Surface Crack Detection by A.C. Potential Method

Research Project

Project/Area Number	63850025
Research Category	Grant-in-Aid for Developmental Scientific Research
Allocation Type	Single-year Grants
Research Field	材料力学
Research Institution	Faculty of Science and Engineering Ritsumeikan University
Principal Investigator	OHNAMI Masateru Faculty of Sci. & Eng. Ritsumeikan Univ. Prof., 理工学部, 教授 (60066587)
Co-Investigator(Kenkyū-buntansha)	FUJII Tsutomu Tokyo Koki Seizousho Ltd., Testing Machine Technical Dept., Technical Headquarte, 技術部, 課長 SAKANE Masao Faculty of Sci. & Eng. Ritsumeikan Univ. Ass. Pro., 理工学部, 助手 (20111130)
Project Period (FY)	1988 – 1989
Project Status	Completed (Fiscal Year 1989)
Budget Amount *help	¥6,700,000 (Direct Cost: ¥6,700,000) Fiscal Year 1989: ¥900,000 (Direct Cost: ¥900,000) Fiscal Year 1988: ¥5,800,000 (Direct Cost: ¥5,800,000)
Keywords	alternative current / potential method / crack detection / skin effect / surface crack / spectrum analyze / inside defect / 交流電位差法 / 直流電位差法 / き裂検出 / 境界要素法 / 有限要素法
Research Abstract	The crack detection system was developed using a.c. potential drop method. In this system, the skin effect of a.c. was applied. The surface crack measurements were carried out using the system and the main conclusions obtained are as follows. 1. The new a.c. potential crack detection system was developed, where the skin effect of a.c. was effectively applied. The system was composed of function generator, high frequency power amplifier, lockin amplifier, FFT analyzer and micro computer. The maximum current and frequency of the system are respectively 5A and 20 KHz. The system was confirmed to have a designed performance. 2. Surface crack measurements were carried out using the a.c. potential system. Used was an a.c. sinusoidal wave with frequencies between 50 Hz to 10 KHz. For the smaller crack, the a.c. potential with higher frequencies was more increased while for the larger crack, that with lower frequencies was specifically increased. The skin effect of a.c. was successfully used in the potential system developed to detect the small surface crack effectively. 3. For the efficient measurement, the rectangular a.c. wave which has the power spectrum range between 50 Hz and 5 KHz was used. The detected rectangular a.c. potential raised by cracks was analyzed by FFT analyzer into the power spectrum. The potential of higher frequencies was more increased by the smaller surface crack while that of lower frequencies was more increased by the larger surface crack. The a.c. potential method using the rectangular wave shortened the testing time 50 times in comparison with the sinusoidal method. 4. The a.c. potential method suing the rectangular a.c. was applied to the inside defect detection. The a.c. potential with higher frequencies was more increased if the defect was near the surface but that with lower frequencies was more increased when the defect was apart from the surface.