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A message from Dr. Ken P. Chong

The deadline of October 1, 2006 for my program of Mechanics & Structures of Materials was inadvertently omitted in our website. However, at the beginning of our CMS home page there are 2 deadlines listed for all programs. In the meantime any unsolicited proposals for my program, please put in GPG 04-23 as the Program Announcement [1st box]. In the 2nd box put in my program name [Mechanics & Structures of Materials].

Rui Huang's picture

Surface effects on thin film wrinkling

A recent discussion here about the effect of surface stress on vibrations of microcantilever has gained some interest from our members. A few years ago, Zhigang and I looked at surface effect on buckling of a thin elastic film on a viscous layer (Huang and Suo, Thin Solid Films 429, 273-281, 2003). Although the physical phenomena (buckling vs vibrations) are different, the conclusion is quite consistent with Wei Hong and Pradeep's comments toward the end of the discussion. That is, surface stress only contributes as a residual stress and thus does not affect the buckling wavelength (frequency in space in analogy to frequency in time for vibrations).

Zhigang Suo's picture

7 reasons to post your original ideas in iMechanica

1. iMechanica is free for all to use. iMechanica is hosted on a server at the School of Engineering and Applied Sciences, of Harvard University, and is managed by a team of volunteers -- mechanicians just like you. You pay nothing to post, and readers pay nothing to read. The limit of each upload file is 50MB, and each user is given 1GB server space.

Ting Tsui's picture

Constraint Effects on Thin Film Channel Cracking Behavior

Channel CrackOne of the most common forms of cohesive failure observed in brittle thin film subjected to a tensile residual stress is channel cracking, a fracture mode in which through-film cracks propagate in the film. The crack growth rate depends on intrinsic film properties, residual stress, the presence of reactive species in the environments, and the precise film stack.

Jeffrey Kysar's picture

Analytical solutions for plastic deformation around voids in anisotropic single crystals

It is well established that the growth of microscopic voids near a crack tip plays a fundamental role in establishing the fracture behavior of ductile metals. Mechanics analyses of plastic void growth have typically assumed the plastic properties of the surrounding metal to be isotropic. However voids are typically of the order of magnitude of one micron so that they exist within individual grains of the metal, or along grain boundaries, at least at the initial growth stage. For that reason, the plastic properties of the material surrounding the void are most properly treated as being anisotropic, rather than isotropic.

In the uploaded preprint, the stress state and deformation state are derived around a cylindrical void in a hexagonal close packed single crystal. The orientation of the cylindrical void and the loading state relative to the crystal are chosen so that the deformation state is one of plane strain. The active slip systems reduce to a total of three slip systems which act within the plane of plane strain. The solution shows that the deformation state consists of angular sectors around the void within which only one slip system is active. Further, it is shown that the stress state and deformation state exhibit self-similarity both radially and circumferentially, as well as periodicity along certain logarithmic spirals which emanate from the void surface.

Konstantin Volokh's picture

Why fingerprints are different

A possible explanation of the variety of fingerprints comes from the consideration of the mechanics of tissue growth. Formation of fingerprints can be a result of the surface buckling of the growing skin. Remarkably, the surface bifurcation enjoys infinite multiplicity. The latter can be a reason for the variety of fingerprints. Tissue morphogenesis with the surface buckling mechanism and the growth theory underlying this mechanism are presented in the attached notes.

Jun He's picture

Materials Impact on Interconnects Process Technology and Reliability

M.A. Hussein and Jun He (Intel Corporation)

IEEE Transactions on Semiconductor Manufacturing, vol. 18, No. 1, p.69-85, 2005

In this work, we explain how the manufacturing technology and reliability for advanced interconnects is impacted by the choice of metallization and interlayer dielectric (ILD) materials. The replacement of aluminum alloys by copper, as the metal of choice at the 130nm technology node, mandated notable changes in integration, metallization, and patterning technologies. Those changes directly impacted the reliability performance of the interconnect system. Although further improvement in interconnect performance is being pursued through utilizing progressively lower dielectric constant (low-k) ILD materials from one technology node to another, the inherent weak mechanical strength of low-k ILDs and the potential for degradation in the dielectric constant during processing, pose serious challenges to the implementation of such materials in high volume manufacturing. We will consider the cases of two ILD materials; carbon-doped silicon dioxide (CDO) and low-k spin-on-polymer to illustrate the impact of ILD choice on the process technology and reliability of copper interconnects. preprint pdf 2.49 MB

Jie-Hua Zhao's picture


Flip-chip plastic ball grid array (FC-PBGA) packages are widely used in high performance components. However, its die back is normally under tensile stress at low temperatures. This paper presents a probabilistic mechanics approach to predict the die failure rate in the FC-PBGA qualification process. The methodology consists of three parts:

