Micromechanical Experimental Study On Tensile Fracture Of Rock

Research on the mechanical response of rock when subjected to tension is of great significance for analyzing and predicting the service time and failure form of geotechnical engineering.Generally the tensile strength of rock materials such as rock and concrete is very small compared to compressive strength and shear strength,this has led researchers to tend to ignore the effects of rock damage.In recent years,relevant scholars have devoted themselves to the study of tensile strength of rock.However,most of them focus on the tensile failure of macroscopic specimens,and the mesoscopic mechanism of material destruction is masked.In addition,when the numerical simulation experiment is carried out using the data obtained by the macroscopic experiment,the simulation result cannot be perfectly reproduced in the details of the material instability and destruction due to the fact that the model fineness and the calculation time cannot be simultaneously satisfied.In this paper,the modular under microscope mechanical test system is used to study the micro-scale mechanics of rock,combined with the conventional mechanical test data,and the selection of parameters and failure constitutive is studied by 4D-LSM.The related researches are as follows:(1)An algorithm for analyzing discontinuous deformation is proposed.Processing the discontinuous surface images collected during the experiment.Combined with the digital image correlation method,the calculation accuracy of the displacement at the discontinuous surface during the test is improved.In addition,in terms of the problem of the elastic modulus cannot be measured for meso-mechanical tests,we propose to use digital image correlation method to solve,and the hardware of the digital image correlation method is proved to the effectiveness of this method in solving the problem.(2)Rock macroscopic and microscopic mechanical tests were carried out,and the mechanical parameters of rock specimens at multiple scales were obtained,mainly carried out the unconfined compression test of the macroscopic scale of rock specimens,the Brazilian splitting test,the direct tensile test of the mesoscale,and the cyclic load test.In order to solve the problems caused by the heterogeneity and anisotropy of rock specimens,a three-dimensional printer was introduced,the mechanical properties of the 3D printed specimens were improved by the corresponding pretreatment,and the mechanical properties at the mesoscale were obtained,and further explored the influence of different bedding angles on the tensile strength of 3D printed specimens;prefabricated cracks are designed with stainless steel,tried a variety of cemented surface generation methods,the force and displacement curves at the cemented surface at the time of fracture of the test piece were obtained.(3)The numerical simulation experiment was carried out using 4D-LSM,and the method of generating particle model was first proposed,the rapid generation of particle files is realized by means of STL files.Based on this,the data curves of continuous deformation of particles and contact surfaces are explored;The damage parameters of the specimens with loss of strength were analyzed by macroscopic and microscopic experimental parameters,and the effects of reduction effects and parameter variability were discussed;The influence of the stiffness parameters of the contact surface on the test curve when the discontinuous deformation of the contact surface occurs is explored,and the proposed formula for parameter selection is given;The influence of the post-peak constitutive on the curvature of the peak curve at the time of failure was analyzed.The contact parameters and elastic parameters under cyclic loading were calibrated by the test curve.