Numerical Simulation Of Detection Of Concrete Crack Based On Rayleigh Wave Method

Rayleigh wave, which propagates along the free surface of semi-infinite elastic medium, is a kind of polarized waves. The characteristics of Rayleigh wave are the long wavelength, large amplitude and so on. Based on this characteristics, Rayleigh wave has been widely applied into the field of geophysics, engineering exploration, nondestructive testing and so on. In this paper, the propagation characteristics of Rayleigh wave in homogeneous media, layered media analyzed based on analytical method and the propagation characteristics of Rayleigh wave in media of concret containing crack based on numerical method. By setting different conditions of the surface crack and internal crack, the method is proposed is to detect crack. The main achievements and innovations are as follows:(1) Rayleigh wave dispersion curves were studied in layered medium, and a positive(Knopoff Fast Algorithm) design program is achieved based on MATLAB. The dispersion curves of Rayleigh wave are obtained, the variation of which are closely related to conditions of media.(2) The curve between transfer coefficient ? and d ? is obtained by setting different frequencies of excitation sources and different lengths of surface cracks. The curve segments of d ? ?0.4,1?? ?0.3 is selectied as the basis to judge. In practice, transfer coefficient falls between 0.3 and 1 by changing the frequency of the incident Rayleigh wave. The d ? is get from curve between transfer coefficient ? and d ?, easy to obtain the lengths of surface crack.(3) The elastic waves propagation of concrete containing surface crack were analyzed. The formulas of surface crack length and angle are obtained based on the difference of propagation time of Rayleigh wave and diffracted Longitudinal wave.(4) A new method to detect internal crack is proposed. The horizontal position of internal crack can be detected by Rayleigh wave amplitude-distance curve. AI(Amplitude Index)is proposed. the depth of internal crack can be detected by AI-h T curve and the angle of internal crack can be detected by AI-α curve(5) Another new method to detect internal crack is proposed. VI(Amplitude Index)is proposed and the depth of internal crack can be detected by VI-hT curve. But the angle of internal crack cannot be detected based on the method. The horizontal position of internal crack can be detected based on the difference of propagation time of incident Rayleigh wave and reflection Rayleigh wave.