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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
  • For comments on a particular post, say post number 474, the feed is: crss/node/474

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.

Zhigang Suo's picture

Books, essays and websites that have influenced the development of iMechanica

In this blog entry, I'll maintain a list of books, essays and websites that have influenced me in developing iMechanica. I'll also list my notes on them whenever available. Because iMechanica shares many common problems with other online communities, it is natural that we find solutions discovered by other online communities helpful. At the same time, iMechanica is unique in some respects, and has its own unique problems, so that we cannot adopt any methods or viewpoints without adjustment.

Ning Wang's picture

Critical role of cytoskeletal prestress in cellular stiffening

In his recent comment, Isabey discussed the issue of external stress/strain induced cellular stiffening. While the mechanism of this behavior is not fully understood and deserves further investigation, I would like to mention the cellular stiffening (increase of shear stiffness) that depends on the level of the endogenous contractile prestress (pre-tension) generated by myosin II-actin interactions.

Giuseppe Carbone's picture

Stick slip instabilities of hot cracks in rubber: The influence of flash temperature

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Here you find a preprint version of a paper published in PRL 95, 114301 (2005) [also see Eur. Phys. J. E. 17, 261-281 (2005)] where the authors present a theory to explain why instabilities, e.g. stick-slip motion, is observed when cracks propagate in rubber materials.

Mike Ciavarella's picture

Some notes on Luan and Robbin's papers on contact and adhesion at atomic scale

As I promised, I start with some brief notes on themes loved by Ken Johnson to hopefully raise some interest for discussion on iMechanica. Regards, Mike

L. Roy Xu's picture

Tensile strength and fracture toughness of nanocomposite materials

Are not as high as we expected although very stiff and strong nanotubes or nanofibers (Young’s modulus E~1000GPa) are added into soft polymer matrices like epoxy (E~4GPa).  In our early investigation on the  systematic mechanical property characterizations of nanocomposites (Xu et al., Journal of Composite Materials, 2004--among top 5 in 2005;and top 10 in 2006 of the Most-Frequently-Read Articles in Journal of Composite Materials.) have shown that there was a very small increase (sometimes even decrease) of critical ultimate tensile/bending strengths, and mode-I fracture toughnesses in spite of complete chemical treatments of the interfacial bonding area, and uniform dispersions of nanofibers (click to view a TEM image). Similar experimental results were often reported in recent years. Therefore, mechanics analysis is extremely valuable before we make these “expensive” nanocomposite materials. Our goal is to provide in-depth mechanics insight, and future directions for nanocomposite development. Till now, nanocomposite materials are promising as multi-functional materials, rather than structural materials. Here we mainly focus on two critical parameters for structural materials: tensile strength and fracture toughness. We notice that other mechanical parameters such as compressive strengths and Young’s moduli of nanocomposite materials have slight increase over their matrices.

What are the current research areas in computational mechanics?

Hello mechanicians,

What are the current research areas in computational mechanics? What is the future of CM? Where can one find such information on the net? Is there a central location?

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