Effects of an External Magnetic Field on Polymeric Foam-Ferromagnet Composites
Composite lightweight materials based on a polymeric matrix with embedded magnetic micro-particles have been developed. The application of a magnetic field (MF) during the foaming of samples induced the alignment of magnetic particles along the MF lines, forming reinforcing chain-like structures. The presence of aligned micro-particles imparted an anisotropic mechanical behavior along the particle alignment direction, thus strongly improving mechanical stiffness and strength compared to randomly filled systems. The application of a MF on pre-strained samples during the magneto-mechanical characterization resulted in a direct relationship between the measured variation of the elastic modulus of the foam and the time dependent intensity of the applied MF (also for a magnetic field strength as low as 200 kA/m). In particular, all reinforced samples pre-strained in the linear elastic region of the stress-strain curve exhibited a magneto-strictive response (negative variation of the measured stress). On the contrary, a positive variation of the measured stress (strengthening effect) was detected in samples with aligned particles at pre-strains above the yield point. This behavior has been related to the tendency of chain-like aggregates in buckled cell edges to re-align along the MF lines.
M. D'Auria et al., "Effects of an External Magnetic Field on Polymeric Foam-Ferromagnet Composites", Advances in Science and Technology, Vol. 97, pp. 30-35, 2017