A New AMB Configuration for Measurement of Material Damping in Metals

Material damping can be determined by measuring the damping of eigenmodes of vibrations in probe rods. Conventionally, these probes are supported mechanically and the supports must be moved to the nodes of the vibrational mode considered. Nevertheless, for materials with low damping, considerable amounts of energy may still be dissipated in the supports, thereby affecting the measurement of intrinsic damping of the material. Support losses may be considerably reduced, however, if the rod is suspended magnetically. Furthermore, no support adjustment is required even if this measurement for several eigenmodes is desired. In this paper, the damping of longitudinal vibrations in magnetically levitated steel rods is described. The results show values of intrinsic damping which are in some cases four times lower than those measured using conventional set-ups. The magnetic support uses a homogeneous magnetic field in order to avoid eddy currents. A description of the set-up as well as experimental results are included.