Modelling Ferromagnetic Fiber Alignment in Viscous Fluids Under Static Magnetic Fields

When conventional polymer processing methods (e.g. extrusion or injection molding) are used to process discontinuous fiber composites, the obtained fiber orientation distribution is often the result of the processing conditions, part geometry and flow behavior of the material. The current state of the art in polymer processing does not allow a targeted control of the fiber distribution to improve the fmal part properties. Magnetic manipulation of a dispersed phase using a static magnetic field was already used for several types of fiber geometries and materials. Therefore, magnetic control of fiber orientation in a polymer melt would surpass the current state of the art. This paper used the technique to study the dynamical behavior of a single high aspect ratio ferromagnetic fiber submerged in a polydimethylsiloxane (PDMS) matrix. The magnetic response of the fiber as a function of the aspect ratio, the matrix viscosity and the magnetic field strength is discussed. To predict the rate of fiber realignment, two numerical models are evaluated. These models focus on the different forces acting on the solid fiber during the realignment and have shown to be effective for diamagnetic materials. The modelling results show a good prediction of the experiments for all variated parameters in the process.