Mullins effect in elastomers filled with particles aligned by a magnetic field

Abstract

Magnetorheological elastomers (MRE) are particulate composite materials, whose fillers are structured by a magnetic field during curing. These particles are brought in quasi-contact by the field, in a chain-like unidirectional structure. Due to this organization the local stresses between the particles is high and debonding between particles and elastomer occur at low strain. We have experimentally studied and analytically modeled the progressive breaking of the polymer-to-particle bonds. The two cases of strong and weak bonds between elastomers and particles have been studied. The analytical model correctly reproduces the stress strain curve in the presence of a debonding process although overestimating the size of the debonding cavity which is obtained by comparison between experiments and FEM simulations. The extension of the model to a chain of spheres allows to well explain the Mullins effect on MRE. Furthermore it is shown that the quality of the bonds between the particles and the elastomer does not influence the change of stiffness brought by the application of a magnetic field.

Superparamagnetic anisotropic elastomer connectors exhibiting reversible magneto-piezoresistivity

“…Analogously to what happens with the elastic properties of the material, this can be justified by the absence of Mullins effect [19][20][21]. The same behavior is observed with the resistivity curves as a function of the applied magnetic field.…”

“…The fillers and the matrix appear contactless after curing. This separation is possibly the reason why the so-called Mullins effect [19][20][21] was not observed in the cured structured filler-elastomer composites studied here. The Mullins effect refers to appreciable changes in the physical properties of the composite after the first compression or extension and is attributed to relative displacements between filler and the matrix induced when a strain is applied for the first time.…”

“…The correlation coefficients ( 2 ) for the exponential fits of stress-strain curves are about 0.9998 for all the measurements. Also a third-order deformation approximation (Mooney-Rivlin law with five parameters) fits the elastomer micromechanics behavior very well [14,19,20]. The reproducibility of the elastic measurements and of the recovered E values from the exponential fits is very high for a given sample, with intra-sample variability lower than 1.5% after successive determinations (about ten for each sample).…”

“…Figure 5a shows the typical behavior of a composite under repeated compression, in pressure versus time curves, in which three cycles of slow-compression and fast decompression are illustrated. It is clear from Figure 5a that the composites display a remarkable elastic behavior (the same magnitude of pressure was required to achieve a 20% strain in consecutive cycles of compression) interpretable as the absence of appreciable Mullins effect [19][20][21]. This behavior was observed regardless the direction of compression ( or  respect to the chains), probably because of the separation (non-adhesion) between the polymer matrix and chains (see Figure 3c).…”

Anisotropic Reinforcement of Nanocomposites Tuned by Magnetic Orientation of the Filler Network

“…The design of a functional nanocomposite material with the possibility to orient the filler inside the matrix should allow to tune macroscopic material properties, and in particular the mechanical ones, using a simple external magnetic field. This concept has been explored in the past twenty years by many research teams, mostly studying the effect of micron-size particles or fibres (needles) [2][3][4][5] . Two routes are possible: applying the field on the material after synthesis or applying it during the synthesis.…”