Study on Fracture Behavior of Nickel-Based Single Crystal Superalloy subjected to High Temperature Fatigue using Digital Image Correlation

Abstract Anisotropic mechanical behavior of nickel-based single crystal superalloy ( N B S C S ) is studied based on the displacement field near the crack tip during the fatigue crack growth at980°C. A new distortion calibration technique for bi-prism-based single-lens 3D digital image correlation ( B S L 3 D D I C ) is proposed to in-situ and on-line characterize 3D full-field deformation with high precision. Virtual displacement extensometers ( V D E s ) are arranged from the displacement field for the crack opening displacement ( C O D ) determination. To the best of our knowledge, the effect of V D E s locations on the precision of C O D measurement is first theoretically analyzed, and the arrangement of V D E s has been optimized. Noticeably, similar quantitative analyses are conducted to determine crack opening ratio ( C O R ) 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 ( S I F ) expressed as K eff I and mode-Ⅱ effective S I F ( K eff Π ), but also theoretical S I F ( K theo I ), crack opening S I F ( K open I ) and crack opening load ratio ( C O L R ) are obtained. Based on these important fatigue parameters, modified Paris’ law is used to describe the high-temperature anisotropic crack growth behavior.