User login

Navigation

Mike Ciavarella's picture

Contact mechanics of rough surfaces: is Persson's theory better than Greenwood & Willamson?

A recent string of papers originated from Persson's paper in the physics literature contain a number of interesting new ideas, but compare, of the many theories for randomly rough surfaces, only Persson's and Bush et al, BGT. These papers often assume the original Greenwood and Williamson (GW) theory [1] to be inaccurate, but unfortunately do not test it, assuming BGT to be its better version. The original GW however is, I will show below, still the best paper and method today (not surprisingly, as not many papers have the level of 1300 citations), containing generally less assumptions than any other model, including the constitutive equation which does not need to be elastic! I just submitted this Letter to the Editor: On "Contact mechanics of real vs. randomly rough surfaces: A Green's function molecular dynamics study" by C. Campaña and M. H. Müser, EPL, 77 (2007) 38005. C. Campaña and M. H. Müser also make several questionable statements, including a dubious interpretation of their own results, and do not even cite the original GW paper; hence, we find useful to make some comments.

MichelleLOyen's picture

Making iMechanica a better global forum

Choose a channel featured in the header of iMechanica: 

It was recently pointed out that much of the technical literature is inaccessible to the English speaking world, having been published in other languages such as Russian or Chinese. At the moment iMechanica is primarily an English-language website and we are therefore potentially limiting the discussion based on language.

Zhigang Suo's picture

Poroelasticity, or migration of matter in elastic solids

A sponge is an elastic solid with connected pores. When immersed in water, the sponge absorbs water. When a saturated sponge is squeezed, water will come out. More generally, the subject is known as diffusion in elastic solids, or elasticity of fluid-infiltrated porous solids, or poroelasticity. The theory has been applied to diverse phenomena. Here are a few examples.

Zhigang Suo's picture

How to receive posts and comments in your email?

You can receive posts and comments by email. They are faster than uploading webpages. They come into folders other than your regular emails, so you don't need to look at the posts if you have no time.

I use Thunderbird. Other email applications might have the similar feature. (If your email applications do not have this feature, you can always set up a feed reader.)

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).

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

Choose a channel featured in the header of iMechanica: 

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.

Pages

Subscribe to iMechanica RSS Subscribe to iMechanica - All comments

Recent comments

More comments

Syndicate

Subscribe to Syndicate