Experimental Study On Fracture Properties Of High Strength Concrete Beams Based On Finite Fracture Mechanics

As a typical heterogeneous quasi-brittle material,the development of fracture process zone has a great influence on the fracture characteristics.Once concrete cracks in engineering,it may cause corrosion of steel bar,and affect the safety and durability of structure.Therefore,it is of great significance to study the fracture characteristics of high strength concrete like ordinary concrete.In this paper,the finite Fracture mechanics(FFM)method is used to study and analyze the fracture failure of high strength concrete,which is based on the finite fracture mechanics framework.The fracture failure of quasi-brittle materials is characterized by the assumption that the "finite distance" of crack propagation is a structural parameter rather than a material parameter.The results are determined by the energy and stress(strain)criteria.The finite fracture mechanics method overcomes the defects of the traditional stress criterion and the energy criterion.The strength of structure can be predicted by the criterion.Finally,the damage of high strength concrete three-point bending beam and the development process of the whole fracture process zone are studied by digital image correlation method.The initial joint height ratio and beam height crack are analyzed.Maximum failure stress at joint tip,The main conclusions of this paper are as follows:(1)The initial crack load and instability load of three-point bending beam are measured by resistance method,and the initial joint height ratio,beam height and span are analyzed.The results show that both the initial crack load and the maximum load become smaller with the increase of the initial joint height ratio,and the ratio of the initial crack load to the maximum load is kept between 0.65 and 0.75.(2)The crack opening displacement and fracture process zone length of the specimen under different loads were measured by digital image correlation method(DICM).The results show that the crack opening displacement under arbitrary load can be accurately measured by the weight DICM.The length of fracture zone decreases with the increase of the initial fracture height ratio and increases with the increase of the specimen span.(3)The theoretical models of double K fracture toughness and double G fracture toughness are used to analyze the stress intensity factor and fracture toughness of the initial fracture height ratio.The results show that the instability toughness and the initial fracture toughness do not change with the initial crack height ratio and the span,and the instability toughness and the instability toughness can be used as the characterization of the inherent fracture properties of the material.(4)The influence of the finite fracture mechanics model(FFM)and fracture criterion on the theoretical data is analyzed.The theoretical analysis shows that the maximum failure stress at the crack tip of the three point bending beam decreases with the increase of the initial joint height ratio and the span,and the length of the fracture process will gradually diminish with the increase of the ratio of the initial seam height to the increase of the span.The gradual change is big.