Elastomers

How can we induce twist in tubular structures without applying a torque?

In nature, such behavior is enabled by material anisotropy. In our new work, we show that isotropic bi-layer tubes with twist incompatible layers can twist upon inflation and extension.
Interestingly, the direction of twist can spontaneously reverse as the load increases!

Check out our new paper at EML:
https://www.sciencedirect.com/science/article/pii/S2352431621000766

Dear colleagues,
We invite you to see the preprint of our new paper "Flexoelectricity in soft elastomers and the molecular mechanisms underpinning the design and emergence of giant flexoelectricity" that will appear in PNAS. Here we present a molecular-to-continuum scale theory for the flexoelectric effect in elastomers. The theory unveils a mechanism for achieving giant flexoelectricity--which finds support in prior experimental results; it is then leveraged for designing elastomers for 1) piezoelectricity, 2) tuning the direction of flexoelectricity, and 3) flexoelectricity which is invariant with respect to spurious deformations (https://doi.org/10.1073/pnas.2102477118).

We have discovered a peculiar form of fracture that occurs in a highly stretchable silicone elastomer (Smooth-On Ecoflex 00–30). Under certain conditions, cracks propagate in a direction perpendicular to the initial pre-cut and in the direction of the applied load. In other words, the crack deviates from the standard trajectory and instead propagates perpendicular to that trajectory. The crack arrests stably, and thus the material ahead of the crack front continues to sustain load, thereby enabling enormous stretchabilities. We call this phenomenon 'sideways' and stable cracking.

One Ph.D. candidate position is available in the Fall 2017 in the Elastomer Research Center (Cermel) at the Laboratory of Mechanics and Rheology (LMR) in the Polytechnic School of the University of Tours in France.

Job description

The aim of this Ph.D. is to extend the comprehension of the local mechanisms involved in elastomer materials, in order to faithfully reproduce their behavior in finite element models. The Ph.D. applicant is expected to carry out both theoretical and experimental work.

The rapid and efficient development of soft active materials requires readily available, compact testing equipment. We propose a desktop-sized, cost-efficient, and open source radial stretching system as an alternative to commercially available biaxial and uniaxial stretching devices. It allows for doubling the diameter of an elastomer membrane while measuring the applied force. Our development enables significant cost reduction (<300 €) and increase the availability of equibiaxial deformation measurements for scientific material analysis.

Electroactive soft elastomers require huge electric field for a meaningful actuation. We demonstrate, by means of numerical simulation, that this can be dramatically reduced and large deformations can be achieved with suitably designed heterogeneous actuators. The mechanism by which the enhancement is attained is illustrated with the aid of both idealized and periodic models.

Elastomers are outstanding in their ability to repeatedly endure large deformations, and they are often applied where fatigue performance is a critical consideration. Because the macromolecular structure of elastomers gives rise to a number of unique behaviors, appropriately specialized methods are needed to characterize, analyze, and design for durability. This 2-day course provides the know-how for engineering durable elastomeric components and systems. The course is taught at Axel Products, and includes live demos of typical behavior.