Study On Fracture Behavior Of Hydraulic Concrete Based On DIC And Acoustic Emission Technology

The crack propagation law of hydraulic concrete is the basis for structural design and safety evaluation of concrete hydraulic,but so far,there are still deficiencies in this area.In order to study the fracture performance of hydraulic concrete,wedge splitting tensile tests under different loading rates（0.1mm/s,0.01mm/s,0.001mm/s）and different loading conditions（monotonic loading,cyclic loading）are carried out on hydraulic concrete cube specimens with precast cracks with different notch to height ratios（0.3,0.4,0.5）.The rate effect and size effect of hydraulic concrete crack propagation under monotonic loading,cyclic loading are analyzed.At the same time,DIC method and acoustic emission technique are used to monitor the crack evolution process and the acoustic emission hydraulic concrete real time.The variation rules of acoustic emission parameters such as acoustic emission amplitude,ringing count and energy are analyzed,and the model has been established based on acoustic emission parameters.The following conclusions are drawn:（1）Under monotonic loading,the peak load,initial fracture toughness,unstable fracture toughness and fracture energy of hydraulic concrete increase with the increase of loading rate.The fracture of hydraulic concrete has obvious strain rate effect.Influenced by the boundary effect,the CTOD expansion rate in the post peak stage increases with the increase of loading rate,while the crack length decreases with the increase of loading rate.（2）Under monotonic loading,with the increase of notch to height ratio,the peak load,instability fracture toughness and fracture energy of hydraulic concrete fracture gradually decrease,showing obvious size effect,while the initiation fracture toughness is basically unchanged.When the crack tip displacement reaches the critical value CTODc,the virtual crack length reaches the maximum and decreases with the increase of notch to height ratio.The macroscopic crack propagation velocity and effective crack length decrease with the increase of notch to height ratio.（3）Under cyclic loading,the opening displacement at the crack tip increases back and forth with the increase of the number of cycles,and the hydraulic concrete shows the phenomenon of stiffness degradation.With the increase of loading rate,the peak load increases gradually,the residual bearing capacity decreases gradually,and the effective crack length shows the trend of reciprocating increase,the shorter is.With the increase of notch to height ratio,the peak load,secant modulus,stiffness attenuation rate,crack length and width are gradually reduced,and the reduction of crack opening displacement is basically unchanged.（4）With the increase of loading rate,the number of acoustic emission events decreases gradually,the more intense the energy fluctuation of acoustic emission,the more obvious the amplitude mutation,the more frequent the b value fluctuation,the weaker the Kaiser effect,and the more serious the hydraulicage of hydraulic concrete.With the increase of notch to height ratio,the cumulative ringing count and event number of acoustic emissions gradually decrease,and show the characteristics of four stages,reflecting the boundary effect of fracture failure.In addition,this paper constructs the concrete hydraulicage model by using the acoustic emission ring number,analyzes the hydraulicage degree of concrete under different loading conditions,and reveals the crack propagation mechanism of hydraulic concrete.