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Plastic Deformation Recovery in Freestanding Nanocrystalline Aluminum and Gold Thin Films


Science 30 March 2007:
Vol. 315. no. 5820, pp. 1831 - 1834
DOI: 10.1126/science.1137580
Jagannathan Rajagopalan, Jong H. Han, M. Taher A. Saif*
In nanocrystalline metals, lack of intragranular dislocation sources leads to plastic deformation mechanisms that substantially differ from those in coarse-grained metals. However, irrespective of grain size, plastic deformation is considered irrecoverable. We show experimentally that plastically deformed nanocrystalline aluminum and gold films with grain sizes of 65 nanometers and 50 nanometers, respectively, recovered a substantial fraction (50 to 100%) of plastic strain after unloading. This recoverywas time dependent and was expedited at higher temperatures. Furthermore, the stress-strain characteristics during the next loading remained almost unchanged when strain recovery was complete.These observations in two dissimilar face-centered cubic metals suggest that strain recovery might be characteristic of other metals with similar grain sizes and crystalline packing.

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Jinglei Yang's picture

Self-healing polymers - an introduction

I'm now working on the preparation and characterization of self-healing polymers, a promising branch in materials science. The following is a general conception of this kind of materials system. (Pasted from our group website http://www.autonomic.uiuc.edu.) I may introduce some of my current work later.

Arash_Kheradvar's picture

Characterization of myocardial viscoelastic behavior based on ventricular harmonic motion

Our current ability to accurately measure ventricular global contractile behavior remains unsatisfactory due to the lack of quantitative diagnostic indexes that can assess the mechanical properties of myocardial tissue.

A posteriori error estimation (indication) for extended finite element methods (XFEM)

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Extended finite element methods (XFEM) have been employed in computational fracture mechanics contexts since their inception in 1999. Although some work has been performed, leading to the first adaptive strategies for the generalised finite element method (GFEM), little or no work has been published on error estimation and adaptive approximations for XFEM. A first attempt at this challenging problem is published here: 

A book on mechanics that would pique your curiosity

I am happy to recommend the following book for your general reading.

Ranganath, G.S., ``Mysterious Motions and other Intriguing Phenomena in Physics," Hyderabad, India: Universities Press (2001)

Liu's picture

Motion of precision linear bearings on nanometre scale

A systematic characterization of the motion and friction of a linear bearing with rolling elements used for nanopositioning reveals an explicit distinction of static and rolling friction. The effects

Thickness dependent critical strain in Cu films adherent to polymer substrate

For the polymer-supported metal thin films that are finding increasing applications, the critical strain to nucleate microcracks ( εc ) should be more meaningful than the generally measured rupture strain. In this paper, we develop both electrical resistance method and microcrack analyzing method to determine εc of polymer-supported Cu films simply but precisely. Significant thickness dependence has been clearly revealed for εc of the polymer-supported Cu films, i.e., thinner is the film lower is εc . This dependence is suggested to cause by the constraint effect of refining grain size on the dislocation movability.

SHIH Choon Fong's picture

Innovation and Integration in the Changing Global Higher Education Landscape

I’m delighted that mechanicians now have this platform to discuss our work as well as share ideas and perspectives. While we advance knowledge in our field and come up with innovative solutions for engineering and materials problems, I believe that we also have a responsibility to speak on issues of global significance, especially where the power of science and technology can be harnessed to address challenges and issues impacting the world.

Zhigang Suo's picture

Self-assembled structures in a viscoelastic liquid

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About a year ago, Zak Stone introduced me to YouTube with this video titled amazing liquid. I wonder how much of this behavior is understood. There must be a lot of fantastic videos of mechanical phenomena on YouTube. Perhaps we can embed them in iMechanica, and comment on them. Teng Li has provided an instruction of how to embed videos. You can check out a few other interesting videos in iMechanica video channel.

Mohsin Hamzah's picture

Constitutive Modelling of Elastomers

Rubber or rubber-like materials, or generally elastomers, sustain large elastic deformations. The problems of such cases are non-linear, the non-linearity came from two sources, the first one due to materials, and the second is geomertrical non-linearity. Elastomers are, also, viscoelastic, i.e. time and temperature dependent.

Alexander A. Spector's picture

NEW TEXTBOOK ON BIOMECHANICS

Recently I received a message from the Cambridge University Press regarding a coming text on biomechanics entitled Introductory Biomechanics, From Cells to Organisms. by C. Ross Ethier and Craig A. Simmonds. I ordered an exam copy, went through, and found it very interesting. It covers cellular biomechanics, hemodynamics, circulatory system, ocular biomechanics, muscles and movement, and skeletal biomechanics. Each section has a significant number of problems. I examined closely the part on cellular biomechanics which is one of the main areas of my research and teaching interests, and enjoyed reading it. The cellular mechanics is presented in its interrelation to cell structure and biology (there are nice images of cells and their components to use for teaching). The main techniques of probing the cell, such as micropipette aspiration, AFM, optical tweezers, and magnetic cytometry, are considered. Models of the cytoskeleton (tensergity, foams) are also introduced. The math is limited to linear equations, one-dimensional or axisymmetric problems, but it seems appropriate for the introductory level. In addition, some results of computational (finite element) modeling are also included. I certainly expect that this textbook will be quite useful in my teaching. The web site http://www.cambridge.org/us/catalogue/catalogue.asp?isbn=9780521841122 has more details on the book.

