Strain localization characteristics of perforation failure of perforated speci-mens

The leakage of peri-hole crack in drilling hole is one of the reasons for low gas drainage concentration,and the crack is formed by strain localization zone.In order to explore the relationship between strain localized zone characteristics and macroscopic cracks,the uniaxial compression failure test of the pore-containing specimens was carried out,and the digital speckle correlation measurement method was used to obtain the surface damage image sequence of the specimen and the full field strain during the failure process.The distribution characteristics,stress changes and energy evolution processes of strain localized zones at different stages were analyzed.The results show that the strain localized zone is divided into main tensile (T1),normal shear (NS),second main tensile (T2) and oblique shear (IS),macroscopic main crack according to the force and distribution characteristics.It is formed by T2,NS and IS strain localized zone penetration.The dominant factor for forming the T1 and T2 strain localization zone is tensile stress.The NS strain localization zone is formed by the combination of tensile stress and compressive stress,and IS strain localization.The dominant factor of the belt is compressive stress.The energy accumulation of the T2,NS and IS strain localized zones is 2.2,1.8 and 1.6 times of the T1 strain localized zone,respectively.When loading to 73.6% of the strain,the T1 strain localized zone releases the energy first,resulting in micro-fracture and stress peaks.Afterwards,the T1 strain localization zone continuously releases energy,and the energy change of the T2 strain localization zone decreases,increases and decreases,and the energy change of the localized zone of NS and IS strains increases and decreases,indicating that the nature of the damage process is the whole energy adjustment of the sample,the energy adjustment is related to the evolution of the localized bands.The results show the characteristics of the strain localization zone around hole during the failure process of the sample containing hole,and reveal the nature of the inclined fracture in the strain concentration zone of hole.