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

本文研究了基于逆分析的电磁测量裂纹和缺陷识别的主动式和被动式电势CT （computer tomography）方法。主要研究结果总结如下：1。通过数值和实验验证了被动电位CT法在板试件中贯穿裂纹识别中的适用性。裂纹存在时，粘接在试样表面的压电薄膜的电势分布呈现双峰特征。结果表明，基于所提出的逆分析方案，可以从两个峰的特征参数中识别出裂纹。该方法成功地推广到利用两峰之比识别倾斜裂纹。结果表明，即使两个裂纹位置很近，应用赤池信息准则（AIC）也能估计出裂纹数。研究了用被动电位CT法识别背面三维表面裂纹的方法。在压电薄膜上发现了一种特征电位分布，可用于三维裂纹识别。将被动电位法应用于复合材料层合板的分层识别。结果表明，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。结果表明，被动电位CT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.