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Experimental Nanomechanics

Xiaodong Li's picture

Colleagues and friends,

As 2007 is approaching, our community will have a new platform for information exchange and discussion – J-club (please see previous posts. I would like to propose a topic for upcoming issue (May issue? if possible) – “experimental nanomechanics.” The extremely small dimensions of nano building blocks such as nanotubes, nanowires and nanoparticles present challenges for existing instruments, methodologies and theories.Modeling and computational work is strongly dependent upon accurate (reliable) experimental results which are still lacking. I believe that this topic is timely and of great interest to both experimental and modeling parties.

This post is a call for suggestions for the proposed topic. Please contact me (lixiao@engr.sc.edu) or leave comments below.

Dear professor Li   I strongly agree with your proposed topic"experimental nanomechanics". as all of us well known, the experiment is the most important part of research. at present, many breakthroughs depend greatly on the experimental instruments. taking my research topic for an example, I am involving in the investigation of size effect of submicron microcrystal single crystal, in the meantime, the unixial compression of microcrystal using the nanoindentation outfitted with a flat diamond indenter played a dominant role in the ultimate results, as far as I know, the misalignment during the unixial compression testing may lead the variation of elastic modulus, further affect the yielding strength,etc, it is my personal opinion that the advance of nano-test instruments will provide many means and opportunities with the development of mechanics at micro of nano scale.whereas, the advancement of nano-test intruments contrarily rely on the development of nanomechanics, so they represent the both side of a coin.

Hello, Prof. Li. Your proposed topic is obviously deserved for J Club. However, I think that topic of "nanomechanics" is too broad to be considered in a single issue. We may consider "nanomechanics" to a few issues in J Club.

For the topic, I would suggest one possible topic, that is, "resonator for nanomechanics" in an area of "nanomechanics". Specifically, in recent decade, resonators have taken attention because of their capability of sensitive detection of nanomechanical behavior. For instance, the quantum mechanical behavior has recently depicted by micromechanical resonators (e.g. See Roukes' paper and Schwab's paper). Also, resonators have allowed sensitive detection of molecules even in zeptogram (Roukes' paper published at Nano Letters). So, I think that this topic may be one of interesting nanomechanics topics.

Also, I think, the other topics such as CNT, nanoindentation, single molecule experiments, etc. may be valuable to be taken into account for an issue in J Club. Maybe we need to select the possible representative topics for paper review in J Club.

Anyway, I hope that this "nanomechanics" topic may be well developed by Editor, Hosts, and anyone who is interested in "nanomechanics".

Kilho

I think that it is also possible to consider "Computational Nanomechanics" ("Multi-scale Modeling") for J Club. As we have known, the "computational nanomechanics" has appeared since the work by M Ortiz and R Phillips in "multi-scale modeling" that combines the FEM and molecular model. Many researchers have applied this method to analyzing crack problem (e.g. See Buehler's paper), protein mechanics (e.g. See Schulten's paper; Gohlke's paper; Buehler's paper; etc.), CNT nanomechanics (e.g. See YG Huang's paper), fluid mechanics (e.g. Engquist's paper), etc.

It may be valuable to take into account "computational nanomechanics" ("multi-scale modeling") for future issues in J Club.

Kilho

MichelleLOyen's picture

I agree this is an excellent choice for the J-club and also agree that it should be split into several distinct themes.  In addition to those proposed above, I'd love to see some discussion of the breakdown of continuum mechanics at nm-scales.  I also fully support nanoindentation (and nanotribology) as a separate topic (or two) from other aspects of nanomechanics.  We will be running the popular "Fundamentals of Nanoindentation and Nanotribology" topic at the Fall MRS meeting in 2007 and a tie-in with timing and content of the J-club would be one interesting mechanism to get J-club members together in person for a live discussion.  We can organize a room in the evening and even possibly arrange a panel, as was done for the topic of time-dependence in nanoindentation at the 2004 meeting. 

