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Zhigang Suo's blog

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Mechanics of supercooled liquids

In a pure liquid, molecules touch one another but change neighbors frequently.  External forces cause the liquid to change shape by viscous flow.  Thermal agitation causes  molecules to undergo self-diffusion.  The two phenomena--viscous flow and self-diffusion--often result from a single rate-limiting process:  molecules change neighbors.  This simple picture is amply confirmed by the Stokes-Einstein relation, which links the viscosity and self-diffusivity for many liquids over wide ranges of temperature.

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Viscosity

The attached notes are written for a course on plasticity.  I will update new posts on my twitter account:  https://twitter.com/zhigangsuo.  

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Strain hardening

The attached notes are written for a course on plasticity.  I will update new posts on my twitter account:  https://twitter.com/zhigangsuo.  Rheology is the science of deformation. This science poses a question for every material: given a history of stress, how do we find the history of strain?

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Perfect Plasticity

These notes are writen for part of a course on plasticity.

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Stress-strain curve of a metal

These notes are part of a course on plasticity.

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Plasticity

I am teaching this course this semester.  I'll post notes as I write them.  Links to the notes are listed in this post.  I will also notify updates on twitter:  https://twitter.com/zhigangsuo

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Basic Equations in Fluid Mechanics

I wrote these notes as a background for teaching elasticity and plasticity.  Even in this most basic formulation, the dilation of the fluid is viscoelastic.

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Fundamental discoveries in mechanics in recent decade or so

A previous post, Getting Ready for Extreme Mechanics Letters, contained the following paragraph:

“We seek papers from researchers in all disciplines. Mechanics appeals to talents of all kinds. Good mechanics has long been created by people from many fields, by Galileo, Newton, Maxwell and Faraday, as well as by Watt, Darwin, Wright brothers and Whitesides. People make discoveries in mechanics often when doing something else (e.g., in seeking evidence for the existence of God, in building cathedrals, in flying airplanes, in laying transatlantic telegraph cables, in fabricating microprocessors, in watching cells move, in fracking for gas, in inventing optical tweezers, in creating soft lithography, in developing wearable or implantable electronics). Mechanics discovered in one field invariably finds applications in other fields.”

Here I would like to give several examples of papers published in recent decade or so. I will link each paper to its citations on Google Scholar, so that you can have an overview of the influence of the paper on other researchers.

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What do we want EML to be? How do we get there?

Starting a new journal is risky.  Starting a new journal in mechanics is particularly risky.  The responses to the two recent posts are encouraging, however.

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Getting ready for Extreme Mechanics Letters

We are launching a new journal, Extreme Mechanics Letters. EML will publish letter-sized papers. We aim to achieve rapid communication. Our goal is to have the accepted papers published within 6-8 weeks upon submission. We aim to build a home at the frontier of engineering, medicine, science and entertainment, where advances are rapid and mechanics matters. We seek papers from researchers in all disciplines.

We will start to review submissions on 1 October 2014, and publish first papers by 1 December 2014. The beginning issues will be freely accessible online, and printed copies will be distributed at conferences.

We love to publish your extremely new ideas on extremely useful and extremely interesting mechanics. Please submit your papers soon.

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Bioinspiration and biointegration

The nervous system has long been an inspiration for the engineer.  Here is an example in a popular textbook on neuroscience.  When a person steps on a nail, the sensor in his foot sends a signal to his brain, the brain sends a signal to his muscle, and he lifts his foot.  The example illustrates the sensor, actuator and processor in the nervous system.

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Elastic strain engineering for unprecedented materials properties

Ju Li, Zhiwei Shan and Evan Ma have edited the February 2014 issue of the MRS Bulletin devoted to the effects of elastic strains on solid-state devices.

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Harvard Seeks Senior Lecturer in Applied Mathematics

The Harvard School of Engineering and Applied Sciences seeks applicants for the position of Senior Lecturer in Applied Mathematics, with an expected start date of July 1, 2014. This position will be for five years and may be renewed.  Deadlin for application is 15 March 2014.  See further information.  See also a position for Applied Math Fellows.

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Division of Labor

I have updated my notes on "Energe Release Rate.  Fracture Energy".  I will use my twitter account to update my teaching, research, and reading.  You will get an automatic update if you subscribe to my twitter account.

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Inglis (1913) vs. Griffith (1921)

I have updated my notes on the Griffith paper.  I added more description on the experimental determination of surface tension of solids.  Griiffith himself determined the surface tension of glass by an experimental setup.  Udin et al (1949) described a setup based on the same principle.  This setup is now known as the zero creep experiment.

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The toughest hydrogel in the world

The class started today.  I'll be teaching fracture mechanics this semester.  I'll be mostly using the class notes I wrote in 2010, but will post updated ones. 

In today's class I covered "Trouble with linear elastic theory of strength."  I have just posted updated notes of the lecture.  The new notes begin with the follwoing paragraphs.

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Massvolume vs. Spacetime

Apples and oranges. Each element in a set is a pile containing some number of apples and some number of oranges.  Adding two piles means putting them together, resulting in a pile in the set. Multiplying a pile and a real number r means finding in the set a pile r times the amount.  We model each pile as a vector, and the set as a two-dimensional vector space over the field of real numbers.

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Scalar done wrong

When I was updating my very brief notes on tensors, it occurred to me to post on iMechanica a request for recommendation of textbooks on linear algebra.  I was delighted to see Arash respond.  I then asked for his opinion about the definition of tensor.  He responded again, and we seemed to agree.  Then Amit joined the discussion, and then others.  That thread has become very interesting and very long.

But I have another issue with the way we use linear algebra.  I wish to get your opinion. The issue is about scalars.

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Textbook on linear algebra

Linear algebra is significant to many aspects of mechanics.  For some years I have been using the book by Shilov.  But this book may or may not be a good one to recommend to a student, depending on his or her prior experience.  On StackExchange Mathematics, there are several excellent threads discussing textbooks of linear algebra.  A particular recommendation was made for

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Collecting phenomena of large elastic deformation

It might be fun for us to work together to collect phenomena of large elastic deformation.  These phenomena will enliven teaching and motivate research.  As inspiration, here are two albums of fluid motion

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Principal stress

These notes are written to supplement ES 240 Solid Mechanics.

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The Feynman Lectures on Physics, reproduced in HTML of exceptional high quality

Caltech has made the Feynman Lectures on Physics, Vol I, freely accessible online.  The quality of the HTML file is exceptionally high.  Take a look at the preface to learn how this electronic version was produced.

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