| The existence of concrete fracture process zone makes the linear elastic fracture mechanics(LEFM)no longer applicable to the fracture analysis of concrete structures and is also responsible for the concrete size effect.It is an urgent problem in the field of mechanics of concrete materials to study the characteristics of fracture process zone of concrete.So far,there has not been a universally accepted conclusion in the research on the fracture mechanism of concrete materials at home and abroad,and the problem of how to get the softening parameters of concrete has not been solved.In this paper,the displacement distribution law of the fracture process zone of three-point bending beam specimens is analyzed using a combination of experimental studies and numerical calculations to further clarify the concrete fracture mechanism and mechanical properties of the process zone.The size effect of concrete fracture parameters in the height and thickness directions of the specimens was investigated.The main works carried out in this paper are as follows.(1)Digital image correlation(DIC)technique was used to observe the crack expansion of three-point bending beam specimens with precast cracks during the whole process of loading,and the crack initiation point and crack initiation load of concrete three-point bending beam specimens were measured by the resistive strain gauge method.(2)The distribution of crack opening displacement along the fracture process zone in the three-point bending beam fracture test of concrete material was studied by the fracture displacement field obtained from the experimental study,and the size of the fracture process zone corresponding to different loading levels and the variation of the slope of the crack opening displacement distribution with the height and thickness of the specimen were analyzed.(3)The displacement of the crack along the fracture process zone is linear distribution through DIC fracture test,and the softening parameters of concrete are obtained on this basis.The crack distribution of opening displacement and extension length and slope of displacement distribution calculated by the model under different loads were compared with the experimental results.(4)Based on the experimental results,the fracture parameters in the fracture test of concrete three-point bending specimens were calculated from the parameters of the fracture process zone of concrete.The influence of the specimen height and thickness aspects on each fracture parameter was studied.The model for obtaining softening parameters established in this paper was compared with the double-K fracture model and the size effect model to explain the size effect phenomenon of concrete. |
