High-Temperature Fracture Mechanics Parameter Measurement and Yielding Zone Analysis of Superalloy GH4169 Based on Single-Lens 3D Digital Image Correlation

Fracture mechanics parameters are crucial for evaluating the failure of a material; furthermore, the yielding zone near the crack tip is closely related to the ultimate bearing capacity. How to characterize these parameters has drawn a lot of attention from mechanics researchers. Currently, the digital image correlation (DIC) method, due to its advantage of being able to perform full-field, non-contact measurements, has great potential for application in the measurement of the mentioned parameters. In this paper, a bi-prism-based single lens (BSL) 3D DIC technique was utilized to determine the fracture mechanics parameters and the yielding zone size of the Ni-based superalloy GH4169 at room temperature and 650 degrees C. In the measurement, the displacement fields of single-edge cracked specimens under a uniaxial tensile load were measured using the BSL 3D DIC system. And then, the J integral and stress intensity factor K at room and high temperature were calculated from the displacement fields. Finally, the J integral calculated using the path integral method (J _ 1) and the J integral converted from the stress intensity factor K (J _ 2) were used to evaluate the yielding condition near the crack tip Yoneyama et al. (Strain 50(2):147-160, 2014), while a specific value was also determined as the critical small-scale yielding load from the variations of J _ 1 and J _ 2. Additionally, the relationship between the yielding zone size r(p), calculated from K and the value increment J = J _ 2 - J _ 1 was established, which was found to be linear. On the r(p) - increment J curve, the intercept on the r(p) axis could be regarded as the critical size of small-scale yielding zone.