iMechanica - Viscoelastic Contacts - Comments

viscoelastic indentation adhesion

MichelleLOyen — Sun, 10 Feb 2008 17:15:17 -0500

A good set of papers come recently out of the lab of Kathy Wahl, including these:

Ebenstein DM, Wahl KJ. "A comparison of JKR-based methods to analyze quasi-static and dynamic indentation force curves", Journal of Colloid and Interface Science, 298(2):652-662 (2006).

Wahl KJ, Asif SAS, Greenwood JA, Johnson KL, Oscillating adhesive contacts between micron-scale tips and compliant polymers. Journal of Colloid and Interface Science, Volume 296, Issue 1, 1 April 2006, Pages 178-188.

I also enjoyed:

Basire C and Fretigny C, Kinetics of adhesion on a viscoelastic sample by force microscopy. Tribology Lett. 10 (2001) 189-93.

Hope that helps!

suggest me some papers regarding below issue

krishnaraokorada — Sat, 09 Feb 2008 04:04:02 -0500

I am doing experiments of adhesion by using both film and indenter(PDMS hemi sphere) made by PDMS. I want to know about the validity of application of JKR theory for this and please suggest me some papers regarding this.

thank you

suggest me some papers if both the film and indenter are elastic

krishnaraokorada — Sat, 09 Feb 2008 03:13:14 -0500

thank you

Finding work of adhesion on a non-control film(PDMS)

krishnaraokorada — Fri, 02 Nov 2007 06:47:57 -0400

Is there any method to find work of adhesion for a non-control film in which JKR equation is not applicable(linear fit)?Thank you

Here is the link

Seungtae Choi — Mon, 21 May 2007 11:51:03 -0400

The strain was approximately 10 % in average sense. Your point is quite right since PDMS is elastic up to quite large strain level, but it can be viscoelastic. We did find time-dependent behavior of PDMS. Even we observed residual deformation (we can say it as viscoplastic behavior). You can see the results from the link.

http://me.kaist.ac.kr/~fracture/stchoi/Nanoindentation.pdf

Seungtae Choi

R&D Staff Member

Micro Systems Lab, SAIT

Republic of Korea

Viscoelastic nanoindentation in bone

MichelleLOyen — Mon, 21 May 2007 11:45:53 -0400

I agree that viscoelastic indentation has received little historical interest but this does seem to be changing quickly! The recent burst in activity in the literature seems to be driven separately by interests in polymer (and polymer-matrix composite) characterisation and by biological material studies. My own motivations were originally in characterising biological materials, and we are finally starting to make some progress.

A study on variability in sharp (Berkovich) viscoelastic nanoindentation on bone was just published:

Oyen ML and Ko C-C: Examination of Local Variations in Viscous, Elastic, and Plastic Indentation Responses in Healing Bone, Journal of Materials Science: Materials in Medicine, 18 (2007) 623-8.

(Inexplicably it has not yet appeared on the journal's website but I posted a preprint previously here .)

This is in addition to two recent works on spherical indentation viscoelasticity in bone:

Bembey AK, Oyen ML, Bushby AJ, Boyde A: Viscoelastic properties of bone as a function of hydration state determined by nanoindentation. Philosophical Magazine, 86(33-35) (2006) 5691 - 5703.

Bembey AK, Bushby AJ, Boyde A, Ferguson VL, Oyen ML: Hydration Effects on the Micro-Mechanical Properties of Bone. Journal of Materials Research, 21 (2006) 1962-8.

And an invited review paper:

Oyen ML and Bushby AJ, Viscoelastic Effects in Small-Scale Indentation of Biological Materials.

published in International Journal of Surface Science and Engineering 2007 - Vol. 1, No.2/3 pp. 180 - 197 .

Viscoelasticity in PDMS thin films?

MichelleLOyen — Mon, 21 May 2007 11:33:34 -0400

How much viscoelastic deformation were you seeing in PDMS? Its response is the closest thing to a time-independent elastic material as I have ever seen!

A few other recent papers have considered indentation viscoelasticity in thin films:

Oyen ML, Cook RF, Moody NR, and Emerson JA: Indentation Responses of Time-Dependent Films on Stiff Substrates, Journal of Materials Research, 19 (2004) 2487-97. Erratum in Journal of Materials Research, 19 (2004) 3120-1.

Zhang CY, Zhang YW, Zeng KY, Extracting the mechanical properties of a viscoelastic polymeric film on a hard elastic substrate. J. Mater. Res. 2004, 19(10):3053-61.

And of course the classic paper for this problem (flat punch indentation of compliant film on soft substrate) is actually in the biomechanics literature:

Hayes WC, Keer LM, Herrmann G, Mockros LF, A mathematical analysis for indentation tests of articular cartilage. J Biomech 1972, 5(5):541-51.

