soft active materials
We are looking for a highly-motivated research
fellow to work in the area of applied mechanics and materials.
The project is on energy harvesting using soft active materials. This is a joint effort between the Institute of High Performance Computing (A*STAR), and the National
University of Singapore. The applicant
must hold a PhD degree, prior post-doctoral experience is not required. Relevant
experience in (1) experiments and/or (2) finite element modeling and simulation
Dielectric Elastomers (DE) are promising materials for developing soft machines (e.g., a human-made octopus). The principle of actuation has gained to DE the name "artificial muscles" since they can undergo large deformation when excited by an electric field. Another class of active materials that can be actuated by external field is Magnetoactive Elastomers (MAE). Although MAE and DE share mathematical similarities, the physics is different. Electric field can induce polarization in elastomers, and hence generate electrostatic stresses within the material. As a response to the electrically induced stresses, the material deforms. For MAE the situation is different: elastomers are magnetically inactive, and a similar to DE effect is achieved by mixing the elastomer with magnetically active particles (e.g., carbonyl iron, nickel or Terfenol-D). Thus, due to the magnetic interaction of the particles embedded in a soft matrix, the composite can deform and modify overall stiffness as a response to a magnetic field. The performance of these composites can be further enhanced by optimizing microstructures. Indeed, a similar idea applies for designing DE composites with enhanced properties. These composites, once manufactured can solve the bottle-neck problem of DE technology - the need in extremely high electric fields for meaningful actuations, and potentially lead to a breakthrough in the technology.
Dear colleagues and friends,
On behalf of the editorial board, I would like to introduce our new Journal, Soft Robotics (SoRo) to the mechanics community. SoRo is an innovative peer-reviewed journal dedicated to the science and engineering of soft materials in mobile machines. The Journal breaks new ground as the first to answer the urgent need for research on robotic technology that can safely interact with living systems and function in complex natural or human-built environments.
In the process of electro-mechanical transduction of
ionic polymer-metal composites (IPMCs), the transport of ion and water molecule
plays an important role. In this paper, the theoretical transport models of
IPMCs are critically reviewed, with particular emphasis on the recent
developments in the latest decade. The models can be divided into three classes,
thermodynamics of irreversible process model, frictional model and Nernst-Planck
(NP) equation model. To some extent the three models can be transformed into
each other, but their differences are also obvious arising from the various
mechanisms that considered in different models. The transport of ion and water
molecule in IPMCs is compared with that in membrane electrode assembly and
We have studied the elastic response of actin networks with both compliant and rigid crosslinks by modeling molecular motors as force dipoles. Our finite element simulations show that for compliant crosslinkers such as filamin A, the network can be stiffened by two orders of magnitude while stiffening achieved with incompliant linkers such as scruin is significantly smaller, typically a factor of two, in excellent agreement with recent experiments. We show that the differences arise from the fact that the motors are able to stretch the compliant crosslinks to the fullest possible extent, which in turn causes to the deformation of the filaments. With increasing applied strain, the filaments further deform leading to a stiffened elastic response.
At the invitation of Yonggang Huang, I’ll give 4-hour lectures at the NSF Summer Institute Course on the Mechanics of Soft Materials. I attach the slides of the lectures, to be given on Monday, 10 May 2010. An abstract of the lectures follows.
Recent experiments have shown that a voltage can induce a large deformation in an elastomer of interpenetrating networks. We describe a model of interpenetrating networks of long and short chains. As the voltage ramps up, the elastomer may undergo a snap-through instability. The network with long chains fills the space and keeps elastomer compliant at small to modest deformation. The network with short chains acts as a safety net that restrains the elastomer from thinning down excessively, averting electrical breakdown. It appears possible to find a dielectric elastomer capable of giant deformation of actuation. You can read the paper, or take a look at the slides posted here.