透過回折波を利用した亀裂先端位置測定法

Abstract

There are many measurement methods of crack characteristics, and some of them have received practical application. Many of them are using P-wave velocity to measure the crack characteristics. The measurements of P-wave velocity are influenced by the frequency of P-wave. In order to measure P-wave velocity with high accuracy, high frequency P-wave is needed. However, the higher P-wave velocity is, the larger the absorption of transmitted wave is. In many cases of in-situ measurements by using high frequency P-wave, the accuracy of measurements become low, for the reason that the effective transmitted distance is short and S/N ratio is low. In the present paper, the measurement method of crack tip position which is free from frequency of P-wave is proposed. This method uses the diffracted P-wave from the tip of a crack. The polarity of first motion of diffracted P-wave from the tip of a crack is dependent on the angle of incidence , the angle of diffraction and Poisson ratio of media. The measurement of the angle of incidence and the angle of diffraction where the polarity is changed is free from the frequency of P-wave. Therefore this methods is not influenced from the frequency of P-wave, and the suitable frequency by the condition of in-situ measurement can be selected. In the persent paper, the applicability of proposed theory about the change of the polarity of first motion of diffracted P-wave from the tip of a crack to in-situ measurement is studied. As the result of theoretical study and experimental study using Inada granite, it was clarified that the measurement using the proposed theory was effective to the measurement of crack tip position.