Experimental and Numerical Study on Mixed Mode I-II Fatigue Crack Propagation in Concrete

Abstract

To ensure the safety of concrete structures under fatigue loading, the fatigue crack propagation in concrete needs to be evaluated accurately. In this paper, a numerical method for mixed mode I-II fatigue crack propagation in concrete is proposed, in which the stress intensity factor (SIF)-based crack propagation criterion is employed, and the degradation of the cohesive force under fatigue loading is considered quantitatively. To validate the applicability of the numerical method, the mixed mode I-II fatigue fracture test of the three-point bending (TPB) beam is conducted. The fatigue crack propagation length is measured with the digital image correlation (DIC) method. Eventually, the applicability of the numerical method is validated by a reasonable agreement between the numerically derived crack propagation path, crack mouth opening displacement (CMOD), crack mouth sliding displacement (CMSD), crack propagation length, and mode I SIF and the experimental results. It is concluded that the proposed numerical method can be used to evaluate the mixed mode I-II fatigue crack propagation process of concrete when the initial fracture toughness, Poisson’s ratio, and Young’s modulus under static loading and the tension-softening constitutive relation under fatigue loading are given. In addition, the experimental results indicate that the mixed mode I-II fatigue failure of concrete occurs when the mode I SIF reaches a critical value, regardless of the fatigue load level and the fatigue life. The numerical results show that the mixed mode I-II fatigue crack propagation path is independent of the fatigue load level and approximately identical to that under static loading. In practical engineering, many concrete structures such as concrete pavements may be subjected to fatigue loads, e.g., cyclic vehicle loads. Under the fatigue loads, the crack would initiate, propagate, and even cause the fatigue failure of the concrete structures. Meanwhile, due to the complexity of the fatigue loads, the crack path could not be predicted in advance, making the evaluation of the fatigue performance more difficult. Therefore, a thorough investigation of the fatigue fracture properties of concrete is of great theoretical significance and practical application value. In this study, a numerical method for predicting the mixed mode I-II fatigue fracture performance of concrete is presented. With the numerical method, the crack propagation length, crack propagation path, deflection, crack opening displacement, crack sliding displacement, and eventual fatigue life of the concrete structures could be reasonably predicted. The numerical results could provide significant references to the fatigue life prediction of concrete structures in service, such as concrete pavement. In addition, the predicted fatigue crack length and crack path would also be helpful to the reinforcement and repair of concrete structures.