from 15 countries), the EPFL school of continuing education presents the second XFEM course.

MichelleLOyen's picture

NYT Article "The Ultimate Distance Learning"

I stumbled on this article in the NY Times "The Ultimate Distance Learning" (free registration required to view) about the establishment of University distance learning activities within the Second Life online community.

Zhigang Suo's picture

An infinite whiteboard on the Internet

We mechanicians like to argue over a whiteboard, but we are often too far apart. Skype allows us to phone each other, and Google Doc allows us to write together. Both Skype and Google Doc work over long distance and free of charge. But still, we'd like to sketch a little figure and write a few equations. We miss our whiteboard.

Helpful Math for Continuum Mechanics

If you would like a copy of my lecture notes (on matrix algebra, indicial notation, vectors, tensors, vector calculus, groups, curvilinear coordinates and calculus of variations) they are available at

Markus J. Buehler's picture

Mesoscale modeling of mechanics of carbon nanotubes: Self-assembly, self-folding and fracture

Using concepts of hierarchical multi-scale modeling, we report development of a mesoscopic model for single wall carbon nanotubes with parameters completely derived from full atomistic simulations. The parameters in the mesoscopic model are fit to reproduce elastic, fracture and adhesion properties of carbon nanotubes, in this article demonstrated for (5,5) carbon nanotubes. The mesoscale model enables one to model the dynamics of systems with hundreds of ultra-long carbon nanotubes over time scales approaching microseconds.

Systematization Schemes for Mechanics and Concept Maps

1. Introductory

Recently, there has been some active discussion on topics like:
-- Open-source textbooks
-- Comparing lecture notes
-- Unification of mechanics
-- Wikipedia and Citizendium

Hassan Aref's picture

iMechanica and Citizendium - the perfect union?

Most visitors/users of iMehanica will be aware of Wikipedia. Well, there is a new project of this kind underway. To quote from its "mission statement":

Teng Li's picture

The future role of iMechanica

Since iMechanica went official on 9 September 2006, its growth has always been accelerating. As of 22 February 2007, the total number of hits on iMechanica reaches 1,000,000+, iMechanica has 1252 registered users, 908 posts and 1308 comments.

Notes on Fracture of Thin Films and Multilayers

Lecture note of fracture mechanics of thin films and multilayers given at the Technical University of Denmark.

Michael H. Suo's picture

How to subscribe to RSS feeds for comments

You can now subscribe to RSS feeds of comments, as follows:

  • For all new comments made on iMechanica, the feed is: crss
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2007 ASME-IMECE session on "Analyses of Fracture in Bones and Bone Like Materials At Multiple Length-Scales"

Fracture in bone is a complex process that depends on the volume fraction (the relative fraction of bone tissue vs. void space), the architecture (the geometrical arrangement of the tissue), the mechanical properties of the bone tissue itself, and the applied loads. Theoretical approaches to the fracture of porous materials have been developed but their application to bone may be limited as they assume homogeneity of both the structure and the underlying material. The adaptation of the mechanical properties of bone to its loading history results in substantial heterogeneity of mechanical properties primarily due to the wide range of loads applied in the skeleton. Furthermore, bone diseases as well as pharmaceutical treatments for bone diseases can also affect the heterogeneity of material properties. All the above effects are intricately linked with bone micro-structure which incorporates collagen and mineral at the nanoscale in widely varying topological manners. With a wide ranging heterogeneity in length-scales of bone fracture it becomes imperative that fracture and failure analyses of bones are carried out at multiple lengthscales using a combination of modeling and experimental approaches. In this mini-symposium computational, experimental, and theoretical presentation of research on analyzing fracture of cortical as well as cancellous bone architectures are solicited. Presentations on computational and theoretical method development, experimental behavior characterization, and forming a link between theory and experiments are all strongly encouraged.

2007 Melosh Competition Finalists Announced

The six finalists for the 19th Annual Robert J. Melosh Medal Competition for the Best Student Paper in Finite Element Analysis were announced last Friday. They are

Baskar Ganapathysubramanian, Cornell University

Perturbation analysis of a wavy film in a multi-layered structure

A free surface in a multi-layer can experience an undulation due to surface diffusion during fabrication or etching process. In order to analyze the undulation, the elasticity solution for the undulating film is needed. Considering the undulation as a perturbation of a flat surface, a boundary value problem for 2D elasticity is formulated. The solution procedure is straightforward, but very lengthy especially for a multi-layer.

MichelleLOyen's picture

8th European Symposium on Nanomechanical Testing: "nanomech 8"

Attached is the first announcement and call for papers for "nanomech 8", the 8th European Symposium on Nanomechanical Testing to be held in Huckelhoven, Germany, 3rd-5th September, 2007. Full details are also available at the conference website. The special focus for this year's meeting is "Across the scales: Size effects and scaling phenomena in micro- and nano-mechanics". Abstracts are due 5th May, 2007.

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