University of Cambridge > > Engineering - Mechanics and Materials Seminar Series > Magnetorheological elastomers: from micro-deformation mechanisms to macroscopic instabilities and applications

Magnetorheological elastomers: from micro-deformation mechanisms to macroscopic instabilities and applications

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Magnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. In addition, these composite materials can deform at very large strains due to the presence of the soft polymeric matrix without fracturing. From an unconventional point of view, a remarkable property of these materials is that while they can become unstable by combined magneto-mechanical loading, their response is well controlled in the post-instability regime. This, in turn, allows us to try to operate these materials in this critically stable region. These instabilities can lead to extreme responses such as wrinkles (for haptic applications), actively controlled stiffness (for cell-growth) and acoustic properties with only marginal changes in the externally applied magnetic fields. Unlike the current modeling of hierarchical composites, MREs require the development of advanced coupled nonlinear magneto-mechanical models in order to tailor the desired macroscopic instability response at finite strains.

In this work, we study the response of such an assembly subjected to transverse magnetic fields and in-plane stresses. The film is made up of a transversely isotropic MRE material, whose energy density has been obtained experimentally, while the substrate is a non-magnetic isotropic pure polymer/gel. An analytical solution to this problem is presented in 2D, which shows that for adequately soft substrates there is a finite-wavelength buckling mode under a transverse magnetic field. Moreover, the critical magnetic field can be substantially reduced in the presence of an adequately large compressive prestress of the assembly, thus opening the possibility of controlling haptic interfaces with low magnetic fields.

Short Biography

Kostas Danas was born (1981) and raised in Kozani, Greece and studied at the Department of Mechanical Engineering at the University of Thessaly, Volos, Greece where he received his Dipl. Ing. (2003) with highest honors (rank 1st). He received his M.Sc (2004) from the University of Pennsylvania and his Ph.D. (2008) from the University of Pennsylvania and the Ecole Polytechique, France. After the end of his graduate studies, he moved to the University of Cambridge as a postdoctoral Research Associate. In 2009, he applied for a research faculty position at the Centre National de la Recherche Scientifique (C.N.R.S.) where he was ranked 1st in the section of solid mechanics and he obtained a tenured Research Professor position at Ecole Polytechnique, France in the Laboratory of Solid Mechanics (LMS). His main research interests are in the field of solid mechanics and composite materials with an emphasis on the theoretical and numerical description of constitutive laws for composites. He is currently working on the modeling of microstructured active elastomers as well as on the fracture of metallic porous materials.

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