iMechanica - education - Comments

Hi Andreas

Michael A. Graham — Tue, 15 Jul 2008 16:19:58 -0400

I've never used the built-in visco-elastic model in Abaqus, so I cannot be much of a help. I looked up that portion of the manual, but obviously I don't see anything you do not.

I think what you need to do really is to divide by the initial values. That gives you normalized values, but scaling them so that a certain value (in this case, the initial value) is 1. This sort of normalization is employed in many engineering problems.

Abaqus does not have built-in, nonlinear viscoelastic models (to the best of my knowledge). To perform a simulation with nonlinear viscoelasticity, you would need to use a UMAT user subroutine to define the material behaviour for Abaqus.

Good luck!

You can examine the

Volkan_HH — Wed, 09 Jul 2008 08:01:52 -0400

You can examine the documentation at http://www.cfg.cornell.edu/software/software_documentation.htm . Below, I will try to explain how to install, start and use the program in a very basic way.

- In order to use Franc3d, you should first install cygwin inclusing XFree 86 package, which is fully free from http://www.cygwin.com/ . If you are not sure which packets to install, just install every package. Install it, for example, directly to main directory of C.

- Go to Cornell site again and download Franc3d, OSM and BES from the page http://www.cfg.cornell.edu/software/software.htm

- Unzip the these files for example directly into C/cywin folder. That is it for installation.

- Then go to c:\cygwin\usr\X11R6\bin\startxwin.bat (or wherever you installed cygwin) to open a bash shell.

- Here when you two times go to an upper directory (that is, type cd .. (that is write "cd blank dot dot" and press enter two times)) you can reach to c/cygwin. Here if you type "dir" for example, you can see the directory listing. As you already copied your franc, OSM and Bes here just type OSM.EXE

- OSM starts. You can use OSM to create your own model files. It is a fairly strong software to design relatively simpler geometries. But if you are modelling very complex components, it may be better to import them from one of the accepted formats. You will see these formats on the right side of the OSM screen.

- Save your OSM file first in OSM format (while you may in the future play with the geometry) then as a Franc3d file

- Close OSM and write on the bash shell franc3d.exe

-Franc3d starts. Import the geometry via "read geometry file" button on the upper left side of the screen.

- Add a crack

- Define material properties and boundary conditions

- Mesh the model

-Save the file as a BES file

-Press "run bes analysis" button

-Import the results via "read bes file" button

-Enjoy your results

That is it. Of course about how to draw the model or how to create a good mesh, it is much better if you first read the manuals and examples.

Regards,

Volkan

Thank you zhangzhuo

hitzhangzhuo — Mon, 30 Jun 2008 07:59:13 -0400

Thank you

zhangzhuo hitzhangzhuo@gamil.com

a related thread on meshless methods

Zhigang Suo — Sat, 21 Jun 2008 17:25:13 -0400

Please also see a related thread: The future of meshless methods.

SED

Hui-Hui Dai — Fri, 20 Jun 2008 05:00:55 -0400

In a recent paper (International Journal of Solids and Structures 45 (2008) 2613–2628), we have used SED (or DSED) as a fracture criterion. The reason is that we manage to construct the analytical solution for the localization in a three-dimensional slender cylinder which gives the point-wise strain energy distribution and then it is easy to use the DSED. I thought that the work is related to the discussions on this topic so I provide the title and abstract below.

On constructing the analytical solutions for localizations in a slender cylinder composed of an incompressible hyperelastic material

Hui-Hui Dai a,*, Yanhong Hao b, Zhen Chen c

a Department of Mathematics and Liu Bie Ju Centre for Mathematical Sciences, City University of Hong Kong, 83 TatChee Avenue,

Kowloon Tong, Hong Kong

b Department of Mathematics, City University of Hong Kong, 83 TatChee Avenue, Kowloon Tong, Hong Kong

c Department of Civil and Environmental Engineering, University of Missouri-Columbia, Columbia, MO 65211-2200, USA

Abstract

In this paper, we study the localization phenomena in a slender cylinder composed of an incompressible hyperelastic material subjected to axial tension. We aim to construct the analytical solutions based on a three-dimensional setting and use the analytical results to describe the key features observed in the experiments by others. Using a novel approach of coupled series-asymptotic expansions, we derive the normal form equation of the original governing nonlinear partial differential equations. By writing the normal form equation into a first-order dynamical system and with the help of the phase plane, we manage to solve two boundary-value problems analytically. The explicit solution expressions (in terms of integrals) are obtained. By analyzing the solutions, we find that the width of the localization zone depends on the material parameters but remains almost unchanged for the same material in the post-peak region. Also, it is found that when the radius–length ratio is relatively small there is a snap-back phenomenon. These results are well in agreement with the experimental observations. Through an energy analysis, we also deduce the preferred configuration and give a prediction when a snap-through can happen. Finally, based on the maximum-energy-distortion theory, an analytical criterion for the onset of material failure is provided.

