INTERNAL FRICTION STUDIES ON BELL METAL AND WOOD.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK ORDNANCE RESEARCH LAB
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The internal friction of bell metal and wood is of general interest not only from the standpoint of material testing but also for providing a physical explanation of the musical properties of these materials. An electrodynamic type apparatus was used to excite freely suspended rod samples in the longitudinal, bending and torsional modes of vibration at low levels of stress amplitude over the audible frequency range. The techniques of loss factor measurements are described. Experimental results are presented which verify a relaxation-type behavior in the losses of bell metal due to intercrystalline heat flow. Measurements on five different types of wood indicate the general behavior of losses associated with Youngs modulus and shear for propagation in rods oriented along the grain. The losses of one cross-grain specimen are reported. Dependence of losses on amplitude of applied stresses, rod geometry and moisture content in wood are observed and noted. Author