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. Many concrete structures are subjected to fatigue loads in service, such as concrete pavements and bridge decks suffering from cyclic vehicle loads. Under fatigue loading, the crack gradually propagates, resulting in the fatigue failure of concrete structures. Therefore, it is critical to investigate the fatigue crack propagation process of concrete such that the safety assessment of concrete structures can be conducted. In this study, a prediction model for mixed mode I–II fatigue fracture of concrete is proposed based on the well-known Paris law. When the SIFs at the crack tip are calculated based on the finite-element method, the whole fatigue crack propagation process and fatigue life of concrete structures with different reliability can be reasonably predicted using the proposed model. Furthermore, the stability analysis of fatigue crack and the reinforcement and repair of cracked concrete structures can be conducted timely according to the predicted fatigue crack propagation length and fatigue life. In general, the proposed model is of great significance to guarantee the safety of concrete structures under fatigue loading, e.g., concrete pavements and bridge decks. [ABSTRACT FROM AUTHOR]