iMechanica - industry - Comments

i need your emeil adreess

mohamed ali — Thu, 13 Mar 2008 08:59:12 -0400

i need your emeil adreess

subdivision method to solve integral with weak singularity

mohamed ali — Thu, 13 Mar 2008 08:57:19 -0400

i need this papers about the use of subdivision method to solve integral with weak singularity in bem

- J O Lachat & J O watson " effective numerical treatment of boundary inegral equation " a new formulation for three dimenssional elasostatics Int .Jr.Numer.methods .Eng.211-228(1958)

I read Kindle yesterday

Kewei Li — Tue, 01 Jan 2008 07:56:10 -0500

I read Kindle yesterday in local newspaper. It makes e-reading much like paper-based, what's more, it saves a lot.

Kevin Kelly on the future of books

Zhigang Suo — Sat, 29 Dec 2007 21:11:52 -0500

The Best of Technology Writing 2007 is out. One particular selection caught my eyes: "Scan This Book!" by Kevin Kelly, published in the New York Times, on 14 May 2006. The article is truly delightful and thoughtful. Kelly is an exceptional writer and a visionary. Another one of his articles, "We Are the Web", inspired me in early days of iMechanica.

The future of knowledge?

Zhigang Suo — Mon, 19 Nov 2007 20:45:17 -0500

I have been using this slide in my talks on large-area electronics. The slide is not about future; it is about the present. On the left are books, magazines, newspapers, maps, etc., the technologies that we have been using for centuries to distribute and display knowledge. These technologies have been with us for so long that we almost forget that they are just displays, rather than knowledge itself.

On the right is a LCD, a display technology so pervasive today that we tend to forget that they are in the mass market only for about 10 years.

We live in an exciting time. For all these centuries we had no computers. Now we do. In last decade or so the Internet has in effect made the whole world into a single, giant computer. An individual person is at the same time a user of this computer and a part of this computer.

While I'm trying to extrapolate from what I see to what and how I will teach next year, Michael and his young friends are talking about the ultimate method of learning.

What will be the future of display? What will be the future of knowledge? What should we teach?

Ignore my previous comment

Sivakkumar Arjunon — Wed, 15 Aug 2007 11:16:58 -0400

Hey Nathan,

I saw your profile after i posted my previous comment. Please ignore that.

Thanks,

Shiva

Response to your question

Rongmei niu — Wed, 28 Mar 2007 20:40:02 -0400

Hi Nanshu,

Cracks density is the total cracks length per unit area in this paper. in case of parallel channel cracks , the average crack spacing is often used. Howerver, as to the zigzag cracks, i thinkit is reasonable to use cracks length per unit area.

I donot understand what is you meaning of the second question. And the modulus of Cu from my test is about 80~100GPa. How about you?

Regards!

Rongmei

Justification for 2D modeling of island delamination

Nanshu Lu — Wed, 28 Mar 2007 12:05:23 -0400

Xuanhe, very interesting question.

You're right, from engineering point of view the ideal modeling should be 3D, multilayer structure, true flaws... as real as possible. Intuitively, the corners of a square shape island should have higher driving force so that these areas are more susceptible for debonding. However, here I can give three justifications for our 2D modeling of island delamination.

First, from some experimental pictures of island delamination (Fig. 7 in Lacour et al, JAP 100 014913, 2006 and Fig. 11 in Bhttacharya et al, JES 153 (3) G259, 2006) we can see debonding occurs at both corners and laterals of the square island. Thus our 2D modeling is reasonable for the later one.

Second, even if the crack front is a 2D curve (many people modeling the 3D corner crack with quarter circular front) our delamination criterion says the energy release rate of each point on the front should reach interface toughness Γ(Ψ), where Ψ is the mode mix angle. So sometimes this 3D problem can be reduced to a 2D problem.

Last but not least, the main purpose of our scientific research is to try to understand the natural laws and intrinsic mechanisms. We make as many as possible simplifications so that the main object gets emphasized. Starting from 2D study we can find out how elastic mismatch, island size and crack size can influence the energy release rate, which is of great guidance for 3D problem. Meanwhile, 3D modeling is of high calculation and time cost. Comparing the gain and cost we just adopted 2D modeling.

