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Superplastic carbon nanotubes

Nature 439, 281 (2006)

The theoretical maximum tensile strain — that is, elongation — of a single-walled carbon nanotube is almost 20%, but in practice only 6% is achieved. Here we show that, at high temperatures, individual single-walled carbon nanotubes can undergo superplastic deformation, becoming nearly 280% longer and 15 times narrower before breaking. This superplastic deformation is the result of the nucleation and motion of kinks in the structure, and could prove useful in helping to strengthen and toughen ceramics and other nanocomposites at high temperatures.

Xin Zhang's picture

Size-dependent creep behavior of plasma-enhanced chemical vapor deposited silicon oxide films

The time-dependent plastic deformation (creep) behaviors of both the as-deposited and annealed plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiOx) films were probed by nanoindentation load relaxation tests at room temperature. Our experiments found a strong size effect in the creep responses of the as-deposited PECVD SiOx thin films, which was much reduced after rapid thermal annealing (RTA). Based on the experimental results, the deformation mechanism is depicted by the "shear transformation zone" (STZ) based amorphous plasticity theories. The physical origin of the STZ is elucidated and linked with the shear banding dynamics. It is postulated that the high strain gradient at shallow indentation depths may be responsible for the reduction in the stress exponent n=∂log(strain rate)/∂log(stress), characteristic of a more homogenous flow behavior.

splacour's picture

Mechanisms of reversible stretchability of thin metal films on elastomeric substrates

Gold films on an elastomeric substrate can be stretched and relaxed reversibly by tens of percents. The films initially form in two different structures, one continuous and the other containing tri-branched microcracks. We have identified the mechanism of elastic stretchability in the films with microcracks. The metal, which is much stiffer than the elastomer, forms a percolating network.

Zhigang Suo's picture

We Are Mechanicians

In early days of Applied Mechanics News, I encountered a practical problem. How do we call ourselves? I began with a phrase "people in the international community of applied mechanics". The phrase is inclusive and descriptive, but is too long, too timid and too clumsy. It is like calling entropy "the logarithm of the number of quantum states". I have also heard the phrase "mechanics people", which I don't like either. It sounds too folksy, like calling a gynecologist a women's doctor.

What can mechanicians do in fusion research?

More than fifty years ago, people realized that we can use fusion for energy, but the problem remains where and how to keep a plasma of 100 million degrees centigrade.

For TOKAMAK, one of the approaches to use the fusion power, now comes the news: "On 21 November, Ministers from the seven ITER Parties came together to sign the agreement to establish the international Organization that will implement ITER."

Ning Wang's picture

Long-distance propagation of forces in a cell

What might be the differences, if there is any, between mechanical signaling and chemical signaling in a living cell?

Teng Li's picture

The Future of Cell Phone?

Here is one answer from Nokia.


Nokia 888 communicator, a concept design which recently won the Nokia's Benelux Design Award. It uses liquid battery, flexible touch display, speech recognition, touch sensitive body cover which lets it understand and adjust to the environment. It has a simple programmable body mechanism so that it changes forms in different situations. Don't forget to enjoy a video demo of this cell phone of future.
Yet one more future application of flexible electronics, it's clear there're great mechanics and materials challenges in making electronic devices flexible. It will be great mechanicians can help accelerate the advance of this emerging technology.

The 2nd International Conference on Heterogeneous Material Mechanics (ICHMM-2008)

ICHMM 2008 seeks dissemination of recent, leading edge research results as well as in-depth discussions of future directions in the challenging subject of heterogeneous material mechanics. Sessions in the Huangshan International Hotel will focus on recent original research developments, while invited panel discussins in the subsequent Huangshan Mountain retreat aim to stimulate future research directions.

Co-Chairs

J. Fan, Alfred University, USA and Chongqing University

The topics of interest are:

Elastic model for proteins (polymers)

There has been a lot of attention on the study of mechanics of proteins and/or single molecules. Such study was typically implemented by using classical molecular dynamics (MD) simulation. In spite of ability to describe the dynamics of biological macromolecules (e.g. proteins), MD simulation exhibits the computational restriction in the spatial and temporal scale. In order to overcome such computational limitation, the coarse-grained model has recently been taken into account. In this review, I would take a look at a couple of coarse-grained models of protein molecules.

Zhigang Suo's picture

How to ask a question in a forum?

If you have a question about iMechanica or about mechanics, you can first try to find the answer by using the search form at the upper right corner of iMechanica. If you cannot find the answer, you can ask the question in a forum by following steps:

What is the status of open source finite element code?

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FEMs are widely used in education, research, and industries. What is the prospect of having a vibrant community to evolve an open-source finite element code? What are the potential benefits for such a community and code? Has anybody tried?

