The experimental investigation of the fast and slow dynamics of the torsional waves in the polycrystalline copper

The results of an experimental study of the fast and slow dynamics of torsional waves in acoustic resonators made of polycrystalline copper using two methods: resonant (at a frequency of 3 kHz) and pulsed (at a frequency of 138 kHz) are presented. In both cases, as the amplitude was increased, a linear decrease of the velocity of the torsional waves was observed. A comparison with similar results obtained using longitudinal waves was made. For torsional waves, the relative frequency change is approximately 2 times less than for longitudinal waves. As the amplitude of the probing signal is increased, nonlinear absorption of both torsional and longitudinal waves is observed. The observed dependences of the absorption and velocity of torsional waves from the amplitude of the probing signal are explained by the presence in the sample of a structural elastic nonlinearity.