iMechanica - viscoelasticity - Comments

Thanks

Andreas Burger — Sat, 26 Jul 2008 21:29:52 -0400

thanks for the link Aaron

Andreas

ABAQUS viscoelasticity

Aaron Goh — Wed, 23 Jul 2008 11:09:00 -0400

Andreas,

This has been discussed before:check out this thread:

http://imechanica.org/node/1784

ABAQUS does have a user-friendly way of modelling non-linear viscoelasticity.

Hi Andreas

Mike 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!

That's good news indeed.

Albert F Yee — Sun, 27 Apr 2008 18:01:42 -0400

That's good news indeed. I've been looking for such a book for reference and teaching.

Thanks! Unfortunately, we

cbrinson — Sun, 27 Apr 2008 11:58:56 -0400

Thanks! Unfortunately, we did not go into shape memory polymers. A topic saved for the second edition!

Great!

Xiang Chen — Sat, 26 Apr 2008 15:22:36 -0400

I'm just in need of such a book. Is there specific discussion on shape memory polymers?

RE: Internship available in FEA of Elastomers

Muralidhar Seshadri — Thu, 17 Apr 2008 18:31:46 -0400

This internship position is now closed. Thanks for the interest of all those who applied.

Sample determination

Manfred Achenbach — Mon, 31 Dec 2007 15:40:39 -0500

Sample determination methods for the viscoelastic model can be found at

http://www.viscodata.de/

Bone specimen preparation and nanoindentation measurments

Gregory FAVARO — Tue, 25 Sep 2007 05:28:36 -0400

Dear all,

We are working a since 5 years in Bone and dentine application with Geneva Hospital
(Prof. Patrick Amman).
Actually in Geneva
they cut the bone with a microtome and polish its but the biggest difficulty is
to measure the Nanoindentation with the good hydratation! Actually we re-hydrated
the bones but we have develop a liquid cell to measure the bone in
humidity!

We really need to compare the result in wet atmosphere if we want simulate
the reality!

Please see this very interesting article about intrinsic Nanoindentation for
bones! http://www.csm-instruments.com/new/contenus/e/doc/bulletins/AB_24.pdf

Do not hesitate to contact me for furteher information

Bone specimen preparation

MichelleLOyen — Mon, 03 Sep 2007 05:55:36 -0400

A slow diamond saw (like Buehler Isomet) is also very common and quite useful for bone and tooth specimen preparation, and allows for samples with more variety in sizes than microtoming.

More discussion during MRS meeting

Rohit Khanna — Mon, 03 Sep 2007 01:36:48 -0400

Thank you Prof Michelle for the response. I did not get much responses from imehanica community. may be this subject is not of great interest to many of imechanica members. I hope by coming MRS meeting, i will have a good reason to tell you, why research in this direction is important. You are absolutely right in saying that hydration state limits adhesion. It may be good to study on fundamental science aspect.

I have a poster in your symposium on Fundamentals of nanoindentation and nanotribology. It will be great to have useful discussion with you. This time, i don't see a big crowd of researchers for this symposium.

Best wishes,

Rohit

Adhesion, nanoindentation and biological things

MichelleLOyen — Sat, 01 Sep 2007 14:03:04 -0400

Very nice summary, Rohit.

Just one comment on perhaps why this has been a bit neglected as a topic... many of the biological materials of interest to researchers are fundamentally hydrated. For example, tissues in the body are in wet environments, as are plant materials. The hydration state has a fundamental effect in these materials' mechanical behavior in general, but also seems to limit the adhesion with a hard, stiff indenter. In fact, I had a colleague once tell me to put a thin water film on PDMS and that would limit adhesion effects in AFM-based indentation analysis.

Educational workshops

Rohit Khanna — Fri, 31 Aug 2007 00:03:16 -0400

Hi, Ferguson... i read your opinion about the current state of the research about mechanics of soft materials. I agree with you that there are also non-experts also in this field which may be biologist, material scientists etc.... May be because of lack of exposure in this field, the research has not progressed much in this direction. It is practically impossible for just one or two groups to be active in this area, the contribution has to come from a large group of researchers and then, only we can expect advancement in science and technology. I personaly believe that experts in this field should take the initiative to educate the researchers who are non-experts in this field. It may be good to organize educational workshops. I had been to such a workshop, quite recently in UIUC, on Cell mechanosenstivity, which dealt with various topics of interest like cell adhesion, cell mechanics, cell-biomaterial interactions etc. Experts in the field like Prof. Dennis Discher (UPENN), Prof. Michael Sheetz and many others, presented a review of the literature in these topics, and we also had hands-on experience on some experiments.

I hope to know your opinion on this.

Best wishes,

Rohit Khanna

Adhesion effects in nanoindentation

Rohit Khanna — Thu, 30 Aug 2007 23:46:11 -0400

Apart from the review of biomechanics literature presented by Michelle, Li and others, there are another important issues which need to be addressed. I agree that bonding is quite different in soft materials. Another research field which is not majorly touched by many of the researchers is the adhesion effects seen during unloading from a soft substrate. They do affect the elastic modulus measurement. There have been recent studies on such effects on soft material like polydimethysiloxane (PDMS). We know that there are limitations on the part of instrumentation unavailability, due to which accurate determination of time-dependent properties of soft materials has not been succeded to much extent. But i am surprised, why research has not progressed in looking at adhesion effects in nanoindentation. There has been model development to take into account such effects for last 35 years. First paper had come from Prof. K L Johnson who did a pioneered in establishing the theory of adhesion effects.

One can not ignore adhesion effects without which accurate determination of elastic modulus is not possible as far as my understanding is concerned.

I have done some review on this topic with the hope that it does not go un-noticed.

Adhesion is observed as a region of negative load during unloading in a load-displacement curve. Adhesion between the diamond tip and the sample can interfere with the measurement of indentation modulus using the compliance method for polymers and tissues [1-4]. Recent research reports on nanoindentation of soft polymers [1,4] have mentioned that the compliance method overestimates the modulus when there is significant tip-sample adhesion. For indentation with spherical tip, Johnson-Kendall-Roberts (JKR) [5] adhesion model has been shown to be give more accurate measurement of sample modulus [1,4,6]. The JKR method can be described as, first starting the indent out of contact and then capturing a full force curve as the tip approaches, indents, and retracts from the sample [6-8]. These force curves have been commonly used in AFM to measure the adhesive forces [9,10], but not yet applied to many nanoindentation studies of biomaterials.

1. Carrillo, F., et al., J. Mater. Res.(2005) 20, 2820
2. Klapperich, C., et al., J. Tribol. – Trans. ASME(2001) 123, 624.
3. Grunlan, J. C., et al., Rev. Sci. Instrum.(2001) 72, 2804
4. Carrillo, F., et al., J. Mater. Res.(2006) 21, 535
5. Johnson, K. L., et al., Proc. R. Soc. London, Ser. A(1971) 324, 301.
6. Ebenstein, D. M., and Wahl, K. J., J. Colloid Interface Sci.(2006) 298, 652
7. Wahl, K. J., et al., J. Colloid Interface Sci.(2005) 296, 178
8. Giri, M., et al., Langmuir (2001) 17, 2973.
9. Butt, H. J., et al., Surf. Sci. Rep.(2005) 59, 1
10. Cappella, B., and Dietler, G., Surf. Sci. Rep.(1999) 34, 1

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Best regards,

Rohit Khanna

Hello Professor Thank you

Chul jin Syn — Thu, 30 Aug 2007 10:45:35 -0400

Hello Professor

Thank you for your suggestion.

We used the water jet to prepare bone specimens. The microtome method will be worked for ideal specimens.