Zhigang Suo's blog
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.
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.
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.
The qualitative picture of fracture may be well-understood, across disparate scales of length and time, from the distortion of electron clouds, to the jiggling of atoms, to the motion of dislocations, to the extension of the crack, to the load-carrying capacity of a structure. This statement by itself, however, is of limited value: it offers little help to the engineer trying to prevent fracture of a structure. Hypes of multiscale computation aside, no reliable method exists today to predict fracture by computation alone.
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.
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.
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.
A vector represents different objects as a single entity. A pile containing some number of apples and some number of oranges is a vector. The addition of two vectors does not require us to add apples and oranges. Rather, in adding two piles, we add apples to apples, and oranges to oranges. The addition of vectors generalizes the addition of numbers: adding two vectors corresponds to adding two lists of numbers in parallel.
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.
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 textbooks of linear algebra at three levels. Do you have any recommendations?
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
These notes are written to supplement ES 240 Solid Mechanics.
In a paper just published in Science, we describe a class of devices fabricated using stretchable, transparent, ionic conductors. These devices are highly deformable and fully transparent. They can operate at frequencies above 10 kHz and voltages above 10 kV. We demonstrate a fully transparent loudspeaker that plays music. See a YouTube video. The Supplementary Materials contain experimental methods, theory, and more movies. The Science magazine conducted a podcast interview, which covered some of the same ground in this post.
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.
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.
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.
You may also wish to follow the ongoing discussion on the topic.
This classic paper is attached
Xuanhe Zhao, of Duke University, has just accepted our invitation to be the next Editor of the iMechanica Journal Club. The Journal Club was initiated in January 2007, soon after the launch of iMechanica. A glance at the list of past Themes and Discussion Leaders gives an impression of vibrant topics and dynamic researchers at the frontier of mechanics. iMechanica is fortunate to have a succession of excellent Editors. Xuanhe is an exceptionally creative and energetic researcher: his reserch is deep and wide-ranging. We look forward to his leadership, and to many more challenging and charming Themes and Discussion Leaders.
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.
In recent months iPad 3 has made a difference for me. The resolution of iPad 3 is so good that color pictures often look better on screen than in print. iPad lets me read comfortably anywhere. I’d choose to read a book with iPad even if I have the same book in printed form. I wish iPad were available when I was young and had a lot of time for reading. I would have read all these large biology books in bed.
With the help of my sons, I get things organized by using the following software.
Full announcement of the meeting (in both Chinese and English)
申请注册. 2012年7月15日 500-1000字摘 http://22.214.171.124:8888/member/contribute_forumregister.jspx
会议日程. 2012年10月6日 - 10月8日, 华中科技大学
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Full announcement of the meeting (in both Chinese and English)
Sigurd Wagner and Siegfried Bauer have just edited an exciting issue of the MRS Bulletin: Materials for Stretchable Electronics. All articles contain phenomena related to mechanics. Here is the abstract of my contribution: Mechanics of Stretchable Electronics and Soft Machines. In the emerging field of soft machines, large deformation of soft materials is harnessed to provide functions such as regulating flow in microfluidics, shaping light in adaptive optics, harvesting energy from ocean waves, and stretching electronics to interface with living tissues. Soft materials, however, do not provide all of the requisite functions; rather, soft machines are mostly hybrids of soft and hard materials. In addition to requiring stretchable electronics, soft machines often use soft materials that can deform in response to stimuli other than mechanical forces. Dielectric elastomers deform under a voltage. Hydrogels swell in response to changes in humidity, pH, temperature, and salt concentration. How does mechanics meet geometry, chemistry, and electrostatics to generate large deformation? How do molecular processes affect the functions of transducers? How efficiently can materials convert energy from one form to another? These questions are stimulating intriguing and useful advances in mechanics. This review highlights the mechanics that enables the creation of soft machines.
John Hutchinson has just pointed out to me the website, shellbuckling.com. 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.
（本招聘广告有效期至2012年12月31日）PDF of this file
为了更好地聚集海外优秀人才、培养国际一流的青年学者、及借此加快建设世界高水平大学的进程，西安交通大学建立了一个新型的、采用美国先进的用人和科研体制管理的研究中心---“国际应用力学中心” International Center for Applied Mechanics (ICAM)。该中心的目标是聚集和培养一流人才，产出一流学术成果，打造国际一流的力学学科。ICAM以独立的tenure-track PI为本，将重点研究国际力学前沿问题及国家重大需求中的关键力学问题，承担国家级的重点和重大项目，并开展高层次国际合作与交流。
ICAM是西安交通大学的一个独立的学术机构，参照美国常春藤盟校的高效和高度扁平化的科研管理体制。中心的学术带头人为国际著名的中青年力学家锁志刚、高华健、陈曦、刘子顺等西安交通大学杰出校友。中心的国际学术顾问包括Hutchinson，Willis，Needleman等世界力学大师。在他们的指导和引领下，ICAM将汇集和激励青年学者成长为有国际影响力的国家级人才。作为西安交通大学机械结构强度与振动国家重点实验室的一个“学术特区”，中心的人才招聘、薪酬、考核、评估、管理与运行等均参照美国的先进体制进行。ICAM实行独立的tenure-track PI制度，使得青年科研人员能够最大限度地发挥其创造力和主导作用，在国际著名学者的指引和激励下快速成长为具有国际能见度的一流学者（且不存在成长的上限）。ICAM将给每位tenure-track PI配备相应的独立的实验室空间和科研平台建设费，研究生招生和国际交流计划单列（不受传统名额限制）。中心的运行模式、人员岗位、人才培养和经费预算等均具有高度灵活性，可为每位tenure-track PI量身定制其发展轨迹。中心充分鼓励有共同兴趣的研究组在中心内部开展全面合作，并大力支持PI和校内外的其它学科（如机械、能动、电子电气、材料、航空航天、土木、生物生医、物理、化学等）的国际国内学者开展广泛的交叉研究。在学校的鼎力支持和中心全体人员的共同努力下，力争在较短时间内将ICAM建设成一个具有鲜明学科交叉特色、拥有世界一流研究水准和较高国际影响力的力学研究中心、成为国际力学学科前沿的领头羊之一。