In this work, fatigue crack propagation tests were carried out at both macroscopic and microscopic scales. The propagation process was monitored using the digital image correlation (DIC) technique, which provided data on the fatigue crack growth rate and the unified constraint parameter A p (a parameter can represent both geometric constraint material constraint), and the correlation between the fatigue crack propagation rate and constraint was studied. Results demonstrate that a linear relationship between the fatigue crack propagation rate and the unified constraint parameter A p can be established for specimens at both scales, indicating a clear correlation between crack growth rate and structural constraint. Moreover, this correlation has been verified across different materials. In addition, based on the observed linear relationship, a new criterion for crack propagation was developed.
Wang et al. (Sun,) studied this question.