Research on Variation Law of Fatigue Crack-tip Displacement and Strain Fields Based on High-speed Digital Image CorrelationMethod

doi:10.3969/j.issn.1000-1093.2015.09.024

Abstract

Abstract: In order to research the variation laws of displacement and strain fields on the fatigue crack tip area of the compact tension（CT）specimen in the stage of steady crack propagation under high frequency sinusoidal alternating load, a method based on the digital image correlation (DIC) and digital high-speed photography technology is proposed. A series of digital speckle images of CT specimen under sinusoidal alternating load are collected by digital high-speed photographic equipment, and the displacement and strain fields on the crack tip in each image are calculated by DIC. The sinusoidal changing strain curve of the feature point on the fatigue crack tip area is obtained by the least square sine wave fitting method, and the characteristic parameters of sinusoidal strain, such as amplitude, frequency, phase and mean load, are calculated. The images of characteristic position in a stress cycle are obtained by comparing the fitted sine curve of strain with the corresponding speckle images. Then the strain values at the tip of CT specimen during one stress cycle are measured by dynamic strain gauge. The results show that the maximum measurement error of strain by DIC method is 4.12% . On this basis, the resonant fatigue crack propagation test is carried out based on the high-speed photography and digital image correlation method, the relationship between strain amplitude values at crack tip and fatigue cycle number before the fatigue crack extension, and the variation laws of displacement and strain fields on crack tip area with the different lengths of fatigue crack are studied.

Key words: apparatus and intruments technology, digital image correlation, high-speed photography, fatigue crack, displacement field, strain field, high frequency resonant loading

CLC Number:

GAO Hong-li， LIU Huan， QI Zi-cheng, LIU Hui， ZHENG Huan-bin. Research on Variation Law of Fatigue Crack-tip Displacement and Strain Fields Based on High-speed Digital Image CorrelationMethod[J]. Acta Armamentarii, 2015, 36(9): 1772-1781.

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