iMechanica - Comments

how did you get

s_gupta — Thu, 17 May 2012 02:23:42 -0400

the stress distribution as a function of space coordinates at a particular instant of time.

Thanks in advance,

Saurabh

Thanks a lot Dr. Mujibur

Jayadeep U. B. — Thu, 17 May 2012 00:45:41 -0400

Thanks a lot Dr. Mujibur Rahman for the helpful suggestions. I have sent an email to your ID given above.

Gravitating sphere

m_rahman — Wed, 16 May 2012 21:42:10 -0400

Jaydeep,

The problem you posed is an interesting one. Some classical solutions in this regard can br found in Love's book on Elasticity Theory. You can also find these solutions, in particular, the solutions of a gravitating sphere as well as a uniformly rotating sphere in A. I. Lurie's book (Theory of Elasticity, Springer, 2005), Chapter V, Sections 3.12 and 3.13.

Of course, if you are talking about accelerating sphere, you will need to resort to the equations of dynamic elasticity. Lame's representation for the displacement vector in terms of a scalar potential and a vector potential allows the equations of dynamic elasticity with body forces to be written down as 2 simple inhomogeneous wave equations (1 scalar wave equation and 1 vector wave equation). They can be solved for the potential functions with your particular body force. You then determine the dispacements and stresses in the sphere, in particular, determine the stresses on the surface of the sphere, and you will see that they are non-zero. But, the original sphere is stress free on the surface. So, you will need to remove these surface stresses. Now, this leads to another classical problem: Determine the elastic field in a sphere with prescribed dynamic tractions on its surface. You will need to solve the equations of dynamic elasticity without body forces for the sphere (in spherical coordinates).This problem can be solved by some standard methods of dynamic elasticity. You will find these methods for instance, in Eringen's book on Elastodynamics. The stresses and displacements found this way should be added to those from the body-force state to give the complete solution to the problem.

I have just silhoutted a scheme that I believe should work. You can contact me at Mujibur.Rahman1@gmail.com, if you need any further detail.

Hope this helps!

Mujibur Rahman

What a great idea. A test

Mike Prime — Wed, 16 May 2012 20:14:41 -0400

What a great idea. A test of a blind prediction, with the conditions and data publicly posted. I look forward to seeing the results.

Michael B. Prime, Los Alamos, New Mexico
http://public.lanl.gov/prime/

what am i doing???????

s_h — Wed, 16 May 2012 19:40:44 -0400

what am i doing???????

Hi All I m working on

mohammad yahari — Wed, 16 May 2012 15:53:59 -0400

Hi All

I m working on plastic connectors who can help me about this.

Thanks

Mohammad

Kewei, Thanks for the

Jingwen Zhang — Wed, 16 May 2012 15:09:58 -0400

Kewei,

Thanks for the reply. The problem is now solved by installing VS version 2008 and Intel Fortran version 11.1. I also met several other errors after installing the compatible software, and finally solved the problems by following the instructions in these posts:

http://software.intel.com/en-us/articles/troubleshooting-fortran-integration-issues-with-visual-studio/

http://polymerfem.com/showthread.php?1602-Abaqus-error-message-quot-LINK-is-not-recognized-quot

http://www.eng-tips.com/viewthread.cfm?qid=202712

Hope those who met the same problem with mine can get helpful infomation there.

Regards,

Jingwen

want to apply for this PhD Position

Harsha Tirumala — Wed, 16 May 2012 08:11:03 -0400

Are International Students eligible to apply ?

I understand how to

Jerry Brown — Tue, 15 May 2012 16:44:50 -0400

I understand how to calculate the Almansi strain. That's covered quite well in many texts on Solid Mechanics. My question is, "How is it used to make calculations?" No one seems to address that issue - Fung, Bower or Holzapfel.

hi is it possibile for

aliadib — Tue, 15 May 2012 16:15:34 -0400

is it possibile for students with PhD degree to apply for this position ?

many thanks

ali adib

Reply

HussamNasreddin — Tue, 15 May 2012 11:36:06 -0400

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Dear Frank,

Thanks for your reply. I have joined the Google group you
proposed, I noticed your generous contribution to helping others there too.

However, many of the links to websites didn’t work on my PC
for some reason including the one here in your message. http://imechanica.org/files/Writing

I would like your opinion on to how to practice writing
UMAT/VUMAT subroutines as I am a beginner. Is there a starting step that you
would recommend because I don’t understand what and how commands are written in
the script.

I didn’t find the manual helpful for this purpose; don’t
know if you would agree?

If you also could provide a VUMAT/UMAT on elasticity, it would
be great. I could then understand its components and apply a state variable
accordingly.

I realise that this is quite a bit to ask for but your help
is very much appreciated.

Many thanks again

Hussam Nasreddin

ESPI hardware

vicsv — Tue, 15 May 2012 10:17:47 -0400

I think you have hardware limitation. Maybe framerate is unsufficient.

I'm not familiar with Optonor software. If you have camera with 40 fps and you use a phase-shifting algorithm, you need about 0,1s to record images. During this time displacements of the tested objects must be less then lambda/10 (lambda is a laser wavelength).

You can try to make smaller ROI to increase framerate of images grabbing.

Another problem could be if inplane displacements are significantly bigger than out-of-plane displacements. This can lead to decreasing or vanishing of a fringe contrast.

You can record fringe patterns without phase-shifting algorithm to avoid averaging. It is requires manually calculation of fringes and computation of deformation using simple formula, but this is hard and time consuming job.

Strain

Kewei Li — Tue, 15 May 2012 00:08:15 -0400

Y C Fung talked about it in his book. I remeber he mentioned how to calculate it from displacement.

Abaqus

Kewei Li — Mon, 14 May 2012 23:31:26 -0400

It looks like you have a problem with Intel Fortran compiler. Make sure you install the right version.

Re: work conjugacy

Amit Acharya — Mon, 14 May 2012 14:55:50 -0400

I actually took a quick look through the paper when it appeared but could not find it discussed in the text - may be I just missed it.