Experimental characterization of Magneto-Rheological Elastomers for constitutive model parameters identification

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Wrinkling to crinkling transitions and curvature localization in a magnetoelastic film bonded to a non-magnetic substrate

International audienceThis work studies experimentally and numerically the post-bifurcation response of a magnetorheological elastomer (MRE) film bonded to a soft non-magnetic (passive) substrate. The film-substrate system is subjected to a combination of an axial mechanical pre-compression and a transverse magnetic field. The non-trivial interaction of the two fields leads to a decrease of the critical magnetic field with applied pre-compression, while the observed wrinkling patterns evolve into crinkles, a bifurcation mode that is defined by the accompanied curvature localization and strong shearing of the side faces of the wrinkled geometry. Using a magneto-elastic variational formulation in a two-dimensional finite element numerical setting, we find that the crinkling is an intrinsic feature of magnetoelasticity and its presence is directly associated with the repulsive magnetic forces of the neighboring wrinkled-crinkled faces. As a result, the presence of the magnetic field prohibits the formation of creases and folds. In an effort to obtain a good quantitative agreement between the numerical and the experimental results, we also introduce an approximate way to model the friction of the lateral film-substrate faces. This analysis reveals the strong effects of friction upon the magneto-mechanical wrinkling modes

Experimental study of heterogeneities in strain and temperature fields at the microstructural level of polycrystalline metals through fully-coupled full-field measurements by Digital Image Correlation and Infrared Thermography

In this paper, we investigate and quantify the thermal effects induced by plastic deformation at the level of the microstructure of a polycrystalline metallic sample. For the first time, this investigation is conducted on a specimen containing hundred of grains. We use a unique experimental setup to access—simultaneously in-situ and in real time—strain and temperature fields of an austenitic stainless steel under tensile loading. We show that strain fields are directly linked to the expression of plasticity at the grain scale. We show, on the other hand, that thermal fields at the last increment of deformation are linked to the microstructural expression of plasticity on a larger lengthscale corresponding, instead, to grain clusters. Hence strain fields exhibit stronger localization features than the temperature fields in terms of both values and space. For a mean temperature rise of 0.75 °C and a global deformation of 2.4% in the fastest quasi-static regime investigated in this paper, the maximum local temperature rise is measured to be 0.88 °C even though local strain in grains can reach up to 6.7%. These fully-coupled measurements also provide the first experimental evidence that an instantaneous coupling takes place within grains between strain gradients and thermal dissipation. Finally, an estimation of a grain-scale field of the fraction of plastic work converted into heat is conducted and shown to be not only heterogeneous but also to be related to the microstructural features of deformation at the surface of the material, namely to the absence or presence of slip bands. The results obtained support the relevance of establishing energy balances and acquiring stored energy data at the microstructural scale where damage localization takes place

Microstructurally-guided explicit continuum models for isotropic magnetorheological elastomers with iron particles

This work provides a family of explicit phenomenological models both in the F−H and F−B variable space. These models are derived directly from an analytical implicit homogenization model for isotropic magnetorheological elastomers (MREs), which, in turn, is assessed via full-field numerical simulations. The proposed phenomenological models are constructed so that they recover the same purely mechanical, initial and saturation magnetization and initial magnetostriction response of the analytical homogenization model for all sets of material parameters, such as the particle volume fraction and the material properties of the constituents (e.g., the matrix shear modulus, the magnetic susceptibility and magnetization saturation of the particles). The functional form of the proposed phenomenological models is based on simple energy functions with small number of calibration parameters thus allowing for the description of magnetoelastic solids more generally such as anisotropic (with particle-chains) ones, polymers comprising ferrofluid particles or particle clusters. This, in turn, makes them suitable to probe a large set of experimental or numerical results. The models of the present study show that in isotropic MREs, the entire magnetization response is insensitive to the shear modulus of the matrix material even when the latter ranges between 0.003-0.3MPa, while the magnetostriction response is extremely sensitive to the mechanical properties of the matrix material

Modelling and Simulation of the Magnetostriction Effect in a Magneto-sensitive Material

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Modelling and Simulation of the Magnetostriction Effect in a Magneto-sensitive Material

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Modelling and Simulation of the Magnetostriction Effect in a Magneto-sensitive Material

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Magnetorheological elastomers: Experimental and modeling aspects

Conference of SEM Annual Conference and Exposition on Experimental and Applied Mechanics, 2015 ; Conference Date: 8 June 2015 Through 11 June 2015; Conference Code:157329International audienceMagnetorheological elastomers (MREs) are active composite materials that deform under a magnetic field because they are made of a soft elastomer matrix filled with magnetizable micrometric particles. Along with short response times and low magnetic inputs, not only do MREs alter their viscoelastic properties and stiffness in response to external magnetic fields but they can also undergo very high deformation states. While the former effect can be exploited in controllable-stiffness devices, the latter is of interest for haptic devices such as tactile interfaces for the visually impaired. In the perspective of developing a persistent tactile MRE surface exhibiting reversible and large out-of-plane deformations, the first part of this work focuses on the fabrication of MREs that can sustain large deformations. In particular, we determine the critical strain threshold up to which the interfacial adhesion between particles and matrix is ensured. In the second part of this work, an experimental setup is developed in order to characterize MRE composites under coupled magneto-mechanical mechanical loading. The experiments conducted on this setup will eventually serve as an input for a continuum model describing magneto-mechanical coupling