Xiaodong Li's picture

Good point! Nanoindentation definitely deserves a focus theme in J-club. In recent years, significant progresses have been made in nanoindentation in terms of theory and experimental (methods and instrumentation). However, we are still facing challenges. Can we measure other mechanical properties (not just hardness and elastic modulus)? Can we measure the mechanical properties of ultra-thin films (of a thickness less than 10 nm, for instance)? We need breakthroughs.  I have proposed that for the upcoming May issue we will first focus on experimental mechanics of nano building blocks. I would like to propose another upcoming issue on nanoindentation. Hope you can join me to host the nanoindentation issue.  

MichelleLOyen's picture

There is no question that we can make measurements other than modulus and hardness with commercial nanoindentation instruments; routine measurement of time-dependent (primarily linearly viscoelastic but also nonlinearly viscoelastic) behavior using indentation experiments has been demonstrated in a number of papers including experimental verification of the techniques by application to both polymers and biological materials. A list of my own ten or so papers on the topic can be found here. For biological materials there is plenty published already on poroelastic analyses as well.

 

I am fully supportive of the future nanoindentation J-club theme but believe I am excluded from hosting based on the "once per year" rule given that I am hosting the biomechanics topic this month. However, I'm sure there are plenty of others out there who might be interested in helping to host this topic!

 

Xiaodong Li's picture

I agree! I think we need someone to host the future issue – nanoindentation. This nanoindentation J-club theme may focus on recent advances in nanoindentation, in particular, on soft materials (viscoelastic - polymers and biomaterials, for example).  Hope that we can present state of the art, challenges and opportunities. 

MichelleLOyen's picture

I'd like to nominate my colleague Virginia Ferguson from Mech. Eng. at the University of Colorado to lead a nanoindentation J-club topic in that case; she is an expert in nanoindentation of biological materials and an occasional iMech participant (mostly by posting comments on biomechanics topics). She would be a perfect leader or co-leader for this emphasis.

Xiaodong Li's picture

Thanks for your nomination. I would like to welcome Virginia Ferguson on board to host this nanoindentation issue. I believe that this topic will attract attention from both experimental and modeling parties.  I will definitely participate in the detailed discussion on this topic since nanoindentaion is also my research focus.

VirginiaLFerguson's picture

If the offer stands, I would love to host a Journal Club discussion on nanoindentation with a special focus on biological materials. Hopefully I can strike up some discussion that will help to foster new ideas to move this field forward. There has been a bit of stagnation with regards to the application of nanoindentation of hard tissues / mineralized biological materials. Perhaps the advances that we can make will not necessarily lie in further development of the nanoindentation technique itself, but with the interpretation of nanomechanical data in the context of additional analysis techniques used to quantify site-specific material composition or microstructure. Or by using nanoindentation to explore time-dependent material behavior... There is still much to be done in our exploration of biological materials at small scales.

This should be fun - I look forward to a good discussion!

Best, Virginia

Pradeep Sharma's picture

Dear Virginia,

Please choose a month! If you look at the planned issues so far, we are booked until June. Anytime after that and before december would work.

VirginiaLFerguson's picture

Dear Pradeep: I would love to host the journal club in August (or any month after that). Please let me know if this will work and I will happily immerse myself in the literature between now and then to find the most compelling articles to discuss. Best, Virginia

Pradeep Sharma's picture

Virginia: thanks for volunteering. I will put you down for August.

Horacio Espinosa's picture

Clearly, experimental nanomechanics is a very important topic that deserves more attention within our community. Despite many recent advances in experimentation, a number of challenges in measuring properties at the nanoscale still remain. For instance, most techniques are indirect and lack the capability to provide real time direct observation of atomic defects and their evolution. In turn, interpretation of these experiments requires a number of assumptions making the discovery effort less rewarding and the findings less convincing.

