iMechanica - interface - Comments

Modelling FGM in abaqus

Ravitej K — Wed, 10 Oct 2007 01:04:59 -0400

hello all,

i am doing my Mtech in iit kanpur, i am working on FGMs. can i model the FGM in abaqus by using layered model with the property is varying with each and every layer. or are there any special element for which we can assign property variation along the thickness?

Genoa software

AndreaTomei — Fri, 31 Aug 2007 05:17:33 -0400

Hi mr Xie

I am a italian student and i am using Genoa for VCCT. I have some problem simulating the propagation of delamination in a plate with an initial central circular zone of delamination subjected to compression.

I select as VCCT path all the nodes of the plate expept the ones belonging to initial circular delamination.

Is it possible that in Genoa VCCT the crack path must be a line and not a surface?
I hope to be clear

Thanks

Andrea

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.

More effects on the modulus of hydrogels

Hua Li — Fri, 20 Jul 2007 08:57:04 -0400

Jerry, I just know this interesting Journal Club by Zhigang's email sent to Lu Chun. Zhigang will stay in IHPC of Singapore from 25 July to 5 Aug. I look forward to an appointment with him to share our work on modeling of smart hydrogels responding to pH, externally applied electric voltage and environmental temperature, respectively.

To my understanding, the modulus of hydrogels is governed not only by crosslinking density, also by others, especially for environmentally responsive (ER) hydrogels. obviously, the modulus of pH-sensitive hydrogel also varies with solution pH. Therefore, development of constitutive models of hydrogel becomes a challenge. A large variety of hydrogels, from very soft state like mucus to hard state like solid, makes it more chahallenging.

Zhigang, thank you for your email sent to Lu Chun

Hua Li — Fri, 20 Jul 2007 08:56:20 -0400

Zhigang, thank you for your email sent to Lu Chun to let me know this interesting Journal Club. I know you will stay in IHPC of Singapore from 25 July to 5 Aug. I look forward to an appointment with you to share our work on modeling of smart hydrogels responding to pH, externally applied electric voltage and environmental temperature, respectively.

To my understanding, there is a large variety of hydrogels, from very soft state like mucus to hard state like solid. Thus it is difficult to develop the constitutive models of hydrogel by a generalized formulation, especially for environmentally responsive (ER) hydrogels. Elastic, vicoelastic or plastic behaviors are observied in various hydorgels.

viscoelasticity vs. poroelasticity

Zhigang Suo — Wed, 18 Jul 2007 15:54:57 -0400

Mishelle:

I'm rereading the thread initated by you on viscoelastic contact, and find many discusions of viscoelastcity and poroelasticity there are very relevant to the Theme of this month. Thank you.

Notes on polyelectrolyte gels

Zhigang Suo — Fri, 13 Jul 2007 09:46:26 -0400

Dear Wei: This is my last day at IFMA. Tomorrow will be the French National Holyday. Denian, Michael, and I will spend the weekend in Lyon over the weekend, and I'll be back to Cambridge on Tuesday.

In response to your concerns over electrical effects, I've written some notes on polyelectrolyte gels in between visits to Puy-de-Dome and Michelin Museum The notes are very rough, and likely contain errors, but I think the basic ideas are sound. Please look at them and we should discuss next week.

Thanks, John. Very nice

H Jerry Qi — Wed, 11 Jul 2007 23:49:39 -0400

Thanks, John. Very nice work on the tribological behaviors of hydrogels. I am also eager to see your work on the failure characteristics of hydrogels.

Jerry

fracture of gels and tribology

John E. Dolbow — Wed, 11 Jul 2007 19:25:29 -0400

Jerry,

This is a great point and I'm glad you brought it up. We've been looking into the failure characteristics of hydrogels for awhile here at Duke, and the results are really interesting. We see many phenomena that are not observed in other "soft" polymers. I hope to find some time to write this up soon.

SRHs also exhibit interesting tribological behavior, with apparent frictional coefficients changing by an order of magnitude with phase state. This is another aspect that is often neglected when hydrogels are discussed for small-scale devices: friction can be a show-stopper. Our work recently appeared in Langmuir .