Study On Damage Evolution Characterization Of Concrete Based On Acoustic Emission Information

Concrete is the most widely used building material in civil engineering.Its mechanical properties are brittle,random and nonlinear.As a heterogeneous multiphase composite material,the catastrophic damage caused by the damage evolution of concrete in service is uncertain.In order to obtain the damage evolution of concrete and the early warning of structural catastrophic damage,the three-points bending and uniaxial quasi-static compression experiences were performed.The whole process of damage evolution of concrete was studied based on acoustic emission.The damage constitutive model of concrete was established based on the micromechanics theory in which the softening effect of material induced by damage was considered.A simultaneous observation test platform for displacement and damage signals was built.The parameters of the acoustic emission acquisition system were calibrated,the signal propagation speed in the sample was measured,and the layout of the acoustic emission sensor was optimized.Through the three-points bending test of concrete beams without guiding crack,the damage evolution process of concrete under tension load was analyzed.The multi-parameters such as the acoustic emission ringing count,energy rate and amplitude frequency extreme value were used to study the process of damage evolution.The application of the amplitude-frequency extreme enriched the multi-parameter system.The law of catastrophic damage caused by damage evolution of concrete material under bending deformation was determined.Through the uniaxial quasi-static compression test,the damage evolution law of concrete under compressive load was analyzed by using the multi-parameter system.Based on the analysis of the acoustic emission characteristic signal and the stress-strain curve of the loading process,the characteristics of concrete damage evolution in different loading stages were obtained.Through three-dimensional screening and two-dimensional projection of acoustic emission events location points,the evolution rule of damage accumulation in the specimen as damage band was determined,and the morphology of damage localization region was described based on Kriging method.The finite element model of concrete random aggregate was established.The material properties were assigned to aggregate,mortar matrix and interface transition zone respectively.The whole process of concrete damage evolution under uniaxial quasi-static compression load conditions was simulated.According to the maximum strain failure criterion,the damage evolution of concrete surface and interior was analyzed in stages.The quantitative relationship between deformation and damage degree was established.A micro-mechanical model of two-phase brittle composite was established based on the classical inclusion theory of composite mechanics.The differential scheme method with damage was improved by the equivalent treatment of cavitation of interface damage.Based on this method,taking concrete as an example,the softening effect of aggregate interface damage on concrete material and the sensitivity of damage amount to material softening effect were analyzed.The secant constitutive model of damage induced softening and damage was proposed based on the assumption of damage equivalent evolution and the softening effect of aggregate damage accumulation on concrete materials.and the stress-strain relationship of concrete was obtained.