Crack Propagation Test And Numerical Simulation Study Of Rocklike Material Based On DIC

Natural rock itself contains many native micro-cracks and defects,and these micro-cracks and defects in rock mass are a crack that contains a large number of multi-scale,multiple layouts,and all micro-cracks and defects interact with each other.In the crack system,these cracks interact with each other to determine the strength of the rock mass and the damage mechanism.In this paper,cracks with different numbers,different sizes,and different layouts in the rock are taken as the object of study.A new type of combination of rock-like material physical testing,digital image correlation(DIC),and numerical simulation tests is studied in detail.The crack initiation and propagation of single cracks and double cracks of different sizes and layouts in rock-like materials obtain crack initiation angles,number of cracks,and crack size,crack layout,crack initiation and propagation,and crack continuity between two cracks.The law of influence.The relationship between crack dip,number of cracks,crack size,crack arrangement and crack initiation strength was obtained.At the same time,the fractal theory mesh method was used to describe the damage degree of rock-like crack systems.The fractal dimension was used as the crack propagation degree.The analytical parameters.The three-dimensional displacement field and strain in the whole field of the specimen surface were obtained using the camera system,and the crack initiation point,extension length and direction of the crack were quantified from a mesoscopic point of view.The analysis of the mechanical properties of the specimen under the macroscopic angle was a An effective way to study the stability of the primary crack system in the rock mass and to destroy the morphology.In this paper,the detailed process of initiation,propagation and penetration of cracks in uniaxial.The main structure of this paper is as follows:The first chapter introduces the research background and significance of the thesis.It also introduces the development status of crack propagation in rock mass system from the aspects of theoretical research,experimental research and numerical analysis at home andabroad,and discusses the theory of digital image correlation method.The principle and application of digital image correlation methods are summarized in various fields.The second chapter: trial design,select appropriate rock-like materials according to previous achievements,and adjust the ratio of materials according to actual conditions;design mold dimensions according to the test plan,and design corresponding crack placement scheme(different crack dip,different Quantity,different crack size,and different layout types;prefabricated crack samples are prepared according to the test design scheme;suitable loading equipment(RMT-301 rock and concrete mechanics test system)and image acquisition device(non-contact)are selected according to the content and purpose of the test study.Full-field strain measurement system VIC-3D).Chapter 3: crack propagation analysis,in the loading process of the specimen,using the image data of the specimen destruction process acquired by the CCD camera,describes the crack initiation sequence,crack initiation mode,connection mode,and penetration mode of the test piece.And by analyzing the crack propagation conditions of different factors(ie different proportions,different quantities,different crack sizes,different spatial arrangements),the analysis of different factors on the peak strength of the sample,cracking mode,connection mode and failure mode influences.The fourth chapter: the fractal dimension of the specimen destruction process,using the box-counting dimension method to calculate the fractal dimension of the specimen during the damage process,study the rock failure process,and quantify the degree of damage.The fifth chapter: obtain the three-dimensional deformation field of the object surface by DIC method,compare the DIC digital speckle non-contact whole field strain measurement system to get the sample displacement,strain cloud diagram and the macroscopic surface crack initiation,connection and the penetration and destruction process of the sample.The damage evolution process and failure mechanism were analyzed in detail.The number of speckles in the analysis area of ??the sample surface during the damage destruction process was statistically analyzed.The damage speckle variables were analyzed and the damage extent of the specimen surface was quantitatively described.Chapter 6: Numerical simulation analysis,based on FLAC-3D numerical simulation of prefabricated crack rock specimens,analysis of crack sample loading process stress,strain cloud diagram,and digital image correlation method observation and analysis of displacement,strain cloud image for comparative analysis As a reference for the damageevolution and failure mechanism of cracked rock materials.Further verify the correctness and effectiveness of digital image correlation methods.Chapter ?: Summarize the main conclusions of this paper,the main deficiencies of the paper's work,and put forward new challenges and prospects for follow-up research.The main conclusions of this paper are:1.Effect of crack geometry on mechanical properties of rock mass(1)With the increase of the crack inclination angle,the mechanical strength of the crack specimen increases,and the crack penetration mode changes from tensile failure to tensile-shear composite failure.