Modified-creep experiment of an elastomer film

Seungtae Choi — Mon, 21 May 2007 11:30:21 -0400

Viscoelastic contact is one of very interesting topics for me. We may encounter many situations involving contacts of soft materials in flexible electronics and bio-related applications. Recently, I have conducted indentation experiments of elastomer films with a flat-ended cylindrical tip. Among various shapes of indenter tips, a flat tip only provides constant area during indentations, which makes it easier than others to analyze the indentation experiments. The attached manuscript is the summary of our experiments, which was recently submitted to a Journal. The theory in the manuscript is based on the evelopment of our solution for the flat indentation on an elastic film bonded to a rigid substrate, which will also be submitted to a Journal shortly. Since PDMS film is so compliant that the head dynamics of Nano Indenter XP system is taken into account. Even though an elastomer film, PDMS (polydimethylsiloxane), was tested, and the indentation depth was approximately 10 % of the film thickness, we uses the linear theory of viscoelasticity to quantify the relaxation modulus in time domain. I hope this indentation method and the results will help our understanding of viscoelastic materials.

Seungtae Choi
R&D Staff Member
Micro Systems Lab, SAIT
Republic of Korea

Hydrogel mechanics

Kaifeng Liu — Mon, 09 Apr 2007 12:21:07 -0400

Fellows,

I agree with Michelle. In soft hydrogels, water content varies from 50%-90%. Fluid flow by no means shall be ignored. Modeling of hydrogel mechanical response is not a easy thing. Current mechanical constitutive models can be classified in two big categories, to my understanding, single phase and multi phase. Among single phase models, various nonlinear elastic (e.g. hyperelastic) and viscoelastic models are out there. Hydrogels show definitely time-dependent behavior in experiments such as compressive creep test. Nonlinear elastic models certainly have limitations in this sense.

Biphasic model that accounts for the fluid flow in a porous media has been used to model cartilage for over 20 years (dated back to Mow V.C. 1980).

It is just recent that this idea is brought into hydrogel mechanics. Some studies used biphasic elastic (Broom and Oloyede 1998; Silva et al 2005;Lei and Szeri 2007) or biphasic viscoelastic model (Olberding and Suh 2006) in their study. More experimental observations are need to understand the fluid flow behavior in hydrogel, especially in surface layer. It is very important not only to the stress-strain response but also to the surface tribological behavior, since hdyrogels are experted to replace articulating load bearing tissues.

I am working on a biphasic viscoelastc model for hdyrogels right now. I would be happy to keep communicating with the community on this forum.

BTW, I love the idea of hydrogel mechanics for the jounal club! Dr. Dolbow, nice to see you here. I enjoy reading your recent publications on hydrogels.

References:

Broom, N. D. and A. Oloyede (1998). "The importance of physicochemical swelling in cartilage illustrated with a model hydrogel system." Biomaterials 19(13): 1179-1188.

Lei, F. and A. Z. Szeri (2007). "Inverse analysis of constitutive models: Biological soft tissues." Journal of Biomechanics 40(4): 936-940.

Mow V.C., Kuci S.C.Lai W.M.and Armstrong C.G.,Biphasic Creep and Stress Relaxation of Artieular Cartilagc in Compression:Thcory and Experiments,J.Biomechanical Engincering,Vol.102,1980,pp73～84

Olberding, J. E. and J. K. F. Suh (2006). "A dual optimization method for the material parameter identification of a biphasic poroviscoelastic hydrogel: Potential application to hypercompliant soft tissues." Journal of Biomechanics 39(13): 2468-2475.

Silva, P., S. Crozier, et al. (2005). "An experimental and finite element poroelastic creep response analysis of an intervertebral hydrogel disc model in axial compression." Journal of Materials Science-Materials in Medicine 16(7): 663-669.

Kaifeng

Some observation on viscoelastic nanoindentation

Gang Huang — Fri, 09 Mar 2007 16:13:15 -0500

It is really good to see some enlightening discussions on viscoelastic contacts in this forum. Not like elastic indentation for which methods have been well established to measure mechanical properties, measuring viscoelastic properties using nanoindentation still remains as a topic not fully paid attention to. In recent years, efforts have been made in the study of viscoelastic indentation, to name a few, such as creep/relaxation behavior during viscoelastic indentation using flat punch indenter, measurements of creep compliance and relaxation modulus using nanoindentation, sharp viscoelastic indentation. For non-experts in this area, a free software from Dr. Hongbing Lu’s group is available for use to solve for creep compliance using constant rate/step loading conditions. When viscoelastic material has varying Poison’s ratio, nanoindentation can be used to measure two independent material functions. Nonetheless, work on viscoelastic indentation, especially on nonlinearly viscoelastic contacts is far from complete. Even in the regime of linear viscoelasticity, a lot of problems still remain unresolved to well understand viscoelastic indentation, such as entire unloading history, indentation on viscoelastic materials with anisotropy, and so on.

thermal effects in hydrogel impacts?

