Mechanical Properties Of 3D Printed Kinked Fissures And The Influence Of Filling Materials Under Uniaxial Tension

Rock mass with natural defects is often encountered in geotechnical engineering.Under the action of complex external force,the existence of fissures,joints and other defects formed by geological tectonic movement often has a great impact on the mechanical properties of rock masses.Under the influence of external disturbance,the initiation,propagation and final penetration of newborn cracks would result in the final fracture of rock masses,which poses a significant threat to the actual geotechnical engineering infrastructure.Therefore,it is one of the hot topics in the field of rock fracture mechanics to study the failure mechanism of rock masses caused by prefabricated fissures.Extensive studies have been conducted in investigating the failure mechanism of rock materials containing prefabricated straight fractures under compression load.However,the pre-existing fissures which formed in rock masses often show non-straight forms,and there are relatively few studies focusing on rock fissures caused by kinked fissures,especially lack of the discussion on the evolution process of kinked fissure under uniaxial tension.Moreover,due to weathering deposition or artificial filling,filling materials often exist in the defects of natural rock masses,so the study of the influence of filling materials on failure characteristics also needs to be further developed.Therefore,the study on the influence of kinked fissures under different filling conditions on the failure mode and mechanical properties of rock-like materials can provide a valuable basis for the exploration of rock failure mechanism.This paper mainly studied the failure characteristics of rock-like materials containing filled kinked fissures under uniaxial tension,and made use of 3D printing technology to produce specimens containing kinked fissures,which presented similar properties to rock materials.With the use of the digital image correlation(DIC)and high-speed camera,the mechanical properties and fracture patterns of rock-like specimens under uniaxial tensile test were investigated.The DIC method was used to obtain the variation information of strain field and displacement field in the process of specimen fracture.By comparing the influences caused by the inclination angle and filling conditions of different branch fissure,it was found that the variation of strain field and displacement field was corresponding to the final fracture mode of rock-like specimens,which provided a basis for monitoring the initiation of newborn cracks.In addition,in this paper,the finite element ABAQUS software was used to carry out numerical simulation of the specimen with the extended finite element method,which further improved the conclusions obtained in the test.The work carried out in this paper were listed as follows:(1)In this paper,the tensile failure mode of rock-like specimens was investigated by recording the fracture process of specimens with a high speed camera.Two failure patterns,namely tip failure and non-tip failure,and three main crack types,namely tensile crack,shear crack,mixed crack,were observed in the tests.It was concluded that the crack causing the final fracture of the specimen tended to be wing crack which appeared firstly and the secondary crack initiated later.The inclination angle of the branch fissure played a decisive role in determining the failure mode of the specimen,and the filling condition mainly affected the formation of secondary crack.(2)Considering the inclination angle and filling condition of branch fissure as variables,choosing gypsum slurry and cement slurry as filling materials,uniaxial tensile tests were carried out on the designed 3D printed rock-like specimens.The mechanical characteristics of rocklike specimens were analyzed through the obtained stress-strain curve and other test data.By comparing the failure properties of the specimens,it was found that the inclination angle of the branch fissure had a decisive effect on the strength of the rock-like specimens.The filling material could improve the tensile strength of the specimen.(3)The extended finite method was used to simulate the test processes,and by comparing the simulation results with the test results,it was verified that the numerical simulation results were in agreement.Furthermore,the failure modes of unfilled and filled specimens with different inclination angles of branch fissures were further simulated,so that further conclusions were obtained.It was concluded that the influence of inclination angle of branch fissure on the failure pattern of the specimen is based on the vertical line.The specimens with the branch fissure located in the half plane of the main fissure were observed non-tip failure under uniaxial tensile action,including the specimens with the branch fissure angle of +45°.However,for specimens with branched fissures outside the semi-planar of main fissure,tip failure occurred(including specimens with branch fissure angle of-135°),which further revealed the fracture failure law of rock-like materials.