| A concern regarding the effect that high temperature and cyclic loading has arisen in many engineering projects such as the exploitation and application of geothermal resource,the deep storage of nuclear waste,oil shale in-situ pyrolysis mining,underground coal gasification and gas storage energy,etc.Therefore,the mechanical properties of rock under real-time temperature and cyclic loading were performed,and the fatigue damage law of rock under long-term temperature and cyclic loading was founded,which can provide theoretical and experimental data for long-term stability research.In this paper,granite is used as the research object,and the fatigue characteristics of granite under real-time temperature and cyclic loading are performed utilizing the multi-functional rock high temperature triaxial testing machine.A series of researches have been carried out from experimental analysis and theoretical research to obtain granite.The fatigue characteristics vary with temperature and stress cycle times.The main research contents and conclusions are as follows:(1)The mechanical properties of granite under 25?~600? were performed utilizing the multi-functional rock high temperature triaxial testing machine.The results show that the uniaxial compressive strength and elastic modulus of granite decrease generally with increasing the temperature.The ultimate strain changes with the temperature in W shape.Specifically,the ultimate strain of granite firstly decreases with rising the temperature from 25? to 200?,secondly increases from 200? to 300?,thirdly decreases from 300? to 500? and then increases from 500? to 600?.(2)With the cyclic loading test on granite samples under different temperatures,it is found that: The increase of elastic modulus mainly occurs in the second stress cycle but is not obvious from the second to the 50 th stress cycle.The elastic modulus of granite increases generally due to cyclic loads,and the increase amplitude is different with different temperatures with the minimum and maximum values at 100? and 400? respectively.(3)Cyclic uniaxial stress-temperature tests are conducted during which stress upper limit is 70% or 85% of the uniaxial compressive strength and peak temperature is 100?~600?.It is found that: When the cyclic stress is 70% uniaxial compressive strength,the cyclic temperature is 100?~400?,the stress–strain curve of granite is sparse in the initial cycle stage,the cyclic temperature is 500?~600?,the stress–strain curve of granite is relatively concentrated,almost does not change along with the number of cycle.When the cyclic stress is up to 85% uniaxial compressive strength,the hysteresis loop area of granite in the first cycle at different temperatures is much large than that of the hysteresis loop area of subsequent cycles,and the stress–strain curves change slightly except the first stress–strain curve.(4)During the 10 times of temperature and stress cycling of granite,the variation of the elastic modulus of the specimen loading curve with the number of cycles corresponds to the first two stages of the fatigue failure law,and it gradually increases.Specifically,the elastic modulus of the loading section at 10 th times is greater than the elastic modulus of the first loading,but the magnitude of the increase in temperature is different.(5)The strain of granite corresponding to the upper limit of the loading stress decreases with the increase of the number of cycles when subjected to cyclic temperature and cyclic stress.Except for 600 ?,the uniaxial compressive strength of the specimen after temperature and stress cycling is greater than the compressive strength at real-time high temperature.(6)Based on the dissipative energy theory,the variation of granite hysteresis energy with the number of cycles during the cyclic loading under real-time temperature and the temperature and stress cycle are analyzed.The deformation and failure characteristics of granite subjected to cyclic temperature and cyclic stress are discussed. |
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