Presumably whoever active in this effort may find support from government funding agencies and industries.

Meshfree Methods: Frequently Asked Questions

Questions about meshfree methods are now addressed in the forum, under the Computational Mechanics subheading.

If you click on a question below, you will be redirected to the forum. I will update this post as more questions are added. Other experts are encouraged to augment my response there.

1. If I have meshfree shape functions that satisfy Kronecker-Delta, can I satisfy essential boundary conditions?

2. Is a mesh required in meshfree methods?

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Liu's picture

Positioning on nanometer scale: fighting friction

Most friction models for automatic control are targeted for the macro world, and are of questionable value for the motion control of the high precision positioing stages. We published a paper recently in Technishes Messen (TM) on a study of the friction behavior in the moving range of micrometers. It provides info for the development of friction models targeted for the motion control in high precision engineering.

The following is the abstract, and the full paper can be downloaded from http://www.atypon-link.com/OLD/doi/abs/10.1524/teme.2006.73.9.500

ABSTRACT Most friction models for automatic control are targeted for the macro world, and are of questionable value for the motion control of the nanopositioning and nanomeasuring machine (NPM) system. We present the frictional behaviour of some selected materials, coatings, lubricants, and bearings tested under running conditions similar to a NPM system. Continuous change of surface properties results in various friction characteristics, which substantiate the further development of tribological coatings, particularly for vacuum applications. We emphasize the system engineering approach in developing friction models, which combines fundamental knowledge of surface science, materials science, and its applications in design, construction and automatic control.

2006 Timoshenko Medal Acceptance Speech by Kenneth L. Johnson

Kenneth L. JohnsonPresented at the Applied Mechanics Dinner of the 2006 Winter Annual Meeting of ASME, Hilton Chicago Hotel, 9 November 2006.

First and formost, I must acknowledge with gratitude the honour of being selected for the Timoshenko medal for 2006.   But since a speech is now expected, I realise that this is not free lunch.  If you know a good pub, this would be a good time to slip away.

When I received  Virgil  Carter's letter informing me that I had been selected,  I could not believe it.  There must have been a mistake;  after all Johnson is a very common name.   I am reminded of my first meeting with  Bernie Budiansk from Harvard,  also a Timoshenko  medallist.   He asked, "Did you write that book on vibration with Bishop?" "No. That was Dan Johnson";  " Did you edit that British Journal of mechanical sciences?":  "No. That was Bill Johnson";   "Who the hell are you!"

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A Recent Book: Meshfree Particle Methods, by Shaofan Li and Wing-Kam Liu

Meshfree Particle Methods is a comprehensive and systematic exposition of particle methods, meshfree Galerkin and partition of unity methods, molecular dynamics methods, and multiscale methods. It presents theoretical foundation, numerical algorithms, as well as applications. Since it was published in 2004, the first print has been sold out. The publisher is preparing the second print.

Mogadalai Gururajan's picture

Eshelby and his two classics (and some more on the side)

Eshelby and the inclusion/inhomogeneity problems

Any materials scientist interested in mechanical behaviour would be aware of the contributions of J.D. Eshelby. With 56 papers, Eshelby revolutionised our understanding of the theory of materials. The problem that I wish to discuss in this page is the elastic stress and strain fields due to an ellipsoidal inclusion/inhomogeneity - a problem that was solved by Eshelby using an elegant thought experiment.

In two papers published in the Proceedings of Royal Society (A) in 1957 and 1959 (Volume 241, p. 376 and Volume 252, p. 561) Eshelby solved the following problem ("with the help of a simple set of imaginary cutting, straining and welding operations"): In his own words,

MichelleLOyen's picture

S. Germain, "Memoir on the Vibrations of Elastic Plates"

I have not read the above-mentioned paper, as I have never been able to find it. However it is said to be "a brilliantly insightful paper which was to lay the foundations of modern elasticity." However, I believe it is also noteworthy for being one of the major contributions by a female mechanician prior to the modern era. For a great biography of Sophie Germain, including a fantastic quote from a letter from Carl Gauss on discovering that she was female--and not "Monsieur Le Blanc"--visit this site (from which the above quote, on the impact of her paper, came).

There are no female mechanicians listed on http://en.wikipedia.org/wiki/Mechanicians but I believe it could be argued that Germain deserves a mention!

Cai Wei's picture

New Book: Computer Simulations of Dislocations, by Vasily V. Bulatov and Wei Cai

Companion web site http://micro.stanford.edu ISBN:0-19-852614-8, Hard cover, 304 pages, Nov. 2006, US $74.50.