Joost Vlassak's picture

The Effect of Water Diffusion on the Adhesion of Organosilicate Glass Film Stacks

Ting Y. Tsui, Andrew J. McKerrow, and Joost J. Vlassak

Published in the Journal of The Mechanics and Physics of Solids, 54 (5), 887-903 (2006)

Abstract – Organosilicate glass (OSG) is a material that is used as a dielectric in advanced integrated circuits. It has a network structure similar to that of amorphous silica where a fraction of the Si-O bonds has been replaced by organic groups. It is well known from prior work that OSG is sensitive to subcritical crack growth as water molecules in the environment are transported to the crack tip and assist in rupturing Si-O bonds at the crack tip. In this study, we demonstrate that exposure of an OSG containing film stack to water prior to fracture results in degradation of the adhesion of the film stack. This degradation is the result of the diffusion of water into the film stack. We propose a quantitative model to predict adhesion degradation as a function of exposure time by coupling the results of independent subcritical crack growth measurements with diffusion concentration profiles. The model agrees well with experimental data and provides a novel method for measuring the water diffusion coefficient in film stacks that contain OSG. This study has important implications for the reliability of advanced integrated circuits.

Ashkan Vaziri's picture

Deformation of the cell nucleus under indentation: Mechanics and Mechanisms

Computational models of the cell nucleus, along with experimental observations, can help in understanding the biomechanics of force-induced nuclear deformation and mechanisms of stress transition throughout the nucleus. Here, we develop a computational model for an isolated nucleus undergoing indentation, which includes separate components representing the nucleoplasm and the nuclear envelope. The nuclear envelope itself is composed of three separate layers: two thin elastic layers representing the inner and outer nuclear membranes and one thicker layer representing the nuclear lamina. The proposed model is capable of separating the structural role of major nuclear components in the force-induced biological response of the nucleus (and ultimately the cell). A systematic analysis is carried out to explore the role of major individual nuclear elements, namely inner and outer membranes, nuclear lamina, and nucleoplasm, as well as the loading and experimental factors such as indentation rate and probe angle, on the biomechanical response of an isolated nucleus in atomic force microscopy indentation experiment.

Microcantilever for biomolecular detections

Microcantilevers have taken much attention as devices for label-free detection of molecules and/or their conformations in solutions and air. Recently, microcantilevers have allowed the nanomechanical mass detection of thin film [1-3], small molecules [4, 5], and biological components such as viruses [6] and vesicles [7] in the order of a pico-gram to a zepto-gram. The great potential of microcantilevers is the sensitive, reliable, fast label-free detection of proteins and/or protein conformations. Specifically, microcantilevers are capable of label-free detection of marker proteins related to diseases, even at a low concentration in solution [8-17]. Microcantilevers, operated in a viscous fluid, have also enabled the real-time monitoring of protein-protein interactions [8, 12-15]. Furthermore, microcantilevers are able to recognize the specific protein conformations [18] and/or reversible conformation changes of proteins/polymers [19, 20].

Demitris Kouris's picture

Associate or Assistant Professor -- Experimental Mechanics of Materials

The Department of Mechanical Engineering at the University of Wyoming invites applications for a tenure-track faculty position. Applicants are sought at the Associate or Assistant Professor level with expertise in experimental mechanics and particularly in emerging areas of science and technology. Such areas include but are not limited to the study of biomaterials, tissue engineering, nanomechanics of engineering materials, as well as thin films and multilayers, fracture, fatigue and damage.

The successful applicant will be expected to establish a strong, funded research program, as well as teach at the graduate and undergraduate levels. She/He will be expected to participate in interdisciplinary research efforts both within and outside the College of Engineering. Minimum qualifications include an earned doctorate in mechanical engineering, materials science/engineering, or a closely related field.