I am mainly an applied mathematician working on "Understanding and Exploiting Nonlinearity" in solids (nonlinear waves, instabilities and phase transitions, etc.). I am not an expert on fracture or damage mechanics and this is my first piece of work related to this area. However, I would certainly like to do more work in this area, in particular, fracture/damage caused by post-bifurcation behaviour (I view the damage caused by localization in a cylinder subject to tension/extension as one of such problems).

Thanks...

Ajit R. Jadhav — Fri, 20 Jun 2008 02:39:11 -0400

"... despite all the barriers... "

Thanks for keeping in mind the context that I was jobless!

As to cynicism: The only antidote to it, it would seem, is to give up your job, blow up all your savings, come on the streets (at least in the financial sense if not more), thereby fulfilling some idiot but influential (and perhaps rich) socialist's or American's (including American businessman's) idea of beign a "scientist" or a "genius" or so (e.g. based on the historical fact that Einstein was just a clerk when he produced his Nobel-winning work, or based on the events in Ayn Rand's fiction that Howard Roark had to go back to the mine for his convictions, etc.). Do that first, and then, start doing what you always wanted to do... As if a scientist (or a moral guru---a man of the intellect, in short) must necessarily be penniless before he can be effective or be taken seriously...

I really can't choose between your kind of cynicism and my kind of optimism (as they appear in the above postings, that is).... Or, may be, we have already switched the moods...

But, thanks anyways... Bye!

Revising my comment on Nobels...

Ajit R. Jadhav — Fri, 20 Jun 2008 02:18:16 -0400

I would like to revise a part of my above comment---the part concerning Perrin and his Nobel.

Before that, a word about my habits... I, like many others, often write here very spontaneously and informally, i.e., in a somewhat lax manner. (I believe that blogs are intermediate to, say, a formal conference talk and a completely informal chat over a cup of coffee....) What happens is that one says something on a blog, and only then begins to think more deeply about it. This is precisely what has happened in the present case.

Soon after posting my above comment, I happened to check the official Nobel site, and learnt (see here) that Perrin was not given a Nobel only for his work involving the Brownian movement (BM), but, overall, "for his work on the discontinuous structure of matter and especially for his discovery of sedimentation equilibrium" (SE).

In forming my judgment, I had relied on second-hand accounts in papers, talks and texts dealing with the BM (many of which had appeared during the 2005 centenial celebrations of the miracle year of Einstein). Relying on these BM-related accounts, I had, somehow, come to form this impression that Perrin had received the Nobel for his work on BM. If this were so, even today, I would tend to think that the work (on BM), taken all by itself, was probably not worth that prize.

Now, of course, Perrin's work on SE---including the very theoretical ideas behind that constructing that set of experiments---is far more brilliant by comparison. Definitely worth at least a strong nomination for a Nobel.

I stand corrected, rather, revised.

Of course, the overall idea in my post remains as it is.

However, in view of the general atmosphere in the media and on the Internet, may I mention a couple of points here before closing: (i) None had contacted or corrected me---I spotted my mistake on my own. (ii) Usually, whenever one says something controversial, there are echoes of it in the media and on the Internet. In this case, there was none. May I take it as an example of the cultured kind of restraint shown by the French... Presuming so, let me thank them (and other Perrin fans, if any) for that.

Re: Projects Available in Pune

Biswajit Banerjee — Fri, 13 Jun 2008 20:12:26 -0400

Ajit,

It's good to see you embark on such an ambitious project despite all the barriers that you have faced. I like your optimism. I suppose I'm getting old and cynical and a bit too pessimistic - but I wish you all the best. Keep us posted on how everything goes.

