Magnetic field-assisted 3D printing of anisotropic magnetorheological elastomers: Performance enhancement and chain alignment mechanism in TPU-CIP composites

This study investigates the potential of magnetic field-assisted 3D printing to enhance the comprehensive performance of magnetorheological elastomers (MREs) in additive manufacturing. Traditional MREs face limitations in structural complexity, while 3D-printed MREs (p-MREs) exhibit inferior balance between absolute and relative magnetorheological (MR) effects due to material constraints. To address this, we developed a method combining thermoplastic polyurethane (TPU) with carbonyl iron powder (CIP) and integrated an auxiliary magnetic field during fused deposition modeling (FDM). A custom-designed SmCo permanent magnet device generated a stable 500 mT field to induce anisotropy and suppress ring-shaped CIP structures. Microstructural analysis via scanning electron microscopy (SEM) and rheological testing revealed that magnetic field-assisted printing improved anisotropy and MR effects, achieving a relative MR effect of 440.6 % and absolute MR effect of 2.0 MPa under 1 T. Compared to isotropic p-MREs (relative MR: 387.2 %, absolute MR: 1.7 MPa), the comprehensive performance was enhanced by 13.8 %, though still lagging behind traditional anisotropic MREs. The study also identified a correlation between chain-like CIP alignment and reduced magnetic hysteresis, suggesting that soft magnetic MREs can mimic hard magnetic behaviors under field assistance. Unlike prior works using hard magnetic fillers, our TPU-CIP p-MREs achieved hard magnetic-like behavior (e.g., twisting) via field-assisted alignment, offering cost and environmental advantages. These findings advance the design of smart materials for applications requiring balanced stiffness and tunability, such as automotive dampers and soft robotics.