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Zhigang Suo's blog

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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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Freely jointed chain

A single strand of polymer is a chain of a large number of monomers.  The monomers are joined by covalent bonds, and two bonded monomers may rotate relative to each other.  At a finite temperature, the polymer rapidly changes from one configuration to another.  When the two ends of the polymer are pulled by a force, the distance between the two ends changes.  The polymer is known as an entropic spring.  These notes are developed as part of statistical thermodynamics to supplement the course on advanced elasticity

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These notes may serve as a reminder of tensor algebra.  The notes supplement the course on advanced elasticity.  Several books are listed at the end of the notes.

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Elasticity of rubber-like materials

In the notes on the general theory of finite deformation, we have left the free energy function unspecified. The notes here describe free energy function commonly used to describe the elasticity of rubber-like materials.  These notes are part of a course on advanced elasticity

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These notes are part of a course on advanced elasticity.  The notes recall several phenomena where both elasticity and surface energy are significant, including

  • Griffith crack
  • Adhesion of flexible structures
  • Wafer bonding
  • Contraction of a soft elastic sheet 

The notes also contain a formulation of combined surface energy and elasticity of finite deformation.  

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Reading PDF files using iPad 3

Reading PDF files of papers and textbooks on computers has long been difficult for me.  The resolution of the screens has been too low.  The computers have been too heavy for reading in couches and beds. 

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Full announcement of the meeting (in both Chinese and English) 

申请条件. 具有海外博士学历(5年以内)或者2013年即将毕业的博士。或者具有国内博士学历,已在海外工作或学习2-4年。在本学科领域取得突出成绩或在领域内发表有高水平学术论文。具备工作经验或博士后研究经验更佳。通过资格审查者,由主办单位邮件通知具体参会事宜.

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A website wholly devoted to buckled shells

John Hutchinson has just pointed out to me the website,  The site is devoted to the mechanics of buckled shells, with downloadable photos, slides, papers, and computer codes.  The site also has a section on buckling people.  The site is created by a veteran buckling person, Dr. David Bushnell, formerly of Lockheed Martin.  Check the site out, and enjoy. 


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