The Dispersion of Supersonic Waves in Cylindrical Rods of Polycrystalline Silver, Nickel, and Magnesium

Abstract

The velocities of elastic waves in polycrystalline rods of silver, nickel, and magnesium were measured at supersonic frequencies ranging from 120 to 750 kc. This was done by mounting the rods in a horizontal position so that one end was supported by a loop of silk thread and the other end passed through a diaphragm into a special box which was filled with transformer oil and which contained the quartz crystal source of supersound. Lycopodium powder scattered along the rod formed wave patterns when the rod was vibrating resonantly and hence wave-lengths could be measured directly. The products of these wave-lengths and the corresponding frequencies as read on the wave meter yield the required velocities. The dispersion theory of Giebe and Blechschmidt was tested by calculating theoretical curves for four of the six rods and comparing these with the corresponding experimental curves. The theory is found adequate to account satisfactorily only for the low frequency dispersion. One reason for its failure in other respects is discussed.