ИСТИНА

The paper presents results of experimental investigations of exural elastic V-waves (EVW) in metallic wedges of isotropic aluminum alloy D16. For the experiments, several wedges with angle apertures of 32 degrees and 60 degrees have been prepared and investigated. Two wedge samples are made of alloy D16, where strong mechanical residual stresses were previously created. For excitation and reception of EVW the piezoelectric transducers are used. EVW recording are also carried out using the POLYTEC laser vibrometer. Ultrasonic measurements are performed using automated ultrasonic complex RITEC RPR-5000. In the frequency range of (0.25 - 3) MHh EVW velocities are measured. Velocity dispersion is found in this frequency range within the experimental errors. In a wedge with angle of 60 degrees at 250 kHz, EVW localization was investigated in the wedge rib using a laser vibrometer. An exponential decrease in the amplitude of the vibrational wave velocity V, depending on the distance from the edge of the wedge, is indicated. Studies of EVW amplitude dependence of its velocity and EVW second harmonic generation have been conducted. In isotropic wedges without permanent deformation, expectedly, amplitude dependence of EVW velocity and EVW second harmonic generation are not observed. (In isotropic solids, second harmonic generation of exural EVW is impossible due the conditions of symmetry). In samples of wedges with residual strains, at excess of a certain level of amplitude of the probe signal on the EVW transmitter, EVW velocity decreasing linear in amplitude is detected. Besides, generation of the second harmonic of elastic EVW is observed in the wedges with residual stress. The dependence of amplitude of the second harmonic on EVW amplitude of the fundamental frequency is linear. Threshold and linear decrease of EVW velocity at EVW amplitude increase, as well as second harmonic generation of EVW can not be explained with classical elastic nonlinearity associated with the anharmonicity of the crystal lattice. Such behavior of the nonlinear properties of the EVW and second-harmonic generation is typical for media with non-classical (structural) nonlinearity and due to the residual strains made in the sample. A discussion of the experimental results is presented. This work was supported by grants RFBR 14-02-00288a