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

本研究涉及的主动和被动电位CT（计算机断层扫描）方法的发展，用于识别裂纹和缺陷的电磁场测量的逆分析的基础上。主要研究结果如下：1.通过数值模拟和实验验证了被动电位CT法在板试件穿透裂纹识别中的适用性。在裂纹存在时，粘贴在试样表面的压电薄膜的电位分布呈现出特征性的双峰。结果表明，基于所提出的反分析方案，可以从两个峰值的特征参数识别裂纹。该方法被成功地推广到斜裂纹的识别，通过使用的两个峰值的比率。研究发现，即使两条裂纹位置很近，应用AIC（Akaike information criterion，赤池信息准则）也能估计出裂纹数。2.采用被动电位CT法对背面断裂的三维表面裂纹进行了识别。在压电薄膜上发现了一个特征电位分布，可以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分层损伤的识别。结果表明，在三点弯曲载荷作用下，通过压电薄膜上的电势分布可以识别层间缺陷，从而证明了被动电势CT法可以定量识别二维和三维裂纹和缺陷。

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.