The Rubber Division, ACS is now accepting online
abstract submissions for the 182nd Technical Meeting being held during the
Rubber Expo at the Duke Energy Center, October 9-11, 2012, in Cincinnati, OH,
USA.  Papers will be judged and awards presented
for Best Paper and Best Paper - Honorable Mention.

Many people puzzle over the nomenclature of the pure shear test. They rightly point out that 1) the Pure Shear test piece is loaded in tension by extending the specimen in the axial direction, and 2) a shearing deformation, by definition, involves the lateral motion of parallel planes. They wonder where is the "shear"? and what does it mean to say that the shear is "pure"?  Here, we review the origins of the terminology. 

The creasing instability of elastomer films under compression is studied by a combination of experiment and numerical simulation.  Experimentally, we attach a stress-free film on a much thicker and stiffer pre-stretched substrate.  When the substrate is partially released, the film is uniaxially compressed, leading to formation of an array of creases beyond a critical strain.  The profile of the folded surface is extracted using confocal fluorescence microscopy, yielding the depths, spacings, and shapes of creases.  Numerically, the onset and development of creases are simulated by introducing appropriately sized defects into a finite-element mesh and allowing the surface of the film to self-contact.  The measurements and simulations are found to be in excellent agreement.

Good day, dear colleges.

The 7th European Conference on Constitutive Models for Rubber will take place in the Dublin Institute of Technology (DIT), Dublin, Ireland, 20-23 September 2011.

Deadline for abstract submission: the 5th of December 2010

Website: http://www.eventelephant.com/eccmr2011dublin

Regards,

   Erwan 

This paper studies the collapse of a void in an elastomer caused by osmosis. The void is filled with liquid water, while the elastomer is surrounded by unsaturated air.  The difference in humidity motivates water molecules to permeate through the elastomer, from inside the void to outside the elastomer, leaving the liquid water inside the void in tension.  When the tension is low, the void reduces size but retains the shape, a mode of deformation which we call breathing.  When the tension is high, the void changes shape, possibly by two types of instability:  buckling and creasing.  The critical conditions for both types of instability are calculated.  A tubular elastomer collapses by buckling if the wall is thin, but by creasing if the wall is thick.  As the tension increases, a thin-walled tube undergoes a buckle-to-crease transition.

This paper can be found at http://www.seas.harvard.edu/suo/papers/233.pdf

ECCMR 2009 - Sixth European Conference on Constitutive Models for Rubber

Held at TU Dresden, Germany, September 7-10, 2009. 

www.eccmr.org

This is a study dealing with the volume variation in filled crystallizable natural (F-NR) and uncrystallizable styrene butadiene (F-SBR) rubbers subjected to cyclic loadings. During their deformation, such materials exhibit volume variation induced by the cavitation phenomenon and the decohesion between particles and the rubber matrix.

this is a study on the competition between cavitation and stress-induced crystallization during the deformation of cis-1,4 polyisoprene rubber. During deformation, this kind of material exhibits volume variation induced by both phenomena. In this study, we propose to measure this volume variation by an original full-field measurement technique. The high resolution of this technique allows us to identify characteristic stretch ratios during mechanical cycles.

At the invitation of David Clarke on behalf of the UCSB/Los Alamos Institute of Multiscale Materials and Structures, I gave the following three lectures:

1. Large deformation and instability in dielectric elastomers
2. Large deformation and instability in swelling polymeric gels
3. Mechanics and electrochemistry of polyelectrolyte gels

The abstracts follow, and the slides are attached at the end of this post.

I'm attaching slides of a talk that I gave yesterday at the Schlumberger-Doll Research Center.  In preparing the talk, I made liberal use of slides prepared by Wei Hong for his own presentations.  The talk is mainly based on the following papers:

I have recently given seminars on Mechanics of Soft Active Materials (SAMs) at several universities, using this set of slides (pdf, 1.4 MB).  I also attach the slides as ppt; please feel free to use anyway you want.  Here is an abstract of the seminars, followed by a list of papers published by my group on the topic.  Each paper has initiated on iMechanica a thread of discussion, to which I'll link.  I'll give a talk at the ASME Congress in Seattle, in Session 10-12-4 Instability in Solids, 9:45 am - 11:15 am, Thursday, 15 November 2007.  

      This letter describes a method to analyze electromechanical stability of dielectric elastomer actuators.  We write the free energy of an actuator using stretches and nominal electric displacement as generalized coordinates, and pre-stresses and voltage as control parameters.  When the Hessian of the free-energy function ceases to be positive-definite, the actuator thins down drastically, often resulting in electrical breakdown.  Our calculation shows that stability of the actuator is markedly enhanced by pre-stresses.

Active polymers are being developed to mimic a salient feature of life: movement in response to stimuli. Large deformation can lead to intriguing phenomena; for example, recent experiments have shown that a voltage can deform a layer of a dielectric elastomer into two coexistent states, one being flat and the other wrinkled. This observation, as well as the needs to analyze large deformation under diverse stimuli, has led us to reexamine the theory of electromechanics. In his classic text, Maxwell showed that electric forces between conductors in a vacuum could be calculated using a field of stress in the vacuum. The Maxwell stress has since been invoked in deformable dielectrics. This practice has been on an insecure theoretical foundation.

Zhigang Suo, Xuanhe Zhao, and William H. Greene