Corner Effects.

Xuanhe Zhao — Tue, 27 Mar 2007 18:48:25 -0400

Hi Nanshu,

Very interesting work. A question. I noticed that you used plane strain assumption for your calculation, because the island's width is usually much higher than its thickness. Have you ever considered the effects of the island's corners, which in my opinion are the highest stress concentration points in this kind of structure, and therefore maybe the crack initiations? In this way, do you you need a 3D simulation to analyse the problem?

-Xuanhe

Nice job

Nanshu Lu — Mon, 26 Mar 2007 22:38:40 -0400

Dear Rongmei,

Congratulations to your new paper and thanks so much for sharing with us. It is very nice work and exactly what I am looking for. I just had a glance and have two questions needing your help,

1. How do you define and measure the crack density?

2. To obtain Cu yield strength did you take the tensile system compliance into account? What Young's modulus for film Cu did you get?

I'll read it more carefully later.

Nanshu

attatchment

Rongmei niu — Mon, 26 Mar 2007 21:29:15 -0400

Dear Nanshu,

I am sorrry for missing the attachment. This paper has been accept, and may be referenced to your experiments.

Regards!

Rongmei

Nice work, Nanshu.

Teng Li — Mon, 26 Mar 2007 17:14:17 -0400

Nanshu,

Very nice work. Thanks for this a wonderful addition to the March Journal Club issue.

I was away in the last several days, and it seems I missed the instructive discussion here. I've added a link in the March issue of Journal Club to this active discussion.

-Teng

My pleasure to answer your question

Nanshu Lu — Mon, 26 Mar 2007 13:13:36 -0400

Dear Rongmei,

Thanks for your recommendation very much. Now with the platform of imechanica, mechanics people can communicate freely all over the world. We are able to find speeches, lecture notes, manuscripts and many other resources here. Actually all of us are fortunate, right?

Regarding to your question about "island", it is actually a very nice design in flexible electronics. In order to be flexible, we need to fabricate inorganic brittle material onto flexible PI substrate. Since the brittle film can only sustain little strain, the film cannot continuously cover the whole substrate surface. Instead, we fabricate a lattice of brittle islands with metallic interconnections. When the substrate is stretched, the deformation is mainly accommodated by the substrate, so that the island and functional materials on it experience relative small strains.

Regarding to "coating", we use it to refer an additional continuous layer covering all over the islands and substrate. It can significantly reduce corner singularity and suppress delamination. A recent study from our group is here.

Regards

pleasure to discuss with you!

Rongmei niu — Mon, 26 Mar 2007 10:58:09 -0400

Dear Nanshu,

I am very pleasure to recommend excellent references to you! but you will find that most of them are from your group. Another paper in Journal of the Mechanics and Physics of Solids48 (2000) P1107――Crack patterns in thin films by Z. Cedric Xia, John W. Hutchinson, may be useful.

I admire and congratulate you that you are so fortunate in a great group, and conveniently communicate and discuss with great people. My major is materials science and engineering, and i only did some experiments, the attatchment in the following is part of the experiments, i sincerely hope it helpful to you! To be frankly, i still did not completely understand your paper. Why use "island" instead of "film or coating"? In the actual application, the films are continuous. Regards

Reply to mode mixity

Nanshu Lu — Sun, 25 Mar 2007 17:21:31 -0400

Thanks, Charlie.

When you request history output for the domain of contour integral there are several choices of the type. To obtain energy release rate only, we just choose "J-integral". To obtain both ERR and Ks, we choose "Stress intensity factors", with prescribing a crack initiation criterion. After calculation is completed, from the history output we can get both K1 and K2 as well as ERR estimated from Ks.

You are right, to present the ABAQUS results in the paper I just assume ε=0 and get my mode mixity simply from tanΨ=K2/K1. This is because our main purpose is to study the behavior of energy release rate.