This book presents a broad collection of models and computational methods - from atomistic to continuum - applied to crystal dislocations. Its purpose is to help students and researchers in computational materials sciences to acquire practical knowledge of relevant simulation methods. Because their behavior spans multiple length and time scales, crystal dislocations present a common ground for an in-depth discussion of a variety of computational approaches, including their relative strengths, weaknesses and inter-connections. The details of the covered methods are presented in the form of "numerical recipes" and illustrated by case studies. A suite of simulation codes and data files is made available on the book's website to help the reader "to learn-by-doing" through solving the exercise problems offered in the book. This book is part of an Oxford Series on Materials Modelling.

jqu's picture

New Book: Fundamentals of Micromechanics of Solids, by Jianmin Qu and Mohammed Cherkaoui

Fundamentals of Micromechanics of Solids, Jianmin Qu, Mohammed Cherkaoui
ISBN: 0-471-46451-1, Hardcover, 400 pages, August 2006, US $120.00

PART I: LINEAR MICROMECHANICS AND BASIC CONCEPTS

Chapter 1 INTRODUCTION

  • 1.1 Background and Motivation
  • 1.2 Objectives
  • 1.3 Organization of Book
  • 1.4 Notation Conventions
  • References

Chapter 2 BASIC EQUATIONS OF CONTINUUM MECHANICS

Jie Wang's picture

The Eighth International Conference on Fundamentals of Fracture

The Eighth International Conference on Fundamentals of Fracture (ICFF VIII) is the successor of the previous seven held at NBS, Gaithersburg (USA, 1983), Gatlinburg (USA, 1985), Irsee (Germany, 1989), Urabandai (Japan, 1993), NIST, Gaithersburg (USA, 1997), Cirencester (UK, 2001), and Nancy (France, 2005). You are warmly invited to participate in ICFF VIII which will be held 3-7 January 2008 in Hong Kong University of Science and Technology, Hong Kong, and in Guangzhou, China. As the previous conferences, ICFF VIII provides an international forum for presentation and discussion of the latest scientific and technological development in fundamentals of fracture. The general theme of ICFF VIII is to cover all aspects of fracture at a fundamental level, including contributions from those working in the disciplines of Continuum Mechanics, Physics, Chemistry, Bioscience, Metallurgy, Ceramics, Polymer Science, etc. You are cordially invited to submit an abstract to join in this memorable event.

History of mechanics

Anyone interested in the history of mechanical technology might find interesting the series that I have published in Mechanical Engineering magazine.

Galileo’s Telescope Lenses

http://www.memagazine.org/oct06/features/clearas/clearas.html

Atmospheric Railway

http://www.memagazine.org/backissues/feb06 /features/tallyho/tallyho.html

Juil Yoon's picture

Why Do Freezing Rocks Break?

As you know, the volumetric expansion by 9% during the water-to-ice transition can generate tremendous pressure in a confined space is a common sense. As a result, one may expect freezing water to also fracture rocks.

However, in a recent article in Science, Bernard Hallet explains the power of the 9% water-to-ice expansion in confined spaces is undeniable, but it may rarely be significant for rocks under natural conditions, because it requires a tight orchestration of unusual conditions. Unless the rocks are essentially saturated with water and frozen from all sides, the expansion can simply be accommodated by the flow of water into empty pores, or out of the rock through its unfrozen side.

I think it may be of interest to mechanics. Read more
I hope to hear opinions from people who know about the breaking mechanics of rocks.

Joost Vlassak's picture

Plastic deformation of freestanding thin films: Experiments and modeling

This is a paper we recently published in JMPS on a study of the mechanical properties on thin films comparing experimental results with discrete dislocation simulations. It provides insight in the strengthening that occurs in thin metal films when surface or interface effects become important.

The abstract is below; the full paper can be downloaded from here

Abstract - Experimental measurements and computational results for the evolution of plastic deformation in freestanding thin films are compared. In the experiments, the stress–strain response of two sets of Cu films is determined in the plane-strain bulge test. One set of samples consists of electroplated Cu films, while the other set is sputter-deposited. Unpassivated films, films passivated on one side and films passivated on both sides are considered. The calculations are carried out within a two-dimensional plane strain framework with the dislocations modeled as line singularities in an isotropic elastic solid. The film is modeled by a unit cell consisting of eight grains, each of which has three slip systems. The film is initially free of dislocations which then nucleate from a specified distribution of Frank–Read sources. The grain boundaries and any film-passivation layer interfaces are taken to be impenetrable to dislocations. Both the experiments and the computations show: (i) a flow strength for the passivated films that is greater than for the unpassivated films and (ii) hysteresis and a Bauschinger effect that increases with increasing pre-strain for passivated films, while for unpassivated films hysteresis and a Bauschinger effect are small or absent. Furthermore, the experimental measurements and computational results for the 0.2% offset yield strength stress, and the evolution of hysteresis and of the Bauschinger effect are in good quantitative agreement.

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