Stephan Rudykh's blog
The Skolkovo Institute of Science and Technology (Skoltech) seeks candidates for tenured and tenure-track positions to begin Fall 2013 or thereafter. Skoltech is an innovative, new, private university located just outside of Moscow, Russia.
by Y. Li, N. Kaynia, S. Rudykh and M. C. Boyce Massachusetts Institute of Technology
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.
Stability of anisotropic magnetorheological elastomers in finite deformations: A micromechanical approach
Stephan Rudykh and Katia Bertoldi
Journal of the Mechanics and Physics of Solids 61 (2013) 949–967
Stability of anisotropic magnetorheological elastomers in finite deformations: A micromechanical approachSubmitted by Stephan Rudykh on Sat, 2013-02-09 00:39.
The stability of anisotropic electroactive polymers is investigated. A general criterion for the onset of instabilities under plane-strain conditions is introduced in terms of a sextic polynomial whose coefficients depend on the instantaneous electroelastic moduli. In a way of an example, the stable domains of layered neo-Hookean dielectrics are determined. It is found that depending on the direction of the electrostatic excitation field relative to the lamination direction, the critical stretch ratios at which instabilities may occur can be either larger or smaller than the ones for the purely mechanical case.
Stephan Rudykh (a), (c), Kaushik Bhattacharya (c) and Gal deBotton (a), (b)
(a) Department of Mechanical Engineering, Ben-Gurion University, 84105 Beer-Sheva, Israel
(b) Department of Biomedical Engineering, Ben-Gurion University, 84105 Beer-Sheva, Israel
(c) Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, United States
Solution to the problem of a spherical balloon made out of an electroactive polymer which is subjected to coupled mechanical and electrical excitations is determined. It is found that for certain material behaviors instabilities that correspond to abrupt changes in the balloon size can be triggered. This can be exploited to electrically control different actuation cycles as well as to use the balloon as a micro-pump.
Macroscopic instabilities of fiber reinforced composites undergoing large deformations are studied. Analytical predictions for the onset of instability are determined by application of a new variational estimate for the behavior of hyperelastic composites. The resulting, closed-form expressions, are compared with corresponding predictions of finite element simulations. The simulations are performed with 3-D models of periodic composites with hexagonal unit cell subjected to compression along the fibers as well as to non-aligned compression. Throughout, the analytical predictions for the failures of neo-Hookean and Gent composites are in agreement with the numerical simulations.
It is found that the critical stretch ratio for Gent composites is close to the one determined for neo-Hookean composites with similar volume fractions and contrasts between the phases properties.
During non-aligned compression the fibers rotate and hence, for some loading directions, the compression along the fibers never reaches the level at which loss of stability may occur.