iMechanica - micromechanics - Comments

seeking PhD position in the area of wood science

rezhumalai — Thu, 31 Jul 2008 06:34:55 -0400

sir
i am R.Ezhumalai working as Scientist at Indian council of Forestry
Research and Education, India.Having qualification B.Sc Forestry and Msc
wood science and technology, I like to do phd in wood science and
technology so in this regard i saw your advertisement For Phd position in the area of wood fibre composites at website (http://www.dtu.dk/English/About_DTU/vacancies.aspx?guid=22340178 ), i want know having a above mentioned qualification can i apply for this phd position .
please reply soon

R.Ezhumalai,Scientist
Institute of Wood Science and Technnology,
18 th Cross,
Malleswaram,
Bangalore-607803,
Mobile:+919449081910

Re: Abaqus, importing from Pro-E, and foam models

Biswajit Banerjee — Wed, 18 Jun 2008 23:07:24 -0400

Hi Prasanna,

I'm afraid that I don't know enough about Abaqus to say anything useful here. But there are quite a few others on this forum and on the Abaqus Yahoo group who use the software and will be able to help you. My own preference would be to just use Abaqus directly for creating the geometry because the foam geometry is relatively simple.

-- Biswajit

About boundary conditions

pthiyaga — Tue, 17 Jun 2008 12:35:26 -0400

Thanks a lot biswajit... I indeed found the info in 'wikipedia' very informative...

Now I have a trivial modelling question...Please dont mind my asking it...

I modelled one unit cell from the data I had in Pro-e and I tried to import it into abaqus.. I wanted it to be a wire because I wanted to model every strut as a beam (open-foam)....

However abaqus imports it as one single object... That is, all the wireframe edges are imported as one single object. Do you know if there is any way I can import this as a bunch of lines.

Thanks a tonne.

-Prasanna

Re: Unit cell of a foam

Biswajit Banerjee — Tue, 17 Jun 2008 00:33:22 -0400

Dear Prasanna,

I'm sure you've already looked at Gibson and Ashby for some pointers. That's of course the first place to go to for information on simple foam models.

The periodicity of tetrakaidodecahedra (more commonly called tetradecahedra - or 14 sided) is a fascinating subject. After seeing you post I looked at Wikipedia and there's a wealth of information there. I hadn't realized that there was a complete list of possible forms of 14-faced objects. The most familiar one (to me) is the the Kelvin cell or Truncated octahedron.

This element can be used to tile space leading to the bitruncated cubic honeycomb. The unit cell for that tiling is a subset of the image below

This is the repeating pattern that you're looking for. From this figure you should be able to figure out which faces and corners need to be assigned periodicity. It won't be as simple as a hex or a cube but it'll be much more fun. For a start you can just take the first 9 cells (any corner region in the figure) and apply standard periodic boundary conditions to the edges of the cube in which they are contained.

-- Biswajit

Effective stiffness of composite

hamanh — Tue, 27 May 2008 11:03:43 -0400

Dear mechanician,

Thank you for useful discussion. I would have one question that: Is it possible to calculate the Exact Value of Effective Stiffness of Fully Periodic medium by One Unit Cell ?

Thank you very much

Regards

Accuracy when volume fraction approaches 1

Henry Tan — Thu, 22 May 2008 12:24:15 -0400

How accurate is the micromechanics estimation when the particle volume fraction approaches 1?

book on Helical Wormlike Chains and free online book

Andrew Norris — Fri, 08 Feb 2008 09:57:50 -0500

Helical Wormlike Chains in Polymer Solutions, by Yamakawa, Hiromi, Springer 1997

This book is technical but very informative. It goes into the details of the WLC model more than any other book that I know of.

Most libraries don't have t hat book - but a good alternative is the older 1971 text "Modern Theory of Polymer Solutions" by Yamakawa which contains a good deal of the same material and is more introductory. And the 1971 book is available for FREE in pdf form here .

Thank you vey much for your

BirosTheo — Thu, 07 Feb 2008 15:21:49 -0500

Thank you vey much for your infos

In the Cowin and Doty's

Almir Uzunovic — Thu, 07 Feb 2008 13:19:02 -0500

In the Cowin and Doty's book "Tissue Mechanics" there is a section related to modelling of spiral structures and issues such as chirality and singularity. While problem is explained from the continuum mechanics' point of view (primarily related to modeling of materials such as wood and horn), the authors provide enough references for further study. The book has it's web site on http://tissue-mechanics.com/

I hope this helps.

