Experimental And Numerical Simulation Study On Failure Behavior Of Three Non-straight Fissures In Rock-like Materials

Fissured rock mass is a kind of common engineering medium,which is often disturbed in the engineering projects and lies in the complex stress field.The original fissures in the rock mass often generate new cracks and further propagate,and eventually coalesce with other fissures to cause local or overall damage,which will endanger the stability of the projects.The mechanism of crack propagation and coalescence is one of the long-standing topics in the field of rock fracture mechanics.At present,the relevant research at home and abroad mainly focuses on the mechanical properties and failure mechanism of brittle materials with prefabricated straight fissures under compression.However,there are not only straight fissures but also non-straight fissures of various shapes in the rock mass.At present,there is relatively little exploration on the evolution process of non-straight fissures from initiation to propagation and failure under tension,and the crack failure behavior and rock bridge through failure mode under the interaction of straight and non-straight fissures have not been actually clarified.Therefore,it is of great significance for fracture mechanics theory and engineering projects to study the failure behavior of non-straight fissures.In this article,two kinds of brittle materials samples containing prefabricated kinked fissures and Y-shaped fissures were prepared for uniaxial tensile tests by 3D printing technology.At the same time,brittle material samples containing prefabricated intermittent K-S composite fissures(one kinked fissure and one straight fissure)are prepared for uniaxial compression tests.The mechanical properties and crack failure behavior of the samples under uniaxial tensile and compression tests were investigated.Besides,RFPA^2Dsoftware was used to carry out the numerical simulation,and the simulation results were compared and verified with the test results.The work done in this article is as follows:(1)In the uniaxial tensile tests,the main fissures inclination angle,branch fissures inclination angle,and branch fissures are taken as variables respectively.Combined with the stress-strain curves,the effects of different variables on the mechanical characteristics,crack propagation and failure mechanism was summarized.The results show that the stress-strain curves of the samples with kinked fissures and Y-shaped fissures are very similar to those of the benchmark straight fissure sample,indicating that the main fissures dominate the failure of the samples;different fissures geometries have great influence on the strength of the samples,but the change of branch fissures length has little effect on the failure mode and crack initiation angle of the prefabricated fissures;two failure modes of kinked fissures and three failure modes of Y-shaped fissures are found in the tests.(2)In the uniaxial compression tests,the branch fissure inclination angle of the kinked fissure in the intermittent K-S composite fissures is used as a variable.Combined with the stress-strain curves,the effects of branch fissure inclination angle on the mechanical characteristics,crack propagation and mechanism of rock bridge coalescence was summarized.Results show that the overall stress-strain behavior of the samples is slightly affected by the kink branch inclination angle with the percentage difference of the peak stresses falling within 10%;the crack initial position is dominated by branch fissure inclination angle,and two crack initiation modes are found,which is similar to the tensile tests;compared to the benchmark straight fissure sample,changing the branch fissure inclination angle has an important influence on the rock bridge coalescence failure mode,and the failure modes can be divided into two types according to whether the rock bridge is coalesced or not.(3)In the process of uniaxial compression,high-speed camera was used to capture the process of crack propagation on the surface of the samples.At the same time,digital image correlation method(DIC)was used to obtain the cloud images of the strain field and displacement field of the samples in different loading stages.It is found that the position of strain concentration in the diagram corresponds to the position of cracks initiate,which provides a basis for judging the position of internal crack in brittle failure monitoring.It sheds light on the interactions of straight and non-straight fissures,the overall deformation,and developing mechanism of fissures in brittle materials with complex defects.(4)The basic theory of real fracture process analysis(RPFA)was introduced,and RPFA^2D was used to numerically simulate the experiments of prefabricated non-straight fissures samples under the two groups.By comparing the crack initiation position,crack initiation direction and propagation path in the experiment results,the effectiveness of RPFA^2D to simulate the failure of rock-like materials was verified,and the whole process of crack initiation,propagation and coalescence in the numerical simulation was analyzed.