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Nonlinear elasticity of biological gels

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I would like to propose the recent papers by Janmey, P.A., and coworkers on the nonlinear elasticity behavior of biopolymer gels for "biomechanics" issue in J Club. In their original work, they proposed the biopolymer network model composed of semi-flexible polymers that behave like a worm-like-chain (WLC) model. Their models surprisingly capture the mechanical response of biopolymer gels such as neuro-filaments. The details of their work are as follows:

Rui Huang's picture

Harry F. Tiersten

(Professor Tiersten in his office, behind a pile of files on his desk.)

Harry F. Tiersten (1930-2006), Professor of Mechanics at Rensselaer Polytechnic Institute, passed away suddenly on June 12, 2006 from a heart attack. Professor Tiersten was one of the founders of continuum electrodynamics. In this paper we present a brief summary of Tiersten’s major contributions to the theories of continuum electrodynamics and their applications.

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Xi Chen's picture

A new website has been created for Prof. Raymond Mindlin, including funding solicitation for the Mindlin Medal

A new website has been recently created for the centennial of Professor Raymond Mindlin. In addition, the Engineering Mechanics Division of ASCE has launched an effort to establish the Mindlin Medal of Applied Mechanics. The goal is to raise about $30,000 to setup an endowment at ASCE.

Teng Li's picture

Delocalizing Strain in a Thin Metal Film on a Polymer Substrate

Teng Li, Zhenyu Huang, Zhichen Xi, Stephanie P. Lacour, Sigurd Wagner, Zhigang Suo, Mechanics of Materials, 37, 261-273 (2005).

Under tension, a freestanding thin metal film usually ruptures at a smaller strain than its bulk counterpart. Often this apparent brittleness does not result from cleavage, but from strain localization, such as necking. By volume conservation, necking causes local elongation. This elongation is much smaller than the film length, and adds little to the overall strain. The film ruptures when the overall strain just exceeds the necking initiation strain, εN , which for a weakly hardening film is not far beyond its elastic limit. Now consider a weakly hardening metal film on a steeply hardening polymer substrate. If the metal film is fully bonded to the polymer substrate, the substrate suppresses large local elongation in the film, so that the metal film may deform uniformly far beyond εN. If the metal film debonds from the substrate, however, the film becomes freestanding and ruptures at a smaller strain than the fully bonded film; the polymer substrate remains intact. We study strain delocalization in the metal film on the polymer substrate by analyzing incipient and large-amplitude nonuniform deformation, as well as debond-assisted necking. The theoretical considerations call for further experiments to clarify the rupture behavior of the metal-on-polymer laminates.

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Tension of Cu film on Pi substrate
Local thinning of Cu film
High ductility of a metal film adherent on a polymer substrate

High ductility of a metal film adherent on a polymer substrate

In recent development of deformable electronics, it has been noticed that thin metal films often rupture at small tensile strains. Here we report experiments with Cu films deposited on polymeric substrates, and show that the rupture strains of the metal films are sensitive to their adhesion to the substrates. Well-bonded Cu films can sustain strains up to 10% without appreciable cracks, and up to 30% with discontinuous microcracks. By contrast, poorly bonded Cu films form channel cracks at strains about 2%. The cracks form by a mixture of strain localization and intergranular fracture.

Konstantin Volokh's picture

Griffith controversy

Using the Griffith energy method for analysis of cavitation under hydrostatic tension we conclude that the critical tension tends to infinity when the cavity radius approaches zero (IJSS, 2006, doi: 10.1016/j.ijsolstr.2006.12.022). The conclusion is physically meaningless, of course. Moreover, if we assume that the failure process occurs at the edge of the cavity then the critical tension should be length-independent for small but finite cavities while the Griffith analysis always exhibits length-dependence. The main Griffith idea - introduction of the surface energy - is controversial because it sets up the characteristic length, say, surface energy over volume energy. By no means is this approach in peace with the length-independent classical continuum mechanics.

Pradeep Sharma's picture

Is rest of the world catching up with us? Perspective from Physical Review Letters...

I had posted this on the amd blog...I am posting it here as well:

Last year I attended the annual American Physical Society conference held in Baltimore (during the week of March 13th). One of the non-technical sessions included presentations by the APS journal editors--Physical Review A/B/C/D/E and Letters---and a panel discussion related to these journals. Since many of our mechanics and materials colleagues nowadays are interested in publishing in these journals, I thought I should post a link to some of the slides (from the editors presentation) that I found interesting. Many of the slides presented at APS are in the linked pdf file that also includes additional (humorous slides!) regarding reviewer issues.

The Ranking of Mechanics Related Journals (2004)

Based on a survey from Journal Citation Report (JCR), we listed below the 2004 Journal Impact Factors (IF) for some mechanics, material science, and solid state physics related scientific journals. Our list and information may not be complete. We welcome readers' input, comments, and information. We also caution readers that using IF as the sole criterion to rank scientific journals' academic reputation may not be objective nor true to a journal's actual scientific merits.

Rui Huang's picture

Nanoscience Initiative Workshop

The Air Force Office of Scientific Research (AFOSR) of the U.S. Air Force Research Laboratory (AFRL) and National Science Council (NSC) in Taiwan are pleased to announce that the 4th U.S. Air Force/Taiwan Nanoscience and Nanotechnology workshop will be held on February 8-9, 2007 at the main campus of the University of Houston. We invite you to join us at the workshop.