MichelleLOyen — Wed, 07 Mar 2007 03:56:06 -0500

I had not thought of this interesting question before. One of the things that makes hydrogels and biological materials critically different from classic engineering materials is water. Wet materials are affected by the weird and wonderful properties of water, which is quite an anomolous liquid. Most importantly in the context of this question, the high thermal conductivity of water (highest of any liquid) helps prevent local thermal fluctuations and temperature changes in "wet" organisms like ourselves and thus I would not necessarily expect a large thermal effect in hydrogel impact.

the thermal effect during viscoelastic contact

Wei Wang — Tue, 06 Mar 2007 17:20:22 -0500

Prof. Dolbow and Michelle

Thank you so much. I think another problem is the thermal effect during viscoelastic contact ( e.g. impact with hydrogel). The heat has to be produced from the energy dissipation during the impact. So it is close related to the thermal mechanical properties of hydrogels(heat conductivity, time scale etc.) Could you talk something about this in the transient impact process from your understanding ? Also I welcome any comments from others.

Thanks.

Viscoelastic

Aaron Goh — Wed, 28 Feb 2007 17:24:34 -0500

Michelle,

You are right, I was tempted to add 'in the timeframe of a typical Instron test' but decided not to and I realise that is a mistake. It is pretty much like the concept of 'yield stress' of soft solids and the duration to measure it which my more enlightened colleagues like to argue about (think shelf-life of products and doing a test to match that time frame).

I think another reason why indentation is popular is that in-vivo it is probably the only test can that can be done!! Imagine probing the swelling of a brain by taking a piece of it to do a compression test....

Michelle, Thank you so much

niteshjain — Wed, 28 Feb 2007 10:36:03 -0500

Michelle,

Thank you so much for your promt response, your suggested reference will be of a great help. I would really appreciate if you let me know if you come acorss any more good references in this area.

Thanks

Nitesh

Resources for nonlinear VE indentation

MichelleLOyen — Wed, 28 Feb 2007 09:29:51 -0500

I don't know offhand of a good single journal reference for the basics of indentation in nonlinearly viscoelastic materials (you may have identified a gap in the current literature!) However, it can't hurt to read up on indentation of linearly viscoelastic materials (section 6.5 in Johnson's Contact Mechanics) and indentation of nonlinear materials (section 6.6 in the same) although the treatment of nonlinearity here is focused on plasticity, not materials with strain-stiffening responses.

I also recommend the book "Creep and Relaxation of Nonlinear Viscoelastic Materials with an Introduction to Linear Viscoelasticity" by Findley, Lai and Onaran as a general text for nonlinear viscoelasticity. However, their treatment of (even linearly viscoelastic) indentation appears to suffer from a lack of awareness of the work of Lee, Radok, Ting (and others) who addressed the moving boundary condition issues that arise with spherical punch geometries.

Viscoelastic Contacts

MichelleLOyen — Tue, 13 Feb 2007 06:11:13 -0500

I was a little bit surprised in the introduction of this new forum to see mention of elastic and plastic contacts but no specific mention of viscoelastic contacts.

In the era of commercially-available instruments for indentation testing, the examination of viscoelastic contact mechanics, both in the context of polymers and biological tissues, seems to have taken on new life. To a first approximation, for indentation testing in the time domain, the fundamental mechanics has not much advanced beyond a few classic papers of the 1960s: Lee and Radok, J. Appl. Mech. 27 (1960) 438 and Ting TCT, J. Appl. Mech. 88 (1966) 845. However, the implementation of techniques for analysis of experimental data has progressed substantially. With spherical indenters the use of linearly viscoelastic models for characterization of a material creep or relaxation function is straightforward. Recent experimental studies have confirmed this, while more lingering questions remain for sharp contacts including Berkovich pyramidal indenters (most commonly shipped with commercial indenters). Sharp contacts seem to give rise to nonlinearly viscoelastic responses. Other topics of recent interest include frequency-domain measurements and examination of oscillating contacts and adhesion. (Although not mentioned in the listing of KLJ's most-loved topics in contact mechanics, viscoelastic contact has been the subject of several recent KLJ publications!) Although research in viscoelastic contact mechanics has been strong in recent years, perhaps a challenge remains in the dissemination of information and the establishment of approachable experimental techniques for use by non-experts.