-- Biswajit

Material models in ABAQUS

Martin J. Gross — Fri, 13 Jun 2008 04:08:44 -0400

Dear Michael,

you wrote that "ABAQUS is known for its powerful material modeling capabilities." This may be right in the area of composite modeling, but if we take a look at (sheet)-metals e.g. aluminum, titan, magnesium, high strength and complex phase steels, which play a decisive role in e.g. deep drawing and crash simulations, the capabilities in ABAQUS are very limited. The only anisotropic yield locus available is the very basic Hill48 yied locus.

For enhanced yield loci in this field of application, take a look at:

www.matfem.de

Regards,

Martin J. Gross

Re: Projects Available in Pune

Ajit R. Jadhav — Fri, 13 Jun 2008 03:53:02 -0400

Biswajit,

0. It would have been nice if you were to get in touch with me while you were still in India this year. Or was it the case that I had *already* scared you off? :)

Anyways, I had shown that projects document to a friend (a former prof.) here in Pune, and he had found it pretty normal... Ditto, for a similar document I had sent out last year to COEP... (Though all the projects had been finalized already, by that time.)

1. About your first * point: I beg to differ about the characterization of these projects. They are not primarily practical. They just try to hit the sweet spot between three different things: academia, currently published research and advances (mostly but not exclusively, academic), and what is regarded as practical in today's industry. ... Now, I am not sure how successful I was in getting to that spot, though... In any case, basically, I am keeping it all in a very fluid state at this stage... Let the student row, is my attitude... If he is passionate about practicality, we could always increase that touch...

I don't want to do an overkill, but here's a fast one. Let's take an example. What I say I propose to do (in that document) is a simulation of an OS. What the institute has just finished teaching a year back or so is Silberschatz' text (without any code or simulator to go with it.) What academic research does is something like improving small parts of MINIX. (See Prof. Tanenbaum's Group at Vrije Uni.---they produce PhDs and publish papers just as in any other academic set-up.) What the industry wants today is Linux. In this context, what I can allow the student to do, in case he really grows passionate about the practicality aspect of it is, for example, to increase the project's emphasis on the file system design, and, perhaps, even drop the simulation nature of the project and let him directly implement a new file system itself (I mean, accessing the real hard disk) on his own. (That was just an example. In place of file system, he could take process management etc.)

Sorry, that was CS, not mechanics, but it was the best example I could think of... (Guess, as a programmer, you would know.) A quick one on the mechanics side would be the following:

The student has finished just the Shigley a year back. I propose an experimental/software toolkit (or library). What academia publishes on is, say, XFEM. What the industry wants is, say, modeling of flutter of wind-mill blades. I can permit the student, if so desires, to take the project away from the simple design of a general toolkit and specialize in nonlinear dynamics--to the extent he wishes to go.

2. As to your second * point. Well, as a student I did the same too, at IIT Madras, about 22 years back. Remarkably, not a single one of the colleagues or friends of my guide had complained---then, or at any point of time later on.

About your closing paragraph: You are right. It *is* hard to find hard-working students. Yet, my experience has been, so far, somewhat different than what you anticipate.

At COEP in particular and in Pune in general, in every batch, I guess there certainly are at least tens, if not hundreds, of students (all branches put together) who *are* that hard-working. And they work that hard primarily because they *are* (or get) that very interested in their project work. It's a minority, but it's a significant one... For example, my document does speak of two MCS and one ME Metallurgy student. That guy had worked pretty well. Not only them... There were a couple of BE (CS) students from COEP in 1995-96 too who I had seen work at close quarters (though I didn't guide them then)... They worked fairly hard. Why, last year, my nephew was in his final year of CS and he wrote thousands of lines of code (emulating a network stack) for his project. Many such people are still found in Pune.

At the same time, what you caution about has also been corroborated by my friend who is currently on the faculty of IIT Bombay. He observed that since everyone these days gets into IT industry, at least at IIT Bombay, no UG student is bothered about working hard on the experimental side of it (in a non-CS dept.). They do the project only for getting their degree, that's all. You tell them something and they will complete only that part. They won't take it further. They won't think about their project. ... Of course, the observation should not be seen as a sweeping generalization. (After all, the same fellow also got award for innovative work done along with his UG students.) And yet, there seemed a lot of truth to it when he spoke. He clearly had seemed *worried* about the trend---not just complaining in a routine teacherly sort of way...

3. About Nobels and all. I do care about Nobel prizes. But I care more for the achivements indicated by those prizes than for the laureates as such. (This is a thoroughly honest statement. It's very natural for me to think that way....)

