The effects of amplitude-dependent internal friction in a low-frequency annealed polycrystalline copper rod resonator

The effects of amplitude-dependent internal friction in a low-frequency rod resonator made of annealed polycrystalline copper are studied experimentally and theoretically. We report the results of measurements of nonlinear losses and resonance frequency shift in the first three longitudinal resonator modes in the frequency range from 2 to 11 kHz. The observed effects are described analytically using the rheological model and the equation of state of a microinhomogeneous medium with hysteretic loss saturation and relaxation of its viscoelastic defects. The values of effective parameters of the hysteretic nonlinearity of the annealed copper sample and their frequency dependences are determined by comparing the experimental and analytical results.