Cellular and Molecular Mechanics

Cellular and Molecular Mechanics I was invited by Dr. Zhigang Suo to write a short piece on “Cellular and Molecular Mechanics”. I am writing this informally to introduce this subject matter rather than talk in vernacular such as mechanotransduction, phosphorylation, etc. I have more formal papers if someone is interested in more detailed discussions on this subject area. This is a field in which I have been working for over a decade now and I find it more exciting every day. The question always is how does mechanics affect biological processes. This is a very interdisciplinary subject matter as mechanists, engineers, physicists, chemists, and biologists have been investigating this process from various perspectives. I am obviously not the first to study this process. For most of us, it is realized from an empirical perspective that mechanics matters to biology, but exactly how mechanics specifically alters biochemistry continues to be highly debated today. Mechanics of course matters in many physiological areas. Your blood flows, your heart pumps, your bone and muscle feel mechanics. Not only does the body experience mechanical stimulation, but it reacts biochemically to it. A wonderful example is when people go into space (NASA) for long periods of time. The bone in one’s body begins to resorb in a similar response mode to what one experiences in aging (osteoporosis). This is primarily due to just the change in the gravity (mechanics). Other diseases are related to these issues including the two biggest killers: heart disease and cancer. While biomechanics on this scale has been studied for awhile (Leonardo Da Vinci, who was interested in mechanics, also wrote one of the first texts on anatomy), the movement to the cellular and molecular scales has brought a tremendous amount of excitement. I consider the cell as one of the ultimate smart materials exhibiting these characteristics. The cell has evolved over millions of years and is designed better than almost any system that we can personally build. Just as the biological eye provides a beautiful template for optics based lenses, much can be learned about building technology (“nanotechnology” and “microtechnology”) through examining the behavior of cells and molecules.

The Fourth China-Japan-Korea Joint Symposium on Optimization of Structural and Mechanical Systems

The Fourth China-Japan-Korea Joint Symposium on Optimization of Structural and Mechanical Systems will be held in Kunming, China, November 6–9, 2006.

Recent advances of computer technology have given powerful practical tools to structural and mechanical designs. Optimal design is one of such area where various theories and methodologies are well developed. It is, however, lacking general interests among field designers and engineers. Innovative optimal design techniques and new applications are yet to be developed. Following the successful first CJK-OSM1 in Xian, China in 1999, second (CJK-OSM2) in Busan, Korea in 2002 and the third (CJK-OSM3) in Kanazawa, Japan in 2004, as agreed among participants in the symposium, the fourth CJK-OSM symposium will be held in Kunming, China during Nov. 6th -Nov. 9th, 2006. As before this will be a forum for exchange of recent research ideas and fostering new developments and new applications. Reflecting current interests from various fields, several new topics are included. The scope is, however, not limited to those listed.

Symposium on Mechanics in Biology and Medicine

This symposium will be part of the 2007 ASME Applied Mechanics and Materials Conference, to be held in the University of Texas in Austin, in June 3-6, 2007.

Student Presentation Competition at USNCCM IX

The 9th US National Congress on Computational Mechanics will feature a student presentation competition. This competition continues in the format pursued at the recent World Congress in Los Angeles. It is open to students who have an abstract accepted for presentation at the Congress.

2000 Timoshenko Medal Acceptance Speech by Rodney J. Clifton

November 9, 2000

Choose a channel featured in the header of iMechanica: 
Pradeep Sharma's picture

Journal Club: Response/Feedback requested

Hello everyone,

I had previously posted this entry on the AMD blog and perhaps it worthwhile to post it again on this forum. I would like to solicit feedback and comments on an idea to further enhance the role and utility of iMechanica.

This inspiration comes from Bell labs and the physics community.....

They started a journal club (year 2003). Each month ONLY 2-3 already published recent journal papers are reviewed and commentary posted in the form of a newsletter. Since only 2-3 papers are reviewed, the selection is much more stringent and careful. The contribution is regular and periodic (monthly). Hence, this newsletter is taken seriously by physicists.

In our case, this can be done within iMechanica. I suspect we could achieve the same kind of interest if we restrict "notable" papers to 1-3 per month and make it a regular monthly feature. In principle anyone could submit a commentary but the blog moderators will select the top 2-3.

The operational rules are open for discussion. Briefly though, I am thinking on the lines of rotating 1-2 moderators with a term of say 2 months. The moderator will receive commentaries on recently published papers RELATED to mechanics area. The moderator will highlight 1-3 notable commentaries in the journal club newsletter. A key requirement must be that the commentaries/paper highlighted are related to mechanics in some form or the other. The concept of rotating moderator is to provide breadth and prevent bias of any one individual. Rotation of journal club moderators will also keep the "work-load" well distributed.

Pradeep Sharma's picture

Collected Works of J.D. Eshelby

Perhaps a post has already been made in this regard; A book containing all the papers by J.D. Eshelby was recently released by Springer. This book is compiled by Markenscoff and Gupta. Congratulations to both of them for such a great idea!

I bought this book last week and it is fascinating to read all of Eshelby's papers in chronological order. Furthermore, I found a few papers that I had not even been aware of. The price, at roughly $195 on Amazon is a bit steep but (in my opinion) well worth it. The book also contains forewords by several researcher who knew Eshelby personally.

