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Zhigang Suo's blog

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String and Elastica

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Some numbers of iMechanica

  • The number of registered users is 6037
  • The number of posts is 2896 (You can see the current number by clicking the newest post).
  • The number of comments is 6943 (You can see the current number by clicking the newest comment.)

Last updated on 19 March 2008

Related post: Some dates of iMechanica

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What Is Mechanics?

So, What is Mechanics? It seems that useful answers ought to depend on who you are talking to. If you are persuading your dean to hire a new faculty member in Mechanics, perhaps you’d like to point out promising research in one area or another, and how foundational mechanics is to the education of future scientists and technologists in (almost) all fields.

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Solid Mechanics Homework 43-46

43. Energy loss
44. Zener model and relaxation test
45. Zener model and cyclic-load test
46. Vibration of a viscoelastic rod

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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.

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Viscoelasticity

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A.A. Griffith: The phenomena of rupture and flow in solids

GRIFFITH AA, The phenomena of rupture and flow in solids. Philosophical Transactions of the Royal Society of London, Sereis A, 221:163-198, 1921.

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Solid Mechanics Homework 39-42

39. A circular transverse wave
40. Creep and recovery
41. Temperature dependence and Mr. Arrhenius
42. A loose nylon bolt

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Mechanics of climbing and attachment in twining plants

In a recent article in Physical Review Letters, Alain Goriely and Sébastien Neukirch offer a mechanical model of how the free tip of a twining plant can hold onto a smooth support, allowing the plant to grow upward. The model also explains why these vines cannot grow on supports of too large a diameter. Read more.

The mechanics involves large deflection and bifurcation of a rod. I hope to hear opinions from people who know about the mechanics of plants.

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Saturated voids in interconnect lines due to thermal strains and electromigration

Zhen Zhang and Zhigang Suo (Harvard), Jun He (Intel)

Attached is a set of slides presented at ASME Congress, 10 November 2006. Thermal strains and electromigration can cause voids to grow in conductor lines on semiconductor chips. This long-standing failure mode is exacerbated by the recent introduction of low-permittivity dielectrics. We describe a method to calculate the volume of a saturated void (VSV), attained in a steady state when each point in a conductor line is in a state of hydrostatic pressure, and the gradient of the pressure along the conductor line balances the electron wind. We show that the VSV will either increase or decrease when the coefficient of thermal expansion of the dielectric increases, and will increase when the elastic modulus of the dielectric decreases. The VSV will also increase when porous dielectrics and ultrathin liners are used. At operation conditions, both thermal strains and electromigration make significant contributions to the VSV. We discuss these results in the context of interconnect design.

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Waves

A file on elastic waves is attached.

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ES 240 Solid Mechanics Project

Updated on 11 October 2008.  Each student creates a distinct project that (a) addresses a phenomenon, and (b) involves a serious use of ABAQUS.   To get some inspiration, see projects of students who took this course in the past.

The project contributes 25% to the grade, distributed as follows.

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Solid Mechanics Homework 34-38

34. Surface acoustic wave device
35. Approximate a rod as a 2DOF system
36. Soft tissues: large difference in velocities of longitudinal and transverse waves
37. A general approach to determine body waves
38. Reflection and refraction of a transverse wave

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Trusses

Notes on the stiffness matrix formulation, used for ES 120, Introduction to the Mechanics of Solids, a sophomore course. This material will not be covered in ES 240, but might provide helpful reading if you do not have this background.

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Solid Mechanics Homework 31-33

31. A machine on a cantilever
32.  A beam on simple supports
33. Vibration of piano strings

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Applied Mechanics Division Committee Meetings in Chicago

Rui Huang's post early today reminded me of writing to all of you who are going to ASME meeting in Chicago, 5-10 November 2006, a short 10 days from today.

As I wrote in September, much of the initial planning for the next year's Congress will happen at the committee meetings this year. These meetings will formulate possible topics for symposiums in the next Congress. Surely you would like to see your favorite topics get picked.

Meetings of all Technical Committees are open to all. Please find the meeting times of the Technical Committees that interest you. You may also want to know who are the Chairs of the 17 Technical Committees in the Applied Mechanics Division.

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Vibration

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Solid Mechanics Homework 26-30

26. Stress-strain relations under the plane strain conditions
27. Getting weak: derive weak statements from differential equations
28. Potential energy and Rayleigh -Ritz method
29. Constant strain triangle
30. Gaussian quadrature

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Two recent articles about mathematicians

If you have not read them, you might find them interesting.

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Solid Mechanics Homework 21-25

21. A fiber in an infinite matrix
22. Anti-plane shear
23. Saint-Venant's principle for orthotropic materials
24. Plane problems with no length scales
25. More scaling relations: a half space filled with a power-law material

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Solid Mechanics Homework 16-20

  • 16. Recommend a textbook that you think will help students in this course.  See recommendations from students who took this course before.
  • 17. Disclination (the cut-and-weld problem)
  • 18. Design a rotating disk to avert plastic deformation
  • 19. A half space of an elastic material subject to a periodic traction on the surface
  • 20. Orthotropy rescaling

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The Boltzmann Distribution

  • A small system in thermal contact with a large system
  • The Boltzmann factor
  • Partition function
  • The probability for a system in thermal equilibrium with a reservoir to be in a specific state
  • The probability for a system in thermal equilibrium with a reservoir to be in a configuration
  • Thermal fluctuation of an RNA molecule
  • A matter of words

Return to the outline of Statistical Mechanics.

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