To illustrate this point, let me give two examples in connection to two problems currently attracting a lot of attention within our community. The first example deals with the mechanical characterization of MWCNTs. It is well known that predictions of high strength (~100 GPa) and modulus (~1 TPa), based on quantum mechanics calculations, have been made for single-walled CNTs. Experimental work carried out in-situ the SEM initially predicted much lower values of modulus and strength for MWCNTs. Recently, values close to these theoretical predictions are being reported based on the same experimental set-up. Because of difficulties in testing these tiny objects and the assumption of outer shell failure in computing strength and modulus, one may wonder if the experimenter is being biased by the knowledge of the theoretical prediction or if indeed the data is accurate and reliable. Our in-situ TEM work recently demonstrated that MWCNT shells may be cross-linked during growth or by beam radiation. The experimental results show that the outer-shell failure assumption is not always valid. In fact, failure may involve simultaneous bond breaking in a number of shells as a function of sample growth conditions, purification history and observation method.

The second example deals with plasticity mechanisms at micro and nanoscales (characteristic dimension below 1 micrometer). Work on freestanding thin films, including our tensile testing of Au in the absence of macroscopic gradients, clearly shows changes in deformation mechanisms below a characteristic dimension. These findings were later reinforced by the testing of Au single crystals in the form of micropillars. Despite all the fascinating findings in this area, important questions are puzzling the community. For instance, some researchers reported very limited or inexistent residual dislocations in the deformed crystals. By contrast, others observed residual dislocation networks on similar sample geometries but not necessarily the same material. The observations were based on FIB prepared TEM samples. Likewise, at the last MRS meeting, a group reported the presence of strain gradients in the single crystal compressed pillars, while another reported absence of strain gradients. Both groups used x-ray diffraction but one conducted the measurement in real time while the other pursued the measurements post-mortem. A similar number of unresolved questions and issues can be advanced for the case of nanowires (NWs). In this case, the experimental evidence is very limited and most of the research work on plasticity and failure has been done using molecular dynamics simulations based on atomic potentials of somewhat unknown accuracy.

The importance of real time observation of plasticity and failure at the atomic scale is clearly illustrated by these examples. Because of this I would be interested in knowing what fresh ideas people can advance in nanomechanics testing beyond nanoindentation and other existing indirect techniques. In other words, a topic of discussion could be: What would be the “ideal” experiment to address these issues? What technological developments would be needed to develop such experiment? How can we use the experiment to assess theoretical and computational models taking into account limitations in computational power? Is there any example in the history of science that offers a paragon with this challenge? What are the similarities?

Now that I did the easy job (ask a bunch of questions), I prepare my self to reflect on your ideas and comments.

By the way, a special issue of the Journal of Experimental Mechanics on Nanomechanics will appear early next year. I hope you will read it and at the same time consider contributing to the journal.

 

Horacio D. Espinosa

Professor of Mechanical Engineering

Northwestern University

Prof. Espinosa, I cannot agree more with you regarding the failure mechanism of MWCNTs. I have experimental evidence showing clearly that it occured by breaking several layers simulyanuously instead of by just breaking the outermost shell. You know those people who worked in the nanotube area in the early days tend to make outragious claims. Unfortunately, many later researchers easily accepted such claims without a second thought. I am also very interested in your comment regarding the cross-link of MWCNTs. Do you have any evidence or any publication regarding this? Thanks! Jianyu Huang (jhuang@sandia.gov)

 

Horacio Espinosa's picture

Thanks for your interest. Indeed, we have a publication currently in press in the JMEMS where we report TEM observations of failure of MWCNTs in which cross-linking has occurred.  I will let you know when the paper is published.

 

Horacio D. Espinosa

Professor of Mechanical Engineering

Northwestern University

Xiaodong Li's picture

It appears that experimental mechanics of nano building blocks (nanotubes, nanowires and nanoparticles) is hot. I propose that May issue center on this theme - experimental mechanics of nano building blocks. This issue will present  state of the art in terms of experimental methodologies, findings, and instrumentation. Please contact me (lixiao@engr.sc.edu) or leave comments below.

Henry Tan's picture

I have an experimental result that shows the evolution of a dynamic process. The result has to be presented in a movie format. Does anyone know any scientific journal (inmechanics of physics) that can publish movies? Thanks a lot.

Xiaodong Li's picture

I think you can try to publish the movie as a support info file in Nano Letters.  If your subject is about nanoscale, I would like to say this is a good place to place your movie.  In the paper, you may need to show the representative images from the movie. Hope this helps.

Henry Tan's picture

Thank you, Xiaodong. I appreciate the help.

It is a pity, however, that my results are not in Nanoscale, but in micrometer scales.

Xiaodong Li's picture

Well, if it is at the microscale, I would like to suggest another journal - Nature Materials. That journal has an option for authors to place a support info file. It will be great if you can use your movie to demonstrate your new findings. I think that our community is also facing the same issue how to publish a movie file in this forum.

Teng Li's picture

Henry:

You're raising an important issue on publishing visualized (video-based) research results.  As Xiaodong pointed out, more and more journals allow authors to publish videos, as supplemental materials.  In the recently launched  Journal of Visualized Experiments (JOVE), videos become the main body of the article, while text description, figures and tables serve as supplemental materials. Currently JOVE invites submissions in all areas of biological sciences.  So far, however, I'm not aware of any video journal in physical sciences.  But I'm positive on its emergence in the near future.

Henry and Xiaodong:

Now you can post video in iMechanica. In an earlier post and the comments there, we discussed the possibility of publishing video type contents in iMechanica by using web video platform, such as YouTube. I wrote a step-by-step instruction in the post on how to publish YouTube videos in iMechanica.  Check out our video channel for more details.  Honglai, if you want, you can upload your video to YouTube and then publish it in iMechanica.

-Teng 

Zhigang Suo's picture

Teng:  you have been behind almost every software enhancement of iMechanica.  You might want to take a look at this screencast of Drupal 5, which mentions that video can be uploaded on a Drupal site. 

It is conceivable that when we upgrade iMechanica to Drupal 5 we can add the option to upload videos.  I'll also have to talk to the IT office at Harvard about hardware requirement and the cost.

Xiaodong Li's picture

Thanks a lot for the messages! The video capability provides a "dynamic" platform for educational purposes as well, like experimental mechanics demos. I think we need to promote such activities here. There may be some free software or free links that we can use. I will search around.

Zhigang Suo's picture

Xiaodong: You are absolutely correct. Videos are powerful media to convey mechanical phenomena. A while back, a channel called "videos" was added to the header of iMechanica. Please click it and take a look. Also, take a look of the comments on Zak Stone's post. You will find some like-minded discussions.

The steps to add a video still seam too cumbersome for an average user, I think. However, this barrier should not prevent a few energetic users from posting videos, or at least posting links to videos. Teng has written a step-by-step instruction of how to post a video.

I do believe that the barrier to posting videos will be lowered as the developers of iMechanica master the back end of Drupal 5. Let me know if you'd like to be a developer.

Xiaodong Li's picture

Thanks a lot for the encouragement. Sure!  I will be very happy to be a developer. Hope we will soon have some videos on iMechanica.  This will be fun for a lot of students as well who may show demos for discussion...

Julia R. Greer's picture

As someone who is very interested in investigating plasticity at nano-scale by pillar compression (and otherwise), of course it would be great to see more experimental nanomechanics topics. As most experiments at that scale are difficult to perform and there is a lot of controversy in modeling, it would be very helpful to start a discussion club. 

 

Julia Rosolovsky Greer

Xiaodong Li's picture

Thanks, Julia. Can you please nominate a paper about micro/nano pillar compression for May issue of J-Club? I think that pillar compression test has attracted much attention.

Rohit Khanna's picture

Hi all,

I wish to discuss on interpreting the nanoindentation data for
viscoelastic-plastic composite materials say polymer based composites.
I have experienced that if the microsructure is not homogeneous, it is
very difficult to meangingful data and normally, spread in elastic
modulus is very large depending on the load.

Second point for discussion is that does modulus mapping technique holds good for viscoelastic-elastic composites?

Can anybody comment on this?

Regards,

Rohit Khanna 

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