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Mike Ciavarella's picture

Italian stress analysis AIAS conference in Ischia --- call for papers Sept.

dear Imechanica users,

a wonderful location for our annual italian conference in stress analysis -- see www.aias2007.it. It is organized by our collegues in Università di Napoli, Prof. Renato Esposito. Attached the call for papers in PDF, and more info are below.

Floating ships of ice and increasing the toughness of glass

http://en.wikipedia.org/wiki/Project_Habakkuk

I was surprised several years ago when delving into the literature to not find any references about addition of nanoparticles to ice, to study their impact on the mechanics of ice.  In short, to make nanocomposites where the matrix is ice.  So, with 2 high school students from IMSA, the Illinois Math and Science Academy, we set about (with their limited time for a bit of research) to try adding some nanoparticles to water and to freeze it.  The students simply used their home freezers to do this, and their mechanics measurements were with a hammer and chisel...

Simpleware signs up reseller in China

Simpleware Ltd., the world leader in image-based meshing software, has signed an agreement with Gaitech International Ltd. to resell the Simpleware suite of software products in China, Hong Kong, Taiwan and Macao.

Simpleware software offers an advanced solution to problems that were previously intractable due to the complexity in geometry reconstruction. Simpleware's technology has opened up numerical analysis (CFD and FEA) to a variety of applications, including biomedical engineering, material characterisation and industrial reverse engineering.

jfmolinari's picture

A new methodology for ranking scientific institutions

 

We extend the pioneering work of J.E. Hirsch, the inventor of the h-index, by proposing a simple and seemingly robust approach for comparing the scientific productivity and visibility of institutions. Our main findings are that i) while the h-index is a sensible criterion for comparing scientists within a given field, it does not directly extend to rank institutions of disparate sizes and journals, ii) however, the h-index, which always increases with paper population, has an universal growth rate for large numbers of papers; iii) thus the h-index of a large population of papers can be decomposed into the product of an impact index and a factor depending on the population size, iv) as a complement to the h-index, this new impact index provides an interesting way to compare the scientific production of institutions (universities, laboratories or journals).

Zhigang Wei's picture

Any suggestion for a fast sparse solver

It seems that a customized FEM code is always necessary for special research purposes. In our group we use a home-made FEM code to simulate arbitrary crack growth in 3D domain with nodal release or re-meshing.

Rui Huang's picture

Thin films: wrinkling vs buckle-delamination

H. Mei, J.Y. Chung, H.-H. Yu, C.M. Stafford, and R. Huang, Buckling modes of elastic thin films on elastic substrates. Applied Physics Letters 90, 151902 (2007).

Two modes of thin film buckling are commonly observed, one with interface delamination (e.g., telephone cord blisters) and the other with no delamination (i.e., wrinkling). Which one would occur for your film?

Joost Vlassak is promoted to Full Professor with Tenure at Harvard

Joost J. Vlassak's pictureWe have just heard the great news that our colleague (iMechanician number 12), Joost Vlassak, has been promoted to Full Professor with Tenure at Harvard.

A new type of bubble raft--challenge for clever students

17 years ago, while a postdoc at IBM meant to be doing other things, I thought about the following. Then recently I visited Ali Argon at MIT, and we discussed conventional bubble rafts and how useful they had been in studies of some problems in mechanics...such as of defects and so on.

Quantum Confinement Induced Strain in Quantum Dots

In the attached pre-print, we investigate quantum confinement induced strain in quantum dots. This paper has been written keeping in mind the condensed matter physics/quantum dot community (accepted for publication in Phy.

L. Roy Xu's picture

A pool filled with non-newtonian fluid

They filled a pool with a mix of cornstarch and water made on a concrete mixer truck. It becomes a non-newtonian fluid. When stress is applied to the liquid it exhibits properties of a solid. Video was recorded at Barcelona, Spain.

Mike Ciavarella's picture

Does anyone know a collection of Lennard Jones potential material constants??

I am trying to find out the theoretical adhesive strength limit of a few materials, or more precisely the ratio adhesive strength limit to elastic modulus. I think this is after all part of the Lennard-Jones constants potential - theoretical adhesive strength limit is simply the maximum of the curve.

Markus J. Buehler's picture

Large-scale hierarchical molecular modeling of nanostructured biological materials

There have been several posts recently discussing new directions in computational mechanics. Here is a review article that appeared recently that may be of interest.

Large-scale hierarchical molecular modeling of nanostructured biological materials

Research directions in computational mechanics

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Dear all,

I just joined this group last week. And, I'd like to share some of reading material that I found regarding research directions in computational mechanics. The paper was published in 2003, written by Tinsley Oden, Belytschko, Babuska and Hughes. It's entitled "Research Directions in Computational Mechanics" (Computer Methods in Applied Mechanics and Engineering, 192, pp 913-922, 2003). They outlined six areas with significant research opportunities in CM:

Mike Ciavarella's picture

clever load normalization parameters for hip joint prosthesis

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A normalising loading parameter useful in summarising the mechanical response of plane, pin in plate-like contacts is extended to axisymmetric, ball in socket-like contacts. Various diagrams reporting

Stress or strain: which one is more fundamental?

In between stress and strain, which one is the more fundamental physical quantity? Or is it the case that each is defined independent of the other and so nothing can be said about their order? Is this the case?

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

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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).

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.

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