And so, sometimes, I do not really care as much for the Nobel laureates as I do for the Nobel *non*-laureates. (Mahatma Gandhi for Peace, Ayn Rand for Literature, a few others in Physics.... The list is not terribly short, I am afraid...)

Also, sometimes, one wonders why someone got a Nobel. For example, Perrin for Physics. (Even though he was a pretty good physicist, it still seems to me that probably the work was not as great as other laureates' work...)

So, overall, just the fact that a Nobel prize winner A has got excited about a student B really does not do too much towards improving my estimate of B---that is the point. At the most, I become curious, that's all. And that too, not about the student, but about what small increment he is going to add to the laureate's main thesis of his lifetime... One gets curious from that angle alone.

4. About your last point. Last semester (Nov. '07), one professor of CS at COEP had indicated a concrete interest in at least one of my BTech project proposals. (Several other professors were generally interested in my ideas too, esp. from Mech. and Met.). But then, last year, as I said, the projects were already in progress.

This year I hope I am not too late. I hope to get a couple of MTech/ME students and a few for BTech... I am not sure how many I could handle, though. I will update in August / September when everything is finalized. In 2005 and 2006, a couple of MTech students had on their own approached me.

5. Last minute addition: I also have projects in both architectural and technical acoustics and their applications... Architectural Acoustics: To predit reverbations and quality of sound inside a theatre. Technical Acoustics: (i) Study of acoustic deflector for a cell-phone: experimental, and computer simulation. (ii) Computer modeling for a novel design of automobile muffler / silencer. (This will be a follow-up on some experimental work which was supervised by my friend who is on the faculty of VIT, Pune.)... All other conditions apply...

Also, still some other ideas...

-----

Anyway, I promise not to reply for a few days here---this reply itself has grown that big.

[PS: Scary, is that what you said? Hmmm.... Seems like some people do not have to bother wearing masks at Halloween times... :) But then, who does those Halloween things here in Pune, anyways?]

-- Ajit

Re: Projects Available in Pune

Biswajit Banerjee — Thu, 12 Jun 2008 19:24:31 -0400

Ajit.

That's one scary document you've got there. My reading of your proposed projects and the associated rules is :

* I've got a number of practical problems that I'd like to see solved

* You the student should be ready to sacrifice a lot (for no pay) in order to get the privilege to work on these projects.

That's just too strict a regimen and I find it hard to think that you'll get any interested students at all. The reality of life is that if you had a Nobel prize (which you don't care about) in hand I'm sure you'd have had hundreds of people respond.

I'm keen to know how your experiment goes.

-- Biswajit

Thanks for sharing. Yi

Yi Han — Thu, 12 Jun 2008 13:00:10 -0400

Thanks for sharing.

Yi Han hyxjtu@gmail.com

Re: Materials

Michael A. Graham — Thu, 12 Jun 2008 10:34:02 -0400

That isn't a question that is very easy to answer. You title your post "Materials" and note that you will be simulating composites. Abaqus is known for its powerful material modeling capabilities, and if you need very specialised material models, Abaqus is probably the way to go. ANSYS has a reputation for being more user friendly. I would probably try to get advice from someone who is familiar with both tools and with the problem you will be solving. Whether I could get help from someone I know would also impact my decision.

Bhavin Patel Graduate

Bhavin — Wed, 11 Jun 2008 19:20:40 -0400

Bhavin Patel
Graduate Student

re: Medicine and Technology

MichelleLOyen — Thu, 05 Jun 2008 07:06:07 -0400

Eric--

sounds brutal re: the NICU. I'd be quite interested to hear what happened off-line, I'd love it if you dropped me an email since a large part of my research in the last 7 or 8 years has concerned mechanical factors in premature birth. I have visited the NICU on many occasions and seen the ultra-preemies born prior to 28 weeks gestation, and have also witnessed the births of three mid-preemies in the 30-35 week gestation range.

Regardless of that, though, you make a great point about medical records. We find this to be particularly true in the context of pregnancy and parenting, that people are more likely that in other instances to have ownership of their own medical records and to carry them from doctor to doctor. One of the biggest problems in harnassing computer technology for this purpose has been privacy laws; the other issue that arises is one of storage space. High resolution x-rays and (even worse) 3-D data sets from CT, MRI or PET scanning require a lot more storage space than the plain text associated with other aspects of the medical record. But this is yet again one of the places where I believe the technology exists and the engineering challenge is to apply existing technology to healthcare.