Research On Failure Process Of Marble With Prefabricated Hole Based On 3D-DIC And Infrared Technology

With the rapid development of economy and the progress of science and technology,it has greatly promoted the development of railway,subway and large-scale water conservancy and hydropower projects.Rock is a direct contact object in the process of engineering construction,which has important significance and influence on engineering construction.The analysis of rock failure process is not only an important subject of rock mechanics,but also of great significance to the prevention of safety accidents in engineering construction.Rock is heterogeneous and discontinuous,which contains a large number of randomly distributed mineral particles and primary defects such as fractures and pores.In this paper,3D-DIC technology and infrared thermal imaging technology are used to observe the uniaxial compression failure process of marble samples with prefabricated holes.The initiation,propagation and penetration process of surface cracks and the final macroscopic failure morphology of the specimens under uniaxial compression are recorded.The evolution nephogram of displacement field,strain field and temperature field in the surface observation area and the observation area are obtained by relevant calculation software the displacement,strain and infrared radiation temperature information of any point are drawn,and the time displacement strain and time temperature curves are drawn.The failure process of the sample is analyzed by the angle of macro damage,micro deformation and infrared radiation energy change(1)The uniaxial compressive strength of marble with prefabricated circular holes decreases with the increase of pore diameter;when k > 1(k is the ratio of long and short axes of elliptical hole),the uniaxial compressive strength of marble with prefabricated elliptical hole increases gradually with the increase of k value;when k < 1,with the increase of k value,the uniaxial compressive strength will first increase and then decrease.(2)In the process of uniaxial compression test of preformed hole marble,in the AB stage(linear elastic deformation stage),the displacement field will show obvious zoning phenomenon,and the strain field localization band will appear.The interface zone of displacement field and the localization band of strain field tend to be semi "X" or "X" shape centered on the hole,and the boundary zone and strain field localization zone of displacement field are often the surface of the specimen the region of crack initiation,propagation and transfixion.It is proved that 3D-DIC technology can accurately predict rock failure.(3)Based on the crack initiation,propagation and transfixion during uniaxial compression loading,and combined with the time displacement strain curve of the observation area,the failure process of marble with prefabricated holes can be roughly divided into two types: type I failure and mode II failure.Mode ? failure: in the process of uniaxial compression loading,the process of crack initiation,propagation and penetration can be observed on the surface of the specimen.In the AB-CD stage(linear elastic deformation stage ? unstable crack growth stage),the displacement and strain curves show multiple local jumping changes due to the unstable propagation of cracks,with large variation range and large fluctuation.In the DE segment(brittle failure stage),the displacement and strain will increase or decrease abruptly.Mode ? failure: during the uniaxial compression loading process of the specimen,the initiation,propagation and penetration of the cracks on the surface of the specimen can not be observed by naked eyes.The time from the initiation to the breakthrough of the surface cracks is very short,and the failure of the samples is very "sudden",and most of them form a semi "X" shape or "X" shape macroscopic failure zone.The displacement and strain curves change little before the DE stage(brittle failure stage)The change trend is stable.In the DE stage(brittle failure stage),the displacement and strain will increase or decrease abruptly,and the change amplitude is often greater than that of type I failure.(4)The displacement and strain of each point on the surface of the specimen are often different.The displacement and strain of the point near the macro failure zone of the specimen change greatly,while the point far away from the macro failure zone changes relatively little.(5)In the process of uniaxial loading,the color temperature distribution of temperature field in OA-CD stage(initial compaction stage ? unstable crack growth stage)changes little.In DE stage(brittle failure stage),obvious local temperature rising zone and local cooling zone will be formed.The area and change range of heating area are often larger than that of cooling zone,so the overall performance is heating up.(6)In the process of uniaxial loading,the maximum temperature,minimum temperature and average temperature in the observation area tend to decrease steadily in the OA-CD stage,with a small change range,which is generally between 0.01 ?and 1 ?.In DE stage,the maximum temperature will increase sharply,and the minimum temperature will drop sharply,with a small change range,generally between0.07 ? and 0.2 ?,The average temperature tends to increase suddenly,but the increase is small,about 0.05 ? to 0.19 ?.