Abstract
Anisotropic mechanical behavior of nickel-based single crystal superalloy (NBSCS) is studied based on the displacement field near the crack tip during the fatigue crack growth at 980°C. A new distortion calibration technique for bi-prism-based single-lens 3D digital image correlation (BSL3DDIC) is proposed to in-situ and on-line characterize 3D full-field deformation with high precision. Virtual displacement extensometers (VDEs) are arranged from the displacement field for the crack opening displacement (COD) determination. To the best of our knowledge, the effect of VDEs locations on the precision of COD measurement is first theoretically analyzed, and the arrangement of VDEs has been optimized. Noticeably, similar quantitative analyses are conducted to determine crack opening ratio (COR) for crack closure evaluation. Moreover, via fitting full-field displacement data to a theoretical model for anisotropic material, not only mode-Ⅰ effective stress intensity factor (SIF) expressed as KeffI and mode-Ⅱ effective SIF (KeffΠ), but also theoretical SIF (KtheoI), crack opening SIF (KopenI) and crack opening load ratio (COLR) are obtained. Based on these important fatigue parameters, modified Paris’ law is used to describe the high-temperature anisotropic crack growth behavior.
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