Modeling of Mixed Mode I-II Fatigue Fracture of Concrete Based on Paris Law

Mixed mode I-II fatigue fracture of concrete is commonly encountered in practical engineering. Accurate prediction of the fatigue crack propagation process and fatigue life is essential to evaluate the safety of concrete structures. In this study, the mixed mode I-II fatigue crack propagation process of the three-point bending (TPB) beam is investigated based on the digital image correlation (DIC) method. The results indicate that the mixed mode I-II crack propagation path under fatigue loading is consistent with that under static loading, and the stress intensity factor (SIF) corresponding to the unstable failure of concrete is constant, regardless of the fatigue load level and specimen size. Based on the experimental results, a unified model for characterizing mixed mode I-II fatigue crack propagation in concrete is developed, where the equivalent SIF amplitude composed of mode-I and mode-II SIF amplitude is introduced into Paris law, and the statistical analysis is conducted to determine the probabilistic distribution of the empirical constant in Paris law. Furthermore, the feasibility of predicting the fatigue life of concrete structures is explored using the proposed model. It is concluded that the fatigue life with different reliability can be obtained when the mixed mode I-II fatigue crack propagation path is determined based on static tests. It is expected that the developed model contributes to the prediction of fatigue life and further safety assessment of concrete structures under fatigue loading.