1991 Fiscal Year Final Research Report Summary
Measurement of Shape of Three-Dimensional Surface Crack by A. C. Electric Potential CT Method Using Frequency Information
| Project/Area Number |
01460091
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
機械材料工学
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| Research Institution | Osaka University |
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Principal Investigator |
KUBO Shiro Osaka University, Faculty of Engineering, Professor, 工学部, 教授 (20107139)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAI Yoshikazu Kobe University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90155656)
OHJI Kiyotsugu Osaka University, Faculty of Engineering, Professor, 工学部, 教授 (20028939)
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| Project Period (FY) |
1989 – 1991
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| Keywords | Non-Destructive Inspection / Electric Potential Method / Surface Crack / Computed Tomography / Inverse Analysis / Fracture Mechanics / Boundary Element Method / Pipe |
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| Research Abstract |
The D. C. electric potential CT (computed tomography) method was extended to measurement of shape of a surface crack from A. C. potential readings. The main results obtained are summarized as follows.
1. Finite element formulation and programming were made for calculating electromagnetic fields in a two-dimensional body under A. C. application, assuming that the fields were stationary and using complex variable representation of filed quantities. The measured A. C. potential distribution agreed fairly well with the calculated distribution.
2. Boundary element formulations were made for calculating three-dimensional electromagnetic fields under very low frequency and very high frequency, and boundary element programming was made. A. C. electric potential in a plate with a surface crack was calculated. An inversion scheme based on the least residual method was developed for estimating the shape of surface crack from several A. C. potential readings. Numerical simulations showed that the estimated crack shape agreed fairly well with the given ones when potential readings had 2 significant digits. The estimated crack shape agreed well potential readings with 3 significant digits were used.
4. Measurement of A. C. potential were made for ferromagnetic and paramagnetic plates with a surface crack. Measured potential readings were used to estimate the crack shape based on the inversion scheme. It was found that fairly good estimation of crack shape can be made, although there remained technical problems unresolved in measuring A. C. potential distribution under high frequencies.
5. Applicability of the optimization techniques in estimating crack shape, location and size based on the least residual method was examined. A hierarchical procedure in the estimation was proposed and was found useful in the estimation. Selection of variables of optimization was also found to be important in attaining efficient estimation.
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