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ES 240 (Fall 2007) Office hour change

To all students in ES 240 this semester,

Due to popular demand my office hour is moved from Tuesday to Thursday 4~5pm starting from this week. The location is changed to Rm. 123, Maxwell Dworkin (33 Oxford Street).

Nanshu

 

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ES 240 (Fall 2007) Homework 6-10

This problem set will be due on Friday, Oct. 4th.

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ES 240 (Fall 2007) Homework 1-5

This problem set is due on Friday, Sep. 28, 2007 in class.

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ES 240 (Fall 2007) Lecture Notes - Elements of Elasticity

The lecture notes are prepared by Prof. Joost Vlassak based on a set of course notes put together by Prof. Suo when he taught ES 240 in 2006, as well as on course notes developed by Prof. Vlassak for ES 246.

Please see attached. 

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NSF Mini Travel Grants - 10th Pan American Congress Appl. Mech

The National Science Foundation (NSF) has made a recent award to help increase graduate student participation at the Tenth Pan American Congress of Applied Mechanics (PACAM X).  These awards will be made in the form of mini-travel grants ($500 - $1,000) for exceptionally qualified students to participate in PACAM X January 7-11, 2008, in beautiful Cancun, Mexico.

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Delamination of stiff islands patterned on stretchable substrates

As another celebration of March Journal Club of Mechanics of Flexible Electronics, this paper has just been submitted.

Abstract 

In one design of flexible electronics, thin-film islands of a stiff material are fabricated on a polymeric substrate, and functional materials are grown on these islands. When the substrate is stretched, the deformation is mainly accommodated by the substrate, and the islands and functional materials experience relatively small strains. Experiments have shown that, however, for a given amount of stretch, the islands exceeding a certain size may delaminate from the substrate. We calculate the energy release rate using a combination of finite element method and complex variable method. Our results show that the energy release rate diminishes as the island size or substrate stiffness decreases. Consequently, the critical island size is large when the substrate is compliant. We also obtain an analytical expression for the energy release rate of debonding islands from a very compliant substrate.

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Free SGTE Alloy Phase Diagrams online

SGTE Alloy Phase Diagrams

In case some of you don't know. Enjoy

BTW, SGTE stands for Scientific Group Thermodata Europe

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Self Introduction for ES 242r PS1 Q1

My name is Nanshu Lu. I am a second year doctoral student in the Suo group at Harvard Engineering and Applied Science.

I obtained my B.S. in Solid Mechanics from the Department of Engineering Mechanics at Tsinghua University, China. You can see my resume here.

My course background includes Strength of Materials, Continuum Mechanics and Fundamental Elasticity taken at Tsinghua University and graduate level Elastisity (ES 240) taught by Prof. J. Rice, Deformation of Solids (APY 293) taught by Prof. F. Spaepen, Fracture (ES 247) and Plasticity (ES 246) taught by Prof. J. Vlassak and Zhigang's another course Advanced Elasticity (ES 241) this semester here at Harvard.

My first teaching experience was TFing Zhigang's ES 240 last semester.

Although I think I've indulged in a systematic cognition of solid mechanics with somewhat solid understanding of this subject, I sometimes do lack a spirit of digesting materials and making them my own. It indeed has occured to me that having a hard time to fish out the proper solution to a novel problem although I've owned all the needed tools and skills. Under the instruction of John and Zhigang I hope I will make the transformation from a student learner to a scholar learner.

Nonlinear fracture mechanics joints main parts of solid mechanics: fracture, elasticity and plasticity, the essential foundation to my research interests of mechanics in thin films, both theories and experiments. One of my subject is about chip packaging interaction. It is well known that nowadays a typical electronic package assembly consists of different materials which are attached together in a variety of ways. No other course will be more proper for this subject than this "Fracture mechanics of thin films and composit materials". Though I've read literatures specialized on thin film debonding I believe taking this course is the most efficient way for me to have profound and comprehensive understanding of fracture mechanics as a whole.

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TWELVE STEPS TO A WINNING RESEARCH PROPOSAL

By George A. Hazelrigg, National Science Foundation

I have been an NSF program director for 18 years. During this time, I have personally administered the review of some 3,000 proposals and been involved in the review of perhaps another 10,000. Through this experience, I have come to see that often there are real differences between winning proposals and losing proposals. The differences are clear. Largely, they are not subjective differences or differences of quality; to a large extent, losing proposals are just plain missing elements that are found in winning proposals. Although I have known this for some time, a recent experience reinforced it.

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ES 246 project: Plane Strain Extrusion - Slip-line Field Solution vs. FEM Solution

Due to maturity of FEM package, slip-line field theory is not widely used these days. However, we shall keep in mind that slip-line field analysis can provide analytical solutions to a number of very difficult problem which may involve huge deformations or velocity discontinuities, e.g. many metal forming processes. To evaluate these two analytical and numerical methods for plasticity I will try a simple example, compare these two solutions and finally get into a conclusion of my own.

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Homework Q39 ~ Q42 is due Friday, Dec. 1

As promised, no homework for Thanksgiving :)

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ABAQUS Computer Assignment #2 (Due Nov. 20)

CA #2 Natural frequency problem

Due on Monday (Nov. 20) in class

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Notes for Computer Assignment #1 Q5

The notes mentioned in the problem (Rice, Solid Mechanics, pp65-68) is attached.

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ABAQUS Tutorial and Assignment #1

1-1 ABAQUS Tutorial: Schedule & Proceedings

1-2 Learning ABAQUS: Begin with ABAQUS Command

1-3 Computer Assignment #1: Plate with circular hole

1-4 CAE Example: Having a sense of ABAQUS CAE

 

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For those who attended office hour today (Oct. 26)

After discussion with Xuanhe, I believe that B=0 for Q21 because there's no cut-and-weld operation here. Then the solusion is exactly the Lame Solution in Cylindrical Shape as in Q8.

What do you think?

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Office Hour Change for Oct. 19

Office hour for tomorrow (Oct. 19 Thursday) will be rescheduled as 4:00pm to 4:30pm.

Sorry about this.

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Office Hour for ES 240

Zhigang Suo: Wed. 3pm Pierce 309

Nanshu Lu: Thur. 4~6pm Pierce 403

Valid for every week except special notification is published.

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George Rankine Irwin (26 February 1907 - 9 October 1998)

G.R. Irwin during WW II.

Dr George Rankine Irwin (26 February 1907 - 9 October 1998) was an American scientist in the field of fracture mechanics and strength of materials. He was internationally known for his study of fracture of materials. Read more...

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Critical Size of Stiff Islands on Stretchable Substrates due to Interface Delamination

One possible design of stretchable integrated circuits consists of functional islands of stiff thin films on a polymer substrate. When such a structure is stretched, the substrate carries most of the deformation while the islands experience little strain. However, in practice, the island/substrate interface can never cohere perfectly. Existing experiments suggest that, interface debonding occurs if the island is larger than a certain size. I am now studying the critical size of stiff islands on stretchable polymer substrates due to thin film delamination, using finite element simulations. We show that the maximum energy release rate of interfacial cracking goes down as island size or substrate stiffness decreases. As a result, the critical island size can be enhanced if the substrate is chosen to be more compliant. An approximate formula is given to predict the energy release rate for the configuration of stiff islands on very compliant substrate.

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2006 ASME Congress, November 5-10, 2006, Chicago, IL

Here is the website for the 2006 ASME Congress. For the applied mechanics program, click "Program Overview", then choose "Applied Mechanics" from the list of topics.

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