User login

You are here

research

Nanshu Lu's picture

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.

Xiaodong Li's picture

A New Class of Composite Materials - Graphene-based Composite Materials

Professor Rodney Ruoff and colleagues at Northwestern University and Purdue University have developed a process that promises to lead to the creation of a new class of composite materials - graphene-based materials. They reported the results of their research in Nature, 442 (2006) 282-286. This team has overcome the difficulties of yielding a uniform distribution of graphene-based sheets in a polymer matrix. Such composites can be readily processed using standard industrial technologies such as moulding and hot-pressing. The technique should be applicable to a wide variety of polymers. The graphene composites may compete with carbon nanotube-based materials in terms of mechanical properties. This new class of composites may stimulate the applied mechanics community to study the fundamental reinforcing mechanisms of graphene sheets from both experimental and theoretical approaches.

Wei Hong's picture

Interplay between elastic interactions and kinetic processes in stepped Si (001) homoepitaxy

A vicinal Si (001) surface may form stripes of terraces, separated by monatomic-layer-high steps of two kinds, SA and SB. As adatoms diffuse on the terraces and attach to or detach from the steps, the steps move. In equilibrium, the steps are equally spaced due to elastic interaction. During deposition, however, SA is less mobile than SB. We model the interplay between the elastic and kinetic effects that drives step motion, and show that during homoepitaxy all the steps may move in a steady state, such that alternating terraces have time-independent, but unequal, widths. The ratio between the widths of neighboring terraces is tunable by the deposition flux and substrate temperature. We study the stability of the steady state mode of growth using both linear perturbation analysis and numerical simulations. We elucidate the delicate roles played by the standard Ehrlich-Schwoebel (ES) barriers and inverse ES barriers in influencing growth stability in the complex system containing (SA+SB) step pairs.

Preprint available in the attachment.

Teng Li's picture

Organic LED could replace light bulb?

Lighting accounts for about 22% of the electricity consumed in buildings in the United States, and 40% of that amount is eaten up by inefficient incandescent light bulbs. The search for economical light sources has been a hot topic.

Recently, scientists have made important progress towards making white organic light-emitting diodes (OLEDs) commercially viable as light source. As reported in a latest Nature article, even at an early stage of development this new source is up to 75% more fficient than today's incandescent sources at similar brightnesses. The traditional light bulb's days could be numbered.

Read media report here.

(Via www.macroelectronics.org)

Rui Huang's picture

EPN - E-print Network

I was notified today that my Web site (http://www.ae.utexas.edu/~ruihuang/) has been included in the E-print Network (EPN). EPN is a fast-growing searchable scientific network of over 20,000 Web sites containing research conducted by researchers - from Nobel Laureates to post-doctoral students - who are offering e-prints of their work via the Internet.

Developed by the Office of Scientific and Technical Information (OSTI) to facilitate the needs of the Department of Energy (DOE) research community, E-print Network enhances dissemination of important research and helps to create opportunities for productive professional contacts.

E-print Network indexes over 900,000 e-prints. Most documents included in the network are recent scientific literature. Functions available to users include conducting full-text searches, searching for documents by contributing author, establishing a personalized alert service to keep abreast of new e-prints, and exploring laboratory Web sites for further details about selected research programs.

Once users find a paper of interest, they can download it from the site hosting the paper. This way you control distribution of your e-prints and can more readily track Web interest in your papers.

My page is listed under both Engineering and Materials Science.

Rui Huang's picture

Modeling Place

Starting from January 2006, my group has been posting in Modeling Place as a blogspot to share research experience and ideas. We will gradually migrate to iMechanica for better publicity and more web functions.

Xi Chen's picture

A molecular dynamics-decorated finite element framework for simulating the mechanical behaviors of biomolecules

Cover of Biophysical JournalOur first paper in biomechanics is featured as the cover of the Biophysical Journal. The paper is attached. Several freelance writers in biophysics have reported this paper in magazines and websites/blogs. This framework is very versatile and powerful, and we are now implementing more details/atomistic features into this phenomenological approach, and the follow-up paper will be submitted soon.

Abstract: The gating pathways of mechanosensitive channels of large conductance (MscL) in two bacteria (Mycobacterium tuberculosis and Escherichia coli) are studied using the finite element method. The phenomenological model treats transmembrane helices as elastic rods and the lipid membrane as an elastic sheet of finite thickness; the model is inspired by the crystal structure of MscL. The interactions between various continuum components are derived from molecular-mechanics energy calculations using the CHARMM all-atom force field. Both bacterial MscLs open fully upon in-plane tension in the membrane and the variation of pore diameter with membrane tension is found to be essentially linear. The estimated gating tension is close to the experimental value. The structural variations along the gating pathway are consistent with previous analyses based on structural models with experimental constraints and biased atomistic molecular-dynamics simulations. Upon membrane bending, neither MscL opens substantially, although there is notable and nonmonotonic variation in the pore radius. This emphasizes that the gating behavior of MscL depends critically on the form of the mechanical perturbation and reinforces the idea that the crucial gating parameter is lateral tension in the membrane rather than the curvature of the

Split singularities and the competition between crack penetration and debond at a bimaterial interface

Zhen Zhang and Zhigang Suo

For a crack impinging upon a bimaterial interface at an angle, the singular stress field is a linear superposition of two modes, usually of unequal exponents, either a pair of complex conjugates, or two unequal real numbers. In the latter case, a stronger and a weaker singularity coexist (known as split singularities). We define a dimensionless parameter, called the local mode mixity, to characterize the proportion of the two modes at the length scale where the processes of fracture occur. We show that the weaker singularity can readily affect whether the crack will penetrate, or debond, the interface.

Teng Li's picture

Review Articles on Flexible Electronics

[img_assist|nid=46|title=|desc=|link=url,http://www.materialstoday.com/2006_issues/april.htm|align=right|width=75|height=100]The cover story of the April 2006 issue of Materials Today features Flexible Electronics. This issue also includes two review articles in this emerging field of research. Access to full text articles is free of charge at http://www.materialstoday.com.

Review Article:

Material challenge for flexible organic devices, by Jay Lewis

Review Article:

Organic and polymer transistors for electronics, by Ananth Dodabalapur

Cover Story:

Jet printing flexible displays, by R.A. Street et al.

Pages

Subscribe to RSS - research

Recent comments

More comments

Syndicate

Subscribe to Syndicate