This study concerns a magnetorheological elastomer (MRE) consisting of a magnetically hard powder and a stiff polymer matrix, so called STH-MRE. This material exhibits some strong constitutive differences with the behavior of MRE based on soft polymer matrix and magnetically hard powder (SOH-MRE). This paper presents a manufacturing process for such a STH-MRE, describes testing procedures to get the magnetic properties, the viscoelastic behavior and the magneto-mechanical coupling, and shares the STH-MRE properties with the scientific community. Firstly, the manufacturing process is detailed. Then, the homogenized magnetic properties and their dependence on the volume fraction and the temperature are discussed. Thereafter, dynamic mechanical analysis is explained and the viscoelastic properties are discussed considering the polymer matrix properties, the volume fraction and the temperature. Magneto-mechanical couplings are investigated in absence of an external magnetic field. The coercive field strenth of composite material and powder are almost equal while the remanent flux density depends on volume fraction. The temperature dependence of the magnetic properties is given as well as homogenization rules. The viscoelastic data of the STH-MRE are provided in a large temperature range and in the mechanical vibration frequency range. The magneto-mechanical coupling due to the remanent magnetization is shown to be negligible.

Magneto-rheological elastomers belong to the class of smart materials whose mechanical properties can be controlled by an external magnetic field. These materials can be integrated into mechatronic systems and submitted to multiple loadings such as temperature, mechanical stress and magnetic field. Thus, the present work is dedicated to the development of a magneto-mechanical bench and on first experimental characterizations of hard magneto-rheological elastomers taking multiphysics coupling into account. Regarding the mechanical loading, the experimental setup is able to create a uniaxial tensile stress in case of low strain (< 1%) without friction effect. In regards to the magnetic loading, a magnetic circuit made of a strong permanent magnet has been designed to impose a variable and a homogeneous magnetic field strength up to 41 kA/m. Experimental analysis has been performed on silicone rubber filled with 36%vol. of NdFeB particles. The purpose was first to investigate the evolution of the Young modulus with or without magnetic field. Results obtained from measurements show that the developed test bench is able to depict the mechanical behavior and phenomena linked to rubber-like material.

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The key issue of this contribution is the magneto-mechanical behavior of a magnetically hard magnetorheological elastomer (H-MRE). A numerical model based on the conservation laws of continuum mechanics and magnetism is presented and then applied to a specific 2-dimensional case of an H-MRE specimen. The interaction between two remanently magnetized particles and its dependence on the relative positioning of the particles to one another are studied. The reaction of the elastomer matrix to the particle-particle interaction is analyzed for three configurations of the particles in the specimen. In a second step, the specimen is exposed to a unidirectional tensile load. It is demonstrated that the magnetization of the particles induces a change in the modulus which strongly depends on the arrangement of the particles in the matrix: an increase as well as a decrease of the modulus are observed. By the help of the principal stresses, three different types of magnetic interactions are identified and assigned to the corresponding softening and stiffening reactions of the specimen.

Materials that have a shape memory are capable to switch between different stable states when external stimuli are applied. This work introduces a new, multi-physical concept for shape memory in assembled composite structures. The concept is called magnetofriction and is based on magnetism, elasticity, contact and friction. In assemblies of permanently magnetized MagnetoActive Elastomers (MAE), the contact pressure is established by magnetic attraction forces. When the assembly is deformed, the contact surfaces slide over each other and the deformed shape is locked by the friction in the interface. A loosening of the contact causes the friction forces to vanish and each part of the assembly recovers its initial state due to the elastic forces in the materials. The contact is restored after the shape recovery. A test assembly, called MagnetoFriction -Shape Memory Polymer (MF-SMP), is used to validate the concept experimentally. It consists of two stacked, permanently magnetized MAE beams. The assembled structure is subjected to a three-point bending test and retains a permanent deformation after the tests. The force displacement response of the MF-SMP reveals that the deformed configuration is stabilized after a first loading cycle. A digital image correlation reveals sliding in the contact interface of the assembly during the first loading. The adhesion, observed in the subsequent loading cycles, is responsible for the shape lock. When the beams are separated manually or by compressed air, the stored deformation vanishes. Magnetofriction is compared to other mechanisms to classify the new concept in the field of shape memory materials.

This paper introduces a new concept for shape memory based on elastic forces and magnetically induced friction forces in composite materials consisting of magnetoactive elastomers (MAEs). Magnetic attraction forces between two MAEs generate a contact pressure at their interface and the friction allows to maintain stable deformed shapes of the so-called Magnetofriction Shape Memory Polymers (MF-SMPs). When the contact is loosened, the friction forces vanish and the elastic forces in each part of the assembly bring the parts back into their initial state where the contact can be established once again. The shape memory effect is studied in three-point bending tests with two stacked MAEs. The global force-displacement relations reveal a hysteretic behavior due to local residual displacements after the test are observed by the help of digital image correlation (DIC). The test structure stores up to 25% of the applied displacement. The local contact state (sliding or sticking) is evaluated in different regions of the MF-SMP which gives an insight into the shape memory mechanism magnetofriction. Two methods for the shape-recovery of the MF-SMP by elastic forces in the MAEs are proposed, a manual separation and an air flow at the interface of the MF-SMP, and a comparison of magnetofriction to other shape memory mechanisms is performed.

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