Soft when needed, stiff when required: magnetic control of mechanical behavior via fluid-inclusion composites

Materials whose mechanical properties can be adjusted under the effect of magnetic fields offer new opportunities for adaptive systems. This study presents new, soft composite materials that integrate a magnetorheological (MR) fluid encapsulated in an elastomeric matrix, and whose spatial distribution of magnetizable particles is dynamically controlled, thereby modifying the flow properties of the MR fluid and hence the stiffness of the composites. Experimental results from both monotonic (simple) and cyclic compression tests performed under various magnetic field strengths (0–500 mT) reveal a significant enhancement in compressive stiffness, mechanical response, and energy dissipation compared with conventional MR elastomers (MREs). Notably, a composite with 13.3 vol% of magnetizable particles achieved up to +60% higher energy dissipation than conventional MREs, and +276% compared to similar MR fluid-filled cavity systems reported in the literature. Monotonic and cyclic compression tests confirmed a strong magnetorheological effect and revealed clear hyperelastic behavior with pronounced Mullins softening, accurately captured using the Mooney-Rivlin model combined with a softening function. These results make MR fluid-based composites highly promising materials for soft robotics, vibration control, and other applications requiring tunable mechanical response and efficient energy dissipation.