Magnetic Particle Reinforced Elastomer Composites for Additive Manufacturing

Development of magnetorheological elastomer (MRE) materials suitable for fused filament fabrication (FFF)-type additive manufacturing processes is performed. Filament materials are thermoplastic polyurethane (TPU) pellets and Fe
₃
O
₄
magnetic particles. A trickling method is employed to introduce the materials into the filament extruder at a constant rate, after which they are mixed in a hopper and extruded at 160 °C. The trickling rate of Fe
₃
O
₄
was controlled to produce different volume concentrations [0%–13% (v/v)]. Micrograph analysis on the cross section of the filaments indicates that magnetic particles are uniformly dispersed in the TPU matrix. As the volume concentration of particles in the matrix is increased over 10% (v/v), the size distribution of magnetic particles is slightly increased, indicating formation of aggregation of magnetic particles. Micropores are observed in the filaments, and the number of pores seem to increase with increasing volume concentration of magnetic particles. A commercial off the shelf (COTS) FFF 3-D printer is successfully used to produce cylindrical MRE samples with different magnetic particle volume concentrations. Magnetorheological (MR) properties of the printed MRE samples are characterized by uniaxial compression testing under different applied magnetic field. Material elastic modulus was found to increase with the intensity of magnetic field for a given magnetic particle volume concentration. The relative MR effect varies from −1.3% to 60% within the studied volume concentrations and applied fields. The samples with 5% (v/v) show the highest MR effect when compared with samples with higher magnetic particle volume concentrations. The results of these experiments confirm that the equivalent energy dissipation of the material rises with the increase in the Fe
₃
O
₄
concentration of MRE.