Here is the amazon link to this book

Ting Zhu's picture

Handbook of Materials Modeling

by S. Yip (Editor), 2005

Book Review
"A new guide to materials modeling largely succeeds in its aim to be the defining reference for the field of computational materials science and represents a huge undertaking..." -- by James Elliott | University of Cambridge, Materials Today, Volume 9, Issues 7-8, July-Aug 2006, Pages 51-52.

Book Description
The first reference of its kind in the rapidly emerging field of computational approachs to materials research, this is a compendium of perspective-providing and topical articles written to inform students and non-specialists of the current status and capabilities of modelling and simulation. From the standpoint of methodology, the development follows a multiscale approach with emphasis on electronic-structure, atomistic, and mesoscale methods, as well as mathematical analysis and rate processes. Basic models are treated across traditional disciplines, not only in the discussion of methods but also in chapters on crystal defects, microstructure, fluids, polymers and soft matter. Written by authors who are actively participating in the current development, this collection of 150 articles has the breadth and depth to be a major contributor toward defining the field of computational materials. In addition, there are 40 commentaries by highly respected researchers, presenting various views that should interest the future generations of the community. Subject Editors: Martin Bazant, MIT; Bruce Boghosian, Tufts University; Richard Catlow, Royal Institution; Long-Qing Chen, Pennsylvania State University; William Curtin, Brown University; Tomas Diaz de la Rubia, Lawrence Livermore National Laboratory; Nicolas Hadjiconstantinou, MIT; Mark F. Horstemeyer, Mississippi State University; Efthimios Kaxiras, Harvard University; L. Mahadevan, Harvard University; Dimitrios Maroudas, University of Massachusetts; Nicola Marzari, MIT; Horia Metiu, University of California Santa Barbara; Gregory C. Rutledge, MIT; David J. Srolovitz, Princeton University; Bernhardt L. Trout, MIT; Dieter Wolf, Argonne National Laboratory.

Ravi-Chandar's picture

McMat 2007 Applied Mechanics and Materials Conference

The McMat 2007 conference, organized by the University of Texas on behalf of the Applied Mechanics and the Materials Divisions of the ASME, will be held in Austin, June 3-7, 2007.

We are now accepting proposals for symposia and abstracts of papers.

Ling Liu's picture

Ninth U.S. National Congress on Computational Mechanics

USNCCM IX, July 22 - 26, 2007
Pre- & Post-Congress Short Courses, July 22 & 26, 2007
Hyatt Regency San Francisco
San Francisco, California

From their inception in 1991, the biennial congresses of the United States Association for Computational Mechanics have become major scientific events, drawing computational engineers and scientists worldwide from government, academia, and industry. The Ninth U.S. National Congress on Computational Mechanics (USNCCM IX), hosted by the University of California, Berkeley, will feature the latest developments in all aspects of computational mechanics, and will broaden the definition of the discipline to include many other computation-oriented areas in engineering and sciences. From applications in nanotechnology and bioengineering, to recent advances in numerical methods and high-performance computing, the technical program will reflect the Congress theme of "Interdisciplinary Computation''. In addition to plenary lectures and minisymposia that highlight the latest trends in computational mechanics, pre- and post-conference short courses addressing advances in multiscale and multiphysics methods, as well as other topics, will be held. Numerous vendor exhibits from Bay Area and national companies and organizations are also planned. Detailed information on USNCCM IX can be found at:

Rui Huang's picture

From students' perspective

I like to keep the mindset of being a student, learning from all sources on all topics I am interested. Recently I have learned quite a lot about mechanics and mechanicians from Applied Mechanics News and its sister blogs and now iMechanica.

With a job as an assistant professor, I always try to motivate my students to become future mechanicians. For this reason, I started Modeling Place as a group blog in January and gently forced my students to participate. Out of the five students I have, two actively participate by posting frequently, two occasionally post, and one dropped out quickly after one post. Together, the blog has been doing reasonably well, in terms of both quantity and quality of posts.

I learned a few tricks in handling images and got to know some interesting works in the general area of mechanics. How about the students? What benefits have they received? I have to ask them. For one, I awarded one student with a little gift as the best post of the semester. More importantly, I believe that they are reading more than they used to do, thus gaining broader knowledge and interest in mechanics and related science. They not only read the posts in the blog but also read from other sources (online or not) to find something to post. Furthermore, they have a place to practice writing. It is a big step from reading to writing, not only for foreign students I think.

It may be still too soon to tell how well this works, but the students themselves should be able to tell us more. If you are a student, I encourage you to comment on this to tell the professors what you like or don't like about iMechanica. At this stage of development, much more features and benefits can be accomodated. Your ideas could shape the future of iMechanica and benefit all students and those considering themselves as students of life.


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