Almir

Graduate student position at Royal Institute of Technology (KTH)

Fred Nilsson — Fri, 11 Jan 2008 11:19:35 -0500

See http://www.hallf.kth.se/NYAJOBB/nyajobb_en.html

The position is at the Department of Solid Mechanics, KTH . The theme of the graduate student project is "Crack growth in rubber and rubber like materials".

Solutions to problems in the new book

Jim S. Olsen — Thu, 01 Nov 2007 14:04:11 -0400

Dear Professor Qu

I am a rather fresh PhD-student who is working on shape memory alloys. The main focus of my work will be on the effect of inclusions on SMA's properties and behaviour. I have taken no formal courses in micromechanics so I basically need to learn it from scratch by myself. I retrieved your book from my supervisor Prof. Zhiliang Zhang and it seems to be a good introduction to micromechanics, which is what I need. My idea is to thoroughly work trough your book to get a basic understanding of this topic. So my question to you is: Have you made solutions to the problems in teh book? And if you do, is it possible to receive a copy of these? It would be very helpful to me at the present stage of my work.

Best Regards

Jim S.
Olsen

PhD
Student

Faculty of Engineering
Science and Technology

Norwegian University of Science and technology

N-7491
Trondheim

Norway

Tel:
0047-73594884

Time scale, size scale and imperfections in "real" materials

Kejie Zhao — Fri, 31 Aug 2007 01:19:00 -0400

Hi Henry,

I agree well with the point micromecanics cannot give the exact value. I did a few works on molecular dynamics simulation, so I want to say some thoughts on this topic within my best knowledge. The main differences lied in micro modeling and macro study may be in three aspects: the time scale, size scale and the imperfections modeling in real materials. As we know most MD simulations are conducted under ps scale and high strain rate (10^6~10^12), it is formidale to simulate the macro experiments due to limited computation resource,especially for quasistatic problems. Of cource there is nothing wrong with MD method, but it is still hard to build general correlations between micro modeling and experiments under current conditions. The second one is the size scale, we know at the atomistic scale, the contiuum assumption is not suitable, and most materials behaves big differently at micro and sub-micro scales. So giving a link between multi scales is sitll an open question, not even the exact value for macro problems. Onthe defect initially induced. As far as I know, since the real materials are always full of various defects, the micro modeling method cannot yet simulation these imperfections.

So I think the micro modeling methods should not put more emphasis on the exact values. Perhaps the mechanicians would benifit most from these methods for some problems that contiuum theory hard to solve, such as the deformation underlying mechanism based on discrete things, like dislocation .etc, and predictions of mechanical behaviors at macro level.

Kejie

Re: why micromechanics cannot give the exact value?

Aaron Goh — Thu, 30 Aug 2007 16:25:12 -0400

Rutgers in 1962 has a review paper on the equations used to relate viscosities with volume concentration of disperse systems. It is about 40 pages long, so even the volume fraction is not simple to account for. But testing such materials is also rather difficult.

Another area concerns compacted/tabletted systems, where predictions of properties of two component tablets (+ porosity = three components) are still not straightforward.

Modelling of RVE in ABAQUS

mafarooqi — Mon, 18 Jun 2007 00:42:03 -0400

Hi All,

Could anyone anyone please tell me how to model a periodic representative volume element in ABAQUS. I tried doing it by creating 2 parts, one a rectangular matrix-part with a square or circular hollow space in the center to accomodate and the second one that represents fiber or inclusion. Then defined 2 materials, each for matrix and inclusion. Finally assemble the two part instances in assembly module. Giving appropriate boundary conditions and loads, meshing the assembly and submitted he job. But it gives error messege: (For heat Transfer problem) No valid output requests have been generated, this may be due to earlier input error or specifications of a non-existant cavity or surface name. The second error messege is: A heat transfer analysis is not meaningful as there is no temperature degrees of freedom in the model.

I followed the same procedure to model the same heat transfer problem using a shell element with a single homogeneous material, the analysis runs well and gives nice results.

Please give suggestions.

Thanks

A good book

Xu Zhang — Sun, 20 May 2007 10:46:03 -0400

I have introduced this book to our library

It's really a goog book for material simulation