Keywords: non-destructive evaluation, crack identification, electric potential method, piezoelectric film, passive method.

ABSTRACT As a consequence of the increase in the number of aged plants and their components, then the nondestructive evaluation and online monitoring are becoming more important. Online monitoring has an advantage that it does not require shutdown of plants. When electric current is applied to a body with a crack, an electric potential distribution develops. By applying inverse analysis schemes [1] to the electric potential distribution appearing on the surface of a cracked body, the present authors proposed the active electric potential computed tomography (CT) method [2].

When a piezoelectric film is pasted on the surface of cracked body subject to a mechanical load the electric potential distribution develops on the film as a result of the direct piezoelectric effect. The present authors proposed the passive electric potential CT method [3,4] using the electric potential distribution on the surface of a piezoelectric film. It was found that a characteristic electric potential distribution appeared on the piezoelectric film when a crack existed in the body. The crack can be identified from the electric potential distribution. An inverse analysis was conducted for crack identification based on a comparison of the electric potential distribution measured on the piezoelectric film and that obtained using the finite element method.

In the present study the passive electric potential CT method was applied to the identification of a part-through three-dimensional crack. The electric potential distribution was calculated using the finite element method taking the piezoelectric effect into account. The least residual method was used in the inverse analysis. In this method the combination of crack parameters minimizing the residual between the measured and calculated electric potential distributions was sought.

Numerical simulations were made of the identification of the part-through three-dimensional cracks. It was found that the passive electric potential CT method was effective for the estimation of the location and size of a square-shaped crack and a round-tipped crack even in the existence of noise at the level of 2%.

1

S. Kubo, "Inverse Problems Related to the Mechanics and Fracture of Solids and Structures", JSME Int. J., Ser. I, 31(2), 157-166, 1988.

2

S. Kubo, T. Sakagami, K. Ohji, "The Electric Potential CT Method for Measuring Two- and Three-Dimensional Cracks", Current Japanese Materials Research - Vol.8 Fracture Mechanics, 235-254, Elsevier Appl. Sci., Soc. Mat. Sci., Japan, 1991.

3

S.-Q. Li, S. Kubo, T. Sakagami, Z.-X. Liu, "Theoretical and Numerical Investigations on Crack Identification Using Piezoelectreic Material-Embedded Structures", Materials Sci. Research Int., 6, 41-48, 2000. doi:10.2472/jsms.49.3Appendix_41

4

D. Shiozawa, S. Kubo, T. Sakagami, "Passive Electric Potential CT Method Using Piezoelectric Material for Crack Identification", Inverse Problems in Science and Engineering, 12(1), 71-79, 2004. doi:10.1080/10682760310001597518

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