Nanshu Lu's picture

Delamination of stiff islands patterned on stretchable substrates

As another celebration of March Journal Club of Mechanics of Flexible Electronics, this paper has just been submitted.

Abstract 

In one design of flexible electronics, thin-film islands of a stiff material are fabricated on a polymeric substrate, and functional materials are grown on these islands. When the substrate is stretched, the deformation is mainly accommodated by the substrate, and the islands and functional materials experience relatively small strains. Experiments have shown that, however, for a given amount of stretch, the islands exceeding a certain size may delaminate from the substrate. We calculate the energy release rate using a combination of finite element method and complex variable method. Our results show that the energy release rate diminishes as the island size or substrate stiffness decreases. Consequently, the critical island size is large when the substrate is compliant. We also obtain an analytical expression for the energy release rate of debonding islands from a very compliant substrate.

Mogadalai Gururajan's picture

Elastic stress driven phase inversion

A typical two phase microstructure consists of a topologically continuous `matrix' phase in which islands of `precipitate' phase are embedded. Usually, the matrix phase is also the majority phase in terms of volume fraction. However, sometimes this relationship between the volume fraction and topology is reversed, and this reversal is known as phase inversion. Such a phase inversion can be driven by an elastic moduli mismatch in two-phase solid systems. In this paper (submitted to Philosophical magazine), we show phase inversion, and the effect of the elastic moduli mismatch and elastic anisotropy on such inversion.

Mogadalai Gururajan's picture

Elastic stress driven rafting

During solid-solid phase transformations elastic stresses arise due to a difference in lattice parameters between the constituent phases. These stresses have a strong influence on the resultant microstructure and its evolution; more specifically, if there be externally applied stresses, the interaction between the applied and the transformation stresses can lead to rafting.

A spectral decomposition problem

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This post is both a question and a test how well Latex2HTML performs. The algebra might be useful for students who are starting off in the field. Please go through the details and comment on the question at the end of the post.

verron's picture

Definition of a new predictor for multiaxial fatigue crack nucleation in rubber

From an engineering point of view, prediction of fatigue crack nucleation in automotive rubber parts is an essential prerequisite for the design of new components. We have derived a new predictor for fatigue crack nucleation in rubber. It is motivated by microscopic mechanisms induced by fatigue and developed in the framework of Configurational Mechanics. As the occurrence of macroscopic fatigue cracks is the consequence of the growth of pre-existing microscopic defects, the energy release rate of these flaws need to be quantified. It is shown that this microstructural evolution is governed by the smallest eigenvalue of the configurational (Eshelby) stress tensor. Indeed, this quantity appears to be a relevant multiaxial fatigue predictor under proportional loading conditions. Then, its generalization to non-proportional multiaxial fatigue problems is derived. Results show that the present predictor, which covers the previously published predictors, is capable to unify multiaxial fatigue data.

On the crack growth resistance of shape memory alloys

With the increasing use of shape memory alloys in recent years, it is important to investigate the effect of cracks. Theoretically, the stress field near the crack tip is unbounded. Hence, a stress-induced transformation occurs, and the martensite phase is expected to appear in the neighborhood of the crack tip, from the very first loading step. In that case, the crack tip region is not governed by the far field stress, but rather by the crack tip stress field. This behavior implies transformation toughening or softening.

Arash_Yavari's picture

On the geometric character of stress in continuum mechanics

This paper shows that the stress field in the classical theory of continuum mechanics
may be taken to be a covector-valued differential two-form. The balance laws and other funda-
mental laws of continuum mechanics may be neatly rewritten in terms of this geometric stress. A

Andrew Norris's picture

Free access to Computational Mechanics back to Vol 1 - but only 'til end of month.

Springer - in an attempt to get customers I suppose - are offering free access to the journal Computational Mechanics, but only for March 2007.

You can access all articles in Computational Mechanics back to vol 1/1, e.g. the first article

E. Reissner
Some aspects of the variational principles problem in elasticity
Volume 1, Issue - 1, First Page - 3, Last Page - 9
DOI - 10.1007/BF00298634
Link - http://www.springerlink.com/content/t52w761088542m68

To get the free access (for the rest of March) go to
http://scientific-direct.net/c.asp?id=650015&c=7fbfc8d9b40ac978&l=31

Rashid K. Abu Al-Rub's picture

Dr. Stelios Kyriakides’ election to the United States National Academy of Engineering

Dr. Stelios KyriakidesPlease joint me in congratulating Dr. Stelios Kyriakides’ (Editor of International Journal of Solids and Structures) for his election to the United States National Academy of Engineering.

zishun liu's picture

Computational Cancer Mechanics

Since Dec. 2006, Institute of High Performance Computing (IHPC) has set up a biophysics research team that comprises research scientists in the fields of biophysics, solid mechanics and fluid mechanics, and has kicked off the "Computational Cancer Mechanics" project.

What's wrong with the way we learn Applied Mechanics?

I was reading professor Zhigang Suo's post titled "What's Wrong with Applied Mechanics", thinking about the large amount of knowledge available. There are so many applications of mechanics that they seem endless in any subfield that one can think of. It made me recall some homework problems that wanted to include real life applications. However, real life applications tend to turn out much more complicated than what can be covered in one homework problem.

Zhigang Suo's picture

How to read new comments at a glance?

As the number of comments increases rapidly, how can anyone keep up? One answer is to use a RSS reader. The service is free, and takes 5 minutes to set up. It allows you to see all new comments at a glance, without clicking on individual ones. Once you have set up your Google Reader, paste the URL for the feed of comments crss

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