Study On The Model Test Of Different Opening Width Crack Propagation

Due to the long-term tectonic stress field, rock is not homogeneous, butinhomogeneous and anisotropicstructure composed ofmanyjoints, cracks, faults, andothersliding surfaces.According toresearchesandengineering practiceathomeandabroad,instabilityand destruction of fractured rock is caused by the slipplane,which is generatedfrom rockinternal cracksopen,expand.Therefore,study onsimilarmodeltests of therock-like material sampleprefabricatedoriginal crackhasimportantguiding significance forthe project. Many researchers have done a lot of workabout the specimens containing two fissures with different spatial distribution, however,the influence of crackopening width on crack initiation, expansion, and connect is notconsidered. In this paper,in orderto explore the impact of the crackopening widthon theinitiational stress、initiationalmode、expansion path、connect mode of crack and thestrength、stress、strainofrock, the following work has been done and the correspondingresults has been made:①According to experimental purpose and condition, a reasonable testing scheme isdetermined. Meanwhile, specimen size is determined and corresponding moulds aremade, moreover, the specimens contain three crack opening width,0.5mm、1mm、2mm,respectively, and five different spatial distribution. The images of the sample loadingprocess are captured by the HG-100K high-speedmotion analysis system, and the wholeprocess of crack initiation, propagation and coalescence is recorded.The samples areloaded with CMT5504electronic universal testing machine under uniaxial compression,corresponding experimental data is obtained by microcomputer system.②There are three newborn crack types:wing crack,secondary coplanar crack andsecondary inclined crack. The influence of crack opening width on the modes of crackinitiation is:with the increment of crack opening width, the types and quantityofnewborn crack have increased.When the crack opening widthare the same,the influenceof crack angle on the modes of crack initiation is:with the increment of crack angle, thetypes of newborn crack have increased.③The influence of crack opening width on the modes of crack coalescence hasthree kinds of situation: with the increment of crack opening width,1) the failure ofsample gradually shifting from pure shear failure to damage caused by the penetrationoftension failure surface and shear failure surface;2) the failure of sample gradually shifting from damage caused by the penetration ofwing crack and secondary inclinedcrack to damage caused by the penetration ofwing crackand secondary coplanar crack;3)to tension failure caused by wing crack lap up to each other, the crack opening widthhaslittle impact on it.When the crack opening width are the same, the influence of crackangle on the modes of crack coalescence is:the failure of sample gradually shifting fromdamage caused by the penetration ofwing crack and secondary inclined crack to shearfailure.④Crack opening width has obvious influence on the mechanicalproperty ofsample.With the increment of crack opening width: the peak strength of sample hasdecresed;the initional stress of sample has incresed, it is easier to crack for sample afterpeak strength; the ultimate strain of sample has decresed. Meanwhile, in the axialstress-strain curves, the crack opening width wider, stress of the samples after the peakintensity has decreased faster, residual deformation shorter.