Effect of attenuation and dispersion on frequency spectrum of vibration in multi-phase materials

Abstract

The sensors and impact sources for impact-resonance test were characterized by point-source/point-receiver technique. It was found that the conical and the pin-type transducers had flat sensitivity to the displacement and velocity of vibration, respectively, in the frequency range of DC-5MHz. And impacts of steel ball drop were explained by the Hertz``s law of contact. The attenuation and dispersion of stress waves in the multi-phase materials such as granite, paste, mortar and concrete were evaluated by the point-source/point-receiver technique with step force of glass capillary breaking. Effect of time shift of input signal on the dispersion relation was discussed. Mortar and paste were found to be less attenuative and dispersive than granite and concrete. The resonant frequencies of vibrations of plates which were excited by steel ball drop were identified by the normal mode frequencies of axi-symmetric flexural vibrations of a thick circular plate. The thickness modes were hardly clarified because of strong resonance of flexural modes. It was found that the number and amplituds of the peak frequencies were decreased by attenuation, and that widths of resonance in frequency spectra were increased by dispersion. The impact resonance test was carried out for the mortar and concrete specimen containing artificial flaws. The thickness vibration modes as well as flexural modes appeared in the frequency spectrum because the circular boundary conditions are not right. The observed peak frequencies in impact resonance tests were identified with the possible normal modes of the blocks, and the depth and size of the flaw were determined by the resonant frequencies of the specimens. The frequency spectra of the mortar and the concrete blocks were similar, even if the peak frequencies and the widths of the peaks of the concrete specimen were slightly higher and broader, respectively than those of the mortar block. The flaw sic, shape and location determined by impact re...