Study On Dynamic Failure Process And Strain-damage Law Of Gray Sandstone Based On SHPB Test

The problem of "low permeability" of uranium reservoir is a key problem in the process of leaching and mining of many sandstone uranium resources at present.Different from the conventional oil or coalbed methane infiltration effect,the uranium reservoir permeability effect requires as far as possible to achieve a uniform network system,so that the leaching solution in the ore layer uniformly distributed migration,but can't produce a significant geometric size of the cracks,so as to avoid the emergence of leaching night of the dominant flow.Assign the permeability of ore rock and their state and is closely related to the damage degree of rock damage,therefore,increases the permeability based on the blasting technology as the background,using SHPB experiment with strain control loop system under different conditions of gray sandstone dynamic impact test,analyzed the different strain rate and strain under the condition of the failure process and failure mechanism of grey sandstone;The damage evolution law of grey sandstone was analyzed from macroscopic and microscopic aspects by combining the wave velocity test experiment and CT scan experiment,and the relationship between damage variables and strain was obtained.Finally,Ansys/Ls-Dyna software is used to simulate the damage process and damage evolution of grey sandstone.The main research contents and conclusions are as follows:(1)In the dynamic impact process of the strain rate from 37.101 s-1 to 79.910 s-1,the stress-strain curve of grey sandstone is mainly divided into two types.One is the stress-strain curve under incomplete failure,with hysteresis at the end.The other type is the stress-strain curve under complete failure.However,the two types of stress-strain curves are generally divided into five stages:micro-fracture compaction stage,linear elastic deformation stage,crack growth stage,stable unloading stage and rapid unloading stage.(2)When the strain rate increased from 37.101 s-1 to 79.910 s-1,the elastic modulus of grey sandstone remained at the same level with the increase of the strain rate,and the strain rate effect was not obvious.The peak stress increases as a quadratic function with the strain rate,and the peak strain increases as an s-shaped function with the strain rate.Gray sandstone destruction form asymmetric conical damage caused by shear failure,with the increase of strain rate conical part gradually reduce until disappear,peripheral flake pieces broken scale decreases,broken in small pieces and powder,gray sandstone under the main damage form of small strain rate of shear failure into a higher strain rate under shear-tensioning mixed destruction.(3)In the control strain dynamic gray sandstone specimen subjected to impact the overall destruction form also presented asymmetric cone damage,failure process characterized by destruction of the early broken area mainly concentrated in the rock,rock destruction shape sheet,with the increase of impact strain,broken zone from outside to inside gradually expand,the volume gradually increase,the rock damage state characterized by large flake pieces is reduced,smaller stripe fragments and powder increase gradually,eventually end conical disappear.(4)The research on the evolution law of macroscopic and microscopic damage shows that the damage grows exponentially with the strain,and the quantitative relationship between the macroscopic damage variable and microscopic damage variable and the strain is obtained by using data fitting.Macroscopic damage and mesoscopic damage variables,although differences in the characterization of rock damage degree,but the change tendency with the increase of strain is relatively consistent,the damage of grey sandstone with the increase of strain is not a simple linear increase,but the strain increase accumulation to strain damage threshold damage degree increases suddenly,strain damage threshold ?'=0.008 3.(5)The numerical simulation results show the gray sandstone under the effect of dynamic impact crushing process,based on the density of crack damage definition method,get the rule of the evolution of the damage variable with strain better consistent with the experimental results of,once again proved that the grey sandstone damage variable with the increase of strain and the strain damage threshold,the threshold for the simulation of the strain injury ?=0.007 45.