Development of flaw evaluation system for large civil structures by using low frequency ultrasonic wave and scattered waveforms

为开发大型混凝土结构无损检测系统，开展了基于逆散射法的弹性材料超声缺陷重建技术研究，提出了二维和三维弹性动力逆散射法。为了充分利用实测数据，进行了散射波测量、衰减测量和相速度测量。通过对Born逆散射法和Kirchhoff逆散射法重建形状的比较，建立了缺陷表征系统。在该方法中，散射波的角差和频率差在极坐标中以傅里叶变换的形式叠加。提出了一种通过将散射波数据从极坐标重新排列到直角坐标来加速反演过程的有效方法，制备了含有缺陷模型的平面具体试件，并通过脉冲回波测量获得了散射波形。以制备好的试件为例，对缺陷模型进行了形状重建，验证了该方法用于混凝土材料流动形状重建的可能性。

The research about the technique of ultrasonic flaw reconstruction in elastic materials based on inverse scattering methods are carried out to develop a non-destructive evaluation system for large civil structures made by concrete materials.In this project, two and three dimensional elastodynamic inverse scattering methods are developed. The scattered wave measurement and the attenuation and phase velocity measurement were carried out for utilization of measured wave data. And, the comparison of reconstructed shapes by Born and Kirchhoff inverse scattering methods brought flaw characterization system.The shape reconstruction of flaws in the concrete materials by Born and Kirchhoff inverse scattering method is investigated. In this method, the angular and frequency diversities of the scattered waves are superposed in the form of the Fourier transform in the polar coordinate. An efficient method to accelerate the inversion process is proposed by rearranging the scattered wave data from the polar coordinate to the rectangular coordinate.The concrete specimens, that contain flaw models and has flat surface, are prepared and the scattered waveforms are acquired from the pulse-echo measurement. The performance of the shape reconstructions is shown for flaw models is the prepared specimens.As the result, the possibility of this method to reconstruct the shape of flow in concrete materials is shown.