The Numerical Simulation Of Fatigue Crack Propagation In Concrete Under Cycle Loading

Concrete is a multiphase composite which is composed of coarse aggregates, cement paste matrix and the interfacial transition zone (ITZ) between the aggregate and the cement paste matrix at the mesoscale. There are many initial defects with the form of micro cracks and micro holes existing in each phase of the concrete, which will affect the fatigue performance and the macro response of the concrete structure combining with the microstructure of materials. Comparing with the static loading condition, the study on the macroscopic and mesoscopic analysis of the concrete under fatigue loading is fewer relatively, but the fatigue problems of concrete are still a problem needed to be solved in the engineering application.In this paper, the mesoscopic and macroscopic analysis method is adopted to analyze the initiation and growth of cracks in concrete and the failure of the specimen during the whole process of loading according to characteristic of fatigue cracks growth in different stages, which indicates the mesoscopic and macroscopic mechanism of fatigue failure of concrete.A multi-phase mesoscopic model of concrete is established, the shape and distribution of aggregates and the thickness of ITZ in which is coincident with the real concrete. The model is established without the hypothesis of the location where cracks initiate, and can reflect the process of the initiation cracks of in concrete. The model is realized by the integrated script program with the language of PYTHON, which improve the analysis efficiently.According to the characteristic of fatigue analysis, the solving process is set based on the cyclic block, which realizes the solving of the structure reaction under fatigue loading efficiently. The material subroutine of mesoscopic phase of concrete is programmed by the language of FORTRAN, which realizes the modelling of the material fatigue damage model relating to the loading numbers and deformation. The accuracy of the material sub-routine is proved.The affection of the randomness of the location, the volume friction of aggregates and the stress level on the cracks growth in concrete and the failure of specimen is analyzed by the mesoscopic model. The result of the numerical simulation indicates that the model is suitable for different loading station and the concrete with different mesoscopic structure.The method of the conversion of the mesoscopic and macroscopic model is proposed in this paper which realized the analysis process suitable for different stages of damage of concrete by properly partitioning the applicable limit of mesoscopic and macroscopic model during the analysis. By the data transmission between mesoscopic and macroscopic model, the analysis processes between mesoscopic and macroscopic model are linked, which ensures the continuity of concrete fatigue analysis. The macroscopic model is established by the program with the language of PYTHON, which realizes the simulation of dynamic growth process of cracks and the fatigue life prediction of concrete. The fatigue parameters in the model are fit by the relative numerical experiments, which are in coincident with the normal value of concrete.The above models which consider the characteristic of different fatigue stages of concrete describe the characteristic of damage evolution and cracks growth in concrete perfectly, and explain the deeply mechanism of concrete fatigue failure.