Two-dimensional skeletal point method for creep-fatigue-interaction life prediction of perforated plates with inclined hole in single-crystal superalloy

To clarify the influence of hole inclination angle on the creep-fatigue-interaction (CFI) life of single-crystal superalloy structures, a two-dimensional skeletal point method (2D-SPM) is proposed and validated. Four types of perforated plate specimens with hole inclination angles of 0°, 30°, 45° and 60° were designed, manufactured, and tested under stress-controlled CFI loading at 900 °C. A visco-plastic constitutive model was employed to simulate the stress and strain evolution, revealing the full process of stress redistribution. The 2D-SPM extracts a characteristic stress by integrating the stress distribution along the closed contour that delineates the stress relaxation zone on the critical cross-section. The predicted CFI lives were compared with those from the nominal stress method, hot point method, conventional skeletal point method (SPM), and theory of critical distances (TCD). Results show that the 2D-SPM achieves the highest prediction accuracy, with an average error of 14.2% and all predicted lives fall within a ±2X scatter band of the experimental results. The conventional SPM also gives acceptable predictions but relies on predefined symmetric paths. The hot point method and TCD are unsuitable for CFI conditions because they ignore stress redistribution. Fracture analysis indicates that cracks initiate at the hole edge, propagate inward, and exhibit predominantly ductile dimpling features, confirming creep-damage-dominated failure. The 2D-SPM provides a reliable and practical tool for life assessment of complex structures with inclined holes.