Magnetorheological Elastomers

National audienceMagnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. Due to their coupled magnetoelastic response, MREs are finding an increasing number of engineering applications. In this work, we present a combined experimental and theoretical study of the macroscopic response of a particular MRE consisting of a rubber matrix phase with spherical carbonyl iron particles. The MRE specimens used in this work are cured in the presence of strong magnetic fields leading to the formation of particle chain structures and thus to an overall transversely isotropic composite. The MRE samples are tested experimentally under uniaxial stresses as well as under simple shear in the absence or in the presence of magnetic fields and for different initial orientations of their particle chains with respect to the mechanical and magnetic loading direction. Using the theoretical framework for finitely strained MREs introduced earlier by the author, we propose a transversely isotropic energy density function that is able to reproduce the experimentally measured magnetization, magnetostriction and simple shear curves under different prestresses, initial particle chain orientations and magnetic fields. Microscopic mechanisms are also proposed to explain i) the counterintuitive effect of dilation under zero or compressive applied mechanical loads for the magnetostriction experiments and ii) the importance of a finite strain constitutive formulation even at small magnetostrictive strains. The model gives an excellent agreement with experiments for relatively moderate magnetic fields but has also been satisfactorily extended to include magnetic fields near saturation

Puckering instability phenomena in the hemispherical cup test

investigated here is the plastic bifurcation of an initially flat circular plate held frictionlessly between a blankholder and a die and deformed by a spherically shaped punch.In view of the large deviations of the prebifurcation solution from proportional loading, a recently developed phenomenological corner theory has been employed and an appropriate bifurcation criterion has been developed. The effects of geometry and material properties on the onset of the (nonaxisymmetric) plastic instability have been investigated using a numerical solution of the resulting equations based on the finite element method.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25841/1/0000404.pd

On the bifurcation and postbifurcation analysis of elastic-plastic solids under general prebifurcation conditions

work we have studied the bifurcation and postbifurcation of elastic-plastic solids whose behavior near the critical point could not be idealized as hypoelastic and thus the "hypoelastic comparison solid" concept of R. Hill's theory is no longer applicable. First a simple continuous model is considered in order to illustrate the different possibilities in the stability behavior of the structures considered here. Next, a general three-dimensional stability analysis for a broad class of rate independent elastic-plastic solids is presented. It is found that for all the constitutive theories considered and for all possible prebifurcation solutions, the bifurcation functional is a simple generalization of Hill's. A completely different postbifurcation analysis is needed, however, in the case where the "hypoelastic comparison solid" concept cannot be used.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25422/1/0000871.pd

Magnetorheological Elastomers: Experiments and Modeling

National audienceMagnetorheological elastomers (MREs) are ferromagnetic particle impregnated elastomers whose mechanical properties are altered by the application of external magnetic fields. Due to their magnetoelastic coupling response MREs are finding an increasing number of engineering applications. The objective of this work is : (a) the experimental study of transversely isotropic MREs (i.e., the particles form chains along a certain direction) that are subjected to prestressing and arbitrary magnetic fields and (b), the phenomenological modeling of these materials using transversely isotropic energy functions.See http://hal.archives-ouvertes.fr/docs/00/59/26/92/ANNEX/r_NHEKI0N4.pd

Surface instabilities in finitely strained solids under static loading

Surface bifurcation in a quasistatically loaded solid is an important instability phenomenon occurring at high levels of strain. After a discussion of theoretical as well as experimental work done in this area, a general formulation for the surface buckling of an incrementally linear three dimensional halfspace is presented and corresponding necessary conditions for the onset of this instability are derived.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25030/1/0000457.pd

Analyse de stabilité d'une nappe fibrée en compression

National audienceL'objectif de ce travail est de modéliser le flambement de nappes fibrées lorsque les câbles sont soumis à une compression axiale. Nous réalisons une analyse de stabilité multi- échelles basée sur le résultat de [1], qui permet de réduire le problème à une cellule élémentaire 2D et de modéliser les modes propres sous forme d'ondes de Bloch. Nous avons choisi de nous placer dans le cas particulier d'une flexion circulaire, mais la méthode proposée est valable pour des chargement plus généraux

Influence of interfacial adhesion on the mechanical response of magneto‑rheological elastomers at high strain

International audiencemacroscopic behavior of the composite only after 80 % deformation in the case of the 30 % volume fraction Mre

Interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations

11International audienceThis work investigates the interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations. Carbonyl iron powder, composed of mechanically soft spherical particles with a median size of 3.5 μm and a volume concentration of 3.5%, was mixed in a soft silicone matrix (Shore 00-20); the compound was then degassed and cured under temperature. The presence of a homogeneous magnetic field of 0.3 T during the curing process allowed the formation of particle chains. Tensile tests of these samples under scanning electron microscope showed interfacial slipping and debonding between the two phases. To improve interfacial adhesion, a silane primer was applied to the iron particles, following two different procedures, before the mixing and crosslinking process, thus giving two additional types of samples. In tensile testing lengthwise to the particle alignment, with engineering strains up to 150%, the structural responses of the different types of samples were compared. An enhanced adhesion of the iron fillers to the silicone matrix resulting in a reinforced matrix and increased tensile strength during the first loading path could be observed. Furthermore, scanning electron microscope images show that a more elaborated particle-matrix interface was obtained with the primer additive

Derivation of higher order gradient continuum theories in 2,3-d non-linear elasticity from periodic lattice models

localization of deformation (in the form of shear bands) at sufficiently high levels of strain, are frequently modeled by gradient type non-local constitutive laws, i.e. continuum theories that include higher order deformation gradients. These models incorporate a length scale for the localized deformation zone and are either postulated or justified from micromechanical considerations. Of interest here is the consistent derivation of such models from a given microstructure and the subsequent investigation of their localization and stability behavior under finite strains.In the interest of simplicity, the microscopic model is a discrete, periodic, non-linear elastic lattice structure in two or three dimensions. The corresponding macroscopic model is a continuum constitutive law involving displacement gradients of all orders. Attention is focused on the simplest such model, namely the one whose energy density includes gradients of the displacements only up to the second order. The relation between the ellipticity of the resulting first (local) and second (non-local) order gradient models at finite strains, the stability of uniform strain solutions and the possibility of localized deformation zones is discussed. The investigations of the resulting continuum are done for two different microstructures, the second one of which approximates the behavior of perfect monatomic crystals in plane strain. Localized strain solutions based on the continuum approximation are possible with the first microstructurc but not with the second. Implications for the stability of three-dimensional crystals using realistic interaction potentials are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31886/1/0000838.pd