Study on Fracture Prediction for Cracks Under Mode II and III Loading Combined With Mode I

Abstract Predicting brittle fractures in beam-to-column connections under mixed-mode loading remains a significant challenge in structural engineering. Traditional approaches predominantlyy focus on mode I crack opening, often neglecting the contributions of modes II and III. This study incorporates a mode quantification approach to address these mixed-mode effects, facilitating more precise assessments of brittle fracture risks. Post-earthquake investigations of the 1994 Northridge and 1995 Kobe earthquakes revealed brittle fractures initiating from ductile crack tips at geometric singularities, such as weld defects and weld access hole boundaries. Despite design improvements aimed at reducing strain concentrations, these regions—characterized by high triaxial stress and strain—remain prone to fracture risks. Effective evaluation methods for brittle fractures at such defects are essential to ensure structural safety. Fracture mechanics-based approaches often fail to account for differences in plastic constraints between laboratory specimens, such as single-edge notched bend specimens, and actual structural defects. To address these issue, this study employs the Weibull stress parameter and extends its application to mixed-mode loading conditions. By introducing a mixed-mode ratio to quantify the contributions of modes I, II, and III, this research improves the predictive accuracy of brittle fracture models.