iMechanica - Journal Club Forum - Comments

Another nice paper on soft tissue strain measurement

MichelleLOyen — Thu, 03 Apr 2008 08:39:01 -0400

H. Lu et al did some beautiful work on higher order effects in Digital Image Correlation, see

Deformation Measurements by Digital Image Correlation: Implementation of a Second-order Displacement Gradient

by H. Lu and P.D. Cary, Experimental Mechanics 40 (2000) 393.

Most algorithms for strain measurement are direct and do not require an assumed functional form to the constitutive model.

My concern is in the time-dependent mechanical behavior of soft tissues in this context. If you deform the sample rapidly and use these data to examine local strains, you might get a very different picture than if you examine the equilibrium configuration, where physical rearrangement of the tissue microstructure might be possible.

egg vs. hen

Zaoyang Guo — Wed, 02 Apr 2008 20:08:00 -0400

Dear Tammy,

Very interest topic. One of my research interests is to develop hyperelastic constitutive model for soft tissue. If the strain measurement requires the constitutive model to be pre-determined, then the experiment vs. model is like egg vs. hen. Which one should come first?

I cannot access the papers you mentioned currently, can you introduce more about the resolution of the strain measurement?

Many thanks,

Zaoyang

Playing with nanotubes.

Karen Peterson — Sun, 16 Mar 2008 20:52:15 -0400

That's true, there is still so much to discover about nanotubes. Hopefully computational modeling will help us improve what we know about the CNT. The Lieber group is doing amazing and i really hope things will work out well.

Karen, rpg games.. in tubes

Manipulation of individual

Jianyu Huang — Thu, 04 Oct 2007 22:48:49 -0400

Manipulation of individual SWCNT has not been possible. Using 200 kV TEM, the SWCNT is likely to be burned rapidly by e-beam irradiation. 80 kV or 120 kV is ideal. At such low kV, your resolution is not that great, hopeless to image point defects. However, if you have a Cs-corrector, it is possible to image point defects, such as 5/7, or individual vacancies. Iiijima's group published some papers in this regard recently.

imechanica get together at MRS

Rohit Khanna — Thu, 04 Oct 2007 00:42:30 -0400

Prof. Oyen,

Regarding imechanica get-together at MRS Fall meeting, i will be happy to volunteer.

Sorry, i checked your post on imechaica today only. let me know if i can help you.

Best Regards,

Rohit

individual SWNT Manipulation

gurpreet — Thu, 06 Sep 2007 03:06:44 -0400

Great website. Great to see all the biggies!!

I was curious if there any group who has done 3-d manipulation of individual SWNTs? is it possible at all? Also is it possible (or how difficult) to see defects in an individual SWNT using 200 kV TEM (F-20)? Please note that I am not talking about a SWNT Rope. Thank You.

Gurpreet Singh

Seeking volunteers for MRS get together planning

MichelleLOyen — Mon, 03 Sep 2007 05:31:54 -0400

I would very much like to have an iMechanica get-together at the MRS fall meeting in Boston (26-30 Nov. 2007). I am seeking at least a few volunteers to help with organization and running of such an event; please reply here or email me if you are willing to get involved!

Michelle

Get-together at MRS FAll 2007

Rohit Khanna — Fri, 31 Aug 2007 02:31:50 -0400

hi,

May i know if you have any plans to organize imechanica get-together during MRS Fall 2007 meeting.

Best wishes,

Rohit

Hydrogel - cont'd

Aaron Goh — Sat, 25 Aug 2007 03:59:27 -0400

Since you mentioned fracture, Jerry, I was wondering, that when a gel sets, is there any residual stress in the gel, such that when the gel is broken into two, the sum of the two parts, in terms of volume, is greater/smaller than the original, and as a result, the water is absorbed/released. I was wondering whether it is common to have mechanically responsive gels.

Poroelastic contact

MichelleLOyen — Mon, 30 Jul 2007 08:06:02 -0400

Our recent preliminary work--on implementing poroelastic contact mechanics models from the literature for analyzing experimental indentation data--has just appeared in proceedings format (link to the paper on the MRS website --free download for members).

Hydrogels' rather slow response to surrounding stimuli

Hua Li — Tue, 24 Jul 2007 08:53:31 -0400

Zhigang, this is a good topic with wide-range applications. Howerer, one of disadvanges of the smart hydrogels is their rather slow response to surrounding stimuli. Maybe an approach is to increase the surface of hydorgel componemt in MEMS devices by optimal design of geometry. Unfortunately, this often weakens the mechanical strength of the hydorgel. I am really interested in any comments on this concern.

Me too

Hua Li — Tue, 24 Jul 2007 08:45:59 -0400

Zhigang, many thanks go to you to take a look on our work. So far we have developed 3 models for simulation of hydrogels responding to solution pH, externally applied electric voltage and surrounding temoerature, respectively. All are based on Nernst-Planck-Poisson system. They are really preliminary work and there are a lot of rooms to improve. I most sincerely appreciate any comments and discussions on them. Further, I also look forward to researchers who are interested in work with us for opening one more window. Yes, I also look forward to meeting you soon.

Hydrogels at small scales

Zhigang Suo — Fri, 20 Jul 2007 22:08:19 -0400

Rui: Here are a few points relevant to your comments.

Indeed, hydogels have been used in small devices so that time delay is very small. One example is hydrogel used to control flows in microfluidics (Beebe 2000). In such a case, once you know the time scale to attain equilibrium, the diffusion process is irrelevant. All you need is an equilibrium theory.
An equilibrium theory of swelling has long been available. For example, you can find the field equations in my lecture notes, and a free energy function from chapter 7 in the book by Treloar.
When the feature size approaches the Debye length, electrical effects can be significant.

hydrogel at nanoscale

Rui Huang — Fri, 20 Jul 2007 10:59:38 -0400

Is it possible that at the nanometer scale (<1000 nm) all the kinetic processes are soon finished and thus what observed in experiments is mainly equilibrium state (suppose that the loading conditions are time-independent)? If so, would an elastic constitutive model (most likely nonlinear due to large deformation) be sufficient to describe or predict the equilibrium state? Thanks.

Hua Li's paper on stimuli-responsive hydrogels

Zhigang Suo — Fri, 20 Jul 2007 09:12:18 -0400

Dear Hua: Great to hear from you! Although we have not met, I have been studying your JAP paper on stimuli-responsive hydrogels. Your paper has put many modeling issues together. I look forward to meeting you in person next week.