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Acta Armamentarii ›› 2022, Vol. 43 ›› Issue (4): 940-951.doi: 10.12382/bgxb.2021.0268

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Fatigue Crack Length Measurement Method Based on Edge Detection and DIC

HUANG Xinwei, SHAN Xiaofeng, GAO Hongli, WANG Chen   

  1. (1.School of Mechanical Engineering,Zhejiang University of Technology,Hangzhou 310023,Zhejiang,China;2.Key Laboratory of Special Purpose Equipment and Advanced Processing Technology of Ministry of Education,Zhejiang University of Technology, Hangzhou 310023,Zhejiang,China)
  • Online:2022-03-17

Abstract: For the difficult detection of crack closure section due to the obvious crack closure phenomenon in advanced high-strength steel plates,a high-precision dynamic measurement method of fatigue crack length based on the combination of edge detection and digital image correlation (DIC) technology is proposed. Two cameras are used to acquire the crack images and speckle images of two sides of the crack specimen during the fatigue crack growth test for processing,which can detect the closed section of the crack which can not be detected by the gray-scale edge detection method,thereby improving measurement accuracy. The fatigue crack growth path is obtained from the crack image by the gray edge detection method, and the crack tip is initially located. Then,the template matching technology is used to map the detected crack path coordinates to the speckle image,and the virtual extensometers are arranged on both sides of the crack tip extension. The opening displacement of virtual extensometer is obtained by DIC. Then the displacement-position curve of extensometer is fitted, the characteristics of the curve are analyzed to obtain the sub-pixel precision abscissa of the fatigue crack tip,and the crack length is accurately calculated. Finally,the results obtained by the edge detection method, the proposed method,and the measuring microscope are compared. The results show that the proposed method has a significant advantage in measurement accuracy compared with the edge detection method. It can be used to effectively detect the closed section of the crack with the measurement accuracy of 8 μm.

Key words: fatiguecrack, cracklengthmeasurement, edgedetection, digitalimagecorrelation, crackclosure, virtualextensometer

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