The linear viscoelastic behaviour of magnetorheological elastomers is analysed in this work according to their formulation and working conditions. This study comprised both the synthesis of different magnetorheological elastomers and the strain and frequency sweep characterization under different magnetic fields and temperatures. The characterization was performed by a Physica MCR 501 rheometer from Anton Paar, equipped with a magnetorheologic cell 70/1T MRD. In the synthesis with a given elastomeric matrix, samples with different magnetic particle content are studied with two types of curing conditions: under the action of a magnetic field (anisotropic magnetorheological elastomers) and without a magnetic field (isotropic magnetorheological elastomers). The working conditions are excitation frequency, temperature and the applied external magnetic field. In this work, a new procedure to determine the linear viscoelastic behaviour is proposed; the loss factor is analysed in addition to analysing the storage modulus to determine the linear viscoelastic region of each sample. The results show that high temperatures and magnetorheological elastomers with higher volume fraction of magnetic particles restrict the linear viscoelastic behaviour of magnetorheological elastomers.

The aim of this work is to study the linear viscoelastic region limit of isotropic magnetorheological elastomers at different compositions and working conditions. Regarding the synthesis process, the matrix and the particle content are analysed. The analysed matrixes are a natural rubber, a silicone rubber and ELASTOSIL Ò silicone, and three particle contents are synthesised. The influence of the characterisation variables on the linear viscoelastic limit, that is, frequency, external magnetic field and temperature, is also analysed. Strain sweep tests are used to determine the dynamic complex modulus. The loss factor and the storage modulus are analysed to define the linear viscoelastic limit of each isotropic magnetorheological elastomer sample in all the working conditions. The results show that the linear viscoelastic region of the magnetorheological elastomers is defined by the loss factor. Moreover, the volumetric particle content reduces and frequency increases the linear viscoelastic region of all the matrixes, whereas the external magnetic field and the temperature influences are matrix dependent.

In this work, a four-parameter fractional derivative viscoelastic model was developed to describe the dynamic shear behaviour of magnetorheological elastomers (MREs) as a function of the matrix, particle content and magnetic field. The material parameters were obtained from experimental data measured with a Physica MCR 501 rheometer from the Anton Paar Company, equipped with a magnetorheological cell. The synthetised isotropic MRE samples were based on room-temperature vulcanising silicone rubber and spherical carbonyl iron powder micro particles as fillers, and seven volumetric particle contents were studied. The influence of particle contents was included in each parameter of the four-parameter fractional derivative model. The dependency of the storage modulus as a function of an external magnetic field (magnetorheological (MR) effect) was studied, and a dipole-dipole interaction model was used. A new three-dimensional magneto-viscoelastic model was developed to couple the viscoelastic model, the particle-matrix interaction and the magneto-induced modulus model, which predicts the influence of the magnetic field and the particle content in the MR effect of isotropic MREs.

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International audienceThe storage modulus variation of anisotropic magnetorheological elastomers (MREs) induced by an external magnetic field was modelled in the frequency domain. This involves synthesising five anisotropic MREs with different particle content and measuring its dynamic and magnetic properties. Dynamic properties were measured using a rheometer equipped with a magnetorheological cell and the magnetic permeability of each sample was measured with a vibrating sample magnetometer. Scanning Electron Microscope images were used to determine particle distribution. A four parameter fractional derivative model was used to describe MRE viscoelasticity in the absence of magnetic field and the fitting error was not larger than 1%. Magneto-induced modulus was also studied and two different models were analysed, the one of Jolly et al. (Smart Mater Struct;5:607 (1999)) and the other one of López-López et al. (J Rheol. 56:1209 (2012)). The first model underestimated the influence of the magnetic field for low particle contents while at high ones it overestimated the magnetic field effect, up to 13%. However, in the second model magnetic permeability values were used, and the error between the model prediction and experimental data did not exceed 7%. Hence, a new linear magneto-viscoelastic model was proposed in frequency domain for anisotropic MREs based on López-López et al. model, which predicts the effect of magnetic field on the dynamic shear modulus in function of particle content and frequency