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

研究了基于逆散射法的弹性材料超声缺陷重建技术，建立了大型混凝土土建结构无损评价系统。本课题发展了二维和三维弹性动力学逆散射方法。利用实测波资料进行了散射波测量、衰减和相速度测量。通过对Born和Kirchhoff反散射法重构形状的比较，建立了缺陷表征体系。研究了用Born和Kirchhoff逆散射法重建混凝土材料中缺陷的形状。在该方法中，散射波的角分异和频率分异在极坐标系中以傅里叶变换的形式叠加。提出了一种将散射波数据从极坐标重新排列到直角坐标的有效方法来加速反演过程。制备了含有缺陷模型且表面平坦的混凝土试件，并通过脉冲回波测量获得了散射波形。用所制备的试样对缺陷模型进行了形状重建。结果表明，该方法可以重建混凝土材料的流动形态。

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.