Development of Identification Method of Defects Embedded in a Body by A.C.Electromagnetic CT Method Using Inverse Analysis of Frequency Response

目前的研究人员提出了直流电势 CT（计算机断层扫描）方法，用于识别嵌入导电体中的二维和三维裂纹。数值模拟和实验证明了该方法的有效性。本研究通过扩展直流电位CT（计算机断层扫描）方法，提出了交流电位CT缺陷识别方法，该方法利用多个交流频率的电位分布来识别裂纹。得到的主要结论如下： 1．采用边界元法对裂纹体的电磁场进行分析，建立交流电势与裂纹长度的标定关系。 2．测量了带有贯穿裂纹的物体的交流电势分布。发现该标定关系良好。 3．计算了频率较高、集肤效应显着时的电势分布。 4．测量三维表面裂纹中的电势分布。发现高频和低频范围内的电势分布可有效识别裂纹。 5．使用全三维电磁场分析进行裂纹识别。发现该方法是有效的。 6．针对多裂纹的识别，提出了融合型遗传算法。 7．通过扩展该方法，对异种材料界面裂纹进行了识别。数值模拟和实验表明了该方法的有效性。

The present investigators proposed the D.C.electric potential CT (computed tomography) method for identification of two- and three- dimensional cracks embedded in an electric conductive body. The usefulness of the method was shown by numerical simulations and experiments. In this study, by extending the D.C.electric potential CT (computed tomography) method, A.C.electric potential CT defect identification method was proposed, in which electric potential distribution for several A.C.frequencies were used to identify the crack. The main conclusions obtained are summarized in the followings.1. Electromagnetic field of cracked body was analyzed using boundary element method to construct calibration relation between A.C.potential and crack length.2. A.C.electric potential distributions were measured for a body with a through crack. It was found that the calibration relation worked well.3. The electric potential distribution was calculated, in the case that the frequency was high and the skin effect was significant.4. Electric potential distribution in a three-dimensional surface crack was measured. It was found the electric potential distributions in the limits of high and low frequencies may be effective to identify the crack.5. Crack identification was made using full three-dimensional electromagnetic field analysis. It was found that the method was useful.6. For the identification of plural cracks fusion type genetic algorithm was proposed.7. Identifiction of interface crack in dissimilar materials was made by extending the method. Nemerical simulations and experiments showed the usefulness of the method.