Study On Rock With Overlapping Crack Destruction Characteristics On Cyclic Loading

In this paper,we use lots of materials like sandstone to make filled and unfilled with different fracture distribution patterns,applying cyclic loading with universal testing machine,test surface deformation field and Internal fracture characteristics with Digital speckle correlation technique and acoustic emission technology,and then summarize the failure law of rock.through the test,we can know:(1)To the filled specimens,when angel of joint-1 orientation with respect to horizontal(α)is 0,the peak strength will first decrease and then grow,with the inclined angle of two joint(γ)grow.when the α is 30 and 60 the peak strength will first grow and then decrease with the γ grow.the α is 45,peak strength will increasing all the time with the γ grow.when the α is 75 peak strength will decreasing all the time with the γ grow.To the unfilled specimens,when the α is 0 and 30 the peak strength will first decrease and then grow with the γ grow.When the α is 45,60 and 75 the peak strength first grow and then decrease with the γ grow.To the filled specimens,the displacement in the last cycle accounts for about 30% of the total displacement.To the unfilled specimens,when the α is 0 and 30,the displacement in the last cycle accounts for about 20% of the total displacement.when the α is 45 to 75,the displacement in the last cycle accounts for about 30% of the total displacement.(2)In the cyclic loading,both filled and unfilled specimens show accumulated acoustic emission ringing count rise at a constant speed curve ladder shaped over time,and most of specimens show that when the α is determined,the accumulated acoustic emission ringing and acoustic emission energy will first decrease and then grow with the γ grow.Both the filled and unfilled specimens show,felicity effect occurs when the stress level reaches 20% to 30% of the peak intensity,the previous cycle before specimen failure F is about 0.7.most specimen at the second cycle F less then 1,and the acoustic emission signal can be observed in the unloading process,As the number of cycles increases,The acoustic emission signals in the unloading stage are gradually obvious,In particular,continuous ae signals can be observed in the unloading phase of the cycle before the whole failure of the specimen,The relationship between the surface strain of the specimen at the cyclic unloading stage in this cycle is,The strain value will increase at the beginning of unloading,and then the strain value decreases as the load continues to fall.(3)The failure mode of the specimen is not affected by filled or unfilled,Can be divided into Tensile failure、tensile-shear failure and Mixed failure.When the α is less than 45,tensile failure often occurs,when the α is more then 45,tensile-shear failure often occurs,The mixed failure often occurs in the specimen with γ greater than 45 degrees.