An Experimental Study on Identification of Delamination in Composite Material by the Passive Electric Potential Ct Method

When a piezoelectric film is glued on the surface of a structure member subjected to mechanical load, a distribution of electric potential is induced. In the existence of defects in the member, a characteristic variation of electric potential is observed. Based on this phenomenon, the passive electric potential CT (computed tomography) method is developed for detecting and identifying defects in a structure. In this study, the applicability of the passive electric potential CT method to the identification of a delamination in a CFRP laminate was experimentally examined. CFRP laminate specimens, which have an artificial interlaminar delamination, were prepared. CFRP laminate specimens with a piezoelectric film on their surface were subjected to three-point bending. The electric potential distribution on the piezoelectric film was measured by a non-contact voltmeter. Characteristic variation reflecting the location and the size of the delamination are observed in the measured electric potential distributions on the piezoelectric film. The effect of the depth of the delamination was also observed. These tendencies of variations in measured electric potentials were similar to those found in the potential calculated by the FEM. In order to identify the delamination from the measured electric potential distribution, an inverse method was constructed based on the least squares residual evaluated between the measured and computed electric potential distributions. The location and size of the delamination were estimated accurately. For the estimation of the depth of delamination, the accuracy was deteriorated with increase in the depth. It was shown that the passive electric potential CT method using piezoelectric film is useful for quantitative identification of interlaminar delamination in laminated composite materials.