Three-dimensional profile reconstruction of a natural SCC colony through electromagnetic NDT methods

2019 Fiscal Year Annual Research Report

• Project/Area Number: 19F19045
• Research Institution: Tohoku University
• Principal Investigator: 遊佐 訓孝 東北大学, 工学研究科, 准教授 (60466779)
• Co-Investigator(Kenkyū-buntansha): GE JIUHAO 東北大学, 工学(系)研究科(研究院), 外国人特別研究員
• Project Period (FY): 2019-07-24 – 2022-03-31
• Keywords: SCC colony / complex crack / space mapping algorithm

Outline of Annual Research Achievements

1) Built the finite element model of rotating eddy current testing technique as the forward model for inversion problem. Two approaches, Ar-reduced based method and commercial software COMSOL were used. 2) Achieved surface profile inversion of complex cracks based on ‘eddy current dipole’ model through rotating eddy current testing technique. Using numerical signals as input, the disturbed eddy current around stress corrosion crack (SCC) colony, ‘T shaped’ and even ‘star shaped’ cracks can be reconstructed. Furthermore, image processing such as edge recognition and skin color recognition were used to separate cracks clearly. 3) Fabricated rotating eddy current probe which contains TMR magnetic sensor. Designed and fabricated bending machine to fabricate stress corrosion crack colony specimen. 4) Studied the information improvement of detected object by mixing signals in different frequencies. Multi gene genetic programming algorithm was used to obtain the optimal combination of frequency component. The experiment results indicate that the new mixed feature can obtain more information than single frequency component. 5) To improve the quantification ability of deep cracks and signal noise ratio in ferromagnetic material detection, the difference between alternating current and direct current magnetization was studied. The results indicate that alternating current magnetization can achieve same purpose to direct current magnetization but without demagnetization process.

Current Status of Research Progress

3: Progress in research has been slightly delayed.

Reason

Because of novel coronavirus, the bending machine which fabricated in Chinese company could not be transported to Japan as scheduled.

Strategy for Future Research Activity

1) In the future, specimens contain single SCC and SCC colony will be fabricated. The signals of single SCC and SCC colony will be measured and compared. The current distribution around SCC colony will be studied; moreover, the characteristic of three dimensional magnetic signals Bx, By and Bz disturbed by SCC colony will be studied.
2) The inversion algorithm for rotating eddy current testing technique will be proposed. Three-dimensional profile reconstruction of SCC colony will be studied.