Several methods have been used to optimize performance of magnetic elastomers by controlling the microstructure, such as magnetic annealing. Another way to introduce anisotropy is Fused Deposition Modeling (FDM), which has been shown to manipulate the magnetic anisotropy of rigid printed parts. However, the use of flexible composite materials has not yet been explored due to additional processing challenges. The primary goal of this study is to demonstrate tunable anisotropy of these materials via 3D printed structures without post-processing as a viable means to tune the performance of magnetic elastomer materials. Here, FDM structures were printed with thermoplastic polyurethane (TPU) polymer and either iron, carbonyl iron, or magnetite particulate. In order to determine the relative effect of different parameters on the magnetic properties, a series of samples were printed combining each material type with different aspect ratios, infill percentages, and infill orientations. A Vibrating Sample Magnetometer (VSM) was used to obtain magnetic hysteresis loops in order to compare the magnetic susceptibility between samples. Results demonstrated that FDM provides a method of achieving the directional signature of magnetic annealing without requiring any post-processing; instead, this manifests through the anisotropy of the part’s internal structure. As such, this concept is referred to as infill magnetic annealing (IMA). These variables were found to form a continuum of tunable magnetic responses. Additionally, the chosen particulate transfers its magnetic signature to the composite material. Overall, the highly customizable and nuanced characteristics of 3D-printed magnetic elastomer structures will allow for its application in a broad range of emerging magneto-mechanical applications such as magnetic actuation and soft robotics.

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Magnetic elastomers with hard or permanent magnetic particulate are able to achieve complex motion not possible from soft magnetic elastomers. Magnetic annealing and fused deposition modeling (FDM) have been used to increase the performance of magnetic composites. This research explores how the magnetoactive properties of hard magnetic elastomers are influenced by magnetic annealing and the addition of the soft magnetic particulate. Three compositions of the thermoplastic magnetic elastomer composite are explored: 15 vol. % SrFe12O19, 10 vol. % SrFe12O19/5 vol. % carbonyl iron, and 5 vol. % SrFe12O19/10 vol. % carbonyl iron. The material is then extruded into FDM filaments. During the extrusion process, some filament is magnetically annealed in an axial applied field. Magnetic hysteresis loops show that the saturation magnetization and coercivity change based on the relative amount of hard and soft magnetic particulate. The presence of only one coercive field indicates magnetic coupling between the hard and soft components. Magnetoactive testing measures each sample’s mechanical deflection angle as a function of transverse applied magnetic field strength. Qualitative and quantitative results reveal that magnetic annealing is critical to the magnetoactive performance of the hard magnetic elastomers. The results also demonstrate that magnetic annealing and increased carbonyl iron both improve the magnetoactive deflection angle for a given applied field. Scanning electron microscopy shows a stratification effect in a range of the filaments. Understanding these hard magnetic elastomers provides insight into how performance can be controlled and optimized by magnetic annealing and combining hard and soft magnetic particulate.

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