Research On Thermal Coupled Fracture Evolution Of Concrete Based On Acoustic Emission Characteristics

The problem of high ground temperature is always the important and difficult point in underground engineering,this phenomenon becomes more and more obvious with the increase of excavation depth,the phenomenon of high ground temperature becomes more and more obvious with the increase of excavation depth.The research background of this thesis is Qilikhattar high temperature diversion tunnel,the influence law of concrete mechanical properties under different temperatures was analyzed,the acoustic emission technology is used to detect the concrete temperature-stress coupling uniaxial compression process in real time,by counting the AE events and changing the law of energy,the failure process of concrete is studied.Based on the actual background of working conditions,generate random polygonal aggregate by Python language,combined with ABAQUS finite element software,a two-dimensional meso-concrete model is generated,to carry out uniaxial compression test under the action of thermodynamic coupling,and extract the numerical calculation results,the result parameters are processed by Python programming,the numerical simulation calculation of acoustic emission is realized and the test results are analyzed mutually,thus providing more research methods for the operation stability of concrete under the high ground temperature environment in practical engineering.The main conclusions of this thesis are as follows:(1)Through the self-designed temperature loading test device,the mechanical properties of concrete under different temperatures can be tested and studied,it is found that the change of temperature will affect the strength,elastic modulus and peak strain of concrete,with the increase of temperature,the strength and elastic modulus of concrete decrease,while the peak strain increases continuously.(2)The number of AE events and energy counts are closely related to the generation of micro cracks in the process of concrete failure damage,it is found that the greater the temperature change,the greater the AE signal,and the changes of AE signal at each stage reflect the degree of concrete rupture damage at each stage.(3)Through thermal-mechanical coupling model,the fracture damage law of concrete with high ground temperature is analyzed from the meso view,and it is found that the thermal stress caused by temperature change is the main reason for the decrease of mechanical properties of concrete.And through the post-processing of the numerical results for acoustic emission numerical simulation,study the relationship between AE event number,crack number and time,and the relationship between AE energy,crack length and time,it is consistent with the AE law of concrete physical test.