Tienchong Chang's picture

Nonlinear stick-spiral model for predicting mechanical behavior of single-walled carbon nanotubes

(PRB,74,245428,2006)  Based on a molecular mechanics concept, a nonlinear stick-spiral model is developed to investigate the mechanical behavior of single walled carbon nanotubes (SWCNTs). The model is capable of predicting not only the initial elastic properties (e.g., Young’s modulus) but also the stress-strain relations of a SWCNT under axial, radial, and torsion conditions. The elastic properties, ultimate stress, and failure strain under various loading conditions are discussed and special attentions have been paid to the effects of the tube chirality and tube size. Some unique mechanical behaviors of chiral SWCNTs, such as axial strain-induced torsion, circumferential strain-induced torsion, and shear strain-induced extension are also studied. The predicted results from the present model are in good agreement with existing data, but very little computational cost is needed to yield them.

A "cool" way to remove hydrogen...and possibly a faster way to grow better crystals?

In growth of essentially every compound material such as GaN, one element always diffuses faster than the other(s) at the growth front. To grow good-quality materials, even the most sluggish element has to be sufficiently mobile, forcing materials growers to go to higher growth temperatures.

Multi-phase hyperelasticity with interface energy effect

Recently, J. Wang, L. Sun and I have formulated some ideas about the effective properties of heterogeneous materials with surface/interface energy effect, which are shown in the attached file.

Papers in the attached file can be viewed as a two-part paper, called “Multi-phase hyperelasticity with interface energy effect” if it is standalone. Part one of this topic is covered in “A theory of hyperelasticity of multi-phase media with surface/interface energy effect”, which provides theoretical background. Part two is covered in “Size-dependent effective properties of a heterogeneous material with interface energy effect: from finite deformation theory to infinitesimal strain analysis”, with more emphasis on application.

Young's modulus of single-walled carbon nanotubes

We report in detail that unlike other materials, carbon nanotubes are so small that changes in structure can affect the Young's modulus. The variation in modulus is attributed to differences in torsional strain, which is the dominant component of the total strain energy. Torsional strain, and correspondingly Young's modulus, increases significantly with decreasing tube diameter and increases slightly with decreasing tube helicity.  Journal of Applied Physics 84, 1939 (1998).

Force response and actin remodeling (agglomeration) in fibroblasts due to lateral indentation

We report the loading and unloading force response of single living adherent fibroblasts due to large lateral indentation obtained by a two-component microelectromechanical systems (MEMS) force sensor. Strong hysteretic force response is observed for all the tested cells. For the loading process, the force response is linear (often with small initial non-linearity) to a deformation scale comparable to the undeformed cell size, followed by plastic yielding. In situ visualization of actin fibers (GFP) reveals that during the indentation process, actin network depolymerizes irreversibly at discrete locations to form well-defined circular actin agglomerates all over the cell, which explains the irreversibility of the force response. Similar agglomeration is observed when the cell is compressed laterally by a micro plate. The distribution pattern of the agglomerates strongly correlates with the arrangement of the actin fibers of the pre-indented cell. The size of the agglomerates increases with time as ta  with a= 2~3 initially,   followed by a=.5~1. The higher growth rate suggests influx of actin into the agglomerates. The slower rate suggests a diffusive spreading, but the diffusion constant is two orders of magnitude lower than that of an actin monomer through the cytoplasm. Actin agglomeration has previously been observed due to biochemical treatment, gamma-radiation, and ischemic injury, and has been identified as a precursor to cell death. We believe, this is the first evidence of actin agglomeration due to mechanical stimuli. The study demonstrates that living cells may initiate similar functionalities in response to dissimilar mechanical and biochemical stimuli.

Axial-Strain-Induced Torsion in Single-Walled Carbon Nanotubes

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Using classical molecular dynamics and empirical potentials, we show that the axial deformation of single-walled carbon nanotubes is coupled to their torsion. The axial-strain-induced torsion is limited to chiral nanotubes—graphite sheets rolled around an axis that breaks its symmetry. Small strain behavior is consistent with chirality and curvature-induced elastic anisotropy (CCIEA)—carbon nanotube rotation is equal and opposite in tension and compression, and decreases with curvature and chirality. The largestrain compressive response is remarkably different.

MichelleLOyen's picture

New Book "Tissue Mechanics"

A new book, "Tissue Mechanics" by SC Cowin and SB Doty is of potential interest to those from a classical mechanics background considering work in biomechanics. Downloadable versions of the first two chapters are available at the book's website along with a full table of contents and other supplemental information.

Xiaodong Li's picture

Experimental Nanomechanics

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Colleagues and friends,

DEPARTMENT CHAIR: San Diego State University, Department of Mechanical Engineering

The Department of Mechanical Engineering invites applications and nominations for the position of Department Chairperson to begin in Fall 2007.

Applicants must hold an earned PhD in Mechanical Engineering or closely related discipline. A record of leadership showing interpersonal skills and organizational ability, strong research background and funding records with recognized professional accomplishments in mechanical engineering, demonstrated ability to interact with industry, and a commitment to excellence in teaching at both undergraduate and graduate levels are required. Mechanical Engineering is one of four departments in the College of Engineering at San Diego State University with an EAC, ABET-accredited B.S. degree program in Mechanical Engineering, as well as M.S. and Ph.D. programs involving students in leading edge research.

Kyung-Suk Kim's picture

Heritage for Experimental Mechanicians

On July 16, 1976, when I was writing my very first paper in U.S. with my lab senior Dr. Prashant Kumar and thesis advisor Professor Rodney J. Clifton to the Journal of Applied Physics, Professor Clifton put a copy of an article on my desk while I was away. The article was "Advice to Young Physicists" by Walther Bothe. It was translated from German to English in Physics Today, September, 1958. I do not know whether this advice still holds for the whole; however, I believe that most of the advice is still valuable for anyone, in particular, an experimentalist, who undertakes a piece of scientific work. Therefore, I would like to share his advice with the society of iMechanica by recollecting it here. - K.-S. Kim


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