Quantitative Evaluation of Structural Damage by Attenuation in Scattering

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The results of the study are summarized as follows.1. The boundary integral equations were formulated for the multiple scattering problem of cracks and the Born series algorithm was developed to solve the system of equations for crack opening displacements.2. The expression to calculate the elastodynamic scattering cross-section was obtained in the form of the summation of the longitudinal and transverse far-field scattering amplitudes. These scattering amplitudes are calculated by the crack opening displacements in the Born series algorithm.3. The effect of the multiple scattering for the elastodynamic scattering cross-section was numerically examined for typical crack configurations. It was suggested that the distance of cracks to neglect the multiple scattering effect is approximately 2d, where d is the diameter of the cracks.4. The approximate relation for the elastodynamic scattering cross-section, the number of cracks in the unit volume and the attenuation induced by the scattering was shown and the effect of the multiple scattering to this relation was examined.5. The specimen which contains distributed cracks was made by the cement based material and the scattering attenuation was measured by the water immersed pitch-catch ultrasonic method. The measured attenuation agreed well with the calculated attenuation in the range of the effective frequency of the transducer.6. A method to estimate the average number of cracks was proposed by using the combined method of the measured scattering attenuation and the calculated elastodynamic scattering cross-section.