Effects of infill orientation and percentage on the magnetoactive properties of 3D printed magnetic elastomer structures

This work investigates how the internal meso structure of fused filament fabrication parts influence the magnetoactive properties of printed magnetic elastomer structures. Elastomers were made by adding 40 wt% magnetite (Fe3O4) to a thermoplastic polyurethane (TPU) matrix. Magnetoactive testing was used to investigate how varying the infill structure affected the mechanical response of the structures within an applied magnetic field. Different infill percentages (40%, 60%, and 100%) and infill orientations (0, 45, and 90 degrees) were tested to account for different mechanical stiffnesses and internal geometries. Each sample was magnetoactively tested with three transverse magnetic field orientations (front, back and top). The samples were placed between two electromagnets, and the angle of deflection was recorded as a function of applied field. The maximum angles of deflection for the testing setup were reached when using lower infill percentages and having infill oriented parallel to the long axis of the sample and transverse to the magnetic field. Transverse fields applied parallel to the print plane (front/back sample orientations) demonstrated the most magnetoaction due to easier alignment of the long side of the sample with the field. This coupled with the 0-degree infill orientation having less crosslinking constraining the bending stiffness led to greater deflection. The magnetic anisotropy of the infill structure likely also contributed to the large response from certain samples. It was concluded that for this fixed base material, it is more important to 3D print structures with lower stiffnesses than more net magnetic particulate (more infill) to achieve the most magnetoaction.