(2)The crack length and crack opening degree are all factors that affect the mechanical strength of the crack specimen.The longer the crack,the lower the strength of the specimen,the easier it is for the cracks to expand.The finer the crack opening,the lower the degree of damage of the rock and the greater the strength.high;(3)The number of cracks is increased from one to two under a 45-degree collinear condition,and the crack strength decreases.(4)The arrangement of cracks also affects the mechanical strength of crack specimens.The vertical crack strength is the lowest,and the collinear crack strength is between vertical and parallel.2.Experimental study of crack propagation law(1)During the uniaxial compression test,the Vic-3D system was used to observe four kinds of morphological cracks,ie,tensile cracks,shear cracks,wing cracks and anti-wing cracks.(2)By analyzing the crack loading of specimens with different cracks in the shaft,the degree of crack propagation during failure of the specimen is analyzed.The analysis results show that the higher the damage degree of the specimen,the higher the fractal dimension of the specimen.Therefore,the fracture dimension of the specimen can be described by the fractal dimension in the single loading process.(3)The loading curve and the speckle damage variable curve have a corresponding relationship during the loading process;Three crack samples under different crack arrangement conditions are analyzed: Collinear,parallel,and vertical crack samples are known to be collinear,parallel,The vertical cracking specimens have different mechanical strengths and the cracked specimens have similar damage levels.From the above analysis of the damage variables of different crack sizes at the collinear line,the higher the mechanicalstrength of the specimens,the lower the damage variable,and vice versa.Low,the higher the damage,the greater the damage variable.Through analysis,it can be concluded that the damage variable of a crack sample is not only determined by the mechanical strength but also by the form of the crack.3.FLAC 3D numerical simulation verification(1)The stress-strain cloud diagrams obtained by numerical simulation are basically distributed symmetrically in the center,and the U-directional displacement gradient changes drastically at different loading periods.From the X-direction strain cloud diagram,it can be clearly seen that the stress concentration occurs at the simulated crack tip.With the increase of the load,the shape of the X-direction strain cloud diagram is mostly dominated by the wing crack and the anti-wing crack.(2)Numerical simulation of parallel crack test specimens and two sets of orthogonal crack test specimens The crack penetration mechanism is basically consistent with the test results.Both are due to the development of wing cracks and anti-wing cracks in the adjacent crack tip.Causes damage.This article innovation and deficiencies1.Innovation:(1)In the indoor model test,the influence of cracks with different crack inclination angles,different crack sizes,different crack numbers,and different crack arrangement patterns on the mechanical strength of the model test was performed,compared to the more studied regular ordered multiple cracks.This is a model test that compares systematically with real crack systems.(2)At the same time as the uniaxial compression test,the propagation law of cracks was recorded and observed using the Vic-3D non-contact full-field strain measurement system recently introduced in the Rock Mechanics Laboratory.2.Inadequacies(1)Due to the limitation of specimen size and crack preparation method,the crack opening degree is only controlled between 0.5mm and 2mm,which can only approximate the simulation of open cracks,and the applicability of closed cracks is poor.(2)In the FLAC 3D numerical modeling process,empty elements are used to simulate the cracks,the joint parameters default to zero,and the actual cracked rock joints have certain cohesion,friction and shear strength.Outlook:The object of this study is to include pre-cracked rock samples.Therefore,in future studies,we will seek to formulate a similar material that is more suitable for simulating the original rock to make the test data more representative;In this paper,the application of the digital image correlation method is not skilled enough to dig out more meaningful test data.It only achieved the regular study of the damage evolution process of cracked specimens,and failed to quantify the degree of damage of the specimen.It is also necessary to continue learning VIC-More applications of 3D.