Reversible and non-reversible motion of NdFeB-particles in magnetorheological elastomers

Magnetorheological elastomers are a class of smart hybrid material where magnetic microparticles are embedded in an elastomer matrix. The combination of elastic and magnetic properties leads to highly complex material behaviour, which is strongly affected by the arrangement and the magnetically induced motion of the magnetic particles. Thus, the knowledge of the internal particle structure is key to gain a deeper understanding of the complex material behaviour. In this paper, X-ray microtomography was applied to analyse the internal particle structure of a magnetorheological elastomer containing magnetically hard NdFeB-particles. A stepwise magnetisation of the material enabled a detailed characterisation of the occurring non-reversible chain formation process. Furthermore, the application of magnetic fields during measurements enabled an analysis of a mostly reversible particle motion occurring in connection with the magnetorheological effect. The collected tomography data of the particle structure was evaluated on a single particle basis as well as by means of a direction-dependent pair correlation function. To provide a scale bridging between macroscopic and microscopic properties, the found results regarding the particle motion were linked to mechanical and magnetic properties of the material.