Defect Identification by the Active and Passive Electric Potential CT (Computer Tomography) Methods Using Spatial Electromagnetic Field Measurements

本文研究了基于反分析的电磁场测量中识别裂纹和缺陷的主动和被动电势CT(CT)方法的发展。主要研究结果如下：1.从数值和实验两个方面考察了被动电势CT方法在平板试件穿透裂纹识别中的适用性。在裂纹存在的情况下，粘贴在试件表面的压电膜的电位分布呈现特征的双峰。结果表明，基于所提出的反分析方法，可以从两个峰值的特征参数中识别出裂纹。该方法被成功地推广到利用两个峰的比值来识别倾斜裂纹。研究发现，即使在两个裂纹位置相近的情况下，应用AIC(Akaike信息准则)也可以估计出裂纹的数目。2.研究了用被动电位CT方法识别三维表面裂纹背面断裂的方法。发现压电膜上的特征电势分布可用于三维裂纹的识别。3.将被动电位法应用于复合材料层合板的分层识别。研究发现，在三点弯曲载荷作用下，压电薄膜上的电势分布可以识别层间缺陷，从而证明被动电势CT方法适用于二维和三维裂纹和缺陷的定量识别。

The present study deals with the development of the active and passive electric potential CT (computed tomography) methods for the identification of cracks and defects from electromagnetic field measurements based on the inverse analyses. The major results obtained are summarized as follows.1.The applicability of the passive electric potential CT method to the identification of a through-thickness crack in a plate specimen was examined numerically and experimentally. In the presence of the crack the electric potential distribution of a piezoelectric film glued on the surface of the specimen showed characteristic two peaks. It was found that the crack can be identified from the characteristic parameters of the two peaks based on the proposed inverse analysis scheme. The method was successfully extended to the identification of an inclined crack by using a ratio of the two peaks. It was found that the crack numbers can be estimated by applying the AIC (Akaike information criterion) even when two cracks are closely located.2.Identification of a three-dimensional surface crack breaking on the back surface by the passive electric potential CT method was examined. A characteristic potential distribution was found on the piezoelectric film which can be used for the three-dimensional crack identification.3.The passive electric potential method was applied to the identification of of delamination in composite laminates. It was found that the interlaminar defect can be identified from the electric potential distribution on the piezoelectric film when the composites are loaded under three-point bending.From these results the passive electric potential CT method was found applicable for quantitative identification of two-